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.
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 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 in plutonium and minor actinides are higher in a fast spectrum.
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[edit] Nuclear reactor design
[edit] 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.
[edit] 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 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.
[edit] 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.
[edit] List of fast reactors
[edit] 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) and PFR (Prototype Fast Reactor), in Caithness, in the Highland area of Scotland. DFR commenced operation in 1959 and produced 14MWe. PFR produced 250MWe.
- 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
[edit] 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
[edit] Currently operating
- Phénix, 1973, France, 233 MWe, restarted 2003 for experiments on transmutation of nuclear waste, scheduled end of life 2014
- Jōyō (常陽?), 1977, Japan
- BN-600, 1981, Russia, 600 MWe, scheduled end of life 2010[1]
- FBTR, 1985, India, 10.5 MWt
[edit] 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 [2]
- BN-800, Russia, planned 2012 [3]
[edit] In design phase
- KALIMER, South Korea, projected 2030[4]
- Generation IV reactor US-proposed international effort, after 2030
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[edit] External links and references
- ANL report on EARLY SOVIET FAST REACTORS
- Article on recent work on fast neutron reactors in Scientific American, December, 2005
- Fast Reactor Data Retrieval and Knowledge Preservation 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.
