Nuclear fuel pellets

Purpose: To reduce the discharging amount of nuclear fission gases and suppress the deceleration of creeping rate. Constitution: In conventional nuclear fuels, pellets comprising crystal grains of substantially constant grain size have been used. If the crystal grain size is large, while the discharging amount of fission gases is reduced at high burning, the creeping rate is decreased, by which pellets are swollen and put into contact with a fuel can thus leading to the destruction of the can. In view of the above according to this invention, a plurality of small crystal grains with the average grain size of less than 20 μm are disposed around large crystal grains with the average grain size of greater than 30 μm. While fissionable gases are formed along with the burning, the discharge of the fission gases is reduced by the large grain size particles to prevent the abnormal increase of the inner pressure in the fuel can. While on the other hand, the creep rate is suppressed by small size of grains at the periphery to prevent the swelling of pellets to eliminate the problems of pellet-fuel can interaction. (Kamimura, M.)