Manufacturing method for nuclear fuel pellet

Molybdenum powders are mixed to nuclear fuel powders comprising uranium oxide or a mixed oxide of uranium dioxide and plutonium dioxide, compression molded, sintered in a reducing atmosphere, and then, annealed in an oxidative atmosphere to convert molybdenum into oxide and caused to be present in a crystal boundary continuously. Then, it is annealed in a reducing atmosphere to reduce molybdenum oxide into metal molybdenum to be deposited in the crystal boundary. That is, metal molybdenum scattered in the nuclear fuel pellet is oxidized and melted into molybdenum trioxide having low melting point, and it covers the crystal grain boundary of the uranium oxide or the mixed oxides. Thereafter, molybdenum trioxide is reduced and metal molybdenum is deposited in the crystal grain boundary. Thus, the metal molybdenum acts as a getter for iodine generated in pellet crystals to reduce the stress corrosion cracks of the cladding tube. Further, thermal conduction rate of the pellet is improved by the molybdenum to lower the temperature of the pellet during reactor operation. (N.H.)