Nuclear fuel assembly

Purpose: To improve the reactor stability by reducing the power at the lower region in the axial direction to decrease the void coefficient and reduce the pressure loss coefficient. Constitution: In a fuel assembly containing nuclear fissible materials as fuels and comprising fuel rods assembled in a lattice-like manner, the enrichment degree of fuels in each of 3 regions as divided along the axial direction of the reactor core is specified from above as e1, e2, e3 (e1>e2>e3). The region e3 is set to a range for 1/20 - 1/4 of the reactor core height from the core bottom. In such a constitution, since the axial power distribution can be flattened and the power at the lower region can be reduced, the void generation point in the axial direction can be transferred upwardly. Accordingly, the void coefficient can be decreased and the pressure loss coefficient can also be reduced. (Aizawa, K.)