Reactor core for LMFBR reactor

A reactor core region comprises a reactor core corresponding region of reactor core fuel assemblies and a reactor core corresponding region of fuel assemblies of low enrichment degree, in which the reactor core corresponding region of the fuel assemblies of low enrichment degree is radially dispersed in the reactor core region. That is, different from conventional axial inhomogenous reactor cores, the low Pu enrichment degree region is radially dispersed and the continuous low Pu enrichment degree regions which causes a problem upon occurrence of reactor core fuel meltdown accident are divided into small sections to enable to decrease the insertion reactivity. Further, the difference between the power of fuel assemblies of low enrichment degree and the power of reactor core fuel assemblies can be made smaller than the difference between the power of inner blanket fuel assemblies and the reactor core fuel assemblies to thereby moderate thermal stripping in reactor upper mechanisms. Further, since the reactor core fuel assemblies of low Pu enrichment are used in the inner blanket region against excess PCMI formed by accumulation of Cs in the upper boundary of the inner blanket, the integrity can be improved. (N.H.)