Reactor core for FBR type reactor

In a reactor core of an LMFBR type reactor, a reactor core region is constituted with a reactor core corresponding region of a high Pu enriched reactor core fuel assembly or a first internal blanket fuel assembly and a reactor core corresponding region of a low Pu enriched reactor core fuel assembly or a second internal blanket fuel assembly in order to improve the breading performance, flatten the axial power distribution and reduce the maximum neutron irradiation dose. The respective regions are distributed in the radial direction of the reactor core region to constitute a not homogeneous reactor core. Since the high Pu enriched region and the low Pu enriched region or the blanket regions are distributed in the reactor core, it is possible to flatten the axial power distribution and increasing the multiplication factor. Further, it is possible to prevent the progress of accidents upon fuel meltdown accident to decrease sodium voids. In addition, thermal striping can be moderated and it is possible to make the reactor core compact or reduce the peaking power. (N.H.)