Nuclear fuel element

Object: To provide sintered nuclear fuel pellets subject to less strain during high temperature sintering and to prevent damage to tubular clad. Structure: The instant nuclear fuel element comprises a plurality of cylindrical sintered nuclear fuel pellets stacked one above another within a tubular clad in the axial direction thereof and each provided with ring-like grooves formed at opposite ends. As the linear output density of fuel progressively increases with the sintering of the nuclear fuel element, with low linear output density the center of the nuclear fuel pellet is hard and has high coefficient of thermal expansion, so that contact pressure between adjacent pellets is concentrated at the center of the end face. With an intermediate linear output density plastic deformation is produced at the center of the nuclear fuel pellet, so that the contact pressure is dispersed from the center toward the edge. With high linear output density the contact pressure is dispersed by the groove, so that the strain radial of the nuclear fuel pellet is held at a minimum