Nuclear Power Plant by: Cris Macaranas


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Nuclear Power Plant by: Cris Macaranas

  1. 1. About one – sixth off the world’s electricity is generated by nuclear power plants over 435 of them are currently in operation around the globe. The nuclear power plant stands on the border between humanity’s greatest hopes and the deepest fears for the future. Nuclear power plant have an important role in our country. Why? Just because it can easily provide electrical energy to produce light, to entertain us while watching television, etc. And it does not contribute to carbon emissions, simply no carbon dioxide (CO2) is given out, therefore it does not cause global warning. A nuclear power plant is a (given) place where people make electricity using heat from nuclear reactions. The plant also has machines which remove heat from the reactor to operate of steam turbine and generator to make electricity. Nuclear power plants are usually near water to remove the heat the reactor makes. But what happens inside a nuclear power plants to such marvels?
  2. 2. Nuclear Power Plants produce to controlled air pollutions such as sulphur and particulates or greenhouse gases. The use of nuclear energy in place of other energy sources helps to keep the air clean, presence the earth’s climate avoid ground level ozone formation and prevent acid rain. Of all energy sources, nuclear energy has perhaps the lowest impact on the environment specially in relation to kilowatts produced because nuclear power plants do not emit harmful gases, require relatively, small area and effectively minimize or negative other impacts. In other words, nuclear power plant is the most “ecologically efficient” provides of all energy sources. Why? Because it produces the most electricity in relation to its minimal environment impact.
  3. 3. HISTORY As of 16 January 2013, the IAEA report there are 439 nuclear power reactors in operation operating in 31 countries. Nuclear power plants are usually considered to be base load stations, since fuel is a small part of the cost of production. Electricity was generated by a nuclear reactor for the first time ever on September 3, 1948 at the X-10 Graphite Reactor in Oak Ridge, Tennessee in the United States, and was the first nuclear power plant to power a light bulb. The second, larger experiment occurred on December 20, 1951 at the EBR- I experimental station near Arco, Idaho in the United States. On June 27, 1954, the world's first nuclear power plant to generate electricity for a grid started operations at the Soviet city of Obninsk. The world's first full scale power station, Calder Hall in England opened on October 17, 1956.
  4. 4. 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.
  5. 5. The Philippine Nuclear Power Plant started in 1958 with the creation of the Philippine Atomic Energy Commission (PAEC) 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.
  6. 6. 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 dormant Pinatubo volcano. By 1984, when the BNPP was nearly complete, its cost had reached $US2.3 billion. Equipped with a Westinghouse light water reactor, it was designed to produce 621 megawatts of electricity.
  7. 7. Marcos was overthrown by the People Power Revolution in 1986. Days after the April 1986 Chernobyl disaster, the succeeding administration of President Corazon Aquino decided not to operate the plant. Among other considerations taken were the strong opposition from Bataan residents and Philippine citizens. The government sued Westinghouse for overpricing and bribery but was ultimately rejected by a United States court. Debt repayment on the plant became the country's biggest single obligation. While successive governments have looked at several proposals to convert the plant into an oil, coal, or gas-fired power station, these options have all been deemed less economically attractive in the long term than simply constructing new power stations.
  8. 8. A nuclear power plant is a thermal power station in which the heat source is a nuclear reactor. As is typical in all conventional thermal power stations the heat is used to generate steam which drives a steam turbine connected to a generator which produces electricity. As of 16 January 2013, the IAEA report there are 439 nuclear power reactors in operation operating in 31 countries. Nuclear power plants are usually considered to be base load stations, since fuel is a small part of the cost of production.
  9. 9. 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.
  10. 10. 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.
  12. 12. A Nuclear Reactor produces and controls the release of energy from splitting the atoms of uranium. The only purpose of a nuclear power plant is to produce electricity. To produce electricity, a power plant needs a source of heat to boil water which becomes steam. The steam then turns a turbine, the turbine an electrical generator, and the generator produces electricity.
  13. 13. BATAAN NUCLEAR POWER PLANT The bataan nuclear power plant (BNPP) is located at napot point, within the municipality of morong, bataan. The plant is similar in design concept with the krsko Nuclear Power Plant in Yugoslavia.. The BNPP employs a westing house – designed pressurized water reactor, light – water moderated and having a two – loop primary cooling system. The reactor core uses a 16 x 16 array of fuel assemblies supplied by westing house. The reactor is designed to operate at a power level of 1,876 mwt (megawatts thermal) equivalent to a maximum net electrical output of 621 MWE (megawatts electric)
  14. 14. 1. WHY DO WE NEED NUCLEAR POWER PLANT? In late 1973, the first world oil crisis erupted. The price of crude oil more than quadrupled from US.$2.55 per barrel in April 1973 to US $10.84 per barrel in December 1974 and at the same time, OPEC imposed a partial oil embargo to the Philippines. With the Philippines 95% dependent on imported oil for its commercial energy consumption, the crisis has unfolded the country’s absolute vulnerability to drastic changes in the international oil market.
  15. 15. In January 1974, the country needed non-oil energy projects for immediate implementation to relieve the grim possibility facing Luzon. Evaluation of existing or indigenous sources of energy needed to meet the projected power demand was undertaken. We were only starting to explore geothermal potential in commercial quantities, the first live well being struck only in November 1974. The 50 MW Pantabangan Multi- Purpose project which was being constructed, was upgraded to 100 MW and the hydro power potentials of other Luzon rivers were looked into. The country’s coal reserves have not yet been established. Minable reserves were established only in 1980 in Semirara Island. Thus, the only viable alternative source of bulk energy seemed to be nuclear power which has been the subject of almost 20 years of exhaustive studies undertaken by both local and foreign experts. Nuclear power, along with geothermal, coal and hydro will be vital in reducing the country’s heavy dependence on high-priced and unreliable imported fuel oil. It will improve the country’s supply of electricity which is vital to a developing economy.
  16. 16. 2. FACILITIES - BNPP has the following principal plant structures: (a) the reactor containment building; (b) the turbine building; (c) the auxiliary building complex; (d) the fuel handling building; (e) the intake structure; and (f) the ultimate heat sink.
  17. 17. 2.1 REACTOR CONTAINMENT BUILDING - This building contains the containment which is enclosed by a concrete shield building. The containment is a free-standing cylindrical steel shell with a hemispherical dome and elliptical bottom designed to withstand maximum temperature and pressure expected from the steam produced if all water in the primary system were expelled into the containment. The containment is normally slightly below atmospheric pressure, so that leakage through the containment walls would at most times be inward from the surroundings. Inside the containment structure, the reactor and other nuclear steam supply system components are shielded with concrete. In addition, a containment spray system and a containment recirculation and associated cooling system are provided to remove post-accident heat. The concrete shield building surrounding the containment provides biological protection against radiation during normal and accident conditions. The building also provides volume space or sealed containment for radioactive releases from the containment during normal and abnormal operation.
  18. 18. 2.2 TURBINE BUILDING - This building contains the low and high pressure steam turbines, the electrical generator and all the power-conversion related equipment.
  19. 19. 2.3 AUXILIARY BUILDING COMPLEX - The building complex includes the control building, the component cooling building, the diesel generator building, the intermediate building and the auxiliary building.
  20. 20. 2.4 FUEL HANDLING BUILDING - The fuel handling building is an integral part of the auxiliary building complex. It contains the spent fuel pool which is lined with stainless steel to prevent leakage of water.
  21. 21. 2.5 INTAKE STRUCTURE - The intake structure is situated along the shoreline of the South China Sea within the nuclear plant perimeter. The structure contains traveling water screens, the circulating water pumps, and auxiliary service equipment, providing waste heat removal function. This structure is connected by a reinforced concrete intake tunnel to the main condenser water boxes and turbine plant auxiliary heat exchangers via valved piping connections. The main condenser water boxes and turbine plant auxiliary heat exchangers are connected by a reinforced concrete discharge tunnel, via valved piping connections, to the sealwell, and then to the South China Sea.
  22. 22. 3. IMPORTANT COMPONENT OF A NUCLEAR POWER PLANT 3.1 Core – It’s the focal point of the reactor, where fuel is contained and nuclear fission reactions take place.
  23. 23. 3.2 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.
  24. 24. 3.3 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.
  25. 25. 3.4 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).
  26. 26. 3.5 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.
  27. 27. 3.6 Vessel – The large steel recipient containing the core, the control rods and the heat-transfer fluid.
  28. 28. 4. SYSTEMS - The conversion to electrical energy takes place indirectly, as in conventional thermal power plants. The heat is produced by fission in a nuclear reactor (a light water reactor). Directly or indirectly, water vapor (steam) is produced. The pressurized steam is then usually fed to a multi- stage steam turbine. Steam turbines in Western nuclear power plants are among the largest steam turbines ever. After the steam turbine has expanded and partially condensed the steam, the remaining vapor is condensed in a condenser. The condenser is a heat exchanger which is connected to a secondary side such as a river or a cooling tower. The water is then pumped back into the nuclear reactor and the cycle begins again. The water-steam cycle corresponds to the Rankine cycle.
  29. 29. 4.1 NUCLEAR REACTORS A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. The most common use of nuclear reactors is for the generation of electric energy and for the propulsion of ships. The nuclear reactor is the heart of the plant. In its central part, the reactor core's heat is generated by controlled nuclear fission. With this heat, a coolant is heated as it is pumped through the reactor and thereby removes the energy from the reactor. Heat from nuclear fission is used to raise steam, which runs through turbines, which in turn powers either ship's propellers or electrical generators.
  30. 30. 4.1.1 Mechanism of Nuclear Reactor - An induced nuclear fission event. A neutron is absorbed by the nucleus of a uranium-235 atom, which in turn splits into fast-moving lighter elements (fission products) and free neutrons. Though both reactors and nuclear weapons rely on nuclear chain-reactions, the rate of reactions in a reactor occurs much more slowly than in a bomb. 4.1.2 Fission - When a large fissile atomic nucleus such as uranium-235 or plutonium- 239 absorbs a neutron, it may undergo nuclear fission. The heavy nucleus splits into two or more lighter nuclei, (the fission products), releasing kinetic energy, gamma radiation, and free neutrons. A portion of these neutrons may later be absorbed by other fissile atoms and trigger further fission events, which release more neutrons, and so on. This is known as a nuclear chain reaction.
  31. 31. 4.1.3 Heat Generation - The kinetic energy of fission products is converted to thermal energy when these nuclei collide with nearby atoms. The reactor absorbs some of the gamma rays produced during fission and converts their energy into heat. Heat is produced by the radioactive decay of fission products and materials that have been activated by neutron absorption. This decay heat-source will remain for some time even after the reactor is shut down. A kilogram of uranium-235 (U-235) converted via nuclear processes releases approximately three million times more energy than a kilogram of coal burned conventionally (7.2 × 1013 joules per kilogram of uranium-235 versus 2.4 × 107 joules per kilogram of coal).
  32. 32. 4.1.4 Cooling - A nuclear reactor coolant — usually water but sometimes a gas or a liquid metal (like liquid sodium) or molten salt — is circulated past the reactor core to absorb the heat that it generates. The heat is carried away from the reactor and is then used to generate steam. Most reactor systems employ a cooling system that is physically separated from the water that will be boiled to produce pressurized steam for the turbines, like the pressurized water reactor. But in some reactors the water for the steam turbines is boiled directly by the reactor core, for example the boiling water reactor. 4.1.5 Reactivity Control - The power output of the reactor is adjusted by controlling how many neutrons are able to create more fissions. Control rods that are made of a neutron poison are used to absorb neutrons. Absorbing more neutrons in a control rod means that there are fewer neutrons available to cause fission, so pushing the control rod deeper into the reactor will reduce its power output, and extracting the control rod will increase it.
  33. 33. 4.1.6 Electrical Power Generation - The energy released in the fission process generates heat, some of which can be converted into usable energy. A common method of harnessing this thermal energy is to use it to boil water to produce pressurized steam which will then drive a steam turbine that turns an alternator and generates electricity.
  34. 34. 4.2 STEAM TURBINE The purpose of the steam turbine is to convert the heat contained in steam into mechanical energy. The engine house with the steam turbine is usually structurally separated from the main reactor building. It is so aligned to prevent debris from the destruction of a turbine in operation from flying towards the reactor. In the case of a pressurized water reactor, the steam turbine is separated from the nuclear system. To detect a leak in the steam generator and thus the passage of radioactive water at an early stage, an activity meter is mounted to track the outlet steam of the steam generator. In contrast, boiling water reactors pass radioactive water through the steam turbine, so the turbine is kept as part of the control area of the nuclear power plant.
  35. 35. 4.2.1 Blade and Stage Design - Steam turbines are made in a variety of sizes ranging from small 0.75 kW units used as mechanical drives for pumps, compressors and other shaft driven equipment, to 1,500,000kW turbines used to generate electricity. Steam turbines are widely used for marine applications for vessel propulsion systems. In recent times gas turbines, as developed for aerospace applications, are being used more and more in the field of power generation once dominated by steam turbines. - Turbine blades are of two basic types, blades and nozzles. Blades move entirely due to the impact of steam on them and their profiles do not converge. This results in a steam velocity drop and essentially no pressure drop as steam moves through the blades. A turbine composed of blades alternating with fixed nozzles is called an impulse turbine, Curtis turbine, Rateau turbine, or Brown-Curtis turbine. Nozzles appear similar to blades, but their profiles converge near the exit. This results in a steam pressure drop and velocity increase as steam moves through the nozzles. Nozzles move due to both the impact of steam on them and the reaction due to the high-velocity steam at the exit. A turbine composed of moving nozzles alternating with fixed nozzles is called a reaction turbine or Parsons turbine. Schematic diagram outlining the difference between an impulse and a 50% reaction turbine
  36. 36. 4.2.2 Steam supply and exhaust conditions - Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam from a boiler in a partially condensed state, typically of a quality near 90%, at a pressure well below atmospheric to a condenser. - Non-condensing or back pressure turbines are most widely used for process steam applications. The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam pressure. These are commonly found at refineries, district heating units, pulp and paper plants, and desalination facilities where large amounts of low pressure process steam are needed. - Reheat turbines are also used almost exclusively in electrical power plants. In a reheat turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is added. The steam then goes back into an intermediate pressure section of the turbine and continues its expansion. - Extracting type turbines are common in all applications. In an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sent to boiler feed water heaters to improve overall cycle efficiency. Extraction flows may be controlled with a valve, or left uncontrolled. - Induction turbines introduce low pressure steam at an intermediate stage to produce additional power. A low-pressure steam turbine working below atmospheric pressure in a nuclear power plant
  37. 37. 4.2.3 Casing or shaft arrangements - These arrangements include single casing, tandem compound and cross compound turbines. Single casing units are the most basic style where a single casing and shaft are coupled to a generator. Tandem compound are used where two or more casings are directly coupled together to drive a single generator. A cross compound turbine arrangement features two or more shafts not in line driving two or more generators that often operate at different speeds. A cross compound turbine is typically used for many large applications.
  38. 38. 4.2.4 A Two – flow Turbine Rotors - The moving steam imparts both a tangential and axial thrust on the turbine shaft, but the axial thrust in a simple turbine is unopposed. To maintain the correct rotor position and balancing, this force must be counteracted by an opposing force. Either thrust bearings can be used for the shaft bearings, or the rotor can be designed so that the steam enters in the middle of the shaft and exits at both ends. The blades in each half face opposite ways, so that the axial forces negate each other but the tangential forces act together. This design of rotor is called two-flow, double-axial-flow, or double-exhaust. This arrangement is common in low-pressure casings of a compound turbine. A two-flow turbine rotor. The steam enters in the middle of the shaft, and exits at each end, balancing the axial force.
  39. 39. 4.3 GENERATOR - The generator converts kinetic energy supplied by the turbine into electrical energy. Low – pole AC Synchronous generators of high rated power are used.
  40. 40. 4.3.1 Dynamo - A dynamo is an electrical generator that produces direct current with the use of a commutator. Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the electric motor, the alternating-current alternator, and the rotary converter. Today, the simpler alternator dominates large scale power generation, for efficiency, reliability and cost reasons. A dynamo has the disadvantages of a mechanical commutator. Also, converting alternating to direct current using power rectification devices (vacuum tube or more recently solid state) is effective and usually economic.
  41. 41. 4.3.2 Alternator - Without a commutator, a dynamo becomes an alternator, which is a synchronous singly fed generator. Alternators produce alternating current with a frequency that is based on the rotational speed of the rotor and the number of magnetic poles. - Automotive alternators produce a varying frequency that changes with engine speed, which is then converted by a rectifier to DC. By comparison, alternators used to feed an electric power grid are generally operated at a speed very close to a specific frequency, for the benefit of AC devices that regulate their speed and performance based on grid frequency. Some devices such as incandescent lamps and ballast-operated fluorescent lamps do not require a constant frequency, but synchronous motors such as in electric wall clocks do require a constant grid frequency. -Typical alternators use a rotating field winding excited with direct current, and a stationary (stator) winding that produces alternating current. Since the rotor field only requires a tiny fraction of the power generated by the machine, the brushes for the field contact can be relatively small. In the case of a brushless exciter, no brushes are used at all and the rotor shaft carries rectifiers to excite the main field winding.
  42. 42. 4.3.3 Induction Generator - An induction generator or asynchronous generator is a type of AC electrical generator that uses the principles of induction motors to produce power. Induction generators operate by mechanically turning their rotor faster than the synchronous speed, giving negative slip. A regular AC asynchronous motor usually can be used as a generator, without any internal modifications. Induction generators are useful in applications such as minihydro power plants, wind turbines, or in reducing high-pressure gas streams to lower pressure, because they can recover energy with relatively simple controls. To operate an induction generator must be excited with a leading voltage; this is usually done by connection to an electrical grid, or sometimes they are self-excited by using phase correcting capacitors.
  43. 43. 4.3.4 MHD Generator - A magneto hydrodynamic generator directly extracts electric power from moving hot gases through a magnetic field, without the use of rotating electromagnetic machinery. MHD generators were originally developed because the output of a plasma MHD generator is a flame, well able to heat the boilers of a steam power plant. The first practical design was the AVCO Mk. 25, developed in 1965. The U.S. government funded substantial development, culminating in a 25 MW demonstration plant in 1987. In the Soviet Union from 1972 until the late 1980s, the MHD plant U 25 was in regular commercial operation on the Moscow power system with a rating of 25 MW, the largest MHD plant rating in the world at that time. MHD generators operated as a topping cycle are currently (2007) less efficient than combined cycle gas turbines.
  44. 44. 4.3.5 Homopolar Generator - A homopolar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A potential difference is created between the center of the disc and the rim (or ends of the cylinder), the electrical polarity depending on the direction of rotation and the orientation of the field. It is also known as a unipolar generator, acyclic generator, disk dynamo, or Faraday disc. The voltage is typically low, on the order of a few volts in the case of small demonstration models, but large research generators can produce hundreds of volts, and some systems have multiple generators in series to produce an even larger voltage. They are unusual in that they can produce tremendous electric current, some more than a million amperes, because the homopolar generator can be made to have very low internal resistance. Faraday disk, the first homopolar generator
  45. 45. 4.3.6Excitation - An electric generator or electric motor that uses field coils rather than permanent magnets requires a current to be present in the field coils for the device to be able to work. If the field coils are not powered, the rotor in a generator can spin without producing any usable electrical energy, while the rotor of a motor may not spin at all. Smaller generators are sometimes self-excited, which means the field coils are powered by the current produced by the generator itself. The field coils are connected in series or parallel with the armature winding. When the generator first starts to turn, the small amount of remanent magnetism present in the iron core provides a magnetic field to get it started, generating a small current in the armature. This flows through the field coils, creating a larger magnetic field which generates a larger armature current. This "bootstrap" process continues until the magnetic field in the core levels off due to saturation and the generator reaches a steady state power output. Very large power station generators often utilize a separate smaller generator to excite the field coils of the larger. In the event of a severe widespread power outage where islanding of power stations has occurred, the stations may need to perform a black start to excite the fields of their largest generators, in order to restore customer power service.
  46. 46. A small early 1900s 75 kVA direct-driven power station AC alternator, with a separate belt-driven exciter generator.
  47. 47. 4.3.7 Electrostatic Generator - An electrostatic generator, or electrostatic machine, is a mechanical device that produces static electricity, or electricity at high voltage and low continuous current. The knowledge of static electricity dates back to the earliest civilizations, but for millennia it remained merely an interesting and mystifying phenomenon, without a theory to explain its behaviour and often confused with magnetism. By the end of the 17th Century, researchers had developed practical means of generating electricity by friction, but the development of electrostatic machines did not begin in earnest until the 18th century, when they became fundamental instruments in the studies about the new science of electricity. Electrostatic generators operate by using manual (or other) power to transform mechanical work into electric energy. Electrostatic generators develop electrostatic charges of opposite signs rendered to two conductors, using only electric forces, and work by using moving plates, drums, or belts to carry electric charge to a high potential electrode. The charge is generated by one of two methods: either the triboelectric effect (friction) or electrostatic induction. A Van de Graaff generator, for class room demonstrations
  48. 48. Suppose that the conditions are as in the figure, with the segment A1 positive and the segment B1 negative. Now, as A1 moves to the left and B1 to the right, their potentials will rise on account of the work done in separating them against attraction. When A1 and neighboring sectors comes opposite the segment B2 of the B plate, which is now in contact with the brush Y, they will cause a displacement of electricity along the conductor between Y and Y1 bringing a negative charge, larger than the positive charge in A1 alone, on Y and sending a positive charge to the segment touching Y1. As A1 moves on, it passes near the brush Z and is partially discharged into the external circuit. It then passes on until, on touching the brush X, has a new charge, this time negative, driven into it by induction from B2 and neighboring sectors. As the machine turns, the process causes exponential increases in the voltages on all positions, until sparking occurs limiting the increase.
  49. 49. 4.3.8 Wimshurst Machine - The Wimshurst influence machine is an electrostatic generator, a machine for generating high voltages developed between 1880 and 1883 by British inventor James Wimshurst (1832–1903). It has a distinctive appearance with two large contra-rotating discs mounted in a vertical plane, two crossed bars with metallic brushes, and a spark gap formed by two metal spheres.
  50. 50. 4.3.9 Van De Graff Generator - A Van de Graaff generator is an electrostatic generator which uses a moving belt to accumulate very high voltages on a hollow metal globe on the top of the stand. It was invented by American physicist Robert J. Van de Graaff in 1929. The potential difference achieved in modern Van de Graaff generators can reach 5 megavolts. The Van de Graaff generator can be thought of as a constant-current source connected in parallel with a capacitor and a very large electrical resistance, so it can produce a visible electrical discharge to a nearby grounding surface which can potentially cause a "spark" depending on the voltage.
  51. 51. 4.4 COOLING SYSTEM - A cooling system removes heat from the reactor core and transports it to another area of the plant, where the thermal energy can be harnessed to produce electricity or to do other useful work. Typically the hot coolant is used as a heat source for a boiler, and the pressurized steam from that boiler powers one or more steam turbine driven electrical generators. 4.5 SAFETY VALVES - In the event of an emergency, two independent safety valves can be used to prevent pipes from bursting or the reactor from exploding. The valves are designed so that they can derive all of the supplied flow rates with little increase in pressure. In the case of the BWR, the steam is directed into the condensate chamber and condenses there. The chambers on a heat exchanger are connected to the intermediate cooling circuit.
  52. 52. 4.6 FEEDWATER PUMP - The water level in the steam generator and nuclear reactor is controlled using the feedwater system. The feedwater pump has the task of taking the water from the condensate system, increasing the pressure and forcing it into either the steam generators (in the case of a pressurized water reactor) or directly into the reactor vessel (for boiling water reactors). 4.7 EMERGEMCY POWER SUPPLY - The emergency power supplies of a nuclear power plant are built up by several layers of redundancy, such as diesel generators, gas turbine generators and battery buffers. The battery backup provides uninterrupted coupling of the diesel/gas turbine units to the power supply network. If necessary, the emergency power supply allows the safe shut down of the nuclear reactor. Less important auxiliary systems such as, for example, heat tracing of pipelines are not supplied by these back ups. The majority of the required power is used to supply the feed pumps in order to cool the reactor and remove the decay heat after a shut down.
  53. 53. 5. HOW DOES A NUCLEAR POWER PLANT PRODUCE ELECTRICITY? - A nuclear power plant is basically steam power that is fuelled by a radioactive element, like uranium. The fuel is placed in a reactor and the individual atoms are allowed to split apart. The splitting process, known as fission, releases great amounts of energy. This energy is used to heat water until it turns to steam. From here, the mechanics of a steam power plant take over. The steam pushes on turbines, which force coils of wire to interact with a magnetic field. This generates on electric current.
  54. 54. ENVIRONMENT / ECONOMIC EFFECT - Nuclear power plant is a controversial subject and multi – billion dollar investments ride on the choice of an energy source. Nuclear power plants typically have high capital costs. But low direct fuel costs, with the costs of fuel extraction, processing, use and sent fuel storage internalized costs. On the other hand construction or capital costs, aside measures to mitigate global warning such as a carbon fax or emissions trading, increasingly favour the economics and nuclear power.
  55. 55. MELTDOWN
  56. 56. 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
  57. 57. DISADVANTAGES • Disposal of nuclear waste is very expensive. As it is radioactive 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.
  58. 58. BASIC TERMS, CONCEPTS, AND DEFINITIONS RELATED TO NUCLEAR ENERGY • Chernobyl: A nuclear power plant in Russia that suffered a meltdown in 1986. The accident released a significant amount of radioactive material into the air, causing the deaths of several dozen people in the following months and resulting in an estimated 4,000 cases of terminal cancer in people as far away as North America. • Fuel Rods: Hollow rods filled with uranium pellets, which are lowered into vats of water prior to the introduction of the neutrons that cause fission. Fuel rods are used in most nuclear power plants. • Meltdown: An accident in which the fuel in a nuclear reactor overheats and melts the containment structures in the plant. • Nuclear Fission: The process of splitting an atom by introducing a neutron into the atom's nucleus, thus creating two lighter atoms and producing heat. • Uranium: A common element, synthesized in stars, which has been present in the earth since its formation and exists in rocks, soil, and water.
  59. 59. CURRENT ISSUES Problems of Nuclear Reactors Concerns about the safety of nuclear fission reactors include the possibility of radiation-releasing nuclear accidents, the problems of radioactive waste disposal, and the possibility of contributing to nuclear weapon proliferation. Although most technical analyses have rated nuclear electricity generation as comparable in safety to coal-powered generation, the low public confidence in nuclear power has blocked further development of nuclear power in the United States. No new nuclear power plants have been ordered since the Three Mile Island accident, and some partially completed projects have been abandoned. As of 1990 about 20% of electricity in the U.S. was generated by nuclear plants, compared to about 75% in France.
  60. 60. Reactor Accidents The nuclear accident at Chernobyl was the worst nuclear accident to date, spewing about 100 million Curies of radioactive material into the environment. By contrast, the accident at Three Mile Island released only some 15 Curies. Though its health effects were minimal, Three Mile Island did perhaps irreparable damage to the level of public confidence in nuclear reactors for electric power production in the United States. Preceding these two high-profile accidents are a number of nuclear accidents with radiation release. These include accidents at the Fermi I reactor near Detroit, at the NRX reactor at Chalk River, Canada, at the Windscale reactor in England, and the SL-1 Reactor at Idaho Falls.
  61. 61. Radioactive Waste Disposal The nuclear fission of uranium-235 produces large quantities of intermediate mass radioisotopes. The mass distribution of these radioisotopes peaks at about mass numbers 95 and 137 , and most of them are radioactive. The most dangerous for environmental release are probably cesium and strontium because of their intermediate half- lives and propensity for reconcentration in the food chain. When spent fuel assemblies are removed from nuclear reactors, they are transported to "swimming pool" storage facilities to dissipate the heat of decay of short-lived isotopes as well as for isolation from the environment. The long term disposal of these wastes remains a major problem. It was assumed that these wastes would be encased in glass and placed in geologic disposal sites in underground salt domes. The site at Yucca Mountain was chosen as a first site, but both technical and political problems have thus far blocked its implementation.
  62. 62. Nuclear Weapons Proliferation One concern about nuclear reactors is that the fuel could be diverted for the production of nuclear weapons. While the the uranium fuel is enriched to only 3-5% and could not easily be further separated to the >90% U-235 needed to produce a bomb, the spent fuel elements contain plutonium- 239. The plutonium could be separated chemically and diverted to nuclear weapons production. Security concerns about the plutonium has thus far blocked any reprocessing of fuel from nuclear power plants. A similar concern exists for fast breeder reactors, where the breeding process produces plutonium-239 for future generations of reactors.
  63. 63. CONCLUSION Nuclear power is an efficient and volatile method of creating electricity using controlled nuclear fission, or, less commonly, nuclear fusion. Most nuclear power plants create energy by submerging uranium molecules in water and then inducing fission in the molecules. This process heats the water, which is transformed into pressurized steam that turns a turbine powering a generator, creating energy. Some nuclear plants use plutonium or thorium instead of uranium, while others fuse hydrogen atoms to create helium atoms, a process that also causes heat and, subsequently, energy. However, uranium fission is overwhelmingly the most popular form of creating nuclear power because the element is more common than plutonium or thorium. Nuclear power plants produce no controlled air pollutants, such as sulfur and particulates, or greenhouse gases. It is important to our lives because it can easily provide electrical energy and no carbon dioxide is given to cause global warning not just like other power station or electrical commissioning.
  64. 64. REFERENCE • The word of physics. Philippine edition. Vern J. Ostdiek. Donald J. Bord • generation/outline-historyofnuclear-energy • • • electricity/nuclear-how.asp • YouTube/Canadian/Nuclear Safety Commission • •