Reactor core for FBR type reactor

In a fuel assembly of an inner blanket fuel region, for use in an FBR type reactor, TRU blanket fuel elements incorporating minor actinoides such as Np, Am and Cm and neutron absorbent fuel elements incorporating neutron absorbent such as B4C are disposed in an identical wrapper tube. A probability of causing nuclear fission when the minor actinoids absorb neutrons is increased, to promote an annihilation effect of long life nuclides due to conversion of minor actinoids to fission products. In addition, during normal reactor operation, neutrons from the reactor core fuels are absorbed to fertile materials and monitor actinoids of the TRU blanket fuel elements. Further, when a coolant density is reduced due to loss of coolants or occurrence of voids, a ratio of neutrons absorbed to the neutron absorbent is increased, to reduce a coolant void reactivity, thereby enabling to improve reactor safety. (N.H.)