Nuclear assembly

Purpose: To decrease unevenness in the Temperature of coolants inside of nuclear fuel assemblies, as well as decrease the pressure loss in the coolants. Constitution: In a nuclear fuel assembly for an lmfbr type reactor, a plurality of nuclear fuel rods are contained approximately in an equal pitch in an outer enclosure, and an upper and a lower blancket fuels each mainly consisting of U-238 are provided at the upper and the lower portion in the axial direction of core fuels respectively. The lower blancket fuel sections at the upstream of the coolant flow are arranged coarsely near the center of the fuel rod bundle and densely at the periphery thereof. (Furukawa, Y.)