Fast-neutron reactor

Shevchenko BN350 nuclear fast reactor and desalination plant situated on the shore of the Caspian Sea. The plant generated 135 MW_e and provided steam for an associated desalination plant. View of the interior of the reactor hall.

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. This results in a larger surplus of neutrons beyond those 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 the Generation IV reactor known as the supercritical water reactor with decreased coolant density may reach a hard enough neutron spectrum to be considered a fast reactor.

All current fast reactors are liquid metal cooled reactors. The early Clementine reactor used mercury coolant and plutonium metal fuel. NaK coolant 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. All large-scale fast reactors have used molten sodium coolant.

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 and 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). Thermal expansion of the fuel itself at increased power can provide quick negative feedback.

Shevchenko BN350 desalination unit. View of the only nuclear-heated desalination unit in the world

History

A 2008 IAEA proposal for a Fast Reactor Knowledge Preservation System^[1] 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

US

• CLEMENTINE, the first fast reactor, built in 1946 at Los Alamos National Laboratory. 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. Decommissioned 1964.
• Fermi 1 near Detroit was a prototype fast breeder reactor that began operating in 1957 and shut down in 1972.
• EBR-II Prototype for the Integral Fast Reactor, 1965-1995?.
• SEFOR in Arkansas, a 20 MWt research reactor which operated from 1969 to 1972.
• 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.

Europe

• DFR (Dounreay Fast Reactor, 1959-1977, 14MWe) and PFR (Prototype Fast Reactor, 1974-1994, 250MWe), in Caithness, in the Highland area of Scotland.
• Rhapsodie in Cadarache (20 then 40 MW) between 1967 and 1982.
• Superphénix, in France, 1200MWe, closed in 1997 due to a political decision and very high costs of operation.
• KNK-II, Germany

USSR

• Small lead-cooled fast reactors used for naval propulsion, particularly by the Soviet Navy.
• 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.

Never operated

• Clinch River Breeder Reactor, USA
• Integral Fast Reactor, USA. Design emphasized fuel cycle based on on-site electrolytic reprocessing. Cancelled 1994 without construction.
• SNR-300, Germany

Currently operating

• Phénix, 1973, France, 233 MWe, restarted 2003 at 140 MWe for experiments on transmutation of nuclear waste for six years, ceased power generation in March 2009, though it will continue in test operation and to continue research programs by CEA until the end of 2009. Scheduled end of life 2014
• Jōyō (常陽^?), 1977-1997 and 2003-, Japan
• BN-600, 1981, Russia, 600 MWe, scheduled end of life 2010^[2]
• 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 2010.
• PFBR, Kalpakkam, India, 500 MWe. Planned to open 2010
• China Experimental Fast Reactor, 65 MWt, planned 2009 ^[3]
• BN-800, Russia, planned operation in 2012 ^[4]

In design phase

• BN-1800, Russia, build starting in 2012, operation in 2018-2020^[5]
• 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^[6]
• Generation IV reactor (Gas·Sodium·Lead cooled) US-proposed international effort, after 2030
• JSFR, Japan, project for a 1500 MWe reactor begin in 1998->2010

Chart

See also

• Nuclear fuel cycle
• Breeder reactor
• Liquid Fluoride Reactor
• Molten-Salt Reactor Experiment
• Lead-cooled fast reactor
• Gas-cooled fast reactor
• Generation IV reactor
• Energy amplifier

External links and references

• ANL report on EARLY SOVIET FAST REACTORS
• Article on recent work on fast neutron reactors in Scientific American, December, 2005
• IAEA Fast Reactor Database
• 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.
• World Nuclear Association: Fast Neutron Reactors

References