LMFBR type reactor

Purpose: To flatten the power distribution for each of the fuel assembly groups in the reactor core. Constitution: Circular assembly pattern is formed by disposing a fuel assembly group using core fuel pellets having a lower plutonium enrichment degree about in the central region of an lmfbr type reactor disposing coaxially to the outer side a fuel assembly group having the same degree of plutonium enrichment and of higher axial core height, disposing further outside thereof a fuel assembly group having a plutonium enrichment degree higher than that of the latter fuel assembly group and of a substantially same core axial height, and disposing a fuel assembly group having a higher core axial height than that of the above fuel assembly group. In the arrangement above, inner and outer blancket assembly groups are provided to each of the assembly groups. (Furukawa, Y.)