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Integral fast reactor

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The Integral Fast Reactor or Advanced Liquid-Metal Reactor is a design for a fast neutron nuclear reactor with a specialized nuclear fuel cycle. A prototype of the reactor was built in the United States, but the project was canceled by the U.S. government in 1994, three years before completion.

The Generation IV Sodium-Cooled Fast Reactor is its successor as the currently proposed U.S sodium-cooled fast breeder reactor design.

Overview

This reactor is cooled by liquid sodium and fueled by a metallic alloy of uranium and plutonium. The fuel is contained in steel cladding with liquid sodium filling in the space between the fuel and the cladding.

Global Significance

  • Most world energy experts, including US Secretary of Energy Steven Chu, believe that renewables are not sufficient to meet the world's energy requirements, even in the US, and that nuclear must be part of the mix. In a major DOE study in 2002, the IFR was judged to be the best nuclear design available. [1]
  • Breeder reactors (such as the IFR) uses almost all of the energy in the uranium (or thorium), thus decreasing fuel requirements by two orders of magnitude. It practically removes concern about fuel supply or energy used in mining – we already have fuel enough for centuries.
  • Breeder reactors can “burn” some components (actinides) of nuclear waste, thus turning the world's biggest headache with respect to nuclear into an asset. The other major waste component, fission products, stabilizes at a lower level of radioactivity from long-lived fission products in a few centuries, rather than tens of thousands of years. The fact that 4th generation reactors will be able to use the waste from 3rd generation plants changes the nuclear story fundamentally – making the combination of 3rd and 4th generation plants a much more attractive energy option than 3rd generation by itself would have been

Safety

In traditional water-cooled reactors the core must be maintained at a high pressure to keep the water liquid at high temperatures. In contrast, since the IFR used a liquid metal as a coolant, the core could operate at close to ambient pressure, dramatically reducing the danger of a loss of coolant accident. The entire reactor core, heat exchangers and primary cooling pumps were immersed in a pool of liquid sodium, making a loss of primary coolant extremely unlikely. The coolant loops were also designed to allow for cooling through natural convection, meaning that in the case of a power loss or unexpected reactor shutdown, the heat from the reactor core would be sufficient to keep the coolant circulating even if the primary cooling pumps were to fail.

The IFR also utilized a passively safe fuel configuration. The fuel and cladding were designed such that when they expanded due to increased temperatures, more neutrons would be able to escape the core thus reducing the rate of the fission chain reaction. At sufficiently high temperatures this effect would completely stop the reactor even without external action from operators or safety systems. This was demonstrated in a series of safety tests on the prototype.

A safety disadvantage of using liquid sodium as coolant arises due to sodium's chemical reactivity. Liquid sodium is extremely flammable and ignites spontaneously on contact with air or water. Thus leaking sodium pipes could give rise to sodium fires, or explosions if the leaked sodium comes into contact with water. To reduce the risk of explosions following a leak of water from the steam turbines the IFR had an extra intermediate coolant loop between the reactor and the turbines. The purpose of this loop was to ensure that any explosion following accidental mixing of sodium and turbine water would be limited to the secondary heat exchanger and not pose a risk to the reactor. The requirement of such an extra loop significantly added to the cost of the reactor.

According to IFR inventor Charles Till, no radioactivity will be released under any circumstance. Under even very, very unlikely circumstances which would lead to a mess in other reactors, the IFR will not even incur damage.

Efficiency and Fuel cycle

Medium-lived fission products
t½
(year) 		Yield
(%) 		Q
(keV) 		βγ
155Eu  4.76 0.0803  252 βγ
85Kr 10.76 0.2180  687 βγ
113mCd 14.1  0.0008  316 β
90Sr 28.9  4.505   2826 β
137Cs 30.23 6.337   1176 βγ
121mSn 43.9  0.00005 390 βγ
151Sm 94.6  0.5314  77 β
Long-lived fission products
Nuclide t1⁄2 Yield Q[a 1] βγ
(Ma) (%)[a 2] (keV)
99Tc 0.211 6.1385 294 β
126Sn 0.230 0.1084 4050[a 3] βγ
79Se 0.327 0.0447 151 β
135Cs 1.33  6.9110[a 4] 269 β
93Zr 1.53  5.4575 91 βγ
107Pd 6.5   1.2499 33 β
129I 16.14   0.8410 194 βγ
  1. ^ Decay energy is split among β, neutrino, and γ if any.
  2. ^ Per 65 thermal neutron fissions of 235U and 35 of 239Pu.
  3. ^ Has decay energy 380 keV, but its decay product 126Sb has decay energy 3.67 MeV.
  4. ^ Lower in thermal reactors because 135Xe, its predecessor, readily absorbs neutrons.

The goals of the IFR project were to increase the efficiency of uranium usage by breeding plutonium and eliminating the need for transuranic isotopes ever to leave the site. The reactor was an unmoderated design running on fast neutrons, designed to allow any transuranic isotope to be consumed (and in some cases used as fuel).

Compared to current light-water reactors with a once-through fuel cycle that induces fission (and derives energy) from less than 1% of the uranium found in nature, the IFR has a very efficient (99.5% of Uranium undergoes fission) fuel cycle.[2] The basic scheme used electrolytic separation to remove transuranics and actinides from the wastes and concentrate them. These concentrated fuels were then reformed, on site, into new fuel elements.

The available fuel metals were never separated from the plutonium, and therefore there was no direct way to use the fuel metals in nuclear weapons. Also, plutonium never had to leave the site, and thus was far less open to unauthorized diversion.

Another important benefit of removing the long half-life transuranics from the waste cycle is that the remaining waste becomes a much shorter-term hazard. After the actinides (reprocessed uranium, plutonium, and minor actinides) are recycled, the remaining radioactive waste isotopes are fission products, with half-life of 90 years (Sm-151) or less or 211,100 years (Tc-99) and more; plus any activation products from the non-fuel reactor components. (Tc-99 and Iodine-129 are also candidates for nuclear transmutation to stable isotopes by neutron capture.)

The result is that within 200 years, such wastes are no more radioactive than the ores of natural radioactive elements.[2]

Key benefits

Buildup of heavy actinides in present thermal reactors,[3] which cannot fission actinide nuclides that have an even number of neutrons. Fast reactors can fission all actinides.
  • The most cost effective and safest solution to the nuclear waste problem. The primary argument for pursuing IFR technology today is that it provides the best solution to the existing nuclear waste problem because 1) IFRs can be fueled from the waste products of existing reactors as well as from the plutonium used in weapons, and 2) the waste from an IFR is both minimal and dangerous only for a relatively short time. The fuel sources also include the depleted uranium (DU) waste that is left over from the uranium enrichment process. In the US, there is more than 10 times the extractable energy from DU waste alone than from coal still in the ground. This is enough energy to power the entire planet for about 700 years at current usage rates.
  • Resolution to all traditional objections to using nuclear power. The promise of the IFR is a better source nuclear power in every respect: safety, cost, waste, and proliferation. Once these plants are proven, there would be no reason to build a traditional (light water reactor) nuclear plant.
  • Manageable waste. Unlike the LWR, the IFR produces a smaller volume of waste since reprocessed uranium is not discarded: about 1/20 the volume as compared to a light water plant of the same size. The high level waste from reprocessing is highly radioactive for only 400 years instead of 10,000 years.
  • Efficiency. Virtually unlimited power. IFRs use virtually all of the energy content in the uranium fuel whereas a traditional light water reactor uses less than 1% of that energy content. This means that IFRs can power the energy needs of the planet for at least 10,000 years.
  • CO2 free. There is no CO2 emitted during the operation of an IFR plant and the generation of electricity.
  • A safer and more economical option. IFRs are safer and more economical than burying the nuclear waste from light water reactors and retired nuclear weapons. It is much more effective to use the nuclear waste to power fast reactors (such as the IFR) than to bury it. By using existing nuclear waste in fast reactors, the highly radioactive, long-lived waste is transformed into a waste product that is much smaller and which only needs to be stored for about 400 years instead of about 10,000 years for a traditional reactor.
  • Flexible re-fueling options. The "makeup fuel" (about 1 ton of makeup fuel to replace the 1 ton of fission product waste that has to be added every year to a 1GWe IFR) can be virtually any actinide, though typically it would either be natural uranium or depleted uranium.
Actinides and fission products by half-life
Actinides[4] by decay chain Half-life
range (a) 		Fission products of 235U by yield[5]
4n 4n + 1 4n + 2 4n + 3 4.5–7% 0.04–1.25% <0.001%
228Ra№ 4–6 a 155Euþ
248Bk[6] > 9 a
244Cmƒ 241Puƒ 250Cf 227Ac№ 10–29 a 90Sr 85Kr 113mCdþ
232Uƒ 238Puƒ 243Cmƒ 29–97 a 137Cs 151Smþ 121mSn
249Cfƒ 242mAmƒ 141–351 a

No fission products have a half-life
in the range of 100 a–210 ka ...

241Amƒ 251Cfƒ[7] 430–900 a
226Ra№ 247Bk 1.3–1.6 ka
240Pu 229Th 246Cmƒ 243Amƒ 4.7–7.4 ka
245Cmƒ 250Cm 8.3–8.5 ka
239Puƒ 24.1 ka
230Th№ 231Pa№ 32–76 ka
236Npƒ 233Uƒ 234U№ 150–250 ka 99Tc₡ 126Sn
248Cm 242Pu 327–375 ka 79Se₡
1.33 Ma 135Cs₡
237Npƒ 1.61–6.5 Ma 93Zr 107Pd
236U 247Cmƒ 15–24 Ma 129I₡
244Pu 80 Ma

... nor beyond 15.7 Ma[8]

232Th№ 238U№ 235Uƒ№ 0.7–14.1 Ga
  • Breeder vs. burner. Like any fast reactor, by changing the material used in the blankets, the IFR can be operated over a spectrum from breeder to self-sufficient to burner. In breeder mode (using U-238 blankets) it will produce more fissile material than it consumes. This is useful for providing fissile material for starting up other IFR plants. Using steel reflectors instead of U-238 blankets, the IFR operates in pure burner mode and is not a net creator of fissile material; on balance it will consume fissile and fertile material and output no actinides but only fission products and activation products. Amount of fissile material needed could be a limiting factor to very widespread deployment of fast reactors, if stocks of surplus weapons plutonium and LWR spent fuel plutonium are not sufficient. To maximize the rate at which fast reactors can be deployed, they can be operated in maximum breeding mode.
  • Enhanced passive safety because of the high thermal conductivity of the fuel. IFRs are able to withstand both a loss of flow without SCRAM and loss of heat sink without SCRAM. In addition to passive shutdown of the reactor, the convection current generated in the primary coolant system will prevent fuel damage (core meltdown). These capabilities were demonstrated in the EBR II.[9] The ultimate point is that no radioactivity will be released under any circumstance. According to IFR inventor Charles Till, under even very, very unlikely circumstances which would lead to a mess in other reactors, the IFR will not even incur damage.
  • Ease of fuel fabrication. Because the sodium fills the space between the fuel and cladding, the fuel need not be precisely fabricated. The fuel is simply cast. Because casting is simple, the fuel can be fabricated remotely, reducing the hazards of its radioactivity.
  • On-site reprocessing. On-site reprocessing by pyroprocessing and electrorefining is simplified because there is no need to stringently reduce the radioactivity of the fuel. Actinides including transuranics can be incorporated into the fuel.
  • Fuel exchange. The IFR's primary fuel is depleted uranium (U-238) mixed with highly enriched uranium and plutonium (perhaps from decommissioned weapons). Because of the IFR's reprocessing capability, the depleted uranium could be replaced by reprocessed uranium from spent fuel from traditional light water reactors.[2]
  • Proliferation hazards. Proliferation hazards are reduced by the high radioactivity of the fuel. Because the fuel contains significant levels of transuranics with high spontaneous fission rates, it is not possible to produce nuclear weapons using IFR fuel without centrifugal separation. This is more difficult than enrichment of natural uranium due to the smaller atomic mass difference between Pu-239 and Pu-240 as compared to U-235 vs U-238, and is rendered even more difficult by the high radioactivity of the fuel. Unlike PUREX reprocessing, the reprocessing of the fuel in an IFR never separates out pure plutonium and cannot be adjusted to do so.
  • Cleaner waste. The two forms of waste produced, a noble metal form and a ceramic form, contain no plutonium or other actinides. The radioactivity of the waste decays to levels similar to the original ore in about 200 years.[2]
  • Greater security. The on-site reprocessing of fuel means that the quantity of nuclear waste leaving the plant is tiny relative to other nuclear facilities.[10] This makes storage simpler and reduces the security risk associated with nuclear waste transportation.
  • Modular design. The commercial version of the IFR (S-PRISM) can be built in a factory and transported on-site. This modular design (311 MWe modules) reduces costs and allows nuclear plants of various sizes (311 MWe and any integer multiple) to be economically constructed.
  • More cost effective reactors. Cost assessments taking account of the complete life cycle show that fast reactors could be no more expensive than the most widely used reactors in the world – water-moderated water-cooled reactors.[11]

Key disadvantages

  • "The plutonium from ALMR recycled fuel would have an isotopic composition similar to that obtained from other spent nuclear fuel sources. Whereas this might make it less than ideal for weapons production, it would still be adequate for unsophisticated nuclear bomb designs. In fact the U.S. government detonated a nuclear device in 1962 using low-grade plutonium typical of that produced by civilian powerplants." [12]
  • "If, instead of processing spent fuel, the ALMR system were used to reprocess irradiated fertile (breeding) material in the electrorefiner, the resulting plutonium would be a superior material, with a nearly ideal isotope composition for nuclear weapons manufacture" [13]
  • "Others counter that actinide removal would offer few if any significant advantages for disposal in a geologic repository because some of the fission product nuclides of greatest concern in scenarios such as groundwater leaching actually have longer half-lives than the radioactive actinides. The concern about a waste cannot end after hundreds of years even if all the actinides are removed when the remaining waste contains radioactive fission products such as technetium-99, iodine-129, and cesium-135 with the halflives between 213,000 and 15.7 million years" [14]
  • Because the current cost of reactor-grade enriched uranium is low compared to the expected cost of large-scale pyroprocessing and electrorefining equipment and the cost of building a secondary coolant loop, the higher fuel costs of a thermal reactor over the expected operating lifetime of the plant are offset by the increased capital cost of an IFR. (Currently in the United States, utilities pay a flat rate of 1/10 of a cent per kilowatt hour for disposal of high level radioactive waste. If this charge were based on the longevity of the waste, then the IFR might become more financially competitive.)
  • Reprocessing nuclear fuel using pyroprocessing and electrorefining has not yet been demonstrated on a commercial scale. As such, investing in a large IFR plant is considered a higher financial risk than a conventional light water reactor.
  • The flammability of sodium is a risk. Sodium burns easily in air, and will ignite spontaneously on contact with water. The use of an intermediate coolant loop between the reactor and the turbines minimizes the risk of a sodium fire in the reactor core.
  • Under neutron bombardment, sodium-24 is produced. This is highly radioactive, emitting an energetic gamma ray of 2.7 MeV followed by a beta decay to form magnesium-24. Half life is only 15 hours, so this isotope is not a long-term hazard - indeed it has medical applications. Nevertheless, the presence of sodium-24 further necessitates the use of the intermediate coolant loop between the reactor and the turbines.
  • The one-time startup material for an IFR must be 20% fissile.

History

Research on the reactor began in 1984 at Argonne National Laboratory in Argonne, Illinois. Argonne is a part of the U.S. Department of Energy's national laboratory system, and is operated on a contract by the University of Chicago.

Argonne previously had a branch campus named "Argonne West" in Idaho Falls, Idaho that is now part of the Idaho National Laboratory. In the past, at the branch campus, physicists from Argonne had built what was known as the Experimental Breeder Reactor II (EBR II). In the mean time, physicists at Argonne had designed the IFR concept, and it was decided that the EBR II would be converted to an IFR. Charles Till, a Canadian physicist from Argonne, was the head of the IFR project, and Yoon Chang, was the deputy head. Till was positioned in Idaho, while Chang was in Illinois.

With the election of President Bill Clinton in 1992, and the appointment of Hazel O'Leary as the Secretary of Energy, there was pressure from the top to cancel the IFR. Sen. John Kerry (D, MA) and O'Leary led the opposition to the reactor, arguing that it would be a threat to non-proliferation efforts, and that it was a continuation of the Clinch River Breeder Reactor Project that had been canceled by Congress.

IFR opponents also presented a report[15] by the DOE's Office of Nuclear Safety regarding a former Argonne employee's allegations that Argonne had retaliated against him for raising concerns about safety, as well as about the quality of research done on the IFR program. The report received international attention, with a notable difference in the coverage it received from major scientific publications. The British journal Nature entitled its article "Report backs whistleblower", and also noted conflicts of interest on the part of a DOE panel that assessed IFR research.[16]. In contrast, the article that appeared in Science was entitled "Was Argonne Whistleblower Really Blowing Smoke?".[17] Remarkably, that article did not disclose that the Director of Argonne National Laboratories, Alan Schriesheim, was a member of the Board of Directors of Science's parent organization, the American Association for the Advancement of Science.[18]

Despite support for the reactor by then-Rep. Richard Durbin (D, IL) and U.S. Senators Carol Mosley Braun (D, IL) and Paul Simon (D, IL), funding for the reactor was slashed, and it was ultimately canceled in 1994 by S.Amdt. 2127 to H.R. 4506.

In 2001, as part of the Generation IV roadmap, the DOE tasked a 242 person team of scientists from DOE, UC Berkeley, MIT, Stanford, ANL, LLNL, Toshiba, Westinghouse, Duke, EPRI, and other institutions to evaluate 19 of the best reactor designs on 27 different criteria. The IFR ranked #1 in their study which was released April 9, 2002.[1]

See also

References

  1. ^ a b DOE Comparitive Study of 19 reactor designs on 27 criteria April 9, 2002
  2. ^ a b c d An Introduction to Argonne National Laboratory's INTEGRAL FAST REACTOR (IFR) PROGRAM
  3. ^ Sasahara, Akihiro (April 2004). "Neutron and Gamma Ray Source Evaluation of LWR High Burn-up UO2 and MOX Spent Fuels". Journal of NUCLEAR SCIENCE and TECHNOLOGY. 41 (4): 448–456. doi:10.3327/jnst.41.448.
  4. ^ Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
  5. ^ Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
  6. ^ Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4.
    "The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk248 with a half-life greater than 9 [years]. No growth of Cf248 was detected, and a lower limit for the β− half-life can be set at about 104 [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]."
  7. ^ This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
  8. ^ Excluding those "classically stable" nuclides with half-lives significantly in excess of 232Th; e.g., while 113mCd has a half-life of only fourteen years, that of 113Cd is eight quadrillion years.
  9. ^ The IFR at Argonne National Laboratory
  10. ^ Estimates from Argonne National Laboratory place the output of waste of a 1000 MWe plant operating at 70% capacity at 1700 pounds/year.
  11. ^ BN-800 as a New Stage in the Development of Fast Sodium-Cooled Reactors
  12. ^ Technical options for the advanced liquid metal reactor, page 34
  13. ^ Technical options for the advanced liquid metal reactor, page 36
  14. ^ Technical options for the advanced liquid metal reactor, page 30
  15. ^ Report of investigation into allegations of retaliation for raising safety and quality of work issues regarding Argonne National Laboratory's Integral Fast Reactor Project, Report Number DOE/NS-0005P, 1991 Dec 01 OSTI Identifier OSTI ID: 6030509,
  16. ^ Report backs whistleblower, Nature 356, 469 (9 April 1992)
  17. ^ Science, Vol. 256, No. 5055, 17 April 1992
  18. ^ http://www.sciencemag.org/cgi/issue_pdf/toc_pdf/256/5055.pdf

U.S. Congress, Office of Technology Assessment (May 1994). Technical Options for the Advanced Liquid Metal Reactor. U.S. Government Printing Office. ISBN 1428920684.

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