PURPOSE: To reduce the integrated discharge amount of a gaseous nuclear fission products (FP) at a high burnup, and to suppress its rapid swelling at the output increasing time, by adding a specific amount of oxide having Ti and Si as the main component or an oxide having Ti, Si, and Al as the main component to a nuclear fuel pellet, so as to make the mean crystal grain diameter a specific value or higher.

CONSTITUTION: This nuclear fuel pellet includs an additive which consists of an oxide having Ti and Si as the main component, or an oxide having Ti, Si, and Al as the main component. A titania silicate (Ti-Si-O) powder of 0.25wt% in the weight part ratio and a uranium deoxide powder are mixed to form a cylindrical compact, and it is sintered at about 1700°C in a reduction ambiance for about 4h, so as to obtain a nuclear fuel pellet in which a phase 9 which consists of Ti-Si-O is precipitated on the crystal grain field of a nuclear fission substance 8. Since the mean crystal grain diameter of the pellet is made about 50μm or more, the atomic composition ratio {Ti/(Ti+Si)} is made about 0.3 or more. In the pellet of the crystal grain diameter about 50μm or more obtained in such a way, the FP gas discharge ratio is reduced lower than the conventional one, and in the pellet of the crystal grain diameter about 95μm or more, the FP gas discharge ratio is made less than half that of the conventional one.