• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content
Nuclear fast reactor
 

Nuclear fast reactor

on

  • 1,836 views

 

Statistics

Views

Total Views
1,836
Views on SlideShare
1,835
Embed Views
1

Actions

Likes
0
Downloads
46
Comments
0

1 Embed 1

http://www.slideshare.net 1

Accessibility

Categories

Upload Details

Uploaded via as Adobe PDF

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

    Nuclear fast reactor Nuclear fast reactor Document Transcript

    • Smarter Use of Fast-neutron reactors could extract much more energy from recycled nuclear fuel, minimize the risks of weapons proliferation and markedly reduce the time nuclear waste must be isolated By William H. Hannum, Gerald E. Marsh and George S. Stanford D espite long-standingpublic concern about the safety of nuclear energy, more andmore people are realizing that it may be the most environmen-tally friendly way to generate large amounts of electricity.Several nations, including Brazil, China, Egypt, Finland, In-dia, Japan, Pakistan, Russia, South Korea and Vietnam, arebuilding or planning nuclear plants. But this global trend hasnot as yet extended to the U.S., where work on the last such If developed sensibly, nuclear power could be truly sustain- able and essentially inexhaustible and could operate without contributing to climate change. In particular, a relatively new form of nuclear technology could overcome the principal drawbacks of current methods — namely, worries about reac- tor accidents, the potential for diversion of nuclear fuel into highly destructive weapons, the management of dangerous, long-lived radioactive waste, and the depletion of global re- JANA BRENNINGfacility began some 30 years ago. serves of economically available uranium. This nuclear fuel84 SCIENTIFIC A MERIC A N DECEMBER 2005 COPYRIGHT 2005 SCIENTIFIC AMERICAN, INC.
    • NUCLEAR WASTE ar power plants contain what are called thermal reactors, which are driven by neutrons of relatively low speed (or ener- gy) ricocheting within their cores. Although thermal reactors generate heat and thus electricity quite efficiently, they cannot minimize the output of radioactive waste. All reactors produce energy by splitting the nuclei of heavy- metal (high-atomic-weight) atoms, mainly uranium or elements derived from uranium. In nature, uranium occurs as a mixture of two isotopes, the easily fissionable uranium 235 (which is said to be “fissile”) and the much more stable uranium 238. The uranium fire in an atomic reactor is both ignited and sustained by neutrons. When the nucleus of a fissile atom is hit by a neutron, especially a slow-moving one, it will most likely cleave (fission), releasing substantial amounts of energy and several other neutrons. Some of these emitted neutrons then strike other nearby fissile atoms, causing them to break apart, thus propagating a nuclear chain reaction. The resulting heat is conveyed out of the reactor, where it turns water into steam that is used to run a turbine that drives an electric generator. Uranium 238 is not fissile; it is called “fissionable” be- cause it sometimes splits when hit by a fast neutron. It is also said to be “fertile,” because when a uranium 238 atom ab- sorbs a neutron without splitting, it transmutes into plutoni- um 239, which, like uranium 235, is fissile and can sustain a chain reaction. After about three years of service, when tech-cycle would combine two innovations: pyrometallurgical pro- nicians typically remove used fuel from one of today’s reac-cessing (a high-temperature method of recycling reactor waste tors because of radiation-related degradation and the deple-into fuel) and advanced fast-neutron reactors capable of burn- tion of the uranium 235, plutonium is contributing more thaning that fuel. With this approach, the radioactivity from the half the power the plant generates.generated waste could drop to safe levels in a few hundred In a thermal reactor, the neutrons, which are born fast, areyears, thereby eliminating the need to segregate waste for tens slowed (or moderated) by interactions with nearby low-atomic-of thousands of years. weight atoms, such as the hydrogen in the water that flows For neutrons to cause nuclear fission efficiently, they must through reactor cores. All but two of the 440 or so commercialbe traveling either slowly or very quickly. Most existing nucle- nuclear reactors operating are thermal, and most of them— in-w w w. s c ia m . c o m SCIENTIFIC A MERIC A N 85 COPYRIGHT 2005 SCIENTIFIC AMERICAN, INC.
    • cluding the 103 U.S. power reactors — left over from the enrichment process. about 1 percent of the spent fuel, they employ water both to slow neutrons and The spent fuel consists of three class- constitute the main source of today’s nu- to carry fission-created heat to the asso- es of materials. The fission products, clear waste problem. The half-lives (the ciated electric generators. Most of these which make up about 5 percent of the period in which radioactivity halves) of thermal systems are what engineers call used fuel, are the true wastes— the ashes, these atoms range up to tens of thousands light-water reactors. if you will, of the fission fire. They com- of years, a feature that led U.S. govern- In any nuclear power plant, heavy- prise a mélange of lighter elements cre- ment regulators to require that the metal atoms are consumed as the fuel ated when the heavy atoms split. The mix planned high-level nuclear waste reposi- “burns.” Even though the plants begin is highly radioactive for its first several tory at Yucca Mountain in Nevada iso- with fuel that has had its uranium 235 years. After a decade or so, the activity is late spent fuel for over 10,000 years. content enriched, most of that easily fis- dominated by two isotopes, cesium 137 sioned uranium is gone after about three and strontium 90. Both are soluble in An Outdated Strategy years. When technicians remove the de- water, so they must be contained very se- e a r ly n u c l e a r engineers expected pleted fuel, only about one twentieth of curely. In around three centuries, those that the plutonium in the spent fuel of the potentially fissionable atoms in it isotopes’ radioactivity declines by a fac- thermal reactors would be removed and (uranium 235, plutonium and uranium tor of 1,000, by which point they have then used in fast-neutron reactors, 238) have been used up, so the so-called become virtually harmless. called fast breeders because they were spent fuel still contains about 95 percent Uranium makes up the bulk of the designed to produce more plutonium of its original energy. In addition, only spent nuclear fuel (around 94 percent); than they consume. Nuclear power pio- about one tenth of the mined uranium this is unfissioned uranium that has lost neers also envisioned an energy econo- ore is converted into fuel in the enrich- most of its uranium 235 and resembles my that would involve open commerce ment process (during which the concen- natural uranium (which is just 0.71 per- in plutonium. Plutonium can be used to tration of uranium 235 is increased con- cent fissile uranium 235). This compo- make bombs, however. As nuclear tech- siderably), so less than a hundredth of the nent is only mildly radioactive and, if nology spread beyond the major super- ore’s total energy content is used to gen- separated from the fission products and powers, this potential application led to erate power in today’s plants. the rest of the material in the spent fuel, worries over uncontrolled proliferation This fact means that the used fuel could readily be stored safely for future of atomic weapons to other states or from current thermal reactors still has the use in lightly protected facilities. even to terrorist groups. potential to stoke many a nuclear fire. Be- The balance of the material— the tru- The Nuclear Non-Proliferation cause the world’s uranium supply is finite ly troubling part — is the transuranic Treaty partially addressed that problem and the continued growth in the num- component, elements heavier than ura- in 1968. States that desired the benefits bers of thermal reactors could exhaust nium. This part of the fuel is mainly a of nuclear power technology could sign the available low-cost uranium reserves blend of plutonium isotopes, with a sig- the treaty and promise not to acquire in a few decades, it makes little sense to nificant presence of americium. Although nuclear weapons, whereupon the weap- discard this spent fuel or the “tailings” the transuranic elements make up only ons-holding nations agreed to assist the others with peaceful applications. Al-Overview/Nuclear Recycling though a cadre of international inspec- tors has since monitored member adher- ■ To minimize global warming, humanity may need to generate much of its ence to the treaty, the effectiveness of future energy using nuclear power technology, which itself releases that international agreement has been essentially no carbon dioxide. spotty because it lacks effective author- ■ Should many more of today’s thermal (or slow-neutron) nuclear power plants ity and enforcement means. be built, however, the world’s reserves of low-cost uranium ore will be tapped Nuclear-weapons designers require out within several decades. In addition, large quantities of highly radioactive plutonium with a very high plutonium waste produced just in the U.S. will have to be stored for at least 10,000 239 isotopic content, whereas plutonium years — much more than can be accommodated by the Yucca Mountain from commercial power plants usually repository in Nevada. Worse, most of the energy that could be extracted from contains substantial quantities of the the original uranium ore would be socked away in that waste. other isotopes of plutonium, making it ■ The utilization of a new, much more efficient nuclear fuel cycle — one based on difficult to use in a bomb. Nevertheless, fast-neutron reactors and the recycling of spent fuel by pyrometallurgical use of plutonium from spent fuel in processing — would allow vastly more of the energy in the earth’s readily weapons is not inconceivable. Hence, available uranium ore to be used to produce electricity. Such a cycle would President Jimmy Carter banned civilian greatly reduce the creation of long-lived reactor waste and could support reprocessing of nuclear fuel in the U.S. nuclear power generation indefinitely. in 1977. He reasoned that if plutonium were not recovered from spent fuel it 86 SCIENTIFIC A MERIC A N DECEMBER 2005 COPYRIGHT 2005 SCIENTIFIC AMERICAN, INC.
    • NEW TYPE OF NUCLEAR REACTOR A safer, more sustainable which rely on relatively slow would burn fuel made by like this: Nuclear fire burning in nuclear power cycle could be moving neutrons to propagate recycling spent fuel from the core would heat the based on the advanced liquid- chain reactions in uranium and thermal reactors. radioactive liquid sodium metal reactor (ALMR) design plutonium fuel. An ALMR-based In most thermal-reactor running through it. Some of the developed in the 1980s by system, in contrast, would use designs, water floods the core heated sodium would be pumped researchers at Argonne fast-moving (energetic) to slow (moderate) neutrons into an intermediate heat National Laboratory. Like all neutrons. This process permits and keep it cool. The ALMR, exchanger (2), where it would atomic power plants, an ALMR- all the uranium and heavier however, employs a pool of transfer its thermal energy to based system would use atoms to be consumed, thereby circulating liquid sodium as the nonradioactive liquid sodium nuclear chain reactions in the allowing vastly more of the coolant (1). Engineers chose flowing through the adjacent but core to produce the heat fuel’s energy to be captured. In sodium because it does not separate pipes (3) of a needed to generate electricity. the near term, the new reactor slow down fast neutrons secondary sodium loop. The Current commercial nuclear substantially and because it nonradioactive sodium (4) would plants feature thermal reactors, conducts heat very well, which in turn bring heat to a final heat improves the efficiency of heat exchanger/steam generator (not delivery to the electric shown), where steam would be generation facility. created in adjacent water-filled Warm air A fast reactor would work pipes. The hot, high-pressure Cool air steam would then be used to turn steam turbines that would drive electricity-producing generators Cooling-system air inlet (not shown). To steam Top of reactor silo and exhaust stack generator Freestanding reactor housing l nd le v e Reactor foundation G r ou 4 Secondary sodium loop Intermediate Sodium pump heat exchanger 3 2 REACTOR SAFEGUARDS ■ During operation, powerful pumps would force sodium Sodium pump coolant through the core. If the Sodium coolant pumps failed, gravity would pumped through circulate the coolant. 1 core ■ If coolant pumps malfunctioned Sodium cycling or stopped, special safety through heat devices would also permit exchanger extra neutrons to leak out of the core, lowering its Nonradioactive temperature. sodium cycling ■ In an emergency, six neutron- through steam absorbing control rods would Liquid-sodium pool Seismic isolator generator drop into the core to shut it down immediately. ■ Should chain reactions Hot reactor core Reactor vessel continue, thousands of (uranium fuel rods) neutron-absorbing boron carbide balls would beDON FOLE Y Base of reactor silo released into the core, guaranteeing shutdown. w w w. s c ia m . c o m SCIENTIFIC A MERIC A N 87 COPYRIGHT 2005 SCIENTIFIC AMERICAN, INC.
    • could not be used to make bombs. Car- below]. Several such reactors have been transuranic atoms will do so as well.ter also wanted America to set an ex- built and used for power generation— in Water cannot be employed in a fastample for the rest of the world. France, France, Japan, Russia, the U.K. and the reactor to carry the heat from the core —Japan, Russia and the U.K. have not, U.S.— two of which are still operating it would slow the fast neutrons. Hence,however, followed suit, so plutonium re- [see “Next-Generation Nuclear Power,” engineers typically use a liquid metalprocessing for use in power plants con- by James A. Lake, Ralph G. Bennett and such as sodium as a coolant and heattinues in a number of nations. John F. Kotek; Scientific American, transporter. Liquid metal has one big ad- January 2002]. vantage over water. Water-cooled sys-An Alternative Approach Fast reactors can extract more energy tems run at very high pressure, so that aw h e n t h e b a n was issued, “repro- from nuclear fuel than thermal reactors small leak can quickly develop into acessing” was synonymous with the do because their rapidly moving (higher- large release of steam and perhaps a seri-PUREX (for plutonium uranium extrac- energy) neutrons cause atomic fissions ous pipe break, with rapid loss of reactortion) method, a technique developed to more efficiently than the slow thermal coolant. Liquid-metal systems, however,meet the need for chemically pure pluto- neutrons do. This effectiveness stems operate at atmospheric pressure, so theynium for atomic weapons. Advanced from two phenomena. At slower speeds, present vastly less potential for a majorfast-neutron reactor technology, how- many more neutrons are absorbed in release. Nevertheless, sodium catches fireever, permits an alternative recycling nonfission reactions and are lost. Second, if exposed to water, so it must be man-strategy that does not involve pure plu- the higher energy of a fast neutron makes aged carefully. Considerable industrialtonium at any stage. Fast reactors can it much more likely that a fertile heavy- experience with handling the substancethus minimize the risk that spent fuel metal atom like uranium 238 will fission has been amassed over the years, andfrom energy production would be used when struck. Because of this fact, not management methods are well devel-for weapons production, while provid- only are uranium 235 and plutonium oped. But sodium fi res have occurred,ing a unique ability to squeeze the maxi- 239 likely to fission in a fast reactor, but and undoubtedly there will be more. Onemum energy out of nuclear fuel [see box an appreciable fraction of the heavier sodium fire began in 1995 at the Monju NEW WAY TO REUSE NUCLEAR FUEL The key to pyrometallurgical recycling of nuclear fuel is the plutonium fuel from fast reactors would go straight to the electrorefining procedure. This process removes the true electrorefiner. Electrorefining resembles electroplating: waste, the fission products, from the uranium, plutonium and spent fuel attached to an anode would be suspended in a the other actinides (heavy radioactive elements) in the spent chemical bath; then electric current would plate out uranium fuel. The actinides are kept mixed with the plutonium so it and other actinides on the cathode. The extracted elements cannot be used directly in weapons. would next be sent to the cathode processor to remove Spent fuel from today’s thermal reactors (uranium and residual salts and cadmium from refining. Finally, the plutonium oxide) would first undergo oxide reduction to remaining uranium and actinides would be cast into fresh fuel convert it to metal, whereas spent metallic uranium and rods, and the salts and cadmium would be recycled. Oxide fuel from thermal reactors Most of the Cathode Casting fission products Heating molds elements Uranium Anode and actinides Metal Crucible Chopped fuel Metal Salts and cadmium New metal fuel rods Chopped metallic fuel from fast reactors OXIDE CATHODE INJECTION DON FOLE Y SPENT FUEL REDUCTION UNIT ELECTROREFINER PROCESSOR CASTING SYSTEM88 SCIENTIFIC A MERIC A N DECEMBER 2005 COPYRIGHT 2005 SCIENTIFIC AMERICAN, INC.
    • fast reactor in Japan. It made a mess in full batch is amassed, operators remove the reactor building but never posed a the electrode. Next they scrape the ac- threat to the integrity of the reactor, and cumulated materials off the electrode, no one was injured or irradiated. Engi- melt them down, cast them into an ingot neers do not consider sodium’s flamma- and pass the ingot to a refabrication line bility to be a major problem. for conversion into fast-reactor fuel. Researchers at Argonne National When the bath becomes saturated with Laboratory began developing fast-reac- fission products, technicians clean the tor technology in the 1950s. In the 1980s solvent and process the extracted fission this research was directed toward a fast products for permanent disposal. reactor (dubbed the advanced liquid- Thus, unlike the current PUREX metal reactor, or ALMR), with metallic method, the pyroprocess collects virtu- fuel cooled by a liquid metal, that was to ally all the transuranic elements (includ- be integrated with a high-temperature ing the plutonium), with considerable pyrometallurgical processing unit for re- carryover of uranium and fission prod- cycling and replenishing the fuel. Nucle- ucts. Only a very small portion of the ar engineers have also investigated sev- transuranic component ends up in the fi- eral other fast-reactor concepts, some nal waste stream, which reduces the burning metallic uranium or plutonium needed isolation time drastically. The fuels, others using oxide fuels. Coolants combination of fission products and of liquid lead or a lead-bismuth solution transuranics is unsuited for weapons or have been used. Metallic fuel, as used in even for thermal-reactor fuel. This mix- the ALMR, is preferable to oxide for sev- ture is, however, not only tolerable but eral reasons: it has some safety advan- advantageous for fueling fast reactors. tages, it will permit faster breeding of Although pyrometallurgical recy- EX TR ACTED UR ANIUM and actinide elements new fuel, and it can more easily be paired cling technology is not quite ready for from spent thermal-reactor fuel are plated out with pyrometallurgical recycling. immediate commercial use, researchers on the cathode of an electrorefiner during the have demonstrated its basic principles. It pyroprocessing procedure. After further Pyroprocessing has been successfully demonstrated on a processing, the metallic fuel can be burned in fast-neutron reactors. t h e p y rom e ta l lu rgic a l process pilot level in operating power plants, (“pyro” for short) extracts from used both in the U.S. and in Russia. It has not with the same electrical capacity, in con- fuel a mix of transuranic elements in- yet functioned, however, on a full pro- trast, is a little more than a single ton of stead of pure plutonium, as in the duction scale. fission products, plus trace amounts of PUREX route. It is based on electroplat- transuranics. ing— using electricity to collect, on a Comparing Cycles Waste management using the ALMR conducting metal electrode, metal ex- t h e op e r at i ng c a pa bi l i t i e s of cycle would be greatly simplified. Be- tracted as ions from a chemical bath. Its thermal and fast reactors are similar in cause the fast-reactor waste would con- name derives from the high tempera- some ways, but in others the differences tain no significant quantity of long-lived tures to which the metals must be sub- are huge [see box on next page]. A transuranics, its radiation would decay jected during the procedure. Two simi- 1,000-megawatt-electric thermal-reac- to the level of the ore from which it came lar approaches have been developed, tor plant, for example, generates more in several hundred years, rather than one in the U.S., the other in Russia. The than 100 tons of spent fuel a year. The tens of thousands. major difference is that the Russians annual waste output from a fast reactor If fast reactors were used exclusively, process ceramic (oxide) fuel, whereas the fuel in an ALMR is metallic. WILLIAM H. HANNUM, GERALD E. MARSH and GEORGE S. STANFORD are physicists who THE AUTHORS In the American pyroprocess [see worked on fast-reactor development before retiring from the U.S. Department of Energy’s box on opposite page], technicians dis- Argonne National Laboratory. Hannum served as head of nuclear physics development solve spent metallic fuel in a chemicalA RGONNE N ATION A L L A BOR ATORY and reactor safety research at the DOE. He was also deputy director general of the Nucle- bath. Then a strong electric current se- ar Energy Agency of the Organization for Economic Co-operation and Development in lectively collects the plutonium and the Paris. Marsh, a fellow of the American Physical Society, worked as a consultant to the U.S. other transuranic elements on an elec- Department of Defense on strategic nuclear technology and policy in the Reagan, Bush trode, along with some of the fission and Clinton administrations and is co-author of The Phantom Defense: America’s Pursuit products and much of the uranium. of the Star Wars Illusion (Praeger Press). Stanford, whose research focused on experi- Most of the fission products and some of mental nuclear physics, reactor physics and fast-reactor safety, is co-author of Nucle- the uranium remain in the bath. When a ar Shadowboxing: Contemporary Threats from Cold War Weaponry (Fidlar Doubleday). w w w. s c ia m . c o m SCIENTIFIC A MERIC A N 89 COPYRIGHT 2005 SCIENTIFIC AMERICAN, INC.
    • COMPARING THREE NUCLEAR FUEL CYCLES Three major approaches to burning nuclear fuel and handling its wastes can be employed; some of their features are noted below. ONCE-THROUGH ROUTE PLUTONIUM RECYCLING FULL RECYCLING Fuel is burned in thermal reactors and is not Fuel is burned in thermal reactors, after which Recycled fuel prepared by pyrometallurgical reprocessed; occurs in the U.S. plutonium is extracted using what is called processing would be burned in advanced fast- PUREX processing; occurs in other neutron reactors; prototype technology developed nations FUEL UTILIZATION 5 percent used in 5 percent 6 percent thermal is used is used reactor 95 percent Somewhat 94 percent more than is wasted is wasted 94 percent is used in fast reactor Less than Initial fuel supply 1 percent is wastedUses about 5 percent of energy in thermal- Uses about 6 percent of energy in original Can recover more than 99 percent of energy reactor fuel and less than 1 percent reactor fuel and less than 1 percent of in spent thermal-reactor fuel of energy in uranium ore (the original energy in uranium ore After spent thermal-reactor fuel runs out, source of fuel) Cannot burn depleted uranium or uranium can burn depleted uranium to recover moreCannot burn depleted uranium (that part in spent fuel than 99 percent of the rest of the energy removed when the ore is enriched) or in uranium ore uranium in spent fuel REQUIRED FACILITIES AND OPERATIONS Red: requires rigorous physical safeguards Orange: needs only moderate physical safeguards Blue: potential risks for future generationsUranium mines Uranium mines On-site fuel fabricationFuel enrichment to concentrate fissile Fuel enrichment On-site pyrometallurgical processing uranium Plutonium blending (mixing) (prompt recycling of spent fuel)Fuel fabrication Off-site fuel fabrication Power plantsPower plants Off-site PUREX reprocessing On-site waste processingInterim waste storage (until waste can be Power plants Storage able to segregate waste for less permanently disposed of) than 500 years Interim waste storagePermanent storage able to (No mining needed for centuries; no uranium securely segregate waste for 10,000 years Off-site waste processing enrichment needed, ever)(Needs no plutonium handling or waste Permanent storage able to securely processing operations) segregate waste for 10,000 years PLUTONIUM FATEIncreasing inventories of plutonium Increasing inventories of plutonium Inventories eventually shrink to only what is in used fuel in used fuel and available for economic trade in use in reactors and in recyclingExcess weapons-grade plutonium degraded Excess weapons-grade plutonium degraded Existing excess weapons-grade plutonium can only slowly by mixing into fresh fuel only slowly by mixing into fresh fuel be degraded rapidly Plutonium in the fuel is too impure for diversion to weapons TYPES OF WASTEEnergy-rich used fuel isolated in containers Energy-rich, highly stable glassy waste Tailored waste forms that would only have to and underground storage facility Waste is radioactive enough to be defined as remain intact for 500 years, after whichWaste is radioactive enough to be defined as “self-protected” for a few hundred years material would no longer be hazardous “self-protected” for a few hundred years against most groups wanting to obtain Lacking plutonium, waste would not be useful DON FOLE Y against most groups wanting to obtain plutonium 239 for building nuclear weapons for making weapons plutonium 239 for building nuclear weapons90 SCIENTIFIC A MERIC A N DECEMBER 2005 COPYRIGHT 2005 SCIENTIFIC AMERICAN, INC.
    • transportation of highly radioactive ma- nalities,” the hard-to-quantify costs of overnight, of course. If we were to beginterials would occur only under two cir- outside effects resulting from using the today, the first of the fast reactors mightcumstances — when the fission product technology. When we burn coal or oil to come online in about 15 years. Notably,waste was shipped to Yucca Mountain make electricity, for example, our soci- that schedule is reasonably compatibleor an alternative site for disposal and ety accepts the detrimental health effects with the planned timetable for shipmentwhen start-up fuel was shipped to a new and the environmental costs they entail. of spent thermal-reactor fuel to Yuccareactor. Commerce in plutonium would Thus, external costs in effect subsidize Mountain. It could instead be sent forbe effectively eliminated. fossil-fuel power generation, either di- recycling into fast-reactor fuel. Some people are advocating that the rectly or via indirect effects on the soci- As today’s thermal reactors reach theU.S. embark on an extensive program of ety as a whole. Even though they are dif- end of their lifetimes, they could be re-PUREX processing of reactor fuel, mak- ficult to reckon, economic comparisons placed by fast reactors. Should that oc-ing mixed oxides of uranium and pluto- that do not take externalities into ac- cur, there would be no need to mine anynium for cycling back into thermal reac- count are unrealistic and misleading. more uranium ore for centuries and notors. Although the mixed oxide (MOX) further requirement, ever, for uraniummethod is currently being used for spoil- Coupling Reactor Types enrichment. For the very long term, re-ing excess weapons plutonium so that it if a dva nced fast r e ac tors come cycling the fuel of fast reactors would becannot be employed in bombs — a good into use, they will at first burn spent so efficient that currently available ura-idea— we think that it would be a mis- thermal-reactor fuel that has been recy- nium supplies could last indefinitely.take to deploy the much larger PUREX cled using pyroprocessing. That waste, Both India and China have recentlyinfrastructure that would be required to which is now “temporarily” stored on announced that they plan to extend theirprocess civilian fuel. The resource gains site, would be transported to plants that energy resources by deploying fast reac-would be modest, whereas the long-term could process it into three output tors. We understand that their first fastwaste problem would remain, and the streams. The first, highly radioactive, reactors will use oxide or carbide fuelentire effort would delay for only a short stream would contain most of the fission rather than metal— a less than optimumtime the need for efficient fast reactors. products, along with unavoidable traces path, chosen presumably because the The fast-reactor system with pyro- of transuranic elements. It would be PUREX reprocessing technology is ma-processing is remarkably versatile. It transformed into a physically stable ture, whereas pyroprocessing has not yetcould be a net consumer or net producer form — perhaps a glasslike substance — been commercially demonstrated.of plutonium, or it could be run in a and then shipped to Yucca Mountain or It is not too soon for the U.S. to com-break-even mode. Operated as a net some other permanent disposal site. plete the basic development of the fast-producer, the system could provide The second stream would capture reactor/pyroprocessing system for me-start-up materials for other fast-reactor virtually all the transuranics, together tallic fuel. For the foreseeable future, thepower plants. As a net consumer, it with some uranium and fission prod- hard truth is this: only nuclear powercould use up excess plutonium and ucts. It would be converted to a metallic can satisfy humanity’s long-term energyweapons materials. If a break-even fast-reactor fuel and then transferred to needs while preserving the environment.mode were chosen, the only additional ALMR-type reactors. For large-scale, sustainable nuclear en-fuel a nuclear plant would need would The third stream, amounting to ergy production to continue, the supplybe a periodic infusion of depleted ura- about 92 percent of the spent thermal- of nuclear fuel must last a long time.nium (uranium from which most of the reactor fuel, would contain the bulk of That means that the nuclear power cyclefissile uranium 235 has been removed) the uranium, now in a depleted state. It must have the characteristics of theto replace the heavy-metal atoms that could be stashed away for future use as ALMR and pyroprocessing. The timehave undergone fission. fast-reactor fuel. seems right to take this new course to- Business studies have indicated that Such a scenario cannot be realized ward sensible energy development.this technology could be economicallycompetitive with existing nuclear power MORE TO EXPLOREtechnologies [see the Dubberly paper in Breeder Reactors: A Renewable Energy Source. Bernard L. Cohen in American Journal of Physics, Vol. 51, No. 1; January 1983.“More to Explore,” on this page]. Cer- The Technology of the Integral Fast Reactor and Its Associated Fuel Cycle. Edited bytainly pyrometallurgical recycling will W. H. Hannum. Progress in Nuclear Energy, Special Issue, Vol. 31, Nos. 1–2; 1997.be dramatically less expensive than Integral Fast Reactors: Source of Safe, Abundant, Non-Polluting Power. George Stanford.PUREX reprocessing, but in truth, the National Policy Analysis Paper #378; December 2001. Available at www.nationalcenter.org/economic viability of the system cannot NPA378.htmlbe known until it is demonstrated. LWR Recycle: Necessity or Impediment? G. S. Stanford in Proceedings of Global 2003. ANS Winter Meeting, New Orleans, November 16–20, 2003. Available at www.nationalcenter.org/ The overall economics of any energy LWRStanford.pdfsource depend not only on direct costs S-PRISM Fuel Cycle Study. Allen Dubberly et al. in Proceedings of ICAPP ’03. Córdoba, Spain,but also on what economists call “exter- May 4–7, 2003, Paper 3144.w w w. s c ia m . c o m SCIENTIFIC A MERIC A N 91 COPYRIGHT 2005 SCIENTIFIC AMERICAN, INC.