|
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. Because absorption in the moderator is a major loss of neutrons in a thermal reactor, a fast reactor has an inherently superior neutron economy; that is, 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.
Coolant Most fast reactors are liquid metal cooled. Early reactors used mercury cooling and plutonium metal fuel; later, NaK cooling was used, and molten lead cooling for naval propulsion units. The latest generation of power stations use MOX fuel and molten sodium cooling. Nuclear fuel In practice sustaining a fission chain reaction with fast neutrons means using relatively highly enriched uranium or plutonium. 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 adding natural or even depleted uranium with no further enrichment required. This is the concept of the fast breeder reactor or FBR. 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. Examples and uses Fast reactors include: As of 2006, new FBRs are planned or under construction in China and India, and construction had resumed on the BN-800 in Russia. See also | ||||||||
|
| |||||||||
 |
|
| |