Integral Fast Reactor

From Wikipedia, the free encyclopedia

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

Contents

[edit] 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.

[edit] Safety

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

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

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

[edit] Efficiency and Fuel cycle

Medium-lived
fission products
Property: t½
Unit: (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
Long-lived
fission products
Property: t½
Unit: (Ma)		 Yield
(%)		 Q *
(KeV)		 βγ
*
99Tc .211 6.1385 294 β
126Sn .230 .1084 4050 βγ
79Se .295 .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  .8410 194 βγ

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 uses less than 1% of the energy in the uranium, the IFR has a very efficient (99.5% usage) 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 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 removed and recycled, the remaining radioactive waste isotopes are fission products, which have half lives of either 90 years (Sm-151) and less, or 211,100 years (Tc-99) and more; plus any neutron activation products from the non-fuel reactor components. (Tc-99 and I-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.[1]

[edit] Key benefits

  • Enhanced passive safety because of the high thermal conductivity of the fuel. Able to withstand both a loss of flow without SCRAM and loss of heat sink without SCRAM.[2][3]
  • Ease of fuel fabrication. Because the sodium fills the space between the fuel and cladding, the fuel need not be precisely fabricated. The fuel is simply cast. Because casting is simple, the fuel can be fabricated remotely, reducing the hazards of its radioactivity.
  • On-site reprocessing by pyroprocessing and electrorefining is simplified because there is no need to stringently reduce the radioactivity of the fuel. Actinides including transuranics can be incorporated into the fuel.
  • Proliferation hazards are reduced by the high radioactivity of the fuel. Because the fuel contains significant levels of transuranics with high spontaneous fission rates, it is not possible to produce nuclear weapons using IFR fuel without centrifugal separation. This is more difficult than enrichment of natural uranium due to the smaller atomic mass difference between Pu-239 and Pu-240 as compared to U-235 vs U-238, and is rendered even more difficult by the high radioactivity of the fuel.
  • 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.[1]
  • The on-site reprocessing of fuel means that the quantity of nuclear waste leaving the plant is tiny relative to other nuclear facilities.[4] This makes storage simpler and reduces the security risk associated with nuclear waste transportation.

[edit] Key disadvantages

  • Because the current cost of reactor-grade enriched uranium is relatively low compared to the expected cost of large-scale pyroprocessing and electrorefining equipment and the cost of building a secondary coolant loop, the higher fuel costs of a thermal reactor over the expected operating lifetime of the plant are offset by the increased capital cost of an IFR. (Currently in the United States, utilities pay a flat rate of 1/10 of a cent per kilowatt hour for disposal of high level radioactive waste. If this charge were based on the longevity of the waste, then the IFR might become more financially competitive.)
  • Reprocessing nuclear fuel using pyroprocessing and electrorefining has not yet been demonstrated on a commercial scale. As such, investing in a large IFR plant is considered a higher financial risk than a conventional light water reactor.
  • The flammability of sodium. 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.

[edit] 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. 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.

[edit] See also

v • d • e
Nuclear technology
Engineering
Material
Power
Core topics
Medicine
Therapies
Weapons

[edit] References

  1. ^ a b An Introduction to Argonne National Laboratory's Integral Fast Reactor (IFR) Program
  2. ^ http://www.anlw.anl.gov/anlw_history/reactors/ebrii_docs/ifr_safety.html
  3. ^ http://www.anlw.anl.gov/anlw_history/reactors/ifr.html
  4. ^ Estimates from Argonne National Laboratory place the output of waste of a 1000 MWe plant operating at 70% capacity at 1700 pounds/year.

[edit] External links