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Fast neutron reactor
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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. Such a reactor needs no neutron moderator, but must use fuel that is relatively rich in fissile material when compared to that required for a thermal reactor.
Nuclear reactor design
Coolant
Water, the most common coolant in thermal reactors, is generally not a feasible coolant for a fast reactor, because it acts as a neutron moderator.
Discussion
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Encyclopedia
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. Such a reactor needs no neutron moderator, but must use fuel that is relatively rich in fissile material when compared to that required for a thermal reactor.
Advantages
- On average, more neutrons per fission are produced from fissions caused by fast neutrons than from those caused by thermal neutrons. Therefore, there is a much larger excess of neutrons not required to sustain the chain reaction. These neutrons can be used to produce extra fuel, or to transmute long-halflife waste to less troublesome isotopes, such as is done at the Phénix reactor near Cadarache in France, or some can be used for each purpose. Though conventional thermal reactors also produce excess neutrons, fast reactors can produce enough of them to breed more fuel than they consume. Such designs are known as fast breeder reactors.
- Fast neutrons also have an advantage in the transmutation of nuclear waste. The reason for this is that the ratio between the fission cross-section and the absorption cross-section of a plutonium or minor actinide nuclide is often higher in a fast spectrum than in a thermal or epithermal spectrum.
Nuclear reactor design
Coolant
Water, the most common coolant in thermal reactors, is generally not a feasible coolant for a fast reactor, because it acts as a neutron moderator. However some variants of the Generation IV reactor known as the supercritical water reactor may technically be considered fast neutron reactors.
All current fast reactors are liquid metal cooled. Early reactors used mercury cooling and plutonium metal fuel. NaK cooling is popular in test reactors due to its low melting point. Molten lead cooling has been used in naval propulsion units as well as some other prototype reactors. Some of the newer generation of power stations use molten sodium cooling.
Gas-cooled fast reactors have been researched as well.
Nuclear fuel
In practice sustaining a fission chain reaction with fast neutrons means using relatively highly enriched uranium or plutonium. The reason for this is that fissile reactions are favored at thermal energies, since the ratio between the Pu239 fission cross-section U238 absorption cross-section is ~100 in a thermal spectrum and 8 in a fast spectrum. Therefore it is impossible to build a fast reactor using only natural uranium fuel. However, it is possible to build a fast reactor that will breed fuel (from fertile material) by producing more fissile material than it consumes. After the initial fuel charge such a reactor can be refueled by reprocessing. Fission products can be replaced by adding natural or even depleted uranium with no further enrichment required. This is the concept of the fast breeder reactor or FBR.
So far, all fast neutron reactors have used either MOX or metal alloy fuel.
Control
Like thermal reactors, fast neutron reactors are controlled by keeping the criticality of the reactor reliant on delayed neutrons, allowing for control utilizing control rods/blades.
However, they cannot rely on Doppler broadening (which affects thermal neutrons) or on negative void coefficient (there is no moderator, so there is no reactivity reduction from moderator boiling).
History
A 2008 IAEA proposal for a Fast Reactor Knowledge Preservation System notes that:
during the past 15 years there has been stagnation in the development of fast reactors in the industrialized countries that were involved, earlier, in intensive development of this area. All studies on fast reactors have been stopped in countries such as Germany, Italy, the United Kingdom and the United States of America and the only work being carried out is related to the decommissioning of fast reactors. Many specialists who were involved in the studies and development work in this area in these countries have already retired or are close to retirement. In countries such as France, Japan and the Russian Federation that are still actively pursuing the evolution of fast reactor technology, the situation is aggravated by the lack of young scientists and engineers moving into this branch of nuclear power.
List of fast reactors
Fast reactors of the past
- Small lead-cooled fast reactors used for naval propulsion, particularly by the Soviet Navy.
- CLEMENTINE, the first fast reactor, built in 1946 at Los Alamos, New Mexico. Plutonium metal fuel, mercury coolant, power 25 kW thermal, used for research, especially as a fast neutron source.
- EBR-I at Idaho Falls, which in 1951 became the first reactor to generate significant amounts of electrical power.
- EBR-II Prototype for the Integral Fast Reactor.
- The Dounreay fast reactors, DFR (Dounreay Fast Reactor, 1959-1977, 14MWe) and PFR (Prototype Fast Reactor, 1974-1994, 250MWe), in Caithness, in the Highland area of Scotland.
- SEFOR in Arkansas, a 20MWt research reactor which operated from 1969 to 1972.
- Rhapsodie in Cadarache (20 then 40 MW) between 1967 and 1982.
- BN-350, constructed by the Soviet Union in Shevchenko (today's Aqtau) on the Caspian Sea, 130MWe plus 80,000 tons of fresh water per day.
- Fast Flux Test Facility, 400MWt, Operated flawlessly from 1982 to 1992, at Hanford Washington, now deactivated, liquid sodium is drained with argon backfill under care and maintenance.
- Superphénix, in France, 1200MWe, closed in 1997 due to a political decision and very high costs of operation.
- KNK-II, Germany
Never operated
- Clinch River Breeder Reactor, USA
- Integral Fast Reactor, a design of fast reactor with an integral fuel cycle, developed and cancelled in the USA in the 1990s.
- SNR-300, Germany
Currently operating
- Phénix, 1973, France, 233 MWe, restarted 2003 for experiments on transmutation of nuclear waste, scheduled end of life 2014
, 1977-1997, 2003-, Japan
- BN-600, 1981, Russia, 600 MWe, scheduled end of life 2010
- FBTR, 1985, India, 10.5 MWt
Under construction
- Monju reactor, 300MWe, in Japan. was closed in 1995 following a serious sodium leak and fire. It is expected to reopen in 2008.
- PFBR, Kalpakkam, India, 500 MWe. Planned to open 2010
- China Experimental Fast Reactor, 65 MWt, planned 2009
- BN-800, Russia, planned operation in 2012
In design phase
- BN-1800, Russia, build starting in 2012, operation in 2018-2020
- Toshiba 4S being developed in Japan and is planned to be shipped to Galena, Alaska (USA) in 2012 (see Galena Nuclear Power Plant)
- KALIMER, 600 MWe, South Korea, projected 2030
- Generation IV reactor US-proposed international effort, after 2030
- JSFR, Japan, project for a 1500 MWe reactor begin in 1998->2010
See also
External links and references
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- seeks to establish a comprehensive, international inventory of fast reactor data and knowledge, which would be sufficient to form the basis for fast reactor development in 30 to 40 years from now.
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