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The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
The nuclear power plant
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The nuclear power plant

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  • 1. The nuclear power plant stands on the border between humanity's greatest hopes and its deepest fears for the future. On one hand, atomic energy offers aclean energy alternative that frees us from the shackles of fossil fuel dependence. On the other, it summons images of disaster: quake-ruptured Japanese power plants belching radioactive steam, the dead zone surrounding Chernobyl's concrete sarcophagus. But what happens inside a nuclear power plant to bring such marvel and misery into being? Imagine following a volt of electricity back through the wall socket, all the way through miles of power lines to the nuclear reactor that generated it. You'd encounter the generator that produces the spark and the turbine that turns it. Next, you'd find the jet of steam that turns the turbine and finally the radioactive uranium bundle that heats water into steam. Welcome to the nuclear reactor core. The water in the reactor also serves as a coolant for the radioactive material, preventing it from overheating and melting down. In March 2011, viewers around the world became well acquainted with this reality as Japanese citizens fled by the tens of thousands from the area surrounding the Fukushima-Daiichi nuclear facility after the most powerful earthquake on record and the ensuing tsunami inflicted serious damage on the plant and several of its reactor units. Among other events, water drained from the reactor core, which in turn made it impossible to control core temperatures. This resulted in overheating and a partial nuclear meltdown [source: NPR]. As of March 1, 2011, there were 443 operating nuclear power reactors spread across the planet in 47 different countries [source: WNA]. In 2009 alone, atomic energy accounted for 14 percent of the world's electrical production. Break that down to the individual country and the percentage skyrockets as high as 76.2 percent for Lithuania and 75.2 for France [source: NEI]. In the United States, 104 nuclear power plants supply 20 percent of the electricity overall, with some states benefiting more than others. In this article, we'll look at just how a nuclear reactor functions inside a power plant, as well as the atomic reaction that releases all that crucial heat. Nuclear power plants, world-wide scroll On December 20, 1951, at the Experimental Breeder Reactor EBR-I in Arco, Idaho, USA, for the first time electricity - illuminating four light bulbs - was produced by nuclear energy. EBR-I was not designed to produce electricity but to validate the breeder reactor concept. First electricity production by nuclear energy Experimental Breeder Reactor EBR-I, 20 Dec.1951, Arco, Idaho, USA On June 26, 1954, at Obninsk, Russia, the nuclear power plant APS-1 with a net electrical output of 5 MW was connected to the power grid, the world's first nuclear power plant that generated electricity for commercial use. On August 27, 1956 the first commercial nuclear power plant, Calder Hall 1, Eng-land, with a net electrical output of 50 MW was connected to the national grid. As of January 18, 2013 in 31 countries 437 nuclear power plant units with an installed electric net capacity of about 372 GW are in operation and 68 plants with an installed capacity of 65 GW are in 15 countries under construction. As of end 2011 the total electricity production since 1951 amounts to 69,760 billion kWh. The cumulative operating experience amounted to 15,080 years by end of 2012. Country In operation Under construction Number Electr. net output MW Number Electr. net output MW Argentina 2 935 1 692
  • 2. Armenia 1 375 - - Belgium 7 5,927 - - Brazil 2 1,884 1 1,245 Bulgaria 2 1,906 - - Canada 19 13,665 - - China Mainland Taiwan 17 6 12,816 5,018 29 2 28,753 2,600 Czech Republic 6 3,766 - - Finland 4 2,736 1 1,600 France 58 63,130 1 1,600 Germany 9 12,068 - - Hungary 4 1,889 - - India 20 4,391 7 4,824 Iran 1 915 - - Japan 50 44,215 3 3,993 Korea, Republic 23 20,754 3 3,640 Mexico 2 1,300 - - Netherlands 1 482 - - Pakistan 3 725 2 630 Romania 2 1,300 - - Russian Federation 33 23,643 11 9,927 Slovakian Republic 4 1,816 2 782 Slovenia 1 688 - - South Africa 2 1,830 - - Spain 8 7,560 - - Sweden 10 9,325 - - Switzerland 5 3,263 - - Ukraine 15 13,107 2 1,900 United Arab Emirates - - 1 1,345 United Kingdom 16 9,246 - - USA 104 101,465 1 1,165 Total 437 372,210 68 65,406 Nuclear power plants world-wide, in operation and under construction, IAEA as of 18 January 2013
  • 3. Number of reactors in operation, worldwide, 2013-01-18 (IAEA 2013, modified) Number of reactors under construction, 2013-01-18 (IAEA 2013, modified)
  • 4. Nuclear share in electricity generation, 2011 (IAEA 2012, modified) Nuclear Power Plants, nuclear power capacity 1995 - 2011 (IAEA 2012) Number of nuclear reactors worldwide by age as of 2013-01-10 (IAEA 2013) Nuclear Power Plants, energy availability factor 1995 - 2011 (IAEA 2012)
  • 5. Generating Electricity & Nuclear Power April 6, 2011 by SBG · 5 Comments The crisis in Japan caused me to do a bit of research which actually startled me. Of course, that isn‘t too difficult of an accomplishment. When I was four years old I thought food came from a clean factory, not animals and weeds, and I assumed traffic lights had sensors and only turned red when necessary. Yeah, way back in the 1950′s I was startled at the primitive planet God had placed me. And that same story seems to be playing out with power plants. I knew coal fueled power plants ―generated‖ electricity and that turbines were involved. But when I heard ―Nuclear Power Stations‖ I assumed there was some really cool nuclear reactions going on where we actually gathered energy from the reaction. OK, OK, call me stupid, I was ―educated‖ in the government school system after all, and I do have a Masters degree, so that tells you how bad our higher education system is. Imagine my shock when I discovered that nuclear power is used just to heat up water into steam in a boiler to power turbines which spin magnets over copper to push the loose electrons off. That‘s it! All they are doing with the extremely planet killing nuclear crap is heating water!!! Creating steam! What the Fat??? OK, let‘s start at the very basic level. Electricity is essentially the movement of electrons. If you can convince some electrons to leave home at a good sprint, you get electricity. See this chart? So the question is, how do you convince a few electrons to leave home, abandon their atom and go elsewhere? Simple! First, you got to find a very slutty electron. Like the electrons in copper. Plain old copper wire has loose electrons that after just two drinks will leave the bar with anyone! Grab some magnets, circle the copper wire, spin the contraption and the slutty copper electrons are off and running, their bras off and zippers sliding. And somehow, you get to turn your computer on. Weird, right? You can actually make your own tiny power station this way, and those of you who attended good elementary schools probably did just that! OK, essentially, that is what is inside those huge power plants, only with lots more copper and magnets. And water. Why? To boil the water into steam to blow turbines around, which has all those copper sluts and magnets. Like this picture below:
  • 6. And what is nuclear energy??? It isn‘t anything different, just that they use the nuclear fuel to heat the water. Granted, the fuel will last a long, long time, and as long as the plants don‘t blow up they generate clean energy. But they just use the nuclear rods to heat water! While these designs are somewhat different, you can see the boiler, the turbines and so forth. Seems to me we could use a lot more wind and water to spin those turbines. What about installing turbines in the ocean to let the gulf stream spin turbines to entice generate electricity? Hell, let‘s install turbines in the windows of the White House, the Senate and Congress??? Hell, the hot air coming from there will spin those turbines so fast we can light up the entire world! That‘s my educational blog post for the day. Month. Maybe year. Nuclear power, or Nuclear energy, is the use of exothermic nuclear processes,[1] to generate useful heat and electricity. The term includes the following heat producing processes, nuclear fission, nuclear decay and nuclear fusion. Presently the nuclear fission of elements in the actinide series of the periodic table produce the vast majority of nuclear energy in the direct service of humankind, withnuclear decay processes, primarily in the form of geothermal energy, and radioisotope thermoelectric generators, in niche uses making up the rest. Nuclear (fission) power stations, that is excluding the contribution from naval nuclear fission reactors, provided about 5.7% of the world's energy and 13% of the world's electricity, in 2012.[2] In 2013, the IAEA report that there are 437 operational nuclear power reactors,[3] in 31 countries.[4] Although not every reactor is producing electricity.[5] In addition, there are approximately 140 naval vessels using nuclear propulsion in operation, powered by some 180 reactors.[6][7][8] As of 2013, attaining a net energy gain from sustainednuclear fusion reactions, excluding natural fusion power sources such as the Sun, remains an ongoing area of international physics andengineering research, but more than 60 years after the first attempts, commercial fusion power production remains unlikely before 2050.[9]
  • 7. There is an ongoing debate about the use of nuclear energy.[10][11][12] Proponents, such as the World Nuclear Association, the IAEA andEnvironmentalists for Nuclear Energy contend that nuclear power is a safe sustainable energy source that reduces carbon emissions.[13] Opponents, such as Greenpeace International and NIRS, contend that nuclear power poses many threats to people and the environment.[14][15][16] Nuclear power plant accidents include the Chernobyl disaster (1986), Fukushima Daiichi nuclear disaster (2011), and the Three Mile Island accident (1979).[17] There have also been some nuclear-powered submarine mishaps.[17][18][19] In terms of lives lost per unit of energy generated, analysis has determined that nuclear power has caused less fatalities per unit of energy generated than the other major sources of energy generation. Energy production from coal, petroleum, natural gas and hydropower has caused a greater number of fatalities per unit of energy generated due to air pollution and energy accident effects.[20][21][22][23][24] However, the economic costs of nuclear power accidents is high, and meltdowns can take decades to clean up. The human costs of evacuations of affected populations and lost livelihoods is also significant.[25][26] Along with other sustainable energy sources, nuclear power is a low carbon power generation method of producing electricity, with an analysis of the literature on its total life cycle emission intensity finding that it is similar to other renewable sources in a comparison ofgreenhouse gas(GHG) emissions per unit of energy generated.[27] With this translating into, from the beginning of nuclear power stationcommercialization in the 1970s, having prevented the emission of approximately 64 gigatonnes of carbon dioxide equivalent(GtCO2-eq)greenhouse gases, gases that would have otherwise resulted from the burning of fossil fuels in thermal power stations.[28] As of 2012, according to the IAEA, worldwide there were 68 civil nuclear power reactors under construction in 15 countries,[3] approximately 28 of which in the Peoples Republic of China (PRC), with the most recent nuclear power reactor, as of May 2013, to be connected to the electrical grid, occurring on February 17, 2013 in Hongyanhe Nuclear Power Plant in the PRC.[29] In the USA, two newGeneration III reactors are under construction at Vogtle. U.S. nuclear industry officials expect five new reactors to enter service by 2020, all at existing plants.[30] In 2013, four aging, uncompetitive, reactors were permanently closed.[31][32] Japan's 2011 Fukushima Daiichi nuclear accident, which occurred in a reactor design from the 1960s, prompted a rethink of nuclear safety and nuclear energy policy in many countries.[33] Germany decided to close all its reactors by 2022, and Italy has banned nuclear power.[33] Following Fukushima, in 2011 the International Energy Agency halved its estimate of additional nuclear generating capacity to be built by 2035.[34][35] In 2011 nuclear power provided 10% of the world's electricity[36] In 2007, the IAEA reported there were 439 nuclear power reactors in operation in the world,[37] operating in 31 countries.[4] However, many have now ceased operation in the wake of the Fukushima nuclear disaster while they are assessed for safety. In 2011 worldwide nuclear output fell by 4.3%, the largest decline on record, on the back of sharp declines in Japan (-44.3%) and Germany (-23.2%).[38] Since commercial nuclear energy began in the mid-1950s, 2008 was the first year that no new nuclear power plant was connected to the grid, although two were connected in 2009.[39][40] Annual generation of nuclear power has been on a slight downward trend since 2007, decreasing 1.8% in 2009 to 2558 TWh with nuclear power meeting 13–14% of the world's electricity demand.[41] One factor in the nuclear power percentage decrease since 2007 has been the prolonged shutdown of large reactors at the Kashiwazaki-Kariwa Nuclear Power Plant in Japan following the Niigata-Chuetsu-Oki earthquake.[41] The United States produces the most nuclear energy, with nuclear power providing 19%[42] of the electricity it consumes, while France produces the highest percentage of its electrical energy from nuclear reactors—80% as of 2006.[43] In the European Union as a whole, nuclear energy provides 30% of the electricity.[44] Nuclear energy policy differs among European Union countries, and some, such asAustria, Estonia, Ireland and Italy, have no active nuclear power stations. In comparison, France has a large number of these plants, with 16 multi-unit stations in current use. In the US, while the coal and gas electricity industry is projected to be worth $85 billion by 2013, nuclear power generators are forecast to be worth $18 billion.[45] Many military and some civilian (such as some icebreaker) ships use nuclear marine propulsion, a form of nuclear propulsion.[46] A few space vehicles have been launched using full-fledged nuclear reactors: the Soviet RORSAT series and the American SNAP-10A. International research is continuing into safety improvements such as passively safe plants,[47] the use of nuclear fusion, and additional uses of process heat such as hydrogen production (in support of a hydrogen economy), for desalinating sea water, and for use in district heating systems. Use in space Main article: Nuclear power in space Both fission and fusion appear promising for space propulsion applications, generating higher mission velocities with less reaction mass. This is due to the much higher energy density of nuclear reactions: some 7 orders of magnitude (10,000,000 times) more energetic than the chemical reactions which power the current generation of rockets. Radioactive decay has been used on a relatively small scale (few kW), mostly to power space missions and experiments by usingradioisotope thermoelectric generators such as those developed at Idaho National Laboratory. History Origins
  • 8. See also: Nuclear fission#History The pursuit of nuclear energy for electricity generation began soon after the discovery in the early 20th century that radioactive elements, such as radium, released immense amounts of energy, according to the principle of mass–energy equivalence. However, means of harnessing such energy was impractical, because intensely radioactive elements were, by their very nature, short-lived (high energy release is correlated with short half-lives). However, the dream of harnessing "atomic energy" was quite strong, even though it was dismissed by such fathers of nuclear physics like Ernest Rutherford as "moonshine."[48] This situation, however, changed in the late 1930s, with the discovery of nuclear fission. In 1932, James Chadwick discovered the neutron,[49] which was immediately recognized as a potential tool for nuclear experimentation because of its lack of an electric charge. Experimentation with bombardment of materials with neutrons led Frédéric and Irène Joliot-Curie to discover induced radioactivity in 1934, which allowed the creation of radium-like elements at much less the price of natural radium.[50] Further work by Enrico Fermi in the 1930s focused on using slow neutrons to increase the effectiveness of induced radioactivity. Experiments bombarding uranium with neutrons led Fermi to believe he had created a new, transuranic element, which was dubbed hesperium.[51] December 2, 1942. A depiction of the scene when scientists observed the world's first man made nuclear reactor, the Chicago Pile-1, as it became self- sustaining/critical at the University of Chicago. But in 1938, German chemists Otto Hahn[52] and Fritz Strassmann, along with Austrian physicist Lise Meitner[53] and Meitner's nephew,Otto Robert Frisch,[54] conducted experiments with the products of neutron-bombarded uranium, as a means of further investigating Fermi's claims. They determined that the relatively tiny neutron split the nucleus of the massive uranium atoms into two roughly equal pieces, contradicting Fermi.[51] This was an extremely surprising result: all other forms of nuclear decay involved only small changes to the mass of the nucleus, whereas this process—dubbed "fission" as a reference to biology—involved a complete rupture of the nucleus. Numerous scientists, including Leó Szilárd, who was one of the first, recognized that if fission reactions released additional neutrons, a self-sustaining nuclear chain reaction could result. Once this was experimentally confirmed and announced by Frédéric Joliot-Curie in 1939, scientists in many countries (including the United States, the United Kingdom, France, Germany, and the Soviet Union) petitioned their governments for support of nuclear fission research, just on the cusp of World War II, for the development of a nuclear weapon.[55] In the United States, where Fermi and Szilárd had both emigrated, this led to the creation of the first man-made reactor, known asChicago Pile-1, which achieved criticality on December 2, 1942. This work became part of the Manhattan Project, which made enriched uranium and built large reactors to breed plutonium for use in the first nuclear weapons, which were used on the cities of Hiroshima and Nagasaki. The first light bulbs ever lit by electricity generated by nuclear power at EBR-1 atArgonne National Laboratory-West. After World War II, the prospects of using "atomic energy" for good, rather than simply for war, was advocated as a reason not to keep all nuclear research controlled by military organizations. However, most scientists agreed that civilian nuclear power would take at least a decade to master, and the fact that nuclear reactors also produced weapons-usable plutonium created a situation in which most national governments (such as those in the United States, the United Kingdom, Canada, and the USSR) attempted to keep reactor research under strict government control and classification. In the United States, reactor research was conducted by the U.S. Atomic Energy Commission, primarily at Oak Ridge, Tennessee, Hanford Site, and Argonne National Laboratory. Work in the United States, United Kingdom, Canada,[56] and USSR proceeded over the course of the late 1940s and early 1950s. Electricity was generated for the first time by a nuclear reactor on December 20, 1951, at the EBR-I experimental station near Arco, Idaho, which initially produced about 100 kW.[57][58] Work was also strongly researched in the US on nuclear marine propulsion, with a test reactor being developed by 1953 (eventually, the USS Nautilus, the first nuclear-powered
  • 9. submarine, would launch in 1955).[59] In 1953, US President Dwight Eisenhower gave his "Atoms for Peace" speech at the United Nations, emphasizing the need to develop "peaceful" uses of nuclear power quickly. This was followed by the 1954 Amendments to the Atomic Energy Act which allowed rapid declassification of U.S. reactor technology and encouraged development by the private sector. Early years Calder Hall nuclear power station in the United Kingdom was the world's first nuclear power station to produce electricity in commercial quantities.[60] On June 27, 1954, the USSR's Obninsk Nuclear Power Plant became the world's first nuclear power plant to generate electricity for apower grid, and produced around 5 megawatts of electric power.[61][62] Later in 1954, Lewis Strauss, then chairman of the United States Atomic Energy Commission (U.S. AEC, forerunner of the U.S. Nuclear Regulatory Commission and the United States Department of Energy) spoke of electricity in the future being "too cheap to meter".[63] Strauss was very likely referring to hydrogen fusion[64] —which was secretly being developed as part of Project Sherwood at the time—but Strauss's statement was interpreted as a promise of very cheap energy from nuclear fission. The U.S. AEC itself had issued far more conservative testimony regarding nuclear fission to the U.S. Congress only months before, projecting that "costs can be brought down... [to]... about the same as the cost of electricity from conventional sources..." [65] Significant disappointment would develop later on, when the new nuclear plants did not provide energy "too cheap to meter." In 1955 the United Nations' "First Geneva Conference", then the world's largest gathering of scientists and engineers, met to explore the technology. In 1957 EURATOM was launched alongside the European Economic Community (the latter is now the European Union). The same year also saw the launch of the International Atomic Energy Agency (IAEA). The Shippingport Atomic Power Stationin Shippingport, Pennsylvania was the first commercial reactor in the USA and was opened in 1957. The world's first commercial nuclear power station, Calder Hall at Windscale, England, was opened in 1956 with an initial capacity of 50 MW (later 200 MW).[60][66] The first commercial nuclear generator to become operational in the United States was the Shippingport Reactor(Pennsylvania, December 1957). One of the first organizations to develop nuclear power was the U.S. Navy, for the purpose of propelling submarines and aircraft carriers. The first nuclear-powered submarine, USS Nautilus (SSN-571), was put to sea in December 1954.[67] Two U.S. nuclear submarines,USS Scorpion and USS Thresher, have been lost at sea. Several serious nuclear and radiation accidents have involved nuclear submarine mishaps.[17][19] The Soviet submarine K-19 reactor accident in 1961 resulted in 8 deaths and more than 30 other people were over-exposed to radiation.[18] The Soviet submarine K-27 reactor accident in 1968 resulted in 9 fatalities and 83 other injuries.[19] The U.S. Army also had a nuclear power program, beginning in 1954. The SM-1 Nuclear Power Plant, at Fort Belvoir, Virginia, was the first power reactor in the U.S. to supply electrical energy to a commercial grid (VEPCO), in April 1957, before Shippingport. The SL-1was a U.S. Army experimental nuclear power reactor at the National Reactor Testing Station in eastern Idaho. It underwent a steam explosion and meltdown in January 1961, which killed its three operators.[68] Development
  • 10. History of the use of nuclear power (top) and the number of active nuclear power plants (bottom). Washington Public Power Supply SystemNuclear Power Plants 3 and 5 were never completed. Installed nuclear capacity initially rose relatively quickly, rising from less than 1 gigawatt (GW) in 1960 to 100 GW in the late 1970s, and 300 GW in the late 1980s. Since the late 1980s worldwide capacity has risen much more slowly, reaching 366 GW in 2005. Between around 1970 and 1990, more than 50 GW of capacity was under construction (peaking at over 150 GW in the late 70s and early 80s) — in 2005, around 25 GW of new capacity was planned. More than two-thirds of all nuclear plants ordered after January 1970 were eventually cancelled.[67] A total of 63 nuclear units were canceled in the USA between 1975 and 1980.[69] During the 1970s and 1980s rising economic costs (related to extended construction times largely due to regulatory changes and pressure-group litigation)[70] and falling fossil fuel prices made nuclear power plants then under construction less attractive. In the 1980s (U.S.) and 1990s (Europe), flat load growth and electricity liberalization also made the addition of large new baseload capacity unattractive. The 1973 oil crisis had a significant effect on countries, such as France and Japan, which had relied more heavily on oil for electric generation (39%[71][verification needed] and 73% respectively) to invest in nuclear power.[72] Some local opposition to nuclear power emerged in the early 1960s,[73] and in the late 1960s some members of the scientific community began to express their concerns.[74] These concerns related to nuclear accidents, nuclear proliferation, high cost of nuclear power plants,nuclear terrorism and radioactive waste disposal.[75] In the early 1970s, there were large protests about a proposed nuclear power plant in Wyhl, Germany. The project was cancelled in 1975 and anti- nuclear success at Wyhl inspired opposition to nuclear power in other parts of Europe and North America.[76][77] By the mid-1970s anti-nuclear activism had moved beyond local protests and politics to gain a wider appeal and influence, and nuclear power became an issue of major public protest.[78] Although it lacked a single co- ordinating organization, and did not have uniform goals, the movement's efforts gained a great deal of attention.[79] In some countries, the nuclear power conflict "reached an intensity unprecedented in the history of technology controversies".[80] 120,000 people attended an anti-nuclear protest in Bonn, Germany, on October 14, 1979, following the Three Mile Island accident.[81] In France, between 1975 and 1977, some 175,000 people protested against nuclear power in ten demonstrations.[81] In West Germany, between February 1975 and April 1979, some 280,000 people were involved in seven demonstrations at nuclear sites. Several site occupations were also attempted. In the aftermath of the Three
  • 11. Mile Island accident in 1979, some 120,000 people attended a demonstration against nuclear power in Bonn.[81] In May 1979, an estimated 70,000 people, including then governor of California Jerry Brown, attended a march and rally against nuclear power in Washington, D.C.[82] Anti-nuclear power groups emerged in every country that has had a nuclear power programme. Some of these anti-nuclear power organisations are reported to have developed considerable expertise on nuclear power and energy issues.[83] The abandoned city of Pripyat with Chernobyl plant in the distance. Health and safety concerns, the 1979 accident at Three Mile Island, and the 1986 Chernobyl disaster played a part in stopping new plant construction in many countries,[84] although the public policy organization, the Brookings Institution states that new nuclear units, at the time of publishing in 2006, had not been built in the U.S. because of soft demand for electricity, and cost overruns on nuclear plants due to regulatory issues and construction delays.[85] By the end of the 1970s it became clear that nuclear power would not grow nearly as dramatically as once believed. Eventually, more than 120 reactor orders in the U.S. were ultimately cancelled[86] and the construction of new reactors ground to a halt. A cover story in the February 11, 1985, issue of Forbes magazine commented on the overall failure of the U.S. nuclear power program, saying it ―ranks as the largest managerial disaster in business history‖.[87] Unlike the Three Mile Island accident, the much more serious Chernobyl accident did not increase regulations affecting Western reactors since the Chernobyl reactors were of the problematic RBMK design only used in the Soviet Union, for example lacking "robust"containment buildings.[88] Many of these RBMK reactors are still in use today. However, changes were made in both the reactors themselves (use of a safer enrichment of uranium) and in the control system (prevention of disabling safety systems), amongst other things, to reduce the possibility of a duplicate accident.[89] An international organization to promote safety awareness and professional development on operators in nuclear facilities was created:WANO; World Association of Nuclear Operators. Opposition in Ireland and Poland prevented nuclear programs there, while Austria (1978), Sweden (1980) and Italy (1987) (influenced by Chernobyl) voted in referendums to oppose or phase out nuclear power. In July 2009, the Italian Parliament passed a law that cancelled the results of an earlier referendum and allowed the immediate start of the Italian nuclear program.[90] After the Fukushima Daiichi nuclear disaster a one year moratorium was placed on nuclear power development,[91] followed by a referendum in which over 94% of voters (turnout 57%) rejected plans for new nuclear power.[92] Nuclear power plant An animation of a Pressurized water reactor in operation. Unlike fossil fuel power plants, the only substance leaving the cooling towers ofnuclear power plants is water vapour and thus does not pollute the air or cause global warming.
  • 12. Main article: Nuclear power plant Just as many conventional thermal power stations generate electricity by harnessing thethermal energy released from burning fossil fuels, nuclear power plants convert the energy released from the nucleus of an atom via nuclear fission that takes place in a nuclear reactor. The heat is removed from the reactor core by a cooling system that uses the heat to generate steam, which drives a steam turbine connected to a generator producing electricity. Life cycle The nuclear fuel cycle begins when uranium is mined, enriched, and manufactured into nuclear fuel, (1) which is delivered to a nuclear power plant. After usage in the power plant, the spent fuel is delivered to a reprocessing plant (2) or to a final repository (3) for geological disposition. In reprocessing 95% of spent fuel can potentially be recycled to be returned to usage in a power plant (4). Main article: Nuclear fuel cycle A nuclear reactor is only part of the life-cycle for nuclear power. The process starts with mining (see Uranium mining). Uranium mines are underground, open-pit, or in-situ leach mines. In any case, the uranium ore is extracted, usually converted into a stable and compact form such as yellowcake, and then transported to a processing facility. Here, the yellowcake is converted to uranium hexafluoride, which is then enriched using various techniques. At this point, the enriched uranium, containing more than the natural 0.7% U-235, is used to make rods of the proper composition and geometry for the particular reactor that the fuel is destined for. The fuel rods will spend about 3 operational cycles (typically 6 years total now) inside the reactor, generally until about 3% of their uranium has been fissioned, then they will be moved to a spent fuel pool where the short lived isotopes generated by fission can decay away. After about 5 years in a spent fuel pool the spent fuel is radioactively and thermally cool enough to handle, and it can be moved to dry storage casks or reprocessed. Conventional fuel resources Main articles: Uranium market and Energy development - Nuclear energy
  • 13. Proportions of the isotopes, uranium-238 (blue) and uranium-235 (red) found naturally, versus grades that areenriched. light water reactors require fuel enriched to (3-4%), while others such as the CANDU reactor uses natural uranium. Uranium is a fairly common element in the Earth's crust. Uranium is approximately as common as tin or germanium in the Earth's crust, and is about 40 times more common than silver.[93] Uranium is a constituent of most rocks, dirt, and of the oceans. The fact that uranium is so spread out is a problem because mining uranium is only economically feasible where there is a large concentration. Still, the world's present measured resources of uranium, economically recoverable at a price of 130 USD/kg, are enough to last for between 70 and 100 years.[94][95][96] Uranium represents a higher level of assured resources than is normal for most minerals. On the basis of analogies with other metallic minerals, a doubling of price from present levels could be expected to create about a tenfold increase in measured resources, over time. According to the OECD in 2006, there is an expected 85 years worth of uranium in identified resources, when that uranium is used inpresent reactor technology, with 670 years of economically recoverable uranium in total conventional resources and phosphate ores, while also using present reactor technology, a resource that is recoverable from between 60-100 US$/kg of Uranium.[97] The OECD have noted that: Even if the nuclear industry expands significantly, sufficient fuel is available for centuries. If advanced breeder reactors could be designed in the future to efficiently utilize recycled or depleted uranium and all actinides, then the resource utilization efficiency would be further improved by an additional factor of eight. For example, the OECD have determined that with a pure fast reactor fuel cycle with a burn up of, and recycling of, all the Uranium andactinides, actinides which presently make up the most hazardous substances in nuclear waste, there is 160,000 years worth of Uranium in total conventional resources and phosphate ore.[98] According to the OECD's red book in 2011, due to increased exploration, known uranium resources have grown by 12.5% since 2008, with this increase translating into greater than a century of uranium available if the metals usage rate were to continue at the 2011 level.[99][100] Current light water reactors make relatively inefficient use of nuclear fuel, fissioning only the very rare uranium-235 isotope. Nuclear reprocessing can make this waste reusable, and more efficient reactor designs, such as the currently under construction Generation III reactors achieve a higher efficiency burn up of the available resources, than the current vintage generation II reactors, which make up the vast majority of reactors worldwide.[101] Breeding Main articles: Breeder reactor and Nuclear power proposed as renewable energy As opposed to current light water reactors which use uranium-235 (0.7% of all natural uranium), fast breeder reactors use uranium-238 (99.3% of all natural uranium). It has been estimated that there is up to five billion years' worth of uranium-238 for use in these power plants.[102] Breeder technology has been used in several reactors, but the high cost of reprocessing fuel safely, at 2006 technological levels, requires uranium prices of more than 200 USD/kg before becoming justified economically.[103] Breeder reactors are still however being pursued as they have the potential to burn up all of the actinides in the present inventory of nuclear waste while also producing power and creating additional quantities of fuel for more reactors via the breeding process.[104][105] In 2005, there were two breeder reactors producing power thePhénix in France, which has since powered down in 2009 after 36 years of operation, and the BN-600 reactor, a reactor constructed in 1980 Beloyarsk, Russia which is still operational as of 2013. The electricity output of BN-600 is 600 MW — Russia plans to expand the nations use of breeder reactors with the BN-800 reactor, scheduled to become operational in 2014,[106] and the technical design of a yet larger breeder, the BN-1200 reactor scheduled to be finalized in 2013, with construction slated for 2015.[107] Japan's Monju breeder reactor restarted (having been shut down in 1995) in 2010 for 3 months, but shut down again after equipment fell into the reactor during reactor checkups, it is planned to become re-operational in late 2013.[108] Both China and India are building breeder reactors. With the Indian 500 MWe Prototype Fast Breeder Reactor scheduled to become operational in 2014, with plans to build five more by 2020.[109] The China Experimental Fast Reactor began producing power in 2011.[110] Another alternative to fast breeders is thermal breeder reactors that use uranium-233 bred from thorium as fission fuel in the thorium fuel cycle. Thorium is about 3.5 times more common than uranium in the Earth's crust, and has different geographic characteristics. This would extend the total practical fissionable resource base by 450%.[111] India's three-stage nuclear power programme features the use of a thorium fuel cycle in the third stage, as it has abundant thorium reserves but little uranium. Solid waste For more details on this topic, see Radioactive waste. See also: List of nuclear waste treatment technologies The most important waste stream from nuclear power plants is spent nuclear fuel. It is primarily composed of unconverted uranium as well as significant quantities of transuranicactinides (plutonium and curium, mostly). In addition, about 3% of it is fission products from nuclear reactions. The actinides (uranium, plutonium, and curium) are responsible for the bulk of the long-term radioactivity, whereas the fission products are responsible for the bulk of the short-term radioactivity.[112] High-level radioactive waste Main article: High-level radioactive waste management
  • 14. A nuclear fuel rod assembly bundle being inspected before entering a reactor. Following interim storage in a spent fuel pool, the bundles of used fuel assemblies of a typical nuclear power station are often stored on site in the likes of the eight dry cask storage vessels pictured above.[113] At Yankee Rowe Nuclear Power Station, which generated 44 billion kilowatt hours of electricity over its lifetime, its complete spent fuel inventory is contained within sixteen casks.[114] The world's nuclear fleet creates about 10,000 metric tons of spent nuclear fuel each year.[115] High-level radioactive waste management concerns management and disposal of highly radioactive materials created during production of nuclear power. The technical issues in accomplishing this are daunting, due to the extremely long periods radioactive wastes remain deadly to living organisms. Of particular concern are two long-lived fission products, Technetium-99 (half-life 220,000 years) and Iodine-129 (half-life 15.7 million years),[116] which dominate spent nuclear fuel radioactivity after a few thousand years. The most troublesome transuranic elements in spent fuel areNeptunium-237 (half-life two million years) and Plutonium-239 (half-life 24,000 years).[117] Consequently, high-level radioactive waste requires sophisticated treatment and management to successfully isolate it from the biosphere. This usually necessitates treatment, followed by a long-term management strategy involving permanent storage, disposal or transformation of the waste into a non-toxic form.[118] Governments around the world are considering a range of waste management and disposal options, usually involving deep-geologic placement, although there has been limited progress toward implementing long-term waste management solutions.[119] This is partly because the timeframes in question when dealing with radioactive waste range from 10,000 to millions of years,[120][121] according to studies based on the effect of estimated radiation doses.[122] Some proposed nuclear reactor designs however such as the American Integral Fast Reactor and the Molten salt reactor can use the nuclear waste from light water reactors as a fuel, transmutating it to isotopes that would be safe after hundreds, instead of tens of thousands of years. This offers a potentially more attractive alternative to deep geological disposal.[123][124][125] Another possibility is the use of thorium in a reactor especially designed for thorium (rather than mixing in thorium with uranium and plutonium (i.e. in existing reactors). Used thorium fuel remains only a few hundreds of years radioactive, instead of tens of thousands of years.[126] Since the fraction of a radioisotope's atoms decaying per unit of time is inversely proportional to its half-life, the relative radioactivity of a quantity of buried human radioactive waste would diminish over time compared to natural radioisotopes (such as the decay chains of 120 trillion tons of thorium and 40 trillion tons of uranium which are at relatively trace concentrations of parts per million each over the crust's 3 * 1019 ton mass).[127][128][129] For instance, over a timeframe of thousands of years, after the most active short half-life radioisotopes decayed, burying U.S. nuclear waste would increase the radioactivity in the top 2000 feet of rock and soil in the United States (10 million km2 ) by ≈ 1 part in 10 million over the cumulative amount of natural radioisotopes in such a volume, although the vicinity of the site would have a far higher concentration of artificial radioisotopes underground than such an average.[130] Low-level radioactive waste See also: Low-level waste The nuclear industry also produces a large volume of low-level radioactive waste in the form of contaminated items like clothing, hand tools, water purifier resins, and (upon decommissioning) the materials of which the reactor itself is built. In the United States, the Nuclear Regulatory Commission has repeatedly attempted to allow low-level materials to be handled as normal waste: landfilled, recycled into consumer items, etcetera.[citation needed] Comparing radioactive waste to industrial toxic waste
  • 15. In countries with nuclear power, radioactive wastes comprise less than 1% of total industrial toxic wastes, much of which remains hazardous for long periods.[101] Overall, nuclear power produces far less waste material by volume than fossil-fuel based power plants.[131] Coal-burning plants are particularly noted for producing large amounts of toxic and mildly radioactive ash due to concentrating naturally occurring metals and mildly radioactive material from the coal.[132] A 2008 report from Oak Ridge National Laboratory concluded that coal power actually results in more radioactivity being released into the environment than nuclear power operation, and that the population effective dose equivalent, or dose to the public from radiation from coal plants is 100 times as much as from the ideal operation of nuclear plants.[133] Indeed, coal ash is much less radioactive than spent nuclear fuel on a weight per weight basis, but coal ash is produced in much higher quantities per unit of energy generated, and this is released directly into the environment as fly ash, whereas nuclear plants use shielding to protect the environment from radioactive materials, for example, in dry cask storage vessels.[134] Waste disposal Disposal of nuclear waste is often said to be the Achilles' heel of the industry.[135] Presently, waste is mainly stored at individual reactor sites and there are over 430 locations around the world where radioactive material continues to accumulate. Some experts suggest that centralized underground repositories which are well- managed, guarded, and monitored, would be a vast improvement.[135] There is an "international consensus on the advisability of storing nuclear waste in deep geological repositories",[136] with the lack of movement of nuclear waste in the 2 billion year old natural nuclear fission reactors in Oklo, Gabon being cited as "a source of essential information today."[137][138] As of 2009 there were no commercial scale purpose built underground repositories in operation.[136][139][140][141] The Waste Isolation Pilot Plant in New Mexico has been taking nuclear waste since 1999 from production reactors, but as the name suggests is a research and development facility. Reprocessing For more details on this topic, see Nuclear reprocessing. Reprocessing can potentially recover up to 95% of the remaining uranium and plutonium in spent nuclear fuel, putting it into new mixed oxide fuel. This produces a reduction in long term radioactivity within the remaining waste, since this is largely short-lived fission products, and reduces its volume by over 90%. Reprocessing of civilian fuel from power reactors is currently done in Britain, France and (formerly) Russia, soon will be done in China and perhaps India, and is being done on an expanding scale in Japan. The full potential of reprocessing has not been achieved because it requires breeder reactors, which are not commercially available. France is generally cited as the most successful reprocessor, but it presently only recycles 28% (by mass) of the yearly fuel use, 7% within France and another 21% in Russia.[142] Reprocessing is not allowed in the U.S.[143] The Obama administration has disallowed reprocessing of nuclear waste, citing nuclear proliferation concerns.[144] In the U.S., spent nuclear fuel is currently all treated as waste.[145] Depleted uranium Main article: Depleted uranium Uranium enrichment produces many tons of depleted uranium (DU) which consists of U-238 with most of the easily fissile U-235 isotope removed. U-238 is a tough metal with several commercial uses—for example, aircraft production, radiation shielding, and armor—as it has a higher density than lead. Depleted uranium is also controversially used in munitions; DU penetrators (bullets or APFSDS tips) "self sharpen", due to uranium's tendency to fracture along shear bands.[146][147] Economics Main article: Economics of new nuclear power plants The Ikata Nuclear Power Plant, apressurized water reactor that cools by utilizing a secondary coolant heat exchangerwith a large body of water, an alternative cooling approach to large cooling towers. The economics of new nuclear power plants is a controversial subject, since there are diverging views on this topic, and multi-billion dollar investments ride on the choice of an energy source. Nuclear power plants typically have high capital costs for building the plant, but low fuel costs. Therefore, comparison with other power generation methods is strongly dependent on assumptions about construction timescales and capital financing for nuclear plants as well as the future costs of fossil fuels and renewables as well as for energy storage solutions for intermittent power sources. Cost estimates also need to take into account plant decommissioning and nuclear wastestorage costs. On the other hand measures to mitigate global warming, such as a carbon tax or carbon emissions trading, may favor the economics of nuclear power.
  • 16. In recent years there has been a slowdown of electricity demand growth and financing has become more difficult, which has an impact on large projects such as nuclear reactors, with very large upfront costs and long project cycles which carry a large variety of risks.[148] In Eastern Europe, a number of long-established projects are struggling to find finance, notably Belene in Bulgaria and the additional reactors at Cernavoda in Romania, and some potential backers have pulled out.[148] Where cheap gas is available and its future supply relatively secure, this also poses a major problem for nuclear projects.[148] Analysis of the economics of nuclear power must take into account who bears the risks of future uncertainties. To date all operating nuclear power plants were developed by state-owned or regulated utility monopolies[149] where many of the risks associated with construction costs, operating performance, fuel price, accident liability and other factors were borne by consumers rather than suppliers. In addition, because the potential liability from a nuclear accident is so great, the full cost of liability insurance is generally limited/capped by the government, which the U.S. Nuclear Regulatory Commission concluded constituted a significant subsidy.[150] Many countries have now liberalized the electricity marketwhere these risks, and the risk of cheaper competitors emerging before capital costs are recovered, are borne by plant suppliers and operators rather than consumers, which leads to a significantly different evaluation of the economics of new nuclear power plants.[151] Following the 2011 Fukushima nuclear accident, costs are expected to increase for currently operating and new nuclear power plants, due to increased requirements for on-site spent fuel management and elevated design basis threats.[152] Accidents and safety, the human and financial costs The 2011 Fukushima Daiichi nuclear accident, the world's worst nuclear accidentsince 1986, displaced 50,000 households after radiation leaked into the air, soil and sea.[153] Radiation checks led to bans of some shipments of vegetables and fish.[154] See also: Energy accidents, Nuclear safety, Nuclear and radiation accidents, and Lists of nuclear disasters and radioactive incidents Some serious nuclear and radiation accidents have occurred. Benjamin K. Sovacool has reported that worldwide there have been 99 accidents at nuclear power plants.[155] Fifty-seven accidents have occurred since the Chernobyl disaster, and 57% (56 out of 99) of all nuclear-related accidents have occurred in the USA.[155][156] Nuclear power plant accidents include the Chernobyl accident (1986) with approximately 60 deaths so far attributed to the accident and a predicted, eventual total death toll, of from 4000 to 25,000 latent cancers deaths. The Fukushima Daiichi nuclear accident (2011), has not caused any radiation related deaths, with a predicted, eventual total death toll, of from 0 to 1000, and the Three Mile Island accident(1979), no causal deaths, cancer or otherwise, have been found in follow up studies of this accident.[17] Nuclear-powered submarine mishaps include the K-19 reactor accident (1961),[18] the K-27 reactor accident (1968),[19] and the K- 431 reactor accident (1985).[17] International research is continuing into safety improvements such as passively safe plants,[47] and the possible future use of nuclear fusion. In terms of lives lost per unit of energy generated, nuclear power has caused fewer accidental deaths per unit of energy generated than all other major sources of energy generation. Energy produced by coal, petroleum, natural gas and hydropower has caused more deaths per unit of energy generated, from air pollution and energy accidents. This is found in the following comparisons, when the immediate nuclear related deaths from accidents are compared to the immediate deaths from these other energy sources,[21] when the latent, or predicted, indirect cancer deaths from nuclear energy accidents are compared to the immediate deaths from the above energy sources,[23][24][157] and when the combined immediate and indirect fatalities from nuclear power and all fossil fuels are compared, fatalities resulting from the mining of the necessary natural resources to power generation and to air pollution.[158] With these data, the use of nuclear power has been calculated to have prevented a considerable number of fatalities, by reducing the proportion of energy that would otherwise have been generated by fossil fuels, and is projected to continue to do so.[159][160] Nuclear power plant accidents, according to Benjamin K. Sovacool, rank first in terms of their economic cost, accounting for 41 percent of all property damage attributed to energy accidents.[161] However analysis presented in the international Journal, Human and Ecological Risk Assessment found that coal, oil, Liquid petroleum gas and hydro accidents have cost more than nuclear power accidents.[162] Following the 2011 Japanese Fukushima nuclear disaster, authorities shut down the nation's 54 nuclear power plants, but it has been estimated that if Japan had never adopted nuclear power, accidents and pollution from coal or gas plants would have caused more lost years of life.[163] As of 2013, the Fukushima site remains highly radioactive, with some 160,000 evacuees still living in temporary housing, and some land will be unfarmable for centuries. The difficult cleanup job will take 40 or more years, and cost tens of billions of dollars.[164][165] Forced evacuation from a nuclear accident may lead to social isolation, anxiety, depression, psychosomatic medical problems, reckless behavior, even suicide. Such was the outcome of the 1986 Chernobyl nuclear disaster in the Ukraine. A comprehensive 2005 study concluded that "the mental health impact of Chernobyl is the
  • 17. largest public health problem unleashed by the accident to date".[166] Frank N. von Hippel, a U.S. scientist, commented on the 2011 Fukushima nuclear disaster, saying that "fear of ionizing radiation could have long-term psychological effects on a large portion of the population in the contaminated areas".[167] Nuclear proliferation Many technologies and materials associated with the creation of a nuclear power program have a dual-use capability, in that they can be used to make nuclear weapons if a country chooses to do so. When this happens a nuclear power program can become a route leading to a nuclear weapon or a public annex to a "secret" weapons program. The concern over Iran's nuclear activities is a case in point.[168] United States and USSR/Russian nuclear weapons stockpiles, 1945-2006.TheMegatons to Megawatts Program was the main driving force behind the sharp reduction in the quantity of nuclear weapons worldwide since the cold war ended.[169][170] However without an increase in nuclear reactors and greater demand for fissile fuel, the cost of dismantling has dissuaded Russia from continuing their disarmament. A fundamental goal for American and global security is to minimize the nuclear proliferation risks associated with the expansion of nuclear power. If this development is "poorly managed or efforts to contain risks are unsuccessful, the nuclear future will be dangerous".[168] The Global Nuclear Energy Partnership is one such international effort to create a distribution network in which developing countries in need of energy, would receive nuclear fuel at a discounted rate, in exchange for that nation agreeing to forgo their own indigenous develop of a uranium enrichment program. According to Benjamin K. Sovacool, a "number of high-ranking officials, even within the United Nations, have argued that they can do little to stop states using nuclear reactors to produce nuclear weapons".[171] A 2009 United Nations report said that: the revival of interest in nuclear power could result in the worldwide dissemination of uranium enrichment and spent fuel reprocessing technologies, which present obvious risks of proliferation as these technologies can produce fissile materials that are directly usable in nuclear weapons.[171] On the other hand, one factor influencing the support of power reactors is due to the appeal that these reactors have at reducing nuclear weapons arsenals through the Megatons to Megawatts Program, a program which has thus far eliminated 425 metric tons of highly enriched uranium, the equivalent of 17,000 nuclear warheads, by converting it into fuel for commercial nuclear reactors, and it is the single most successful non-proliferation program to date.[169] The Megatons to Megawatts Program has been hailed as a major success by anti-nuclear weapon advocates as it has largely been the driving force behind the sharp reduction in the quantity of nuclear weapons worldwide since the cold war ended.[169] However without an increase in nuclear reactors and greater demand for fissile fuel, the cost of dismantling and down blending has dissuaded Russia from continuing their disarmament. Currently, according to Harvard professor Matthew Bunn: The Russians are not remotely interested in extending the program beyond 2013. We've managed to set it up in a way that costs them more and profits them less than them just making new low-enriched uranium for reactors from scratch. But there are other ways to set it up that would be very profitable for them and would also serve some of their strategic interests in boosting their nuclear exports.[172]
  • 18. In the Megatons to Megawatts Program approximately $8 billion of weapons grade uranium is being converted to reactor grade uranium in the elimination of 10,000 nuclear weapons.[173] In April 2012 there were thirty one countries that have civil nuclear power plants.[174] In 2013, Mark Diesendorf says that governments of France, India, North Korea, Pakistan, UK, and South Africa have used nuclear power and/or research reactors to assist nuclear weapons development or to contribute to their supplies of nuclear explosives from military reactors.[175] Environmental issues A 2008 synthesis of 103 studies, published by Benjamin K. Sovacool, estimated that the value of CO2 emissions for nuclear power over the lifecycle of a plant was 66.08 g/kW·h. Comparative results for various renewable powersources were 9–32 g/kW·h.[176] A 2012 study by Yale University arrived at a different value, with the mean value, depending on which Reactor design was analyzed, ranging from 11 to 25 g/kW·h oftotal life cycle nuclear power CO2emissions.[177] Main articles: Environmental effects of nuclear power and Comparisons of life-cycle greenhouse gas emissions Life cycle analysis (LCA) of carbon dioxide emissions show nuclear power as comparable to renewable energy sources. Emissions from burning fossil fuels are many times higher.[176][178][179] According to the United Nations (UNSCEAR), regular nuclear power plant operation including the nuclear fuel cycle causes radioisotope releases into the environment amounting to 0.0002 mSv (milli-Sievert) per year of public exposure as a global average.[180] (Such is small compared to variation in natural background radiation, which averages 2.4 mSv/a globally but frequently varies between 1 mSv/a and 13 mSv/a depending on a person's location as determined by UNSCEAR).[180] As of a 2008 report, the remaining legacy of the worst nuclear power plant accident (Chernobyl) is 0.002 mSv/a in global average exposure (a figure which was 0.04 mSv per person averaged over the entire populace of the Northern Hemisphere in the year of the accident in 1986, although far higher among the most affected local populations and recovery workers).[180] Climate change Climate change causing weather extremes such as heat waves, reduced precipitation levels and droughts can have a significant impact on nuclear energy infrastructure.[181] Seawater is corrosive and so nuclear energy supply is likely to be negatively affected by the freshwater shortage.[181] This generic problem may become increasingly significant over time.[181] This can force nuclear reactors to be shut down, as happened in France during the 2003 and 2006 heat waves. Nuclear power supply was severely diminished by low river flow rates and droughts, which meant rivers had reached the maximum temperatures for cooling reactors.[181] During the heat waves, 17 reactors had to limit output or shut down. 77% of French electricity is produced by nuclear power and in 2009 a similar situation created a 8GW shortage and forced the French government to import electricity.[181] Other cases have been reported from Germany, where extreme temperatures have reduced nuclear power production 9 times due to high temperatures between 1979 and 2007.[181] In particular: the Unterweser nuclear power plant reduced output by 90% between June and September 2003[181] the Isar nuclear power plant cut production by 60% for 14 days due to excess river temperatures and low stream flow in the river Isar in 2006[181] Similar events have happened elsewhere in Europe during those same hot summers.[181] If global warming continues, this disruption is likely to increase. Nuclear decommissioning The price of energy inputs and the environmental costs of every nuclear power plant continue long after the facility has finished generating its last useful electricity. Both nuclear reactors and uranium enrichment facilities must be decommissioned, returning the facility and its parts to a safe enough level to be entrusted for other uses. After a cooling-off period that may last as long as a century, reactors must be dismantled and cut into small pieces to be packed in containers for final disposal. The process is very expensive, time-consuming, dangerous for workers, hazardous to the natural environment, and presents new opportunities for human error, accidents or sabotage.[182] The total energy required for decommissioning can be as much as 50% more than the energy needed for the original construction. In most cases, the decommissioning process costs between US $300 million to US$5.6 billion. Decommissioning at nuclear sites which have experienced a serious accident are the
  • 19. most expensive and time-consuming. In the U.S. there are 13 reactors that have permanently shut down and are in some phase of decommissioning, and none of them have completed the process.[182] Current UK plants are expected to exceed £73bn in decommissioning costs."Nuclear decommissioning costs exceed £73bn". Debate on nuclear power Main article: Nuclear power debate See also: Nuclear energy policy and Anti-nuclear movement The nuclear power debate concerns the controversy[11][12][79] which has surrounded the deployment and use of nuclear fission reactors to generate electricity from nuclear fuel for civilian purposes. The debate about nuclear power peaked during the 1970s and 1980s, when it "reached an intensity unprecedented in the history of technology controversies", in some countries.[80][183] Proponents of nuclear energy contend that nuclear power is a sustainable energy source that reduces carbon emissions and increases energy security by decreasing dependence on imported energy sources.[13] Proponents claim that nuclear power produces virtually no conventional air pollution, such as greenhouse gases and smog, in contrast to the chief viable alternative of fossil fuel. Nuclear power can produce base-load power unlike many renewables which are intermittent energy sources lacking large-scale and cheap ways of storing energy.[184] M. King Hubbert saw oil as a resource that would run out, and proposed nuclear energy as a replacement energy source.[185] Proponents claim that the risks of storing waste are small and can be further reduced by using the latest technology in newer reactors, and the operational safety record in the Western world is excellent when compared to the other major kinds of power plants.[186] Opponents believe that nuclear power poses many threats to people and the environment.[14][15][16] These threats include the problems of processing, transport and storage of radioactive nuclear waste, the risk of nuclear weapons proliferation and terrorism, as well as health risks and environmental damage from uranium mining.[187][188] They also contend that reactors themselves are enormously complex machines where many things can and do go wrong; and there have been serious nuclear accidents.[189][190] Critics do not believe that the risks of using nuclear fission as a power source can be fully offset through the development of new technology. They also argue that when all the energy-intensive stages of the nuclear fuel chain are considered, from uranium mining to nuclear decommissioning, nuclear power is neither a low-carbon nor an economical electricity source.[191][192][193] Arguments of economics and safety are used by both sides of the debate. Comparison with renewable energy See also: Nuclear power proposed as renewable energy Nuclear power has been compared to renewable energy as neither produce greenhouse gases in operation and both have low lifecycle greenhouse gas emissions.[194] The cost of both nuclear power and wind power are dominated by plant construction costs, although the operation and maintenance costs for nuclear power were estimated in 2008 to be slightly higher than wind power according to the US Energy Information Administration [195] and considerably cheaper according to Lazard.[196] A typical nuclear power plant has an economic lifespan of around 40 years, while wind turbines have a lifespan of around 25 years, according to Lappeenranta University of Technology.[197] However, wind turbines are much easier to decommission and replace with new ones, extending the life of the wind farm indefinitely, where as nuclear facilities must be closed at the end of their useful life. There is however no spent fuel that needs to be stored or reprocessed with conventional renewable energy sources.[198] A nuclear plant needs to be disassembled and removed. Much of the disassembled nuclear plant needs to be stored as low level nuclear waste.[199] The cost of nuclear power has followed an increasing trend, as has the installation cost of wind power from approximately 2002, whereas the cost of electricity is declining in wind power.[200] In about 2011, wind power became as inexpensive as natural gas, and anti-nuclear groups have suggested that in 2010 solar power became cheaper than nuclear power.[201][202] Data from the EIA in 2011 estimated that in 2016, solar will have a levelized cost of electricity almost twice that of nuclear (21¢/kWh for solar, 11.39¢/kWh for nuclear), and wind somewhat less (9.7¢/kWh). Wind power and photovoltaics are variable renewable energy sources, meaning they are not dispatchable, and locally can be unavailable for days on end. Both, like nuclear, require buffering, with pumped hydrostorage.[203] However due to nuclear powers capacity factor of 80-90%, in comparison tointermittent wind power's 30-40%, the requirements for pumped storage are much less than those needed for wind power. From a safety stand point, nuclear power, in terms of lives lost per unit of electricity delivered, is comparable to and in some cases, lower than many renewable energysources.[20][21][204] In the United Kingdom, the amount of energy produced from renewable energy is expected to exceed that from nuclear power by 2018,[205] and Scotland plans to obtain all electricity from renewable energy by 2020.[206] In 2012 the share of electricity generated by renewable sources in Germany was 21.9%, compared to 16.0% for nuclear power after Germany shut down 7-8 of its 18 nuclear reactors in 2011.[207] The majority of installed renewable energy across the world is in the form of Hydro power.
  • 20. Nuclear renaissance Main article: Nuclear renaissance Since about 2001 the term "nuclear renaissance" has been used to refer to a possible nuclear power industry revival, driven by rising fossil fuel prices and new concerns about meeting greenhouse gas emission limits. Being able to rely on an uninterrupted domestic supply of electricity is also a factor. In the words of the French, "We have no coal, we have no oil, we have no gas, we have no choice."[208] Improvements in nuclear reactor safety, and the public's waning memory of past nuclear accidents (Three Mile Island in 1979 and Chernobyl in 1986), as well as of the plant construction cost overruns of the 1970s and 80s, are lowering public resistance to new nuclear construction.[209] At the same time, various barriers to a nuclear renaissance have been identified. These include: unfavourable economics compared to other sources of energy, slowness in addressing climate change, industrial bottlenecks and personnel shortages in nuclear sector, and the unresolved nuclear waste issue. There are also concerns about more accidents, security, and nuclear weapons proliferation.[39][210][211][212] New reactors under construction in Finland and France, which were meant to lead a nuclear renaissance, have been delayed and are running over- budget.[213][214][215] China has 20 new reactors under construction,[216] and there are also a considerable number of new reactors being built in South Korea, India, and Russia. At least 100 older and smaller reactors will "most probably be closed over the next 10-15 years".[217] In 2007 the Kashiwazaki-Kariwa Nuclear Power Plant, the world's largest nuclear power plant, suffered earthquake damage, and in 2011 the nuclear emergencies at Japan'sFukushima I Nuclear Power Plant and other nuclear facilities raised questions over the future of the renaissance.[218][219][220][221][222] Platts has reported that "the crisis at Japan's Fukushima nuclear plants has prompted leading energy-consuming countries to review the safety of their existing reactors and cast doubt on the speed and scale of planned expansions around the world".[223] Many countries are re-evaluating their nuclear energy programs and in April 2011 a study by UBS predicted that around 30 nuclear plants could be closed world-wide as a result, with those located in seismic zones or close to national boundaries being the most likely to shut. The UBS analysts believe that 'even pro-nuclear counties such as France will be forced to close at least two reactors to demonstrate political action and restore the public acceptability of nuclear power', noting that the events at Fukushima 'cast doubt on the idea that even an advanced economy can master nuclear safety'.[224] Canadian uranium-mining company Cameco expects the size of world's fleet of operating reactors in 2020 to increase by about 90 reactors, 10% less than before the Fukushima accident.[225] Future of the industry See also: List of prospective nuclear units in the United States, Nuclear power in the United States, Nuclear energy policy, and Mitigation of global warming Brunswick Nuclear Plant discharge canal According to the World Nuclear Association, globally during the 1980s one new nuclear reactor started up every 17 days on average, and by the year 2015 this rate could increase to one every 5 days.[226] As of 2007, Watts Bar 1 in Tennessee, which came on-line on February 7, 1996, was the last U.S. commercial nuclear reactor to go on-line. This is often quoted as evidence of a successful worldwide campaign for nuclear power phase-out. However, even in the U.S. and throughout Europe, investment in research and in the nuclear fuel cycle has continued, and some nuclear industry experts[227] predict electricity shortages, fossil fuel price increases, global warming and heavy metal emissions from fossil fuel use, new technology such as passively safe plants, and national energy security will renew the demand for nuclear power plants. There is a possible impediment to production of nuclear power plants as only a few companies worldwide have the capacity to forge single-piece reactor pressure vessels,[228] which are necessary in the most common reactor designs. Utilities across the world are submitting orders years in advance of any actual need for these vessels. Other manufacturers are examining various options, including making the component themselves, or finding ways to make a similar item using alternate methods.[229] Other solutions include using designs that do not require single-piece forged pressure vessels such as Canada's Advanced CANDU Reactors or Sodium-cooled Fast Reactors.
  • 21. The Bruce Nuclear Generating Station, the largest nuclear power facility in the world[230] China has 25 reactors under construction, with plans to build more,[231] while in the US the licenses of almost half its reactors have been extended to 60 years,[232] and plans to build another dozen are under serious consideration.[233] China may achieve its long-term plan of having 40,000 megawatts of nuclear power capacity four to five years ahead of schedule.[234] However, according to a government research unit, China must not build "too many nuclear power reactors too quickly", in order to avoid a shortfall of fuel, equipment and qualified plant workers.[235] In the USA, two new Generation III reactors are under construction at Vogtle, a dual construction project which marks the end of a 34 year period of stagnation in the US construction of civil nuclear power reactors. The station operator licenses of almost half the present 104 power reactors in the US, as of 2008, have been given extensions to 60 years.[236] As of 2012, U.S. nuclear industry officials expect five new reactors to enter service by 2020, all at existing plants.[30] In 2013, four aging, uncompetitive, reactors were permanently closed.[237][32] Relevant state legislatures are trying to close Vermont Yankee and Indian Point Nuclear Power Plant.[32] The U.S. NRC and the U.S. Department of Energy have initiated research into Light water reactor sustainability which is hoped will lead to allowing extensions of reactor licenses beyond 60 years, in increments of 20 years, provided that safety can be maintained, as the loss in non-CO2-emitting generation capacity by retiring reactors "may serve to challenge U.S. energy security, potentially resulting in increased greenhouse gas emissions, and contributing to an imbalance between electric supply and demand."[238] Nuclear phase out Main article: Nuclear power phase-out Eight of the seventeen operating reactors in Germany were permanently shut down following the March 2011 Fukushima nuclear disaster. Following the Fukushima I nuclear accidents, the International Energy Agency halved its estimate of additional nuclear generating capacity to be built by 2035.[34][35] Platts has reported that "the crisis at Japan's Fukushima nuclear plants has prompted leading energy-consuming countries to review the safety of their existing reactors and cast doubt on the speed and scale of planned expansions around the world".[223] In 2011, The Economist reported that nuclear power "looks dangerous, unpopular, expensive and risky", and that "it is replaceable with relative ease and could be forgone with no huge structural shifts in the way the world works".[239] In early April 2011, analysts at Swiss-based investment bank UBS said: "At Fukushima, four reactors have been out of control for weeks, casting doubt on whether even an advanced economy can master nuclear safety . . .. We believe the Fukushima accident was the most serious ever for the credibility of nuclear power".[240] In 2011, Deutsche Bank analysts concluded that "the global impact of the Fukushima accident is a fundamental shift in public perception with regard to how a nation prioritizes and values its populations health, safety, security, and natural environment when determining its current and future energy pathways". As a consequence,
  • 22. "renewable energy will be a clear long-term winner in most energy systems, a conclusion supported by many voter surveys conducted over the past few weeks. At the same time, we consider natural gas to be, at the very least, an important transition fuel, especially in those regions where it is considered secure".[241] In September 2011, German engineering giant Siemens announced it will withdraw entirely from the nuclear industry, as a response to the Fukushima nuclear disaster in Japan, and said that it would no longer build nuclear power plants anywhere in the world. The company‘s chairman, Peter Löscher, said that "Siemens was ending plans to cooperate with Rosatom, the Russian state-controlled nuclear power company, in the construction of dozens of nuclear plants throughout Russia over the coming two decades".[242][243] Also in September 2011, IAEA Director General Yukiya Amano said the Japanese nuclear disaster "caused deep public anxiety throughout the world and damaged confidence in nuclear power".[244] In February 2012, the United States Nuclear Regulatory Commission approved the construction of two additional reactors at the Vogtle Electric Generating Plant, the first reactors to be approved in over 30 years since the Three Mile Island accident,[245] but NRC Chairman Gregory Jaczko cast a dissenting vote citing safety concerns stemming from Japan's 2011 Fukushima nuclear disaster, and saying "I cannot support issuing this license as if Fukushima never happened".[246] One week after Southern received the license to begin major construction on the two new reactors, a dozen environmental and anti-nuclear groups are suing to stop the Plant Vogtle expansion project, saying "public safety and environmental problems since Japan's Fukushima Daiichi nuclear reactor accident have not been taken into account".[247] Countries such as Australia, Austria, Denmark, Greece, Ireland, Italy, Latvia, Liechtenstein, Luxembourg, Malta, Portugal, Israel, Malaysia, New Zealand, and Norway have no nuclear power reactors and remain opposed to nuclear power.[248][249] However, by contrast, some countries remain in favor, and financially support nuclear fusion research, including EU wide funding of the ITER project.[250][251] Worldwide wind power has been increasing at 26%/year, and solar power at 58%/year, from 2006 to 2011, as a replacement for thermal generation of electricity.[252] Advanced concepts Main article: Generation IV reactor Current fission reactors in operation around the world are second or third generation systems, with most of the first-generation systems having been retired some time ago. Research into advanced generation IV reactor types was officially started by the Generation IV International Forum (GIF) based on eight technology goals, including to improve nuclear safety, improve proliferation resistance, minimize waste, improve natural resource utilization, the ability to consume existing nuclear waste in the production of electricity, and decrease the cost to build and run such plants. Most of these reactors differ significantly from current operating light water reactors, and are generally not expected to be available for commercial construction before 2030.[253] The nuclear reactors to be built at Vogtle are new AP1000 third generation reactors, which are said to have safety improvements over older power reactors.[245] However, John Ma, a senior structural engineer at the NRC, is concerned that some parts of the AP1000 steel skin are so brittle that the "impact energy" from a plane strike or storm driven projectile could shatter the wall.[254] Edwin Lyman, a senior staff scientist at the Union of Concerned Scientists, is concerned about the strength of the steel containment vessel and the concrete shield building around the AP1000.[254][255] The Union of Concerned Scientists has referred to the European Pressurized Reactor, currently under construction in China, Finland and France, as the only new reactor design under consideration in the United States that "...appears to have the potential to be significantly safer and more secure against attack than today's reactors."[256] One disadvantage of any new reactor technology is that safety risks may be greater initially as reactor operators have little experience with the new design. Nuclear engineer David Lochbaum has explained that almost all serious nuclear accidents have occurred with what was at the time the most recent technology. He argues that "the problem with new reactors and accidents is twofold: scenarios arise that are impossible to plan for in simulations; and humans make mistakes".[257] As one director of a U.S. research laboratory put it, "fabrication, construction, operation, and maintenance of new reactors will face a steep learning curve: advanced technologies will have a heightened risk of accidents and mistakes. The technology may be proven, but people are not".[257] Hybrid nuclear fusion-fission Hybrid nuclear power is a proposed means of generating power by use of a combination of nuclear fusion and fission processes. The concept dates to the 1950s, and was briefly advocated by Hans Bethe during the 1970s, but largely remained unexplored until a revival of interest in 2009, due to delays in the realization of pure fusion. When a sustained nuclear fusion power plant is built, it has the potential to be capable of extracting all the fission energy that remains in spent fission fuel, reducing the volume of nuclear waste by orders of magnitude, and more importantly, eliminating all actinides present in the spent fuel, substances which cause security concerns.[258] Nuclear fusion Main articles: Nuclear fusion and Fusion power Nuclear fusion reactions have the potential to be safer and generate less radioactive waste than fission.[259][260] These reactions appear potentially viable, though technically quite difficult and have yet to be created on a scale that could be used in a functional power plant. Fusion power has been under intense theoretical and experimental investigation since the 1950s. Nuclear fusion, in the form of the International Thermonuclear Experimental Reactor is predicted to achieve an energy return on investment between 2020 and 2030. With a follow on commercial nuclear fusion power station, DEMO, estimated to be operational by 2030.[9][261] There is also suggestions for a power plant based upon a different fusion approach, that of a Inertial fusion power plant.
  • 23. Fusion powered electricity generation was initially believed to be readily achievable, as fission power had been. However, the extreme requirements for continuous reactions andplasma containment led to projections being extended by several decades. In 2010, more than 60 years after the first attempts, commercial power production was still believed to be unlikely before 2050.[9] Nuclear power organizations There are multiple organizations which have taken a position on nuclear power – some are proponents, and some are opponents. Outline History of Nuclear Energy (Updated June 2010) The science of atomic radiation, atomic change and nuclear fission was developed from 1895 to 1945, much of it in the last six of those years. Over 1939-45, most development was focused on the atomic bomb. From 1945 attention was given to harnessing this energy in a controlled fashion for naval propulsion and for making electricity. Since 1956 the prime focus has been on the technological evolution of reliable nuclear power plants. Exploring the nature of the atom Uranium was discovered in 1789 by Martin Klaproth, a German chemist, and named after the planet Uranus. Ionising radiation was discovered by Wilhelm Rontgen in 1895, by passing an electric current through an evacuated glass tube and producing continuous X-rays. Then in 1896 Henri Becquerel found that pitchblende (an ore containing radium and uranium) caused a photographic plate to darken. He went on to demonstrate that this was due to beta radiation (electrons) and alpha particles (helium nuclei) being emitted. Villard found a third type of radiation from pitchblende: gamma rays, which were much the same as X-rays. Then in 1896 Pierre and Marie Curie gave the name 'radioactivity' to this phenomenon, and in 1898 isolated polonium and radium from the pitchblende. Radium was later used in medical treatment. In 1898 Samuel Prescott showed that radiation destroyed bacteria in food. In 1902 Ernest Rutherford showed that radioactivity as a spontaneous event emitting an alpha or beta particle from the nucleus created a different element. He went on to develop a fuller understanding of atoms and in 1919 he fired alpha particles from a radium source into nitrogen and found that nuclear rearrangement was occurring, with formation of oxygen. Niels Bohr was another scientist who advanced our understanding of the atom and the way electrons were arranged around its nucleus through to the 1940s. By 1911 Frederick Soddy discovered that naturally-radioactive elements had a number of different isotopes (radionuclides), with the same chemistry. Also in 1911, George de Hevesy showed that such radionuclides were invaluable as tracers, because minute amounts could readily be detected with simple instruments. In 1932 James Chadwick discovered the neutron. Also in 1932 Cockcroft and Walton produced nuclear transformations by bombarding atoms with accelerated protons, then in 1934 Irene Curie and Frederic Joliot found that some such transformations created artificial radionuclides. The next year Enrico Fermi found that a much greater variety of artificial radionuclides could be formed when neutrons were used instead of protons. Fermi continued his experiments, mostly producing heavier elements from his targets, but also, with uranium, some much lighter ones. At the end of 1938 Otto Hahn and Fritz Strassman in Berlin showed that the new lighter elements were barium and others which were about half the mass of uranium, thereby demonstrating that atomic fission had occurred. Lise Meitner and her nephew Otto Frisch, working under Niels Bohr, then explained this by suggesting that the neutron was captured by the nucleus, causing severe vibration leading to the nucleus splitting into two not quite equal parts. They calculated the energy release from this fission as about 200 million electron volts. Frisch then confirmed this figure experimentally in January 1939. This was the first experimental confirmation of Albert Einstein's paper putting forward the equivalence between mass and energy, which had been published in 1905. Harnessing nuclear fission These 1939 developments sparked activity in many laboratories. Hahn and Strassman showed that fission not only released a lot of energy but that it also released additional neutrons which could cause fission in other uranium nuclei and possibly a self-sustaining chain reaction leading to an enormous release of energy. This suggestion was soon confirmed experimentally by Joliot and his co-workers in Paris, and Leo Szilard working with Fermi in New York. Bohr soon proposed that fission was much more likely to occur in the uranium-235 isotope than in U-238 and that fission would occur more effectively with slow- moving neutrons than with fast neutrons, the latter point being confirmed by Szilard and Fermi, who proposed using a 'moderator' to slow down the emitted neutrons. Bohr and Wheeler extended these ideas into what became the classical analysis of the fission process, and their paper was published only two days before war broke out in 1939. Another important factor was that U-235 was then known to comprise only 0.7% of natural uranium, with the other 99.3% being U-238, with similar chemical properties. Hence the separation of the two to obtain pure U-235 would be difficult and would require the use of their very slightly different physical properties. This increase in the proportion of the U-235 isotope became known as 'enrichment'.
  • 24. The remaining piece of the fission/atomic bomb concept was provided in 1939 by Francis Perrin who introduced the concept of the critical mass of uranium required to produce a self-sustaining release of energy. His theories were extended by Rudolf Peierls at Birmingham University and the resulting calculations were of considerable importance in the development of the atomic bomb. Perrin's group in Paris continued their studies and demonstrated that a chain reaction could be sustained in a uranium-water mixture (the water being used to slow down the neutrons) provided external neutrons were injected into the system. They also demonstrated the idea of introducing neutron-absorbing material to limit the multiplication of neutrons and thus control the nuclear reaction (which is the basis for the operation of a nuclear power station). Peierls had been a student of Werner Heisenberg, who from April 1939 presided over the German nuclear energy project under the German Ordnance Office. Initially this was directed towards military applications, but by 1942 the military objective was abandoned as impractical. However, the existence of the German Uranverein project provided the main incentive for wartime development of the atomic bomb by Britain and the USA. Nuclear physics in Russia Russian nuclear physics predates the Bolshevik Revolution by more than a decade. Work on radioactive minerals found in central Asia began in 1900 and the St Petersburg Academy of Sciences began a large-scale investigation in 1909. The 1917 Revolution gave a boost to scientific research and over 10 physics institutes were established in major Russian towns, particularly St Petersburg, in the years which followed. In the 1920s and early 1930s many prominent Russian physicists worked abroad, encouraged by the new regime initially as the best way to raise the level of expertise quickly. These included Kirill Sinelnikov, Pyotr Kapitsa and Vladimir Vernadsky. By the early 1930s there were several research centres specialising in nuclear physics. Kirill Sinelnikov returned from Cambridge in 1931 to organise a department at the Ukrainian Physico-Technical Institute (FTI) in Kharkov which had been set up in 1928. Academician Abram Ioffe formed another group at Leningrad FTI (including the young Igor Kurchatov), which in 1933 became the Department of Nuclear Physics under Kurchatov with four separate laboratories. By the end of the decade, there were cyclotrons installed at the Radium Institute and Leningrad FTI (the biggest in Europe). But by this time many scientists were beginning to fall victim to Stalin's purges -- half the staff of Kharkov FTI, for instance, was arrested in 1939. Nevertheless, 1940 saw great advances being made in the understanding of nuclear fission including the possibility of a chain reaction. At the urging of Kurchatov and his colleagues, the Academy of Sciences set up a "Committee for the Problem of Uranium" in June 1940 chaired by Vitaly Khlopin, and a fund was established to investigate the central Asian uranium deposits. Germany's invasion of Russia in 1941 turned much of this fundamental research to potential military applications. Conceiving the atomic bomb British scientists had kept pressure on their government. The refugee physicists Peierls and Frisch (who had stayed in England with Peierls after the outbreak of war), gave a major impetus to the concept of the atomic bomb in a three-page document known as the Frisch-Peierls Memorandum. In this they predicted that an amount of about 5kg of pure U-235 could make a very powerful atomic bomb equivalent to several thousand tonnes of dynamite. They also suggested how such a bomb could be detonated, how the U-235 could be produced, and what the radiation effects might be in addition to the explosive effects. They proposed thermal diffusion as a suitable method for separating the U-235 from the natural uranium. This memorandum stimulated a considerable response in Britain at a time when there was little interest in the USA. A group of eminent scientists known as the MAUD Committee was set up in Britain and supervised research at the Universities of Birmingham, Bristol, Cambridge, Liverpool and Oxford. The chemical problems of producing gaseous compounds of uranium and pure uranium metal were studied at Birmingham University and Imperial Chemical Industries (ICI). Dr Philip Baxter at ICI made the first small batch of gaseous uranium hexafluoride for Professor James Chadwick in 1940. ICI received a formal contract later in 1940 to make 3kg of this vital material for the future work. Most of the other research was funded by the universities themselves. Two important developments came from the work at Cambridge. The first was experimental proof that a chain reaction could be sustained with slow neutrons in a mixture of uranium oxide and heavy water, ie. the output of neutrons was greater than the input. The second was by Bretscher and Feather based on earlier work by Halban and Kowarski soon after they arrived in Britain from Paris. When U-235 and U-238 absorb slow neutrons, the probability of fission in U-235 is much greater than in U-238. The U-238 is more likely to form a new isotope U-239, and this isotope rapidly emits an electron to become a new element with a mass of 239 and an Atomic Number of 93. This element also emits an electron and becomes a new element of mass 239 and Atomic Number 94, which has a much greater half-life. Bretscher and Feather argued on theoretical grounds that element 94 would be readily fissionable by slow and fast neutrons, and had the added advantages that it was chemically different to uranium and therefore could easily be separated from it. This new development was also confirmed in independent work by McMillan and Abelson in the USA in 1940. Dr Kemmer of the Cambridge team proposed the names neptunium for the new element # 93 and plutonium for # 94 by analogy with the outer planets Neptune and Pluto beyond Uranus (uranium, element # 92). The Americans fortuitously suggested the same names, and the identification of plutonium in 1941 is generally credited to Glenn Seaborg. Developing the concepts
  • 25. By the end of 1940 remarkable progress had been made by the several groups of scientists coordinated by the MAUD Committee and for the expenditure of a relatively small amount of money. All of this work was kept secret, whereas in the USA several publications continued to appear in 1940 and there was also little sense of urgency. By March 1941 one of the most uncertain pieces of information was confirmed - the fission cross-section of U-235. Peierls and Frisch had initially predicted in 1940 that almost every collision of a neutron with a U-235 atom would result in fission, and that both slow and fast neutrons would be equally effective. It was later discerned that slow neutrons were very much more effective, which was of enormous significance for nuclear reactors but fairly academic in the bomb context. Peierls then stated that there was now no doubt that the whole scheme for a bomb was feasible provided highly enriched U-235 could be obtained. The predicted critical size for a sphere of U-235 metal was about 8kg, which might be reduced by use of an appropriate material for reflecting neutrons. However, direct measurements on U-235 were still necessary and the British pushed for urgent production of a few micrograms. The final outcome of the MAUD Committee was two summary reports in July 1941. One was on 'Use of Uranium for a Bomb' and the other was on 'Use of Uranium as a Source of Power'. The first report concluded that a bomb was feasible and that one containing some 12 kg of active material would be equivalent to 1,800 tons of TNT and would release large quantities of radioactive substances which would make places near the explosion site dangerous to humans for a long period. It estimated that a plant to produce 1kg of U-235 per day would cost ?5 million and would require a large skilled labour force that was also needed for other parts of the war effort. Suggesting that the Germans could also be working on the bomb, it recommended that the work should be continued with high priority in cooperation with the Americans, even though they seemed to be concentrating on the future use of uranium for power and naval propulsion. The second MAUD Report concluded that the controlled fission of uranium could be used to provide energy in the form of heat for use in machines, as well as providing large quantities of radioisotopes which could be used as substitutes for radium. It referred to the use of heavy water and possibly graphite as moderators for the fast neutrons, and that even ordinary water could be used if the uranium was enriched in the U-235 isotope. It concluded that the 'uranium boiler' had considerable promise for future peaceful uses but that it was not worth considering during the present war. The Committee recommended that Halban and Kowarski should move to the USA where there were plans to make heavy water on a large scale. The possibility that the new element plutonium might be more suitable than U-235 was mentioned, so that the work in this area by Bretscher and Feather should be continued in Britain. The two reports led to a complete reorganisation of work on the bomb and the 'boiler'. It was claimed that the work of the committee had put the British in the lead and that "in its fifteen months' existence it had proved itself one of the most effective scientific committees that ever existed". The basic decision that the bomb project would be pursued urgently was taken by the Prime Minister, Winston Churchill, with the agreement of the Chiefs of Staff. The reports also led to high level reviews in the USA, particularly by a Committee of the National Academy of Sciences, initially concentrating on the nuclear power aspect. Little emphasis was given to the bomb concept until 7 December 1941, when the Japanese attacked Pearl Harbour and the Americans entered the war directly. The huge resources of the USA were then applied without reservation to developing atomic bombs. The Manhattan Project The Americans increased their effort rapidly and soon outstripped the British. Research continued in each country with some exchange of information. Several of the key British scientists visited the USA early in 1942 and were given full access to all of the information available. The Americans were pursuing three enrichment processes in parallel: Professor Lawrence was studying electromagnetic separation at Berkeley (University of California), E. V. Murphree of Standard Oil was studying the centrifuge method developed by Professor Beams, and Professor Urey was coordinating the gaseous diffusion work at Columbia University. Responsibility for building a reactor to produce fissile plutonium was given to Arthur Compton at the University of Chicago. The British were only examining gaseous diffusion. In June 1942 the US Army took over process development, engineering design, procurement of materials and site selection for pilot plants for four methods of making fissionable material (because none of the four had been shown to be clearly superior at that point) as well as the production of heavy water. With this change, information flow to Britain dried up. This was a major setback to the British and the Canadians who had been collaborating on heavy water production and on several aspects of the research program. Thereafter, Churchill sought information on the cost of building a diffusion plant, a heavy water plant and an atomic reactor in Britain. After many months of negotiations an agreement was finally signed by Mr Churchill and President Roosevelt in Quebec in August 1943, according to which the British handed over all of their reports to the Americans and in return received copies of General Groves' progress reports to the President. The latter showed that the entire US program would cost over $1,000 million, all for the bomb, as no work was being done on other applications of nuclear energy. Construction of production plants for electromagnetic separation (in calutrons) and gaseous diffusion was well under way. An experimental graphite pile constructed by Fermi had operated at the University of Chicago in December 1942 ?the first controlled nuclear chain reaction.
  • 26. A full-scale production reactor for plutonium was being constructed at Argonne, with further ones at Oak Ridge and then Hanford, plus a reprocessing plant to extract the plutonium. Four plants for heavy water production were being built, one in Canada and three in the USA. A team under Robert Oppenheimer at Los Alamos in New Mexico was working on the design and construction of both U-235 and Pu-239 bombs. The outcome of the huge effort, with assistance from the British teams, was that sufficient Pu-239 and highly enriched U-235 (from calutrons and diffusion at Oak Ridge) was produced by mid-1945. The uranium mostly originated from the Belgian Congo. The first atomic device tested successfully at Alamagordo in New Mexico on 16 July 1945. It used plutonium made in a nuclear pile. The teams did not consider that it was necessary to test a simpler U-235 device. The first atomic bomb, which contained U-235, was dropped on Hiroshima on 6 August 1945. The second bomb, containing Pu-239, was dropped on Nagasaki on 9 August. That same day, the USSR declared war on Japan. On 10 August 1945 the Japanese Government surrendered. The Soviet bomb Initially Stalin was not enthusiastic about diverting resources to develop an atomic bomb, until intelligence reports suggested that such research was under way in Germany, Britain and the USA. Consultations with Academicians Ioffe, Kapitsa, Khlopin and Vernadsky convinced him that a bomb could be developed relatively quickly and he initiated a modest research program in 1942. Igor Kurchatov, then relatively young and unknown, was chosen to head it and in 1943 he became Director of Laboratory No.2 recently established on the outskirts of Moscow. This was later renamed LIPAN, then became the Kurchatov Institute of Atomic Energy. Overall responsibility for the bomb program rested with Security Chief Lavrenti Beria and its administration was undertaken by the First Main Directorate (later called the Ministry of Medium Machine Building). Research had three main aims: to achieve a controlled chain reaction; to investigate methods of isotope separation; and to look at designs for both enriched uranium and plutonium bombs. Attempts were made to initiate a chain reaction using two different types of atomic pile: one with graphite as a moderator and the other with heavy water. Three possible methods of isotope separation were studied: counter-current thermal diffusion, gaseous diffusion and electromagnetic separation. After the defeat of Nazi Germany in May 1945, German scientists were "recruited" to the bomb program to work in particular on isotope separation to produce enriched uranium. This included research into gas centrifuge technology in addition to the three other enrichment technologies. The test of the first US atomic bomb in July 1945 had little impact on the Soviet effort, but by this time, Kurchatov was making good progress towards both a uranium and a plutonium bomb. He had begun to design an industrial scale reactor for the production of plutonium, while those scientists working on uranium isotope separation were making advances with the gaseous diffusion method. It was the bombing of Hiroshima and Nagasaki the following month which gave the program a high profile and construction began in November 1945 of a new city in the Urals which would house the first plutonium production reactors -- Chelyabinsk-40 (Later known as Chelyabinsk-65 or the Mayak production association). This was the first of ten secret nuclear cities to be built in the Soviet Union. The first of five reactors at Chelyabinsk-65 came on line in 1948. This town also housed a processing plant for extracting plutonium from irradiated uranium. As for uranium enrichment technology, it was decided in late 1945 to begin construction of the first gaseous diffusion plant at Verkh-Neyvinsk (later the closed city of Sverdlovsk-44), some 50 kilometres from Yekaterinburg (formerly Sverdlovsk) in the Urals. Special design bureaux were set up at the Leningrad Kirov Metallurgical and Machine-Building Plant and at the Gorky (Nizhny Novgorod) Machine Building Plant. Support was provided by a group of German scientists working at the Sukhumi Physical Technical Institute. In April 1946 design work on the bomb was shifted to Design Bureau-11 -- a new centre at Sarova some 400 kilometres from Moscow (subsequently the closed city of Arzamas-16). More specialists were brought in to the program including metallurgist Yefim Slavsky who was given the immediate task of producing the very pure graphite Kurchatov needed for his plutonium production pile constructed at Laboratory No. 2 known as F-1. The pile was operated for the first time in December 1946. Support was also given by Laboratory No.3 in Moscow -- now the Institute of Theoretical and Experimental Physics -- which had been working on nuclear reactors. Work at Arzamas-16 was influenced by foreign intelligence gathering and the first device was based closely on the Nagasaki bomb (a plutonium device). In August 1947 a test site was established near Semipalatinsk in Kazakhstan and was ready for the detonation two years later of the first bomb, RSD-1. Even before this was tested in August 1949, another group of scientists led by Igor Tamm and including Andrei Sakharov had begun work on a hydrogen bomb. Revival of the 'nuclear boiler' By the end of World War II, the project predicted and described in detail only five and a half years before in the Frisch-Peierls Memorandum had been brought to partial fruition, and attention could turn to the peaceful and directly beneficial application of nuclear energy. Post-war, weapons development continued on both sides of the "iron curtain", but a new focus was on harnessing the great atomic power, now dramatically (if tragically) demonstrated, for making steam and electricity.
  • 27. In the course of developing nuclear weapons the Soviet Union and the West had acquired a range of new technologies and scientists realised that the tremendous heat produced in the process could be tapped either for direct use or for generating electricity. It was also clear that this new form of energy would allow development of compact long-lasting power sources which could have various applications, not least for shipping, and especially in submarines. The first nuclear reactor to produce electricity (albeit a trivial amount) was the small Experimental Breeder reactor (EBR-1) designed and operated by Argonne National Laboratory and sited in Idaho, USA. The reactor started up in December 1951. In 1953 President Eisenhower proposed his "Atoms for Peace" program, which reoriented significant research effort towards electricity generation and set the course for civil nuclear energy development in the USA. In the Soviet Union, work was under way at various centres to refine existing reactor designs and develop new ones. The Institute of Physics and Power Engineering (FEI) was set up in May 1946 at the then-closed city of Obninsk, 100 km southwest of Moscow, to develop nuclear power technology. The existing graphite- moderated channel-type plutonium production reactor was modified for heat and electricity generation and in June 1954 the world's first nuclear powered electricity generator began operation at the FEI in Obninsk. The AM-1 (Atom Mirny -- peaceful atom) reactor was water-cooled and graphite-moderated, with a design capacity of 30 MWt or 5 MWe. It was similar in principle to the plutonium production reactors in the closed military cities and served as a prototype for other graphite channel reactor designs including the Chernobyl-type RBMK (reaktor bolshoi moshchnosty kanalny -- high power channel reactor) reactors. AM-1 produced electricity until 1959 and was used until 2000 as a research facility and for the production of isotopes. Also in the 1950s FEI at Obninsk was developing fast breeder reactors (FBRs) and lead-bismuth reactors for the navy. In April 1955 the BR-1 (bystry reaktor -- fast reactor) fast neutron reactor began operating. It produced no power but led directly to the BR-5 which started up in 1959 with a capacity of 5MWt which was used to do the basic research necessary for designing sodium-cooled FBRs. It was upgraded and modernised in 1973 and then underwent major reconstruction in 1983 to become the BR-10 with a capacity of 8 MWt which is now used to investigate fuel endurance, to study materials and to produce isotopes. The main US effort was under Admiral Hyman Rickover, which developed the Pressurised Water Reactor (PWR) for naval (particularly submarine) use. The PWR used enriched uranium oxide fuel and was moderated and cooled by ordinary (light) water. The Mark 1 prototype naval reactor started up in March 1953 in Idaho, and the first nuclear-powered submarine, USS Nautilus, was launched in 1954. In 1959 both USA and USSR launched their first nuclear-powered surface vessels. The Mark 1 reactor led to the US Atomic Energy Commission building the 60 MWe Shippingport demonstration PWR reactor in Pennsylvania, which started up in 1957 and operated until 1982. Since the USA had a virtual monopoly on uranium enrichment in the West, British development took a different tack and resulted in a series of reactors fuelled by natural uranium metal, moderated by graphite, and gas-cooled. The first of these 50 MWe Magnox types, Calder Hall-1, started up in 1956 and ran until 2003. However, after 1963 (and 26 units) no more were commenced. Britain next embraced the Advanced Gas-Cooled Reactor (using enriched oxide fuel) before conceding the pragmatic virtues of the PWR design. Nuclear energy goes commercial In the USA, Westinghouse designed the first fully commercial PWR of 250 MWe, Yankee Rowe, which started up in 1960 and operated to 1992. Meanwhile the boiling water reactor (BWR) was developed by the Argonne National Laboratory, and the first one, Dresden-1 of 250 MWe, designed by General Electric, was started up earlier in 1960. A prototype BWR, Vallecitos, ran from 1957 to 1963. By the end of the 1960s, orders were being placed for PWR and BWR reactor units of more than 1000 MWe. Canadian reactor development headed down a quite different track, using natural uranium fuel and heavy water as a moderator and coolant. The first unit started up in 1962. This CANDU design continues to be refined. France started out with a gas-graphite design similar to Magnox and the first reactor started up in 1956. Commercial models operated from 1959. It then settled on three successive generations of standardised PWRs, which was a very cost-effective strategy. In 1964 the first two Soviet nuclear power plants were commissioned. A 100 MW boiling water graphite channel reactor began operating in Beloyarsk (Urals). In Novovoronezh (Volga region) a new design -- a small (210 MW) pressurised water reactor (PWR) known as a VVER (veda-vodyanoi energetichesky reaktor -- water cooled power reactor) was built. The first large RBMK (1,000 MW - high-power channel reactor) started up at Sosnovy Bor near Leningrad in 1973 and in the Arctic northwest a VVER with a rated capacity of 440 MW began operating. This was superseded by a 1000 MWe version which became a standard design. In Kazakhstan the world's first commercial prototype fast neutron reactor (the BN-350) started up in 1972, producing 120 MW of electricity and heat to desalinate Caspian seawater. In the USA, UK, France and Russia a number of experimental fast neutron reactors produced electricity from 1959, the last of these closing in 2009. This left Russia's BN-600 as the only commercial fast reactor.
  • 28. Around the world, with few exceptions, other countries have chosen light-water designs for their nuclear power programs, so that today 60% of the world capacity is PWR and 21% BWR. The nuclear power brown-out From the late 1970s to about 2002 the nuclear power industry suffered some decline and stagnation. Few new reactors were ordered, the number coming on line from mid 1980s little more than matched retirements, though capacity increased by nearly one third and output increased 60% due to capacity plus improved load factors. The share of nuclear in world electricity from mid 1980s was fairly constant at 16-17%. Many reactor orders from the 1970s were cancelled. The uranium price dropped accordingly, and also because of an increase in secondary supplies. Oil companies which had entered the uranium field bailed out, and there was a consolidation of uranium producers. However, by the late 1990s the first of the third-generation reactors was commissioned - Kashiwazaki-Kariwa 6 - a 1350 MWe Advanced BWR, in Japan. This was a sign of the recovery to come. Nuclear renaissance In the new century several factors have combined to revive the prospects for nuclear power. First is realisation of the scale of projected increased electricity demand worldwide, but particularly in rapidly-developing countries. Secondly is awareness of the importance of energy security, and thirdly is the need to limit carbon emissions due to concern about global warming. These factors coincide with the availability of a new generation of nuclear power reactors, and in 2004 the first of the late third-generation units was ordered for Finland - a 1600 MWe European PWR (EPR). A similar unit is planned for France as the first of a full fleet replacement there. In the USA the 2005 Energy Policy Act provided incentives for establishing new-generation power reactors there. But plans in Europe and North America are overshadowed by those in China, India, Japan and South Korea. China alone plans a sixfold increase in nuclear power capacity by 2020, and has more than one hundred further large units proposed and backed by credible political determination and popular support. A large portion of these are the latest western design, expedited by modular construction. The history of nuclear power thus starts with science in Europe, blossoms in UK and USA with the latter's technological might, languishes for a few decades, then has a new growth spurt in east Asia. Main sources: Atomic Rise and Fall, the Australian Atomic Energy Commission 1953-1987, by Clarence Hardy, Glen Haven (PO Box 85, Peakhurst, NSW 2210), 1999. Chapter 1 provides the major source for 1939-45. Radiation in Perspective, OECD NEA, 1997. Nuclear Fear, by Spencer Weart, Harvard UP, 1988. Judith Perera (Russian material). Nuclear Power Reactors (updated June 2013) Most nuclear electricity is generated using just two kinds of reactors which were developed in the 1950s and improved since. New designs are coming forward and some are in operation as the first generation reactors come to the end of their operating lives. Around 13% of the world's electricity is produced from nuclear energy, more than from all sources worldwide in 1960. A nuclear reactor produces and controls the release of energy from splitting the atoms of certain elements. In a nuclear power reactor, the energy released is used as heat to make steam to generate electricity. (In a research reactor the main purpose is to utilise the actual neutrons produced in the core. In most naval reactors, steam drives a turbine directly for propulsion.) The principles for using nuclear power to produce electricity are the same for most types of reactor. The energy released from continuous fission of the atoms of the fuel is harnessed as heat in either a gas or water, and is used to produce steam. The steam is used to drive the turbines which produce electricity (as in most fossil fuel plants). The world's first nuclear reactors operated naturally in a uranium deposit about two billion years ago. These were in rich uranium orebodies and moderated by percolating rainwater. Those at Oklo in west Africa, each less than 100 kW thermal, together consumed about six tonnes of that uranium. Today, reactors derived from designs originally developed for propelling submarines and large naval ships generate about 85% of the world's nuclear electricity. The main design is the pressurised water reactor (PWR) which has water at over 300°C under pressure in its primary cooling/heat transfer circuit, and generates steam in a secondary circuit. The less numerous boiling water reactor (BWR) makes steam in the primary circuit above the reactor core, at similar temperatures and pressure.
  • 29. Both types use water as both coolant and moderator, to slow neutrons. Since water normally boils at 100°C, they have robust steel pressure vessels or tubes to enable the higher operating temperature. (Another type uses heavy water, with deuterium atoms, as moderator. Hence the term ‗light water‘ is used to differentiate.) Components of a nuclear reactor There are several components common to most types of reactors: Fuel. Uranium is the basic fuel. Usually pellets of uranium oxide (UO2) are arranged in tubes to form fuel rods. The rods are arranged into fuel assemblies in the reactor core.* * In a new reactor with new fuel a neutron source is needed to get the reaction going. Usually this is beryllium mixed with polonium, radium or other alpha-emitter. Alpha particles from the decay cause a release of neutrons from the beryllium as it turns to carbon-12. Restarting a reactor with some used fuel may not require this, as there may be enough neutrons to achieve criticality when control rods are removed. Moderator. Material in the core which slows down the neutrons released from fission so that they cause more fission. It is usually water, but may be heavy water or graphite. Control rods. These are made with neutron-absorbing material such as cadmium, hafnium or boron, and are inserted or withdrawn from the core to control the rate of reaction, or to halt it.* In some PWR reactors, special control rods are used to enable the core to sustain a low level of power efficiently. (Secondary control systems involve other neutron absorbers, usually boron in the coolant – its concentration can be adjusted over time as the fuel burns up.) * In fission, most of the neutrons are released promptly, but some are delayed. These are crucial in enabling a chain reacting system (or reactor) to be controllable and to be able to be held precisely critical. Coolant. A fluid circulating through the core so as to transfer the heat from it. In light water reactors the water moderator functions also as primary coolant. Except in BWRs, there is secondary coolant circuit where the water becomes steam. (See also later section on primary coolant characteristics) Pressure vessel or pressure tubes. Usually a robust steel vessel containing the reactor core and moderator/coolant, but it may be a series of tubes holding the fuel and conveying the coolant through the surrounding moderator. Steam generator.(not in BWR) Part of the cooling system where the high-pressure primary coolant bringing heat from the reactor is used to make steam for the turbine, in a secondary circuit. Essentially a heat exchanger like a motor car radiator*. Reactors may have up to four 'loops', each with a steam generator. * These are large heat exchangers for transferring heat from one fluid to another – here from high-pressure primary circuit in PWR to secondary circuit where water turns to steam. Each structure weighs up to 800 tonnes and contains from 300 to 16,000 tubes about 2 cm diameter for the primary coolant, which is radioactive due to nitrogen-16 (N-16, formed by neutron bombardment of oxygen, with half-life of 7 seconds). The secondary water must flow through the support structures for the tubes. The whole thing needs to be designed so that the tubes don't vibrate and fret, operated so that deposits do not build up to impede the flow, and maintained chemically to avoid corrosion. Tubes which fail and leak are plugged, and surplus capacity is designed to allow for this. Leaks can be detected by monitoring N-16 levels in the steam as it leaves the steam generator. Containment. The structure around the reactor and associated steam generators which is designed to protect it from outside intrusion and to protect those outside from the effects of radiation in case of any serious malfunction inside. It is typically a metre-thick concrete and steel structure. There are several different types of reactors as indicated in the following Table. Nuclear power plants in commercial operation Reactor type Main Countries Number GWe Fuel Coolant Moderator Pressurised Water Reactor (PWR) US, France, Japan, Russia, China 271 270.4 enriched UO2 water water Boiling Water Reactor (BWR) US, Japan, Sweden 84 81.2 enriched UO2 water water Pressurised Heavy Water Reactor 'CANDU' (PHWR) Canada 48 27.1 natural UO2 heavy water heavy water Gas-cooled Reactor (AGR & Magnox) UK 17 9.6 natural U (metal), enriched UO2 CO2 graphite Light Water Graphite Reactor (RBMK & EGP) Russia 11 + 4 10.4 enriched UO2 water graphite Fast Neutron Reactor (FBR) Russia 1 0.6 PuO2 and UO2 liquid sodium none TOTAL 436 399.3 GWe = capacity in thousands of megawatts (gross) Source: Nuclear Engineering International Handbook 2011, updated to 1/1/12 For reactors under construction: see paper Plans for New Reactors Worldwide. Fuelling a nuclear power reactor Most reactors need to be shut down for refuelling, so that the pressure vessel can be opened up. In this case refuelling is at intervals of 1-2 years, when a quarter to a third of the fuel assemblies are replaced with fresh ones. The CANDU and RBMK types have pressure tubes (rather than a pressure vessel enclosing the reactor core) and can be refuelled under load by disconnecting individual pressure tubes. If graphite or heavy water is used as moderator, it is possible to run a power reactor on natural instead of enriched uranium. Natural uranium has the same elemental composition as when it was mined (0.7% U-235, over 99.2% U-238), enriched uranium has had the proportion of the fissile isotope (U-235) increased by a process
  • 30. called enrichment, commonly to 3.5 - 5.0%. In this case the moderator can be ordinary water, and such reactors are collectively called light water reactors. Because the light water absorbs neutrons as well as slowing them, it is less efficient as a moderator than heavy water or graphite. During operation, some of the U-238 is changed to plutonium, and Pu-239 ends up providing about one third of the energy from the fuel. In most reactors the fuel is ceramic uranium oxide (UO2 with a melting point of 2800°C) and most is enriched. The fuel pellets (usually about 1 cm diameter and 1.5 cm long) are typically arranged in a long zirconium alloy (zircaloy) tube to form a fuel rod, the zirconium being hard, corrosion-resistant and permeable to neutrons.* Numerous rods form a fuel assembly, which is an open lattice and can be lifted into and out of the reactor core. In the most common reactors these are about 3.5 to 4 metres long. *Zirconium is an important mineral for nuclear power, where it finds its main use. It is therefore subject to controls on trading. It is normally contaminated with hafnium, a neutron absorber, so very pure 'nuclear grade' Zr is used to make the zircaloy, which is about 98% Zr plus tin, iron, chromium and sometimes nickel to enhance its strength. Burnable poisons are often used (especially in BWR) in fuel or coolant to even out the performance of the reactor over time from fresh fuel being loaded to refuelling. These are neutron absorbers which decay under neutron exposure, compensating for the progressive build up of neutron absorbers in the fuel as it is burned. The best known is gadolinium, which is a vital ingredient of fuel in naval reactors where installing fresh fuel is very inconvenient, so reactors are designed to run more than a decade between refuellings. The power rating of a nuclear power reactor Nuclear power plant reactor power outputs are quoted in three ways: Thermal MWt, which depends on the design of the actual nuclear reactor itself, and relates to the quantity and quality of the steam it produces. Gross electrical MWe indicates the power produced by the attached steam turbine and generator, and also takes into account the ambient temperature for the condenser circuit (cooler means more electric power, warmer means less). Rated gross power assumes certain conditions with both. Net electrical MWe, which is the power available to be sent out from the plant to the grid, after deducting the electrical power needed to run the reactor (cooling and feed-water pumps, etc.) and the rest of the plant.* * Net electrical MWe and gross MWe vary slightly from summer to winter, so normally the lower summer figure, or an average figure, is used. If the summer figure is quoted plants may show a capacity factor greater than 100% in cooler times. Some design options, such as powering the main large feed-water pumps with electric motors (as in EPR) rather than steam turbines (taking steam before it gets to the main turbine-generator), explains some gross to net differences between different reactor types. The EPR has a relatively large drop from gross to net MWe for this reason. The relationship between these is expressed in two ways: Thermal efficiency %, the ratio of gross MWe to thermal MW. This relates to the difference in temperature between the steam from the reactor and the cooling water. It is often 33-37%. Net efficiency %, the ratio of net MWe achieved to thermal MW. This is a little lower, and allows for plant usage. In WNA papers and figures and WNN items, generally net MWe is used for operating plants, and gross MWe for those under construction or planned/proposed.
  • 31. Pressurised Water Reactor (PWR) This is the most common type, with over 230 in use for power generation and several hundred more employed for naval propulsion. The design of PWRs originated as asubmarine power plant. PWRs use ordinary water as both coolant and moderator. The design is distinguished by having a primary cooling circuit which flows through the core of the reactor under very high pressure, and a secondary circuit in which steam is generated to drive the turbine. In Russia these are known as VVER types - water-moderated and -cooled. A PWR has fuel assemblies of 200-300 rods each, arranged vertically in the core, and a large reactor would have about 150-250 fuel assemblies with 80-100 tonnes of uranium. Water in the reactor core reaches about 325°C, hence it must be kept under about 150 times atmospheric pressure to prevent it boiling. Pressure is maintained by steam in a pressuriser (see diagram). In the primary cooling circuit the water is also the moderator, and if any of it turned to steam the fission reaction would slow down. This negative feedback effect is one of the safety features of the type. The secondary shutdown system involves adding boron to the primary circuit. The secondary circuit is under less pressure and the water here boils in the heat exchangers which are thus steam generators. The steam drives the turbine to produce electricity, and is then condensed and returned to the heat exchangers in contact with the primary circuit. Boiling Water Reactor (BWR) This design has many similarities to the PWR, except that there is only a single circuit in which the water is at lower pressure (about 75 times atmospheric pressure) so that it boils in the core at about 285°C. The reactor is designed to operate with 12-15% of the water in the top part of the core as steam, and hence with less moderating effect and thus efficiency there. BWR units can operate in load-following mode more readily then PWRs. The steam passes through drier plates (steam separators) above the core and then directly to the turbines, which are thus part of the reactor circuit. Since the water around the core of a reactor is always contaminated with traces of radionuclides, it means that the turbine must be shielded and radiological protection provided during maintenance. The cost of this tends to balance the savings due to the simpler design. Most of the radioactivity in the water is very short-lived*, so the turbine hall can be entered soon after the reactor is shut down. * mostly N-16, with a 7 second half-life A BWR fuel assembly comprises 90-100 fuel rods, and there are up to 750 assemblies in a reactor core, holding up to 140 tonnes of uranium. The secondary control system involves restricting water flow through the core so that more steam in the top part reduces moderation.
  • 32. Pressurised Heavy Water Reactor (PHWR or CANDU) The PHWR reactor design has been developed since the 1950s in Canada as the CANDU, and more recently also in India. It uses natural uranium (0.7% U-235) oxide as fuel, hence needs a more efficient moderator, in this case heavy water (D2O).** ** with the CANDU system, the moderator is enriched (ie water) rather than the fuel, - a cost trade-off. The moderator is in a large tank called a calandria, penetrated by several hundred horizontal pressure tubes which form channels for the fuel, cooled by a flow of heavy water under high pressure in the primary cooling circuit, reaching 290°C. As in the PWR, the primary coolant generates steam in a secondary circuit to drive the turbines. The pressure tube design means that the reactor can be refuelled progressively without shutting down, by isolating individual pressure tubes from the cooling circuit. A CANDU fuel assembly consists of a bundle of 37 half metre long fuel rods (ceramic fuel pellets in zircaloy tubes) plus a support structure, with 12 bundles lying end to end in a fuel channel. Control rods penetrate the calandria vertically, and a secondary shutdown system involves adding gadolinium to the moderator. The heavy water moderator circulating through the body of the calandria vessel also yields some heat (though this circuit is not shown on the diagram above). Newer PHWR designs such as the Advanced Candu Reactor (ACR) have light water cooling and slightly-enriched fuel. CANDU reactors can readily be run on recycled uranium from reprocessing LWR used fuel, or a blend of this and depleted uranium left over from enrichment plants. About 4000 MWe of PWR can then fuel 1000 MWe of CANDU capacity, with addition of depleted uranium. Advanced Gas-cooled Reactor (AGR) These are the second generation of British gas-cooled reactors, using graphite moderator and carbon dioxide as coolant. The fuel is uranium oxide pellets, enriched to 2.5-3.5%, in stainless steel tubes. The carbon dioxide circulates through the core, reaching 650°C and then past steam generator tubes outside it, but still inside the concrete and steel pressure vessel. Control rods penetrate the moderator and a secondary shutdown system involves injecting nitrogen to the coolant.
  • 33. The AGR was developed from the Magnox reactor, also graphite moderated and CO2 cooled, and two of these are still operating in UK. They use natural uranium fuel in metal form. Secondary coolant is water. Light water graphite-moderated reactor (RBMK) This is a Soviet design, developed from plutonium production reactors. It employs long (7 metre) vertical pressure tubes running through graphite moderator, and is cooled by water, which is allowed to boil in the core at 290°C, much as in a BWR. Fuel is low-enriched uranium oxide made up into fuel assemblies 3.5 metres long. With moderation largely due to the fixed graphite, excess boiling simply reduces the cooling and neutron absorbtion without inhibiting the fission reaction, and a positive feedback problem can arise, which is why they have never been built outside the Soviet Union. See appendix on RBMK Reactors for more detail. Advanced reactors Several generations of reactors are commonly distinguished. Generation I reactors were developed in 1950-60s and only one is still running today. They mostly used natural uranium fuel and used graphite as moderator. Generation II reactors are typified by the present US fleet and most in operation elsewhere. They typically use enriched uranium fuel and are mostly cooled and moderated by water. Generation III are the Advanced Reactors evolved from these, the first few of which are in operation in Japan and others are under construction and ready to be ordered. They are developments of the second generation with enhanced safety. There is no clear distinction Gen II to Gen III. Generation IV designs are still on the drawing board and will not be operational before 2020 at the earliest, probably later. They will tend to have closed fuel cycles and burn the long-lived actinides now forming part of spent fuel, so that fission products are the only high-level waste. Of seven designs under development, 4 or 5 will be fast neutron reactors. Four will use fluoride or liquid metal coolants, hence operate at low pressure. Two will be gas-cooled. Most will run at much higher temperatures than today‘s water-cooled reactors. See Generation IV Reactors paper. More than a dozen (Generation III) advanced reactor designs are in various stages of development. Some are evolutionary from the PWR, BWR and CANDU designs above, some are more radical departures. The former include the Advanced Boiling Water Reactor, a few of which are now operating with others under construction. The best-known radical new design has the fuel as large 'pebbles' and uses helium as coolant, at very high temperature, possibly to drive a turbine directly. Considering the closed fuel cycle, Generation 1-3 reactors recycle plutonium (and possibly uranium), while Generation IV are expected to have full actinide recycle. Fast neutron reactors (FNR) Some reactors (only one in commercial service) do not have a moderator and utilise fast neutrons, generating power from plutonium while making more of it from the U-238 isotope in or around the fuel. While they get more than 60 times as much energy from the original uranium compared with the normal reactors, they are expensive to build. Further development of them is likely in the next decade, and the main designs expected to be built in two decades are FNRs. If they are configured to produce more fissile material (plutonium) than they consume they are called Fast Breeder Reactors (FBR). See also Fast Neutron Reactors and Small Reactors papers. Floating nuclear power plants Apart from over 200 nuclear reactors powering various kinds of ships, Rosatom in Russia has set up a subsidiary to supply floating nuclear power plants ranging in size from 70 to 600 MWe. These will be mounted in pairs on a large barge, which will be permanently moored where it is needed to supply power and possibly some desalination to a shore settlement or industrial complex. The first has two 40 MWe reactors based on those in icebreakers and will operate at a remote site in Siberia. Electricity cost is expected to be much lower than from present alternatives. The Russian KLT-40S is a reactor well proven in icebreakers and now proposed for wider use in desalination and, on barges, for remote area power supply. Here a 150 MWt unit produces 35 MWe (gross) as well as up to 35 MW of heat for desalination or district heating. These are designed to run 3-4 years between refuelling and it is envisaged that they will be operated in pairs to allow for outages, with on-board refuelling capability and used fuel storage. At the end of a 12-year operating cycle the whole plant is taken to a central facility for 2-year overhaul and removal of used fuel, before being returned to service. Two units will be mounted on a
  • 34. 21,000 tonne barge. A larger Russian factory-built and barge-mounted reactor is the VBER-150, of 350 MW thermal, 110 MWe. The larger VBER-300 PWR is a 325 MWe unit, originally envisaged in pairs as a floating nuclear power plant, displacing 49,000 tonnes. As a cogeneration plant it is rated at 200 MWe and 1900 GJ/hr. See also Nuclear Power in Russia paper. Lifetime of nuclear reactors Most of today's nuclear plants which were originally designed for 30 or 40-year operating lives. However, with major investments in systems, structures and components lives can be extended, and in several countries there are active programs to extend operating lives. In the USA most of the more than one hundred reactors are expected to be granted licence extensions from 40 to 60 years. This justifies significant capital expenditure in upgrading systems and components, including building in extra performance margins. Some components simply wear out, corrode or degrade to a low level of efficiency. These need to be replaced. Steam generators are the most prominent and expensive of these, and many have been replaced after about 30 years where the reactor otherwise has the prospect of running for 60 years. This is essentially an economic decision. Lesser components are more straightforward to replace as they age. In Candu reactors, pressure tube replacement has been undertaken on some plants after about 30 years operation. A second issue is that of obsolescence. For instance, older reactors have analogue instrument and control systems. Thirdly, the properties of materials may degrade with age, particularly with heat and neutron irradiation. In respect to all these aspects, investment is needed to maintain reliability and safety. Also, periodic safety reviews are undertaken on older plants in line with international safety conventions and principles to ensure that safety margins are maintained. Another important issue is knowledge management (KM) over the full lifecycle from design, through construction and operation to decommissioning for reactors and other facilities. This may span a century and involve several countries, and involve a succession of companies. The plant lifespan will cover several generations of engineers. Data needs to be transferable across several generations of software and IT hardware, as well as being shared with other operators of similar plants.* Significant modifications may be made to the design over the life of the plant, so original documentation is not sufficient, and loss of design base knowledge can have huge implications (eg Pickering A and Bruce A in Ontario). Knowledge management is often a shared responsibility and is essential for effective decision-making and the achievement of plant safety and economics. * ISO15926 covers portability and interoperability for lifecycle open data standard. Also EPRI in 2013 published Advanced Nuclear Technology: New Nuclear Power Plant Information Handover Guide. See also section on Ageing, in Safety of Nuclear Power Reactors paper. Load-following capacity Nuclear power plants are essentially base-load generators, running continuously. This is because their power output cannot readily be ramped up and down on a daily and weekly basis, and in this respect they are similar to most coal-fired plants. (It is also uneconomic to run them at less than full capacity, since they are expensive to build but cheap to run.) However, in some situations it is necessary to vary the output according to daily and weekly load cycles on a regular basis, for instance in France, where there is a very high reliance on nuclear power. While BWRs can be made to follow loads reasonably easily without burning the core unevenly, this is not as readily achieved in a PWR. The ability of a PWR to run at less than full power for much of the time depends on whether it is in the early part of its 18 to 24-month refueling cycle or late in it, and whether it is designed with special control rods which diminish power levels throughout the core without shutting it down. Thus, though the ability on any individual PWR reactor to run on a sustained basis at low power decreases markedly as it progresses through the refueling cycle, there is considerable scope for running a fleet of reactors in load- following mode. See further information in the Nuclear Power in France paper. As fast neutron reactors become established in future years, their ability to load-follow will be a benefit. Primary coolants The advent of some of the designs mentioned above provides opportunity to review the various primary coolants used in nuclear reactors. There is a wide variety – gas, water, light metal, heavy metal and salt: Water or heavy water must be maintained at very high pressure (1000-2200 psi, 7-15 MPa) to enable it to function above 100°C, as in present reactors. This has a major influence on reactor engineering. However, supercritical water around 25 MPa can give 45% thermal efficiency – as at some fossil-fuel power plants today with outlet temperatures of 600°C, and at ultra supercritical levels (30+ MPa) 50% may be attained. Helium must be used at similar pressure (1000-2000 psi, 7-14 MPa) to maintain sufficient density for efficient operation. Again, there are engineering implications, but it can be used in the Brayton cycle to drive a turbine directly. Carbon dioxide was used in early British reactors and their AGRs. It is denser than helium and thus likely to give better thermal conversion efficiency. There is now interest in supercritical CO2 for the Brayton cycle.
  • 35. Sodium, as normally used in fast neutron reactors, melts at 98°C and boils at 883°C at atmospheric pressure, so despite the need to keep it dry the engineering required to contain it is relatively modest. It has high thermal conductivity. However, normally water/steam is used in the secondary circuit to drive a turbine (Rankine cycle) at lower thermal efficiency than the Brayton cycle. In some designs sodium is in a secondary circuit to steam generators. Sodium does not corrode the metals used in the fuel cladding or primary circuit, nor the fuel itself if there is cladding damage. Lead or lead-bismuth eutectic in fast neutron reactors are capable of higher temperature operation. They are transparent to neutrons, aiding efficiency, and since they do not react with water the heat exchanger interface is safer. They do not burn when exposed to air. However, they are corrosive of fuel cladding and steels, which originally limited temperatures to 550°C. With today's materials 650°C can be reached, and in future 700°C is in sight, using oxide dispersion-strengthened steels. A problem is that Pb-Bi yields toxic polonium (Po-210) activation products. Pb-Bi melts at a relatively low 125°C (hence eutectic) and boils at 1670°C, Pb melts at 327°C and boils at 1737°C but is very much more abundant and cheaper to produce than bismuth, hence is envisaged for large-scale use in the future, though freezing must be prevented. The development of nuclear power based on Pb-Bi cooled fast neutron reactors is likely to be limited to a total of 50-100 GWe, basically for small reactors in remote places. In 1998 Russia declassified a lot of research information derived from its experience with submarine reactors, and US interest in using Pb or Pb-Bi for small reactors has increased subsequently. The Gen4 Module (Hyperion) reactor will use lead-bismuth eutectic which is 45% Pb, 55% Bi. Molten fluoride salt boils at 1400°C at atmospheric pressure, so allows several options for use of the heat, including using helium in a secondary Brayton cycle with thermal efficiencies of 48% at 750°C to 59% at 1000°C, or manufacture of hydrogen. Fluoride salts have very low vapor pressure even at red heat, have reasonably good heat transfer properties, are not damaged by radiation, do not react violently with air or water, and are inert to some common structural metals. Low-pressure liquid coolants allow all their heat to be delivered at high temperatures, since the temperature drop in heat exchangers is less than with gas coolants. Also, with a good margin between operating and boiling temperatures, passive cooling for decay heat is readily achieved. The removal of passive decay heat is a vital feature of primary cooling systems, beyond heat transfer to do work. When the fission process stops, fission product decay continues and a substantial amount of heat is added to the core. At the moment of shutdown, this is about 6% of the full power level, but it quickly drops to about 1% as the short-lived fission products decay. This heat could melt the core of a light water reactor unless it is reliably dissipated. Typically some kind of convection flow is relied upon. Top AHTR line is potential, lower one practical today. See also paper on Cooling Power Plants. There is some radioactivity in the cooling water flowing through the core of a water-cooled reactor, due mainly to the activation product nitrogen-16, formed by neutron capture from oxygen. N-16 has a half-life on only 7 seconds but produces high-energy gamma radiation during decay. It is the reason that access to a BWR turbine hall is restricted during actual operation. Nuclear reactors for process heat Producing steam to drive a turbine and generator is relatively easy, and a light water reactor running at 350°C does this readily. As the above section and Figure show, other types of reactor are required for higher temperatures. A 2010 US Department of Energy document quotes 500°C for a liquid metal cooled reactor (FNR), 860°C for a molten salt reactor (MSR), and 950°C for a high temperature gas-cooled reactor (HTR). Lower-temperature reactors can be used with supplemental gas
  • 36. heating to reach higher temperatures, though employing an LWR would not be practical or economic. The DOE said that high reactor outlet temperatures in the range 750 to 950°C were required to satisfy all end user requirements evaluated to date for the Next Generation Nuclear Plant. Primitive reactors The world's oldest known nuclear reactors operated at what is now Oklo in Gabon, West Africa. About 2 billion years ago, at least 17 natural nuclear reactors achieved criticality in a rich deposit of uranium ore. Each operated intermittently at about 20 kW thermal, the reaction ceasing whenever the water turned to steam so that it ceased to function as moderator. At that time the concentration of U-235 in all natural uranium was 3.7 percent instead of 0.7 percent as at present. (U-235 decays much faster than U-238, whose half-life is about the same as the age of the Earth.) These natural chain reactions, started spontaneously by the presence of water acting as a moderator, continued overall for about 2 million years before finally dying away. During this long reaction period about 5.4 tonnes of fission products as well as 1.5 tonnes of plutonium together with other transuranic elements were generated in the orebody. The initial radioactive products have long since decayed into stable elements but close study of the amount and location of these has shown that there was little movement of radioactive wastes during and after the nuclear reactions. Plutonium and the other transuranics remained immobile. Classification by type of nuclear reaction Nuclear fission. All commercial power reactors are based on nuclear fission. They generally use uranium and its product plutonium asnuclear fuel, though a thorium fuel cycle is also possible. Fission reactors can be divided roughly into two classes, depending on the energy of the neutrons that sustain the fission chain reaction: Thermal reactors use slowed or thermal neutrons to keep up the fission of their fuel. Almost all current reactors are of this type. These contain neutron moderator materials that slow neutrons until their neutron temperature is thermalized, that is, until theirkinetic energy approaches the average kinetic energy of the surrounding particles. Thermal neutrons have a far higher cross section (probability) of fissioning the fissile nuclei uranium-235, plutonium- 239, and plutonium-241, and a relatively lower probability of neutron capture by uranium-238 (U-238) compared to the faster neutrons that originally result from fission, allowing use of low-enriched uranium or even natural uranium fuel. The moderator is often also the coolant, usually water under high pressure to increase the boiling point. These are surrounded by a reactor vessel, instrumentation to monitor and control the reactor, radiation shielding, and a containment building. Fast neutron reactors use fast neutrons to cause fission in their fuel. They do not have a neutron moderator, and use less-moderating coolants. Maintaining a chain reaction requires the fuel to be more highly enriched in fissile material (about 20% or more) due to the relatively lower probability of fission versus capture by U-238. Fast reactors have the potential to produce lesstransuranic waste because all actinides are fissionable with fast neutrons,[16] but they are more difficult to build and more expensive to operate. Overall, fast reactors are less common than thermal reactors in most applications. Some early power stations were fast reactors, as are some Russian naval propulsion units. Construction of prototypes is continuing (see fast breeder or generation IV reactors). Nuclear fusion. Fusion power is an experimental technology, generally with hydrogen as fuel. While not suitable for power production, Farnsworth-Hirsch fusors are used to produce neutron radiation. Inside a Nuclear Reactor A nuclear power plant is a lot like most coal or natural gas plants. They all create steam to power the plant. Instead of burning a typical fuel such as natural gas or coal, nuclear power plants use a process called fission to create the steam. Though there are different models used around the world, American nuclear power reactors are either pressurized or boiling water reactors. Fission is the process of splitting an atom, which then releases energy in the form of heat. The fissionable material used in nuclear reactors is uranium, which is found naturally all over the world. Uranium ore, however, is not quite ready to fuel a reactor when it comes out of the ground. The ore contains different forms, or isotopes, of uranium. The isotope used for fission in most reactors is uranium-235, but the predominant isotope found in natural uranium ore is uranium-238. Only around 0.7 percent of natural uranium is U-235, but reactor fuel must consist of at least 3 percent to 5 percent U-235. A process called enrichment is used to increase the amount of U-235.
  • 37. This enriched uranium is then fabricated into ceramic pellets that are about the size of a pencil eraser and then placed into rods. The rods are combined to form bundles, which are then grouped together to form the reactor‘s core. The reaction that ultimately generates electricity starts when an atom of U-235 absorbs a neutron and splits. The process of splitting atoms expels a tremendous amount of heat, some fission byproducts, and more neutrons, which are then absorbed by other uranium atoms. The process is repeated in a chain reaction that is controlled by control rods that are inserted into the reactor core. The heat produced is used to heat water until it turns to steam. The steam turns a turbine, which in turn powers a generator to create nearly 20 percent of the electricity consumed inAmerica. Outside the Reactor Reactors are enclosed within thick steel pressure reactor vessels, which are protected with concrete shielding and enclosed in containment structures made of steel and reinforced concrete that are several feet thick. These layers of defense protect the reactor from outside threats like earthquakes or other natural disasters and the public and environment from the radiation within the reactor. Other important buildings on a nuclear power plant site include the generating room and the iconic cooling towers (though not every plant uses cooling towers). Though the anti-nuclear crowd likes to show billowing cooling towers as symbolic of the dangers of nuclear energy, these are harmless giants that simply cool the superheated water. The vapor that emerges from the towers is not radioactive; rather, it is condensation of the water taken in from a nearby lake or river. Americahas been pursuing and perfecting nuclear energy for over 50 years. Despite competitors such as natural gas, public relations disasters such asThree Mile Island, and cost-inflating government policies, nuclear energy continues to grow. Indeed, five reactors are under construction in theU.S.today. Over the decades, the industry has become safer while at the same time becoming more efficient: In 1980, the average capacity factor (a measure of power actually produced over a specified period of time versus a generator‘s theoretical capacity) was 56.3 percent, whereas in 2011 it was 89 percent. Though the nuclear industry faces some significant challenges—such as nuclear waste storage—nuclear power‘s future is bright. IntroductionNuclear Power Nuclear power provides about 20 percent of the electricity used in the United States. Duke Energy operates 11 nuclear units in the Carolinas at six plant sites. Safety and security have always been the highest priority in Duke Energy‘s nuclear program, which began in the 1960s with the construction of Robinson Nuclear Plant. Our plants are designed, built and operated for safety, with multiple barriers and redundant and diverse safety systems to protect the public, plant workers and the environment. The cost of generating electricity with nuclear power is stable and economical. Among coal, natural gas and oil, nuclear power plants have had the lowest electricity production costs since 2001. Duke Energy has operated nuclear plants for more than 40 years, setting industry benchmarks for safety and efficiency. And, with zero-carbon emissions, it is an important clean-energy resource for the future.
  • 38. How Do Nuclear Plants Work? In a nuclear-fueled power plant – much like a fossil-fueled power plant – water is turned into steam, which in turn drives turbine generators to produce electricity. The difference is the source of heat. At nuclear power plants, the heat to make the steam is created when uranium atoms split – called fission. There is no combustion in a nuclear reactor. Here‘s how the process works. There are two types of nuclear reactors in the United States: Pressurized Water Reactor Pressurized Water Reactors (also known as PWRs) keep water under pressure so that it heats, but does not boil. This heated water is circulated through tubes in steam generators, allowing the water in the steam generators to turn to steam, which then turns the turbine generator. Water from the reactor and the water that is turned into steam are in separate systems and do not mix. View animated image of a Pressurized Water Reactor Source: Nuclear Regulatory Commission View a detailed description of the process. Boiling Water Reactor In Boiling Water Reactors (also known as BWRs), the water heated by fission actually boils and turns into steam to turn the turbine generator. In both PWRs and BWRs, the steam is turned back into water and can be used again in the process. View animated image of a Boiling Water Reactor BackgroundNuclear Power About 20 percent of America‘s electricity is generated from nuclear power. Today there are 104 nuclear power reactors operating in 31 states, and some states, such as South Carolina, generate more than 50 percent of their electricity from nuclear power. Nuclear energy is one of the cleanest fuel sources, accounting for 70 percent of all emission-free electricity generated and emitting no carbon dioxide, sulfur dioxide or nitrogen oxide. Nuclear power plants are important for the clean energy mix, providing a steady base to back up less consistent renewables like solar, hydro and wind power.
  • 39. The U.S. Department of Energy predicts that the U.S. will need 24 percent more electricity by 2035. To meet this increased demand, we will need to generate more electricity than we do today to produce food, to power factories and to drive our productivity, which will require a vast amount of fuel. Click to view larger map Locations of the 104 nuclear power reactors in the U.S. (Source: Nuclear Energy Institute) Although solar power, geothermal energy, wind power and biomass are important to meeting our country‘s rising electricity demand, they‘re currently unable to produce large amounts of energy around the clock like nuclear power. Using nuclear also reduces the need to rely as much on fossil fuel resources like oil, which will be earmarked for transportation purposes and other end-uses, for which we have few or no substitutes. Nuclear energy currently plays a key role in meeting our nation‘s electricity needs and will continue to be an important energy source for the world in years to come. Duke Energy has the ability to produce clean, safe and economical electricity using nuclear energy to meet our customers‘ future electricity needs. Answer: Short Answer: Advantages: Economics. Much more energy results from a small piece of fuel. Environment. No carbon dioxide emissions causing global warming (unlike fossil fuels (coal, oil and natural gas)) Disadvantages: The problem of how to store the dangerous radioactive waste safely The risks of a dangerous accident or terrorist attack at the nuclear power plant the safety risks in mining and transporting the radioactive fuel The safety risks in transporting the radioactive waste The risks of theft of material, possibly for a nuclear bomb Advantages: Nuclear power produces fewer carbon emissions than most other traditional energy sources, probably no more than 40% of what natural gas does. Its carbon emissions come from petrochemicals used in the mining, refinement, enrichment, and transportation of fuel, the construction of the power plant, the decommissioning of the power plant, and the disposal of nuclear waste. Some of these are usually neglected altogether when emissions are calculated, so figures should be regarded with healthy skepticism. In particular, the waste disposal is not usually considered, as the emissions cannot be determined accurately. One advantage that proponents of nuclear power site is that nuclear plants provide a lot of employment. The Vermont Yankee plant, which is one of the smaller plants around, employs 650 people, to produce 620 megawatts of power. Nuclear plants provide baseload power. The plants are always running, except about one month out of every 18 months or so, when they have to shut down for refueling, or when there is some unexpected event.
  • 40. Disadvantages: There is the possibility of environmental contamination for a variety of reasons. One is human error, such as happened at Chernobyl. Another is because radioactivity "poisons" metals, causing pipes, vessels, and so on to weaken and eventually crack, spilling radioactive materials into the environment, which is probably why Vermont Yankee and 26 other plants in the United States have tritium leaks. There have been radiation leaks due to other reasons, in addition, such as unanticipated natural conditions. The economic and environmental costs of catastrophic accident are overwhelming. The economic cost of the Chernobyl Disaster has been estimated as high as a trillion 1995 US dollars. The amount of land rendered unusable for at least several years was about a quarter of the size of New England. The area where there were agricultural losses of one sort or another was about an eighth of the size of the United States. The area left permanently uninhabitable was many square miles. Nuclear plants cannot be sited just anywhere. They must be sited where there are really good heat sinks. This really means they must be sited where there is a lot of water, such as at a lake, river, or ocean. This, in turn, means that any radioactive materials that are released into the environment are dispersed easily. The plants, together with their waste, can also be subject to floods. The waste storage at some sites is only 3 inches above the 500 year flood level, and coastal plants could be subject to damage from tsunami that could occur at high tide or a mega-tsunami at any time. It is impossible for the insurance industry to cover the cost of a catastrophic event at a nuclear site, so the risk is typically covered by the taxpayer, as it is in the United States. Nuclear plants are very costly, more costly than any other source of energy widely used commercially, so governments that want nuclear plants have to subsidize them by loans or direct payment, at taxpayer expense. Owners of nuclear plants cannot afford to dispose of the high level waste. As a result, this is done at taxpayer expense. No one has ever solved the waste disposal problem. In some countries, the waste is exported to countries poor enough to be willing to be paid to store it. In the United States, the waste is stored at the plants until someone figures out what to do with it. When this is done, it will be done at taxpayer expense. The high level waste will be dangerous for over a million years. The time it takes for the waste to be reduced to the radioactivity of uranium ore (which is not all that safe) is approximately six million years. This is a large multiple of the length of human history, and we do not know how to secure it for anything like that length of time. There are dangers of radioactivity we do not understand. For example, men who worked in nuclear plants in the UK and subsequently left for other industries, were found to have a significantly increased risk of having children who developed leukemia, even years after their last exposure to the "normal" levels of radioactivity in the plant. The cost of decommissioning a nuclear plant is enormous. The fuel is running out. We can reprocess fuel, but this is illegal in many countries because of its danger. The fuel willl probably run out at about the same time as oil and well before coal, unless we develop new nuclear technology. Nuclear power can be used to build nuclear bombs. ADVANTAGES: Nuclear power plants don't require a lot of space - they have to be built on the coast, but do not need a large plot like a wind farm. It doesn't contribute to carbon emissions - no CO2 is given out - it therefore does not cause global warming. It does not produce smoke particles to pollute the atmosphere. Nuclear energy is by far the most concentrated form of energy - a lot of energy is produced from a small mass of fuel. This reduces transport costs - (although the fuel is radioactive and therefore each transport that does occur is expensive because of security implications). It is reliable. It does not depend on the weather. We can control the output It is relatively easy to control the output - although the time factor for altering power output is not as small as for fossil fuel stations. It produces a small volume of waste (although that waste is radioactive - see below)
  • 41. DISADVANTAGES: Disposal of nuclear waste is very expensive. As it is radioactijive it has to be disposed of in such a way as it will not pollute the environment. Decommissioning of nuclear power stations is expensive and takes a long time. (In fact we have not ever decommissioned one!) Nuclear accidents can spread radiation producing particles over a wide area, This radiation harms the cells of the body which can make humans sick or even cause death. Illness can appear or strike people years after they were exposed to nuclear radiation and genetic problems can occur too. A possible type of reactor disaster is known as a meltdown. In a meltdown, the fission reaction of an atom goes out of control, which leads to a nuclear explosion releasing great amounts of radioactive particles into the environment. See Chernobyl. Advantage: Nuclear power allows energy to be produced in a way which greatly reduces serious environmental pollution by carbon dioxide from conventional power plants. Reactor A diagram of a fission reaction The reactor is where the reaction takes place. Nuclear reactors use nuclear fission, which breaks the nucleus of a uranium atom into smaller pieces, freeing neutrons in the process. The freed neutrons break other nuclei into smaller pieces, which free further neutrons. The movement of the neutrons generates heat. Control Rods Control rods are made of a substance, such as graphite or cadmium, that absorbs extra neutrons. Since the movement of the neutrons causes the reaction, absorbing the extra neutrons slows down the reaction. Steam Generator The heat from the nuclear reaction is used to heat massive amounts of water in the steam generator. Inside the steam generator are bundles of tubes that keep the water from boiling, allowing it to superheat. Turbines and Generator The superheated water from the steam generator turns turbines. The turbines then operate the generator, which creates the electricity. Cooling Tower The best-known, and most-visible, part of a nuclear power plant is the cooling tower. In the cooling tower, water is cooled down to be used again. Main components of a nuclear reactor Core – It‘s the focal point of the reactor, where fuel is contained and nuclear fission reactions take place. Fuel – Generally, fuel is made of small enriched uranium oxide rods, stacked so as to form cylinders, approx. 4 metres long and with a diameter of about one centimetre. These rods are wrapped in metal sheathes (steel or zirconium alloy), which allow heat to pass through while blocking the radioactive elements produced by fission. Moderator – This is a material placed in the reactor to slow down the neutrons produced by fission, in order to reach the most suitable speed allowing the chain reaction to continue.
  • 42. Depending on the various reactor models, the moderator may consist of graphite, water or heavy water (water where the hydrogen is present as its heavier isotope, deuterium). Heat-transfer fluid (or coolant) - This fluid (liquid or gas) cools the core and carries outside the heat that is produced there. The most commonly used fluid is water, but some types of reactors use different fluids (heavy water, molten sodium, carbon dioxide, helium and other fluids). Control rods – These are rods used in specific materials (silver, indium, cadmium or boron carbide) to control fission inside the core. Since they absorb neutrons, they are capable of controlling the chain reaction which - depending on how deep down the rods are inserted into the core - can be accelerated, slowed down or even stopped, thus changing the capacity of the reactor. Indeed, if necessary, the reactor can be immediately stopped when they are fully inserted. Vessel – The large steel recipient containing the core, the control rods and the heat-transfer fluid. All the components of the reactor are container in a solid concrete structure that guarantees further isolation from external environment. This structure is made of concrete that is one-metre thick, covered by steel. The most recent reactors sometimes contain two containment structures and are designed to defy all types of accidental events, even the impact of an aircraft. What is Uranium? How Does it Work? December 2012 Uranium is a very heavy metal which can be used as an abundant source of concentrated energy. Uranium occurs in most rocks in concentrations of 2 to 4 parts per million and is as common in the Earth's crust as tin, tungsten and molybdenum. Uranium occurs in seawater, and can be recovered from the oceans. Uranium was discovered in 1789 by Martin Klaproth, a German chemist, in the mineral called pitchblende. It was named after the planet Uranus, which had been discovered eight years earlier. Uranium was apparently formed in supernova about 6.6 billion years ago. While it is not common in the solar system, today its slow radioactive decay provides the main source of heat inside the Earth, causing convection and continental drift. The high density of uranium means that it also finds uses in the keels of yachts and as counterweights for aircraft control surfaces, as well as for radiation shielding. Uranium has a melting point is 1132°C. The chemical symbol for uranium is U. The Uranium Atom On a scale arranged according to the increasing mass of their nuclei, uranium is one of the heaviest of all the naturally-occurring elements (Hydrogen is the lightest). Uranium is 18.7 times as dense as water. Like other elements, uranium occurs in several slightly differing forms known as 'isotopes'. These isotopes differ from each other in the number of uncharged particles (neutrons) in the nucleus. Natural uranium as found in the Earth's crust is a mixture largely of two isotopes: uranium-238 (U-238), accounting for 99.3% and uranium-235 (U-235) about 0.7%. The isotope U-235 is important because under certain conditions it can readily be split, yielding a lot of energy. It is therefore said to be 'fissile' and we use the expression 'nuclear fission'. Meanwhile, like all radioactive isotopes, they decay. U-238 decays very slowly, its half-life being about the same as the age of the Earth (4500 million years). This means that it is barely radioactive, less so than many other isotopes in rocks and sand. Nevertheless it generates 0.1 watts/tonne as decay heat and this is enough to warm the Earth's core. U-235 decays slightly faster. Energy from the uranium atom The nucleus of the U-235 atom comprises 92 protons and 143 neutrons (92 + 143 = 235). When the nucleus of a U-235 atom captures a moving neutron it splits in two (fissions) and releases some energy in the form of heat, also two or three additional neutrons are thrown off. If enough of these expelled neutrons cause the nuclei of other U-235 atoms to split, releasing further neutrons, a fission 'chain reaction' can be achieved. When this happens over and over again, many millions of times, a very large amount of heat is produced from a relatively small amount of uranium.
  • 43. It is this process, in effect "burning" uranium, which occurs in a nuclear reactor. The heat is used to make steam to produce electricity. Inside the reactor Nuclear power stations and fossil-fuelled power stations of similar capacity have many features in common. Both require heat to produce steam to drive turbines and generators. In a nuclear power station, however, the fissioning of uranium atoms replaces the burning of coal or gas.In a nuclear reactor the uranium fuel is assembled in such a way that a controlled fission chain reaction can be achieved. The heat created by splitting the U-235 atoms is then used to make steam which spins a turbine to drive a generator, producing electricity. The chain reaction that takes place in the core of a nuclear reactor is controlled by rods which absorb neutrons and which can be inserted or withdrawn to set the reactor at the required power level. The fuel elements are surrounded by a substance called a moderator to slow the speed of the emitted neutrons and thus enable the chain reaction to continue. Water, graphite and heavy water are used as moderators in different types of reactors. Because of the kind of fuel used (ie the concentration of U-235, see below), if there is a major uncorrected malfunction in a reactor the fuel may overheat and melt, but it cannot explode like a bomb. A typical 1000 megawatt (MWe) reactor can provide enough electricity for a modern city of up to one million people. Uranium and Plutonium Whereas the U-235 nucleus is 'fissile', that of U-238 is said to be 'fertile'. This means that it can capture one of the neutrons which are flying about in the core of the reactor and become (indirectly) plutonium-239, which is fissile. Pu-239 is very much like U-235, in that it fissions when hit by a neutron and this also yields a lot of energy. Because there is so much U-238 in a reactor core (most of the fuel), these reactions occur frequently, and in fact about one third of the fuel's energy yield comes from "burning" Pu-239. But sometimes a Pu-239 atom simply captures a neutron without splitting, and it becomes Pu-240. Because the Pu-239 is either progressively "burned" or becomes Pu-240, the longer the fuel stays in the reactor the more Pu-240 is in it. (The significance of this is that when the spent fuel is removed after about three years, the plutonium in it is not suitable for making weapons but can be recycled as fuel.) From uranium ore to reactor fuel Uranium ore can be mined by underground or open-cut methods, depending on its depth. After mining, the ore is crushed and ground up. Then it is treated with acid to dissolve the uranium, which is recovered from solution. Uranium may also be mined by in situ leaching (ISL), where it is dissolved from a porous underground ore body in situ and pumped to the surface. The end product of the mining and milling stages, or of ISL, is uranium oxide concentrate (U3O8). This is the form in which uranium is sold. Before it can be used in a reactor for electricity generation, however, it must undergo a series of processes to produce a useable fuel.
  • 44. For most of the world's reactors, the next step in making the fuel is to convert the uranium oxide into a gas, uranium hexafluoride (UF6), which enables it to be enriched. Enrichment increases the proportion of the uranium-235 isotope from its natural level of 0.7% to 4 - 5%. This enables greater technical efficiency in reactor design and operation, particularly in larger reactors, and allows the use of ordinary water as a moderator. After enrichment, the UF6 gas is converted to uranium dioxide (UO2) which is formed into fuel pellets. These fuel pellets are placed inside thin metal tubes which are assembled in bundles to become the fuel elements or assemblies for the core of the reactor. For reactors which use natural uranium as their fuel (and hence which require graphite or heavy water as a moderator) the U3O8 concentrate simply needs to be refined and converted directly to uranium dioxide. When the uranium fuel has been in the reactor for about three years, the used fuel is removed, stored, and then either reprocessed or disposed of underground (see Nuclear Fuel Cycle or Radioactive Waste Management in this series). Who uses nuclear power? Over 13% of the world's electricity is generated from uranium in nuclear reactors. This amounts to over 2500 billion kWh each year, as much as from all sources of electricity worldwide in 1960. It comes from some 440 nuclear reactors with a total output capacity of about 377 000 megawatts (MWe) operating in 30 countries. Over 60 more reactors are under construction and another 150 are planned. Belgium, Bulgaria, Czech Republic, Finland, France, Hungary, Japan, South Korea, Slovakia, Slovenia, Sweden, Switzerland and Ukraine all get 30% or more of their electricity from nuclear reactors. The USA has over 100 reactors operating, supplying 20% of its electricity. France gets three quarters of its electricity from uranium. See also Table of the World's Nuclear Power Reactors Who has and who mines uranium? Uranium is widespread in many rocks, and even in seawater. However, like other metals, it is seldom sufficiently concentrated to be economically recoverable. Where it is, we speak of an orebody. In defining what is ore, assumptions are made about the cost of mining and the market price of the metal. Uranium reserves are therefore calculated as tonnes recoverable up to a certain cost. Australia's reasonably assured resources and inferred resources of uranium are 1,673,000 tonnes of uranium recoverable at up to US$130/kg U (well under the market 'spot' price), Kazakhstan's are 651,000 tonnes of uranium and Canada's are 485,000 tU. Australia's resources in this category are almost one third of the world's total, Kazakhstan's are 12%, Canada's 9%. Several countries have significant uranium resources. Apart from the top three, they are in order: Russia, South Africa, Namibia, Brazil, Niger, USA, China, Jordan, Uzbekistan, Ukraine and India. Other countries have smaller deposits which could be mined if needed. Kazakhstan is the world's top uranium producer, followed by Canada and then Australia as the main suppliers of uranium to world markets - now over 50,000 tU per year.
  • 45. Uranium is sold only to countries which are signatories of the Nuclear Non-Proliferation Treaty (NPT), and which allow international inspection to verify that it is used only for peaceful purposes. Other uses of nuclear energy Many people, when talking about nuclear energy, have only nuclear reactors (or perhaps nuclear weapons) in mind. Few people realise the extent to which the use of radioisotopes has changed our lives over the last few decades. Using relatively small special-purpose nuclear reactors it is possible to make a wide range of radioactive materials (radioisotopes) at low cost. For this reason the use of artificially-produced radioisotopes has become widespread since the early 1950s, and there are now over 200 "research" reactors in 56 countries producing them. These are essentially neutron factories rather than sources of heat. Radioisotopes In our daily life we need food, water and good health. Today, radioactive isotopes play an important part in the technologies that provide us with all three. They are produced by bombarding small amounts of particular elements with neutrons. In medicine, radioisotopes are widely used for diagnosis and research. Radioactive chemical tracers emit gamma radiation which provides diagnostic information about a person's anatomy and the functioning of specific organs. Radiotherapy also employs radioisotopes in the treatment of some illnesses, such as cancer. More powerful gamma sources are used to sterilise syringes, bandages and other medical equipment. About one person in two in the western world is likely to experience the benefits of nuclear medicine in their lifetime, and gamma sterilisation of equipment is almost universal. In the preservation of food, radioisotopes are used to inhibit the sprouting of root crops after harvesting, to kill parasites and pests, and to control the ripening of stored fruit and vegetables. Irradiated foodstuffs are accepted by world and national health authorities for human consumption in an increasing number of countries. They include potatoes, onions, dried and fresh fruits, grain and grain products, poultry and some fish. Some prepacked foods can also be irradiated. In the growing of crops and breeding livestock, radioisotopes also play an important role. They are used to produce high yielding, disease-resistant and weather- resistant varieties of crops, to study how fertilisers and insecticides work, and to improve the productivity and health of domestic animals. Industrially, and in mining, they are used to examine welds, to detect leaks, to study the rate of wear of metals, and for on-stream analysis of a wide range of minerals and fuels. There are many other uses. A radioisotope derived from the plutonium formed in nuclear reactors is used in most householdsmoke detectors. Radioisotopes are used to detect and analyse pollutants in the environment, and to study the movement of surface water in streams and also of groundwater. Other reactors There are also other uses for reactors. About 200 small nuclear reactors power some 150 ships, mostly submarines, but ranging from icebreakers to aircraft carriers. These can stay at sea for long periods without having to make refuelling stops. In the Russian Arctic where operating conditions are beyond the capability of conventional icebreakers, very powerful nuclear-powered vessels operate almost year-round, where previously only two months could be used each year. The heat produced by nuclear reactors can also be used directly rather than for generating electricity. In Sweden and Russia, for example, it is used to heat buildings and to provide heat for a variety of industrial processes such as water desalination. Nuclear desalination is likely to be a major growth area in the next decade. High-temperature heat from nuclear reactors is likely to be employed in some industrial processes in future, especially for making hydrogen. Military sources Both uranium and plutonium were used to make bombs before they became important for making electricity and radioisotopes. The type of uranium and plutonium for bombs is different from that in a nuclear power plant. Bomb-grade uranium is highly-enriched (>90% U-235, instead of up to 5%); bomb-grade plutonium is fairly pure Pu-239 (>90%, instead of about 60% in reactor-grade) and is made in special reactors. Since the 1990s, due to disarmament, a lot of military uranium has become available for electricity production. The military uranium is diluted about 25:1 with depleted uranium (mostly U-238) from the enrichment process before being used in power generation. Military plutonium is starting to be used similarly, mixed with depleted uranium. Schematic Arrangement of Nuclear Power Plant The schematic arrangement of a nuclear power station is shown below.
  • 46. The whole arrangement can be divided into following main stages. (i)Nuclear Reactor (ii)Heat Exchanger (iii)Steam Turbine (iv)Alternator (i)Nuclear Reactor It is an apparatus in which nuclear fuel(U235)is subjected to nuclear fission.It controls the chain reaction that starts once the fusion is done.If the chain reaction is not controlled,the result will be an explosion due to the fast increase in the energy released. A nuclear reactor is a cylindrical stout pressure vessel and houses fuel rods of Uranium moderator and control rods.The fuel rods constitute the fission materials and release huge amount of energy when bombarded with slow moving neutrons.The moderator consists of graphite rods which enclose the fuel rods.The control rods are of Cadmium and are inserted in the reactor.Cadmium is strong neutron absorber and thus regulates the supply of neutrons for fission.When the control rods are pushed in deep enough,they absorb most of fission neutrons and hence few are available for chain reaction, which therefore stops.However,hence they are being withdrawn,more and more of these fission neutorns cause fission and hence the intensity of chain reaction is increased.Therefore by pulling out the control rods,power of nuclear reactor is increased,whereas by pushing them in,it is reduced.In actual practice,the lowering or raising of control rods is accomplished automatically acoording to the requiremen t of load.The heat produced by the reactor is removed by the coolant, generally a sodium metal.The coolant carries heat to the heat exchanger. (ii)Heat Exchanger The coolant gives up the heat to the heat exchanger which is utilised in raising the steam.After giving up heat,the coolant is again fed to the reactor. (iii)Steam Turbine The stean produced in the heat exchanger is led to the steam turbine througha valve.after doing a useful work in the turbine,the steam is exhausted to the condenser.The condenser condense the steam which is fed to the heat exchangerthrough feed water pump. (iv)Alternator The steam turbine drives the alternator which converts mechanical energy into electrical energy.The output from the alernator is delivered to the bus bars through tansformers,circuit brakers and isolators. Nuclear Power Plant A generating station in which nuclear energy is converted into electrical energy is known as a nuclear power station In nuclear power station, heavy elements such as Uranium (U235) or Thorium (Th232) are subjected to nuclear fission in a special apparatus known as a reactor. The heat energy thus released is utilised in raising steam at high temperature and pressure. The steam runs the steam turbine which converts steam energy into mechanical energy. The turbine drives the alternator which converts mechanical energy into electrical energy. The most important feature of a nuclear power station is that huge amount of electrical energy can be produced from a relatively small amount of nuclear fuel as compared to other conventional types of power stations. It has been found that complete fission of 1 kg. of Uranium (U235) can produce as much energy as can be produced by burning of 4,500 tons of high grade coal. Although the recovery of principal nuclear fuels (i.e.,Uranium and Thorium) is difficult and expensive, yet the total energy content of the estimated world reserves of these fuels are considerably higher than those of conventional fuels, viz., coal, oil and gas. At present, energy crisis is gripping us and, therefore, nuclear energy can be successfully employed for producing low cost electrical energy on a large scale to meet the growing commercial and industrial demands.
  • 47. Advantages i. The amount of fuel requires is quite small. Therefore, there is considerable saving in the cost of fuel transportation. ii. A nuclear power plant requires less space as compared to any other type of the same size. iii. It has low running charges as a small amount of fuel is used for producing bulk electrical energy. iv. This type of plant is very economical for producing bulk electric power. v. It can be located near the load centres because it does not require large quantities of water and need not be near coal mines. Therefore, the cost of primary distribution is reduced. vi. There are large deposits of nuclear fuels available all over the world. Therefore, such plants can ensure continued supply of electrical energy for thousands of years. vii. It ensures reliability of operation. Disadvantages i. The fuel is used is expensive and is difficult to recover. ii. The capital cost on a nuclear power plant is very high as compared to other types of plants. iii. The erection and commissioning of the plant requires greater technical know-how. iv. The fission by-products are generally radioactive and may cause a dangerous amount of radioactive pollusion v. Maintenance charge are high due to lack of standardisation. Moreover, high salaries of specially trained personnel employed to handle the plant further raise the cost. vi. Nuclear power plants are not well suited for varying loads as the reactor does not rrespond to the load fluctuations efficiently. vii. The disposal of the by-products, which are radioactive, is a big problem. They have either to be disposed off in a deep trench or in a sea away from sea-shore. Nuclear power in the Philippines From Wikipedia, the free encyclopedia Nuclear power was considered as a solution to the 1973 oil crisis, in which the Philippines was affected. The Bataan Nuclear Power Plant was built in the early 1980s but never went into operation because it sits on a tectonic fault and volcano. The Fukushima nuclear disaster gave pause to efforts to revive the plant.[1] The Bataan Nuclear Power Plant[edit] Main article: Bataan Nuclear Power Plant Under a regime of martial law, Philippine President Ferdinand Marcos in July 1973 announced the decision to build a nuclear power plant. This was in response to the 1973 oil crisis, as the Middle East oil embargo had put a heavy strain on the Philippine economy, and Marcos believed nuclear power to be the solution to meeting the country's energy demands and decreasing dependence on imported oil.[2] Construction on the Bataan Nuclear Power Plant began in 1976. Following the 1979 Three Mile Island accident in the United States, construction on the BNPP was stopped, and a subsequent safety inquiry into the plant revealed over 4,000 defects. Among the issues raised was that it was built near major earthquake fault lines and close to the then dormantPinatubo volcano.

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