Nuclear fuel assembly

In FBR type reactors, fuel boundle-wrapper tube interaction (BDI) is caused, particularly, near the axial center of the reactor core due to irradiation swelling and creeping. Accordingly, in the present invention, a portion of fuel rods are constituted such that depleted uranium pellets are disposed near the axial center of the reactor core. Further, fuel rods not disposed with depleted uranium pellets near the axial center of the reactor core are disposed such that they are not in adjacent with each other at least in the radial peripheral portion. Thus, even if fuel rods are brought into contact each other by BDI, abrupt temperature rise of fuel cans can be moderated. Further, occurrence of the fuel can failure can remarkably be reduced, to improve the safety. (T.M.)