Patent Number: 056423900
Section: abstract

A uranium-containing nuclear-fuel sintered pellet containing UO.sub.2, (U, Pu)O.sub.2, (U, Th)O.sub.2, (U, RE)O.sub.2, (U, Pu, Th)O.sub.2, (U, Pu, RE)O.sub.2, (U, Th, RE)O.sub.2 or (U, Pu, Th, RE)O.sub.2, wherein RE=rare earth, has a sintered-pellet surface layer being formed of at least 80% by volume of a chemical boron compound UB.sub.x or (U, . . . )B.sub.x, wherein x=2;4;6 or 12, and a remainder of the sintered pellet containing at most 5% by volume of the chemical boron compound. A nuclear-reactor fuel assembly has a fuel rod containing such a uranium-containing nuclear-fuel sintered pellet in a cladding tube with the boron as a burnable absorber for thermal neutrons. The surface layer having the chemical boron compound is obtained by treating the nuclear-fuel sintered pellet with boron or a boron-containing chemical compound at an appropriately high treatment temperature.