Integral Fast Reactor

Integral Fast Reactor

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The Integral Fast Reactor (IFR, originally Advanced Liquid-Metal Reactor
Liquid metal cooled reactor
A liquid metal cooled nuclear reactor, liquid metal fast reactor or LMFR is an advanced type of nuclear reactor where the primary coolant is a liquid metal. Liquid metal cooled reactors were first adapted for nuclear submarine use but have also been extensively studied for power generation...

) is a design for a nuclear reactor
Nuclear reactor
A nuclear reactor is a device to initiate and control a sustained nuclear chain reaction. Most commonly they are used for generating electricity and for the propulsion of ships. Usually heat from nuclear fission is passed to a working fluid , which runs through turbines that power either ship's...

 using fast neutrons and no neutron moderator
Neutron moderator
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235....

 (a "fast" reactor). IFR is distinguished by a nuclear fuel cycle
Nuclear fuel cycle
The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in...

 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
United States Congress
The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C....

 in 1994, three years before completion.

The proposed Generation IV
Generation IV reactor
Generation IV reactors are a set of theoretical nuclear reactor designs currently being researched. Most of these designs are generally not expected to be available for commercial construction before 2030...

 Sodium-Cooled Fast Reactor
Sodium-cooled fast reactor
The sodium-cooled fast reactor or SFR is a Generation IV reactor project to design an advanced fast neutron reactor.It builds on two closely related existing projects, the LMFBR and the Integral Fast Reactor, with the objective of producing a fast-spectrum, sodium-cooled reactor.The reactors are...

 is its closest surviving fast breeder reactor design. Other countries have also designed and operated fast reactors.

Overview


IFR is cooled by liquid sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 and fueled by an alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

 of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 and plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

. The fuel is contained in steel cladding with liquid sodium filling in the space between the fuel and the cladding.

Advantages

  • Breeder reactor
    Breeder reactor
    A breeder reactor is a nuclear reactor capable of generating more fissile material than it consumes because its neutron economy is high enough to breed fissile from fertile material like uranium-238 or thorium-232. Breeders were at first considered superior because of their superior fuel economy...

    s (such as the IFR) could in principle extract almost all of the energy contained in uranium
    Uranium
    Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

     or thorium
    Thorium
    Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

    , decreasing fuel requirements by nearly two orders of magnitude compared to traditional once-through reactors, which extract less than 1% of the energy. This could greatly damp concern about fuel supply or energy used in mining
    Uranium mining
    Uranium mining is the process of extraction of uranium ore from the ground. The worldwide production of uranium in 2009 amounted to 50,572 tonnes, of which 27% was mined in Kazakhstan. Kazakhstan, Canada, and Australia are the top three producers and together account for 63% of world uranium...

    . In fact, with seawater uranium extraction, there is enough fuel for breeder reactors to satisfy our energy needs for 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
    Renewable energy
    Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...

    .

  • Breeder reactors can “burn” longlasting nuclear waste components (actinides: reactor-grade plutonium and minor actinides
    Minor actinides
    The minor actinides are the actinide elements in used nuclear fuel other than uranium and plutonium, which are termed the major actinides. The minor actinides include neptunium, americium, curium, berkelium, californium, einsteinium, and fermium...

    ), turning liability into an asset. Another major waste component, fission product
    Fission product
    Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...

    s, would stabilize at a lower level of radioactivity in a few centuries, rather than tens of thousands of years. The fact that 4th generation reactor
    Generation IV reactor
    Generation IV reactors are a set of theoretical nuclear reactor designs currently being researched. Most of these designs are generally not expected to be available for commercial construction before 2030...

    s are being designed to use the waste from 3rd generation plant
    Generation III reactor
    A generation III reactor is a development of any of the generation II nuclear reactor designs incorporating evolutionary improvements in design developed during the lifetime of the generation II reactor designs...

    s 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 reactor
Light water reactor
The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor...

s (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
Liquid metal cooled reactor
A liquid metal cooled nuclear reactor, liquid metal fast reactor or LMFR is an advanced type of nuclear reactor where the primary coolant is a liquid metal. Liquid metal cooled reactors were first adapted for nuclear submarine use but have also been extensively studied for power generation...

, the core could operate at close to ambient pressure, dramatically reducing the danger of a loss-of-coolant accident. The entire reactor core, heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...

s and primary cooling pumps are immersed in a pool of liquid sodium, making a loss of primary coolant extremely unlikely. The coolant loops are designed to allow for cooling through natural convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

, 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
Passive nuclear safety
Passive nuclear safety is a safety feature of a nuclear reactor that does not require operator actions or electronic feedback in order to shut down safely in the event of a particular type of emergency...

 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.

Liquid sodium presents safety problems because it ignites spontaneously on contact with air and can cause explosions on contact with water. To reduce the risk of explosions following a leak of water from the steam turbines, the IFR design (as with other sodium-cooled fast reactor
Sodium-cooled fast reactor
The sodium-cooled fast reactor or SFR is a Generation IV reactor project to design an advanced fast neutron reactor.It builds on two closely related existing projects, the LMFBR and the Integral Fast Reactor, with the objective of producing a fast-spectrum, sodium-cooled reactor.The reactors are...

s) 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.

Efficiency and fuel cycle


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. 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
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 transuranics from the waste cycle is that the remaining waste becomes a much shorter-term hazard. After the actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...

s (reprocessed uranium
Reprocessed uranium
Reprocessed uranium is the uranium recovered from nuclear reprocessing, as done commercially in France, the UK and Japan and by nuclear weapons states' military plutonium production programs. This uranium actually makes up the bulk of the material separated during reprocessing...

, plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

, and minor actinides
Minor actinides
The minor actinides are the actinide elements in used nuclear fuel other than uranium and plutonium, which are termed the major actinides. The minor actinides include neptunium, americium, curium, berkelium, californium, einsteinium, and fermium...

) are recycled, the remaining radioactive waste
Radioactive waste
Radioactive wastes are wastes that contain radioactive material. Radioactive wastes are usually by-products of nuclear power generation and other applications of nuclear fission or nuclear technology, such as research and medicine...

 isotopes are fission products, with half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 of 90 years (Sm-151) or less or 211,100 years (Tc-99) and more; plus any activation product
Activation product
Activation products are materials made radioactive by neutron activation.Fission products and actinides produced by neutron absorption of nuclear fuel itself are normally referred to by those specific names, and activation product reserved for products of neutron capture by other materials, such as...

s from the non-fuel reactor components. (Tc-99 and Iodine-129
Iodine-129
Iodine-129 is long-lived radioisotope of iodine which occurs naturally, but also is of special interest in the monitoring and effects of man-made nuclear fission decay products, where it serves as both tracer and potential radiological contaminant....

 are also candidates for nuclear transmutation
Nuclear transmutation
Nuclear transmutation is the conversion of one chemical element or isotope into another. In other words, atoms of one element can be changed into atoms of other element by 'transmutation'...

 to stable isotopes by neutron capture
Neutron capture
Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled...

.)

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



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
Depleted uranium
Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...

 (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 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
High level waste
High level waste is a type of nuclear waste created by the reprocessing of spent nuclear fuel. It exists in two main forms:* First and second cycle raffinate and other waste streams created by nuclear reprocessing....

 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.

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
High level waste
High level waste is a type of nuclear waste created by the reprocessing of spent nuclear fuel. It exists in two main forms:* First and second cycle raffinate and other waste streams created by nuclear reprocessing....

 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
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...

 nuclide
Nuclide
A nuclide is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and its nuclear energy state....

s of greatest concern in scenarios such as groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

 leaching
Leaching (chemical science)
Leaching is the process of extracting minerals from a solid by dissolving them in a liquid, either in nature or through an industrial process. In the chemical processing industry, leaching has a variety of commercial applications, including separation of metal from ore using acid, and sugar from...

 actually have longer half-lives than the radioactive actinides. These concerns do not consider the plan to store such materials in insoluble Synroc
Synroc
Synroc, a portmanteau of "synthetic rock", is a means of safely storing radioactive waste. It was pioneered in 1978 by a team led by Dr Ted Ringwood at the Australian National University, with further research undertaken in collaboration with ANSTO at research laboratories in Lucas...

, 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
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

). These persons are concerned with radioactive fission products such as technetium-99
Technetium-99
Technetium-99 is an isotope of technetium which decays with a half-life of 211,000 years to stable ruthenium-99, emitting soft beta rays, but no gamma rays....

, iodine-129
Iodine-129
Iodine-129 is long-lived radioisotope of iodine which occurs naturally, but also is of special interest in the monitoring and effects of man-made nuclear fission decay products, where it serves as both tracer and potential radiological contaminant....

, 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 1%.

Carbon dioxide


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

Fuel cycle


Fast reactor fuel must be at least 20% fissile, greater than the low enriched uranium used in LWRs.
The fissile
Fissile
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. By definition, fissile materials can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons or fast neutrons...

 material could initially include highly enriched uranium or plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...

, from LWR spent fuel, decommissioned nuclear weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...

s, or other sources. During operation the reactor breeds more fissile material from fertile material
Fertile material
Fertile material is a term used to describe nuclides which generally themselves do not undergo induced fission but from which fissile material is generated by neutron absorption and subsequent nuclei conversions...

.

The fertile material in fast reactor fuel can be depleted uranium
Depleted uranium
Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...

 (mostly U-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...

), natural uranium
Natural uranium
Natural uranium refers to refined uranium with the same isotopic ratio as found in nature. It contains 0.7 % uranium-235, 99.3 % uranium-238, and a trace of uranium-234 by weight. In terms of the amount of radioactivity, approximately 2.2 % comes from uranium-235, 48.6 % uranium-238, and 49.2 %...

, or reprocessed uranium
Reprocessed uranium
Reprocessed uranium is the uranium recovered from nuclear reprocessing, as done commercially in France, the UK and Japan and by nuclear weapons states' military plutonium production programs. This uranium actually makes up the bulk of the material separated during reprocessing...

 from spent fuel from traditional light water reactor
Light water reactor
The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor...

s, and even include nonfissile isotopes of plutonium
Isotopes of plutonium
Plutonium is an artificial element, except for trace quantities of primordial 244Pu, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized long before being found in nature, the first isotope synthesized being 238Pu in 1940....

 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 product
Fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus fissions. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons and a large release of energy in the form of heat , gamma rays and neutrinos. The...

s.

The IFR fuel cycle's reprocessing by pyroprocessing
Pyroprocessing
Pyroprocessing is a process in which materials are subjected to high temperatures in order to bring about a chemical or physical change. Pyroprocessing includes such terms as ore-roasting, calcination and sintering...

 (in this case, electrorefining) does not need to produce pure plutonium free of fission product radioactivity as the PUREX
PUREX
PUREX is an acronym standing for Plutonium - URanium EXtraction — de facto standard aqueous nuclear reprocessing method for the recovery of uranium and plutonium from used nuclear fuel. It is based on liquid-liquid extraction ion-exchange.The PUREX process was invented by Herbert H. Anderson and...

 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
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...

 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
Uranium market
The uranium market, like all commodity markets, has a history of volatility, moving not only with the standard forces of supply and demand, but also to whims of geopolitics. It has also evolved particularities of its own in response to the unique nature and use of this material.The only significant...

 of enriched uranium
Enriched uranium
Enriched uranium is a kind of uranium in which the percent composition of uranium-235 has been increased through the process of isotope separation. Natural uranium is 99.284% 238U isotope, with 235U only constituting about 0.711% of its weight...

 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
Thermal reactor
A thermal reactor is a nuclear reactor that uses slow or thermal neutrons. Most power reactors are of this type. These type of reactors use a neutron moderator to slow neutrons until they approach the average kinetic energy of the surrounding particles, that is, to reduce the speed of the neutrons...

 over the expected operating lifetime of the plant are offset by increased capital cost
Capital cost
Capital costs are costs incurred on the purchase of land, buildings, construction and equipment to be used in the production of goods or the rendering of services, in other words, the total cost needed to bring a project to a commercially operable status. However, capital costs are not limited to...

. (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
Financial risk
Financial risk an umbrella term for multiple types of risk associated with financing, including financial transactions that include company loans in risk of default. Risk is a term often used to imply downside risk, meaning the uncertainty of a return and the potential for financial loss...

 than a conventional light water reactor
Light water reactor
The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal 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
Uranium oxide
Uranium oxide is an oxide of the element uranium.The metal uranium forms several oxides:* Uranium dioxide or uranium oxide * Uranium trioxide or 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
Chain reaction
A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events....

. LWRs have less effect from thermal expansion of fuel (since much of the core is the neutron moderator
Neutron moderator
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235....

) but have strong negative feedback
Negative feedback
Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...

 from Doppler broadening
Doppler broadening
In atomic physics, Doppler broadening is the broadening of spectral lines due to the Doppler effect caused by a distribution of velocities of atoms or molecules. Different velocities of the emitting particles result in different shifts, the cumulative effect of which is the line broadening.The...

 (which acts on thermal and epithermal neutrons, not fast neutrons) and negative void coefficient
Void coefficient
In nuclear engineering, the void coefficient is a number that can be used to estimate how much the reactivity of a nuclear reactor changes as voids form in the reactor moderator or coolant...

 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
Long-lived fission product
Long-lived fission products are radioactive materials with a long half-life produced by nuclear fission.-Evolution of radioactivity in nuclear waste:...

 technetium-99
Technetium-99
Technetium-99 is an isotope of technetium which decays with a half-life of 211,000 years to stable ruthenium-99, emitting soft beta rays, but no gamma rays....

 by nuclear transmutation
Nuclear transmutation
Nuclear transmutation is the conversion of one chemical element or isotope into another. In other words, atoms of one element can be changed into atoms of other element by 'transmutation'...

 in the process.

IFRs are able to withstand both a loss of flow without SCRAM
Scram
A scram or SCRAM is an emergency shutdown of a nuclear reactor – though the term has been extended to cover shutdowns of other complex operations, such as server farms and even large model railroads...

 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
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...

 of 2.7 MeV
Electronvolt
In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt...

 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
PUREX
PUREX is an acronym standing for Plutonium - URanium EXtraction — de facto standard aqueous nuclear reprocessing method for the recovery of uranium and plutonium from used nuclear fuel. It is based on liquid-liquid extraction ion-exchange.The PUREX process was invented by Herbert H. Anderson and...

 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
Isotopes of plutonium
Plutonium is an artificial element, except for trace quantities of primordial 244Pu, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized long before being found in nature, the first isotope synthesized being 238Pu in 1940....

 with high spontaneous fission
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...

 rates, it is more difficult, though not impossible, to produce nuclear weapons from high-burnup
Burnup
In nuclear power technology, burnup is a measure of how much energy is extracted from a primary nuclear fuel source...

 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.

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
Spent nuclear fuel
Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor...

 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
Reactor grade plutonium nuclear test
Reactor-grade plutonium is found in spent nuclear fuel that a nuclear reactor has irradiated for years instead of weeks or months, leading to transmutation of much of the fissile, relatively long half-life isotope 239Pu into other isotopes of plutonium that are less fissile or more...

 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
Fertile material
Fertile material is a term used to describe nuclides which generally themselves do not undergo induced fission but from which fissile material is generated by neutron absorption and subsequent nuclei conversions...

 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
S-PRISM
S-PRISM, also called PRISM , is the name of a nuclear power plant design by GE Hitachi Nuclear Energy based on a sodium-cooled fast breeder reactor. The design utilizes reactor modules, each having a power output of 311 MWe, to enable factory fabrication at low cost. The design is based on the...

, 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.

Liquid metal Na coolant


Unlike reactors that use relatively slow low energy (thermal) neutrons, fast neutron reactors need nuclear reactor coolant
Nuclear reactor coolant
A nuclear reactor coolant is a coolant in a nuclear reactor used to remove heat from the nuclear reactor core and transfer it to electrical generators and the environment....

 that does not moderate or block neutrons (like water does in an LWR) so that they have sufficient energy to fission actinide
Actinide
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.The actinide series derives its name from the group 3 element actinium...

 isotopes that are fissionable but not fissile
Fissile
In nuclear engineering, a fissile material is one that is capable of sustaining a chain reaction of nuclear fission. By definition, fissile materials can sustain a chain reaction with neutrons of any energy. The predominant neutron energy may be typified by either slow neutrons or fast neutrons...

. 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. 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
Argonne National Laboratory
Argonne National Laboratory is the first science and engineering research national laboratory in the United States, receiving this designation on July 1, 1946. It is the largest national laboratory by size and scope in the Midwest...

 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
University of Chicago
The University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...

.

Argonne previously had a branch campus named "Argonne West" in Idaho Falls, Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....

 that is now part of the Idaho National Laboratory
Idaho National Laboratory
Idaho National Laboratory is an complex located in the high desert of eastern Idaho, between the town of Arco to the west and the cities of Idaho Falls and Blackfoot to the east. It lies within Butte, Bingham, Bonneville and Jefferson counties...

. In the past, at the branch campus, physicists from Argonne had built what was known as the Experimental Breeder Reactor II
Experimental Breeder Reactor II
Experimental Breeder Reactor-II is a reactor at the Materials and Fuels Complex of the Idaho National Laboratory, formerly the West Campus of Argonne National Laboratory in Idaho....

 (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
Bill Clinton
William Jefferson "Bill" Clinton is an American politician who served as the 42nd President of the United States from 1993 to 2001. Inaugurated at age 46, he was the third-youngest president. He took office at the end of the Cold War, and was the first president of the baby boomer generation...

 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
John Kerry
John Forbes Kerry is the senior United States Senator from Massachusetts, the 10th most senior U.S. Senator and chairman of the Senate Foreign Relations Committee. He was the presidential nominee of the Democratic Party in the 2004 presidential election, but lost to former President George W...

 (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
Clinch River Breeder Reactor Project
The Clinch River Breeder Reactor Project was a joint effort of the U.S. Atomic Energy Commission and the U.S. electric power industry to design and construct a sodium-cooled fast-neutron nuclear reactor...

 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 Sciences 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
Generation IV reactor
Generation IV reactors are a set of theoretical nuclear reactor designs currently being researched. Most of these designs are generally not expected to be available for commercial construction before 2030...

 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
    Experimental Breeder Reactor II
    Experimental Breeder Reactor-II is a reactor at the Materials and Fuels Complex of the Idaho National Laboratory, formerly the West Campus of Argonne National Laboratory in Idaho....

  • Fast breeder reactor
  • Fast neutron reactor
    Fast neutron reactor
    A fast neutron reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons...

  • Gas-cooled fast reactor
    Gas-cooled fast reactor
    The Gas-Cooled Fast Reactor system is a nuclear reactor design which is currently in development. Classed as a Generation IV reactor, it features a fast-neutron spectrum and closed fuel cycle for efficient conversion of fertile uranium and management of actinides...

  • Generation IV reactor
    Generation IV reactor
    Generation IV reactors are a set of theoretical nuclear reactor designs currently being researched. Most of these designs are generally not expected to be available for commercial construction before 2030...

  • Lead-cooled fast reactor
    Lead cooled fast reactor
    The lead-cooled fast reactor is a nuclear power Generation IV reactor that features a fast neutron spectrum, molten lead or lead-bismuth eutectic coolant. Options include a range of plant ratings, including a number of 50 to 150 MWe units featuring long-life, pre-manufactured cores...

  • Light water reactor
    Light water reactor
    The light water reactor is a type of thermal reactor that uses normal water as its coolant and neutron moderator. Thermal reactors are the most common type of nuclear reactor, and light water reactors are the most common type of thermal reactor...

  • Molten salt reactor
    Molten salt reactor
    A molten salt reactor is a type of nuclear fission reactor in which the primary coolant, or even the fuel itself is a molten salt mixture...

  • Sodium-cooled fast reactor
    Sodium-cooled fast reactor
    The sodium-cooled fast reactor or SFR is a Generation IV reactor project to design an advanced fast neutron reactor.It builds on two closely related existing projects, the LMFBR and the Integral Fast Reactor, with the objective of producing a fast-spectrum, sodium-cooled reactor.The reactors are...

  • S-PRISM
    S-PRISM
    S-PRISM, also called PRISM , is the name of a nuclear power plant design by GE Hitachi Nuclear Energy based on a sodium-cooled fast breeder reactor. The design utilizes reactor modules, each having a power output of 311 MWe, to enable factory fabrication at low cost. The design is based on the...

  • Traveling wave reactor
    Traveling wave reactor
    A traveling-wave reactor, or TWR, is a type of conceptual nuclear reactor that theorists speculate can convert fertile material into fissile fuel as it runs using the process of nuclear transmutation...


External links