Integral Fast Reactor

Experimental Breeder Reactor II, which served as the prototype for the Integral Fast Reactor

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

The U.S. Department of Energy built a prototype (the Experimental Breeder Reactor II), but the IFR project was canceled by the US Congress in 1994, three years before completion.

The proposed Generation IV Sodium-Cooled Fast Reactor is its closest surviving fast breeder reactor design. Other countries have also designed and operated fast reactors.

Overview

IFR is cooled by liquid sodium or lead and fueled by an 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. A void above the fuel allows helium and radioactive xenon to be collected safely without significantly increasing pressure inside the fuel element.

Advantages

• Breeder reactors (such as the IFR) could in principle extract almost all of the energy contained in uranium or thorium, decreasing fuel requirements by nearly two orders of magnitude compared to traditional once-through reactors, which extract less than 0.65% of the energy in mined uranium, and less than 5% of the enriched uranium with which they are fueled. This could greatly damp concern about fuel supply or energy used in mining. In fact, with seawater uranium extraction, there is enough fuel for breeder reactors to satisfy our energy needs for as long as the current relationship between the sun and Earth persists, about 5 billion years, thus making nuclear energy as sustainable as solar or wind renewable energy.

• Breeder reactors can “burn” long lasting nuclear waste components (actinides: reactor-grade plutonium and minor actinides), turning liability into an asset. Another major waste component, fission products, would stabilize at a lower level of radioactivity in a few centuries, rather than tens of thousands of years. The fact that 4th generation reactors are being designed to use the waste from 3rd generation plants could change the nuclear story fundamentally—potentially making the combination of 3rd and 4th generation plants a more attractive energy option than 3rd generation by itself would have been, both from the perspective of waste management and energy security.

Safety

In traditional light water reactors (LWRs) the core must be maintained at a high pressure to keep the water liquid at high temperatures. In contrast, since the IFR is 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 are immersed in a pool of liquid sodium or lead, making a loss of primary coolant extremely unlikely. The coolant loops are 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 has passive safety advantages as compared with conventional LWRs. The fuel and cladding are designed such that when they expand due to increased temperatures, more neutrons would be able to escape the core, thus reducing the rate of the fission chain reaction. In other words, an increase in the core temperature will act as a feedback mechanism that decreases the core power. This attribute is known as a negative temperature coefficient of reactivity. Most LWRs also have negative reactivity coefficients; however, in an IFR, this effect is strong enough to stop the reactor from reaching core damage without external action from operators or safety systems. This was demonstrated in a series of safety tests on the prototype. Pete Planchon, the engineer who conducted the tests for an international audience quipped "Back in 1986, we actually gave a small [20 MWe] prototype advanced fast reactor a couple of chances to melt down. It politely refused both times."

Liquid sodium presents safety problems because it ignites spontaneously on contact with air and can cause explosions on contact with water. This was the case at the Monju Nuclear Power Plant in a 1995 accident and fire. To reduce the risk of explosions following a leak of water from the steam turbines, the IFR design (as with other sodium-cooled fast reactors) includes an intermediate liquid-metal coolant loop between the reactor and the steam turbines. The purpose of this loop is 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 itself. Alternative designs use lead instead of sodium as the primary coolant.

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 0.6% of the uranium found in nature, a breeder reactor like the IFR has a very efficient (99.5% of uranium undergoes fission^{[citation needed]}) fuel cycle. The basic scheme used pyroelectric separation, a common method in other metallurgical processes, 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 relatively difficult to use 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.

Comparisons to light-water reactors

Buildup of heavy actinides in current thermal-neutron fission reactors, which cannot fission actinide nuclides that have an even number of neutrons. Fast reactors can fission all actinides.

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 IFR reactors either have a short halflife, which means that they decay quickly and become relatively safe, or a long halflife, which means that they are only slightly radioactive. The total volume of fission products is 1/20th the volume of used fuel produced by a light water plant of the same size, and considered to be waste. 70% of fission products are either stable or have half lives under one year. Technetium-99 and iodine-129, which constitute 6% of fission products, have very long half lives but can be transmuted to isotopes with very short half lives (15.46 seconds and 12.36 hours) by neutron absorption within a reactor, effectively destroying them. Zirconium-93, another 5% of fission products, could in principle be recycled into fuel-pin cladding, where it doesn't matter that it is radioactive. The remaining high level waste from reprocessing, about 200kg per GWe-yr, is less radiotoxic than mined uranium within 300 years.

Edwin Sayre has estimated that a ton of fission products, reduced to metal, has a market value of $16 million.

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.

The on-site reprocessing of fuel means that the volume of nuclear waste leaving the plant is tiny compared to LWR spent fuel. 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.

"Despite the million-fold reduction in radiotoxicity offered by this scheme, some believe 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. These concerns do not consider the plan to store such materials in insoluble Synroc, and do not measure hazards in proportion to those from natural sources such as medical x-rays, cosmic rays, or natural radioactive rocks (such as granite). These persons are concerned with radioactive fission products such as technetium-99, iodine-129, and cesium-135 with half-lives between 213,000 and 15.7 million years"

Efficiency

IFRs use virtually all of the energy content in the uranium fuel whereas a traditional light water reactor uses less than 0.65 of the energy in mined uranium, and less than 5% of the energy in enriched uranium.

Carbon dioxide

Both IFRs and LWRs do not emit CO₂ during operation, although construction and fuel processing result in CO₂ emissions, if energy sources which are not carbon neutral (such as fossil fuels), or CO2 emitting cements are used during the construction process.

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

IFR concept

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. However, the IFR's positive void coefficient could be reduced to an acceptable level by adding technetium to the core, helping destroy the long-lived fission product technetium-99 by nuclear transmutation in the process.

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. The ultimate goal is that no radioactivity will be released under any circumstance.

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. 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, and the smaller mass difference between isotopes.

Proliferation 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." "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"

Reactor design and construction

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

Liquid metal Na coolant

Unlike reactors that use relatively slow low energy (thermal) neutrons, fast neutron reactors need nuclear reactor coolant that does not moderate or block neutrons (like water does in an LWR) so that they have sufficient energy to fission actinide isotopes that are fissionable but not fissile. The core must also be compact and contain as small amount of material that might act as neutron moderators as possible. Metal sodium (Na) coolant in many ways has the most attractive combination of properties for this purpose. In addition to not being a neutron moderator, desirable physical characteristics include:

Low melting temperature. Low vapor pressure. High boiling temperature. Excellent thermal conductivity. Low viscosity. Light weight. Thermal and radiation stability.

Other benefits:

Abundant and low cost material. Cleaning with chlorine produces non-toxic table salt. Compatible with other materials used in the core (does not react or dissolve stainless steel) so no special corrosion protection measures needed. Low pumping power (from light weight and low viscosity). Maintains an oxygen (and water) free environment by reacting with trace amounts to make sodium oxide or sodium hydroxide and hydrogen, thereby protecting other components from corrosion. Light weight (low density) improves resistance to seismic inertia events (earthquakes.)

Drawbacks:

Extreme fire hazard with any significant amounts of air (oxygen) and spontaneous combustion with water, rendering sodium leaks and flooding dangerous. This was the case at the Monju Nuclear Power Plant in a 1995 accident and fire. Reactions with water produce hydrogen which can be explosive. Sodium activation product (isotope) ²⁴Na releases dangerous energetic photons when it decays (however it has a very short half-life of 15 hours). Reactor design keeps ²⁴Na in the reactor pool and carries away heat for power production using a secondary sodium loop, adding costs to construction and maintenance.

Study released by UChicago Argonne

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 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. In contrast, the article that appeared in Science was entitled "Was Argonne Whistleblower Really Blowing Smoke?". 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.

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 (Note: both Illinois Senators voted to cancel the reactor funding in the end).

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.

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

See also

• Experimental Breeder Reactor II
• Fast breeder reactor
• Fast neutron reactor
• Gas-cooled fast reactor
• Generation IV reactor
• Lead-cooled fast reactor
• Light water reactor
• Molten salt reactor
• Sodium-cooled fast reactor
• S-PRISM
• Traveling wave reactor

Further reading

• Tom Blees (2008). Prescription For The Planet: The Painless Remedy for Our Energy & Environmental Crises. BookSurge Publishing. ISBN 1-4196-5582-5. 

• U.S. Congress, Office of Technology Assessment (May 1994). Technical Options for the Advanced Liquid Metal Reactor. U.S. Government Printing Office. ISBN 1-4289-2068-4. http://www.princeton.edu/~ota/disk1/1994/9434/9434.PDF. 

• Charles E. Till, Yoon Il Chang (2011). Plentiful Energy: The Story of the Integral Fast Reactor: The complex history of a simple reactor technology, with emphasis on its scientific bases for non-specialists. CreateSpace. ISBN 1-4663-8460-3. 

• William E. Hannum, Gerald E. Marsh, George S. Stanford (December 2005). "Smarter Use of Nuclear Waste". Scientific American. http://www.scientificamerican.com/article.cfm?id=smarter-use-of-nuclear-waste. 

External links

• The Unofficial IFR home page and (archived) page index
  • Introduction
  • Integral Fast Reactor
  • IFR Metallic Fuel
  • Safety Characteristics
  • Fuel Cycle Facility
  • Fuel Manufacturing Facility
  • The IFR Vision
  • Reactor Burns Waste as Fuel in Nuclear Recycling Experiment
• Integral Fast Reactors: Source of Safe, Abundant, Non-Polluting Power by George S. Stanford, Ph.D.
• The IFR at Argonne National Laboratory
• Frontline interview with Dr. Till.
• IFR Q&A with Tom Blees and George Stanford
• Integral Fast Reactors by Tom Blees, part 2 of 3 Interview with author Tom Blees about IFR.
• The IFR's role in global warming
• Integral Fast Reactor history Documentary (54 minutes) from the mid-1990s about the Integral Fast Reactor
• PRISM IFR (drawing)