About 20 fast-neutron reactors have already been operating, some since the 1950s, and one supplies electricity commercially.

Fast-neutron reactors can fission all actinides, while the thorium fuel cycle produces low levels of transuranics.

There exist cheaper and reasonably safe waste management concepts, such as the long-term geological disposal or transmutation in fast-neutron reactors.

Consequently, all nuclear power reactors (even fast-neutron reactors) rely on delayed neutrons for their criticality.

Fyodor Mitenkov (RUS) - Awarded for development of fast-neutron reactors.

Neutrons are less slowed by interaction with heavy nuclei, so lead and bismuth are not neutron moderators, making this type of reactor a fast-neutron reactor.

Fissile materials can be used to fuel thermal-neutron reactors, with a neutron moderator; fast-neutron reactors, with no moderators; and nuclear explosives.

Like nuclear weapons, which also use unmoderated or "fast" neutrons, these Fast-neutron reactors require much higher concentrations of fissile isotopes in order to sustain a chain reaction.

It is most useful as part of a nuclear fuel cycle utilizing fast-neutron reactors since reprocessed uranium and reactor-grade plutonium both have isotopic compositions not optimal for use in today's thermal-neutron reactors.

"Our two countries presently share a common position on the global security balance," Mr. Putin said after signing four other documents, including accords on banking and energy cooperation and an agreement for Russia to build an experimental fast-neutron reactor in China.

Thermal-neutron reactors (today's nuclear power plants) can reuse reactor-grade plutonium only to a limited degree as MOX fuel, and only for a second cycle; fast-neutron reactors, which are uncommon today, can use this or any other actinide material indefinitely.

A fast-neutron reactor, meaning one with little or no neutron moderator and hence utilising fast neutrons, can be configured as a breeder reactor, producing more fissile material than it consumes, using fertile material in a blanket around the core, or contained in special fuel rods.