Fuel for high temperature gas-cooled reactors

The fuel for high temperature gas-cooled reactors is composed of heat resistant materials such as carbon, graphite and ceramics without using metals, therefore, the safety is very high, high burnup is easily attained, and it is economically attractive in view of the utilization of thorium. The fuel is basically the minute fuel spheres of smaller than 1 mm diameter with four layers of carbon and carbide ceramic coatings. The coating layers are innermost buffer pyrolytic carbon (PyC) layer, high density PyC layer, SiC layer and outermost high density PyC layer. The buffer PyC layer protects the outer high density PyC layer from the damage due to nuclear fission recoil, and becomes the space for FP gas and CO gas. The other layers hold FP, and the SiC layer maintains the strength of a whole coated particle. A coated particle is formed into pellet, compact or ball shape by being mixed with graphite powder and phenol resin or pitch binder. The coated particle can hold FP inside even at 2000 deg C in a short time. The trend of development of the fuel for high temperature gas-cooled reactors in various countries, the behavior of the fuel, the improvement of the fuel and the disposal of spent fuel is reported. (K.I.)