FAST BREEDER REACTOR

PURPOSE:To annihilate transuranium elements along with suppressing a reactivity increment in a region having a positive Na void reactivity by making a region where a plenty of transuranium elements are mixed together, to be a boundary reactor core region to a blanket which has a large neutron leakage. CONSTITUTION:A fast breeder reactor is a nuclear reactor to which a reactor core fuel being loaded with mixed oxides of a plutonium and a uranium, and a blanket fuel consisting mainly of depleted uranium, are loaded, and that a liquid sodium is used as a coolant. The reactor core consists of a region 1 where a mixing ratio of transuranium elements is greater and a region 2 where that ratio is smaller. The region 1 is arranged so as to contact to a radial blanket 3 and an axial blanket 4, as well. Also, according to the figure A, a distribution of a Na void reactivity at the reactor core shows a small positive value at a reactor core center part, and a positive reactivity accompanying Na boiling at the reactor core center region, in an occasion of a hypothetical accident, is much smaller, and therefore a reactor safety can be well maintained.