Integral Fast Reactor: Wikis

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The Integral Fast Reactor (originally Advanced Liquid-Metal Reactor) was a design for a fast reactor (nuclear reactor using fast neutrons and no neutron moderator) distinguished by a nuclear fuel cycle using reprocessing via electrorefining at the reactor site itself.

The U.S. Department of Energy built a prototype but canceled the project in 1994, three years before completion. Predecessors included EBR-II. The Generation IV Sodium-Cooled Fast Reactor is its successor as the currently proposed U.S sodium-cooled fast breeder reactor design. Other countries have also designed and operated their own fast reactors.

Contents

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

Long-lived
fission products
Prop:
Unit:
t½
Ma
Yield
%
Q *
KeV
βγ
*
99Tc 0.211 6.1385 294 β
126Sn 0.230 0.1084 4050 βγ
79Se 0.295 0.0447 151 β
93Zr 1.53 5.4575 91 βγ
135Cs 2.3  6.9110 269 β
107Pd 6.5  1.2499 33 β
129I 15.7  0.8410 194 βγ
  • 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) use almost all of the energy in 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.[2]
  • Breeder reactors can “burn” some components (actinides: reactor-grade plutonium and minor 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 was a liquid metal cooled reactor, 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 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, like other sodium-cooled fast breeder reactors, 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
Prop:
Unit:
t½
a
Yield
%
Q *
KeV
βγ
*
155Eu 4.76 .0803 252 βγ
85Kr 10.76 .2180 687 βγ
113mCd 14.1 .0008 316 β
90Sr 28.9 4.505 2826 β
137Cs 30.23 6.337 1176 βγ
121mSn 43.9 .00005 390 βγ
151Sm 90 .5314 77 β

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, a breeder reactor like the IFR has a very efficient (99.5% of uranium undergoes fission) fuel cycle.[3] 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.[3]

Comparisons to light-water reactors

Buildup of heavy actinides in present thermal reactors,[4] which cannot fission actinide nuclides that have an even number of neutrons. Fast reactors can fission all actinides.
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Nuclear waste

IFR-style reactors produce much less waste than LWR-style reactors, and can even consume other waste as fuel.

The primary argument for pursuing IFR-style technology today is that it provides the best solution to the existing nuclear waste problem because breeder reactors can be fueled from the waste products of existing reactors as well as from the plutonium used in weapons. Depleted uranium (DU) waste can also be used as fuel in IFR reactors.

The waste products of by IFR reactors either have a short halflife, which means that it quickly "burns out" and ends up relatively safe, or a long halflife, which means that they are unlikely to emit a significant amount of protons except from very large quantities. The volume of highly-radioactive waste is 1/20th 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.

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.[3]

The on-site reprocessing of fuel means that the volume of nuclear waste leaving the plant is tiny compared to LWR spent fuel.[5] In fact, in the U.S. most spent LWR fuel has remained in storage at the reactor site instead of being transported for reprocessing or placement in a geological repository. The smaller volumes of high level waste from reprocessing could stay at reactor sites for some time, but are intensely radioactive from medium-lived fission products and need to be stored securely. Repository capacity is constrained not by volume but by heat generation, and heat generation from medium-lived fission products is about the same per unit power from any kind of fission reactor, limiting early repository emplacement.

"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" [6]

Efficiency

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 breeder reactors can power the energy needs of the planet for over a billion years. [7]

Carbon dioxide

IFRs and LWRs both emit no CO2 during operation, although construction and fuel processing may require small CO2 emissions.

Actinides Half-life Fission products
244Cm 241Pu f 250Cf 243Cmf 10–30 y 137Cs 90Sr 85Kr
232 f 238Pu f is for
fissile
69–90 y 151Sm nc➔
4n 249Cf  f 242Amf 141–351 No fission product
has half-life 102
to 2×105 years
241Am 251Cf  f 431–898
240Pu 229Th 246Cm 243Am 5–7 ky
4n 245Cmf 250Cm 239Pu f 8–24 ky
233U    f 230Th 231Pa 32–160
4n+1 234U 4n+3 211–290 99Tc 126Sn 79Se
248Cm 242Pu 340–373 Long-lived fission products
237Np 4n+2 1–2 my 93Zr 135Cs nc➔
236U 4n+1 247Cmf 6–23 107Pd 129I
244Pu 80 my >7% >5% >1% >.1%
232Th 238U 235U    f 0.7–12by fission product yield

Fuel cycle

Fast reactor fuel must be at least 20% fissile, greater than the low enriched uranium used in LWRs. The fissile material could initially include highly enriched uranium or plutonium, from LWR spent fuel, decommissioned nuclear weapons, or other sources. During operation the reactor breeds more fissile material from fertile material.

The fertile material in fast reactor fuel can be depleted uranium (mostly U-238), natural uranium, or reprocessed uranium from spent fuel from traditional light water reactors,[3] and even include nonfissile isotopes of plutonium and minor actinide isotopes. Assuming no leakage of actinides to the waste stream during reprocessing, a 1GWe IFR-style reactor would consume about 1 ton of fertile material per year and produce about 1 ton of fission products.

The IFR fuel cycle's reprocessing by pyroprocessing (in this case, electrorefining) does not need to produce pure plutonium free of fission product radioactivity as the PUREX process is designed to do. The purpose of reprocessing in the IFR fuel cycle is simply to reduce the level of those fission products that are neutron poisons; even those need not be completely removed. The electrorefined spent fuel is highly radioactive, but because new fuel need not be precisely fabricated like LWR fuel pellets but can simply be cast, remote fabrication can be used, reducing exposure to workers.

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 plants. Using steel reflectors instead of U-238 blankets, the reactor operates in pure burner mode and is not a net creator of fissile material; on balance it will consume fissile and fertile material and, assuming loss-free reprocessing, 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.

Because the current cost of 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 increased capital cost. (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, closed fuel cycles might become more financially competitive.)

Reprocessing nuclear fuel using pyroprocessing and electrorefining has not yet been demonstrated on a commercial scale, so investing in a large IFR-style plant may be a higher financial risk than a conventional light water reactor.

Passive safety

The IFR uses metal alloy fuel (uranium/plutonium/zirconium) which is a good conductor of heat, unlike the LWR's (and even some fast breeder reactors') uranium oxide which is a poor conductor of heat and reaches high temperatures at the center of fuel pellets. The IFR also has a smaller volume of fuel, since the fissile material is diluted with fertile material by a ratio of 5 or less, compared to about 30 for LWR fuel. The IFR core requires more heat removal per core volume during operation than the LWR core; but on the other hand, after a shutdown, there is far less trapped heat that is still diffusing out and needs to be removed. However, decay heat generation from short-lived fission products and actinides is comparable in both cases, starting at a high level and decreasing with time elapsed after shutdown.

Self-regulation of the IFR's power level depends mainly on thermal expansion of the fuel which allows more neutrons to escape, damping the chain reaction. LWRs have less effect from thermal expansion of fuel (since much of the core is the neutron moderator) but have strong negative feedback from Doppler broadening (which acts on thermal and epithermal neutrons, not fast neutrons) and negative void coefficient from boiling of the water moderator/coolant; the less dense steam returns fewer and less-thermalized neutrons to the fuel, which are more likely to be captured by U-238 than induce fissions.

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.[8] 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, it would not even incur damage.

The flammability of sodium is a risk to operators. 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.

Proliferation

IFRs and LWRs both produce plutonium, which can be used for weapons production, but the IFR fuel cycle has some design features that make proliferation more difficult. Unlike PUREX reprocessing, the IFR's electrolytic reprocessing, at least of spent fuel itself, need not separate out pure plutonium. The plutonium also stays at the reactor site and can be consumed by the same or other reactors. While it is possible to extract the plutonium, international monitoring of a closed system is claimed to be much easier than one that has external reprocessing.

Because reactor-grade plutonium contains isotopes of plutonium with high spontaneous fission rates, it is more difficult, though not impossible, to produce nuclear weapons from high-burnup spent fuel. This also could be circumvented with isotopic separation, but this is more difficult than uranium enrichment due to the high radioactivity of the plutonium.

Profileration risks are not eliminated. "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." [9] "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" [10]

Reactor design and construction

A commercial version of the IFR, S-PRISM, can be built in a factory and transported to the 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.

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]

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[12] 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.[13]. In contrast, the article that appeared in Science was entitled "Was Argonne Whistleblower Really Blowing Smoke?".[14] 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.[15]

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]

At present there are no Integral Fast Reactors in commercial operation.

See also

References

  1. ^ a b DOE Comparative Study of 19 reactor designs on 27 criteria April 9, 2002
  2. ^ Breeder Reactors: A renewable energy source
  3. ^ a b c d An Introduction to Argonne National Laboratory's INTEGRAL FAST REACTOR (IFR) PROGRAM
  4. ^ 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. http://www.jstage.jst.go.jp/article/jnst/41/4/448/_pdf.  
  5. ^ Estimates from Argonne National Laboratory place the output of waste of a 1000 MWe plant operating at 70% capacity at 1700 pounds/year.
  6. ^ Technical options for the advanced liquid metal reactor, page 30
  7. ^ How long will nuclear energy last?
  8. ^ The IFR at Argonne National Laboratory
  9. ^ Technical options for the advanced liquid metal reactor, page 34
  10. ^ Technical options for the advanced liquid metal reactor, page 36
  11. ^ BN-800 as a New Stage in the Development of Fast Sodium-Cooled Reactors
  12. ^ 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,
  13. ^ Report backs whistleblower, Nature 356, 469 (9 April 1992)
  14. ^ Science, Vol. 256, No. 5055, 17 April 1992
  15. ^ 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. http://books.google.com/books?id=Lr0sPxjBD2MC.  

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