A project “Plumbum-208: a new heat-carrier, decelerator and reflector of neutrons for innovative fast neutron reactors” has been completed by the Department of Theoretical and experimental nuclear reactor physics as a part of Grant of the President of the Russian Federation for Support of Young Russian Scientists. It is aimed at solving of one of nuclear power problems – raising of safety of nuclear reactors.

The ability to control reactors, including fast neutron ones, is determined by the presence of delayed neutrons which are produced by fission products in a short time (several milliseconds to several seconds) after the fission reaction. Prompt neutron fission chain reaction goes extremely quickly and doesn’t lend itself to control. The percentage of delayed neutrons is extremely small and is nearly 0.5% from generated fission products. An emergency input of positive reactivity even of a small percentage of delayed neutrons can lead to the nuclear reactor destruction.

Nuclear reactors are designed in such a manner as to avoid such situations. That is why the fuel composition, materials and active zone construction, and the whole equipment of the nuclear power station should meet stringent requirements. However, this significantly reduces the choice of fuel and construction materials, and the choice of constructive parameters of the reactor active zone, and, after all, doesn’t solve the problem of fast reactor safety under emergency uprise of positive reactivity which is more than the delayed neutrons effective factor.

For the first time the possibility of fission chain reaction retardation for fast reactors’ safety raising has been shown. This is achieved by the active zone surrounding by the low-capture deflector made of Plumbum-208. It forms the flow of reflected neutrons which have a larger life cycle than active zone prompt reactors.

Plumbum-208 isotope is characterized by an extremely low absorption cross section (less than graphite and deuterium have) and the biggest thermal neutron albedo. The use of the deflector based on Plumbum-208 will allow to significantly increase an average neutron life cycle (nearly on 3 orders) which will improve its nuclear safety in case of an emergency input of positive reactivity of effective factor of an order and more.

The project is supervised by Dr.-Ing. Kulikov Gennadiy, Department №5 Senior Teacher who has published more than 30 works. Associate contractor is a post-graduate student Chubko Nikolay.