Fuel particles having pyrolitic carbon coating for nuclear reactors and the manufacture of such fuel

Particle fuel, such as is used in high temperature nuclear reactors, and having the fuel material coated with a pyrolytic carbon coating impermeable to gaseous fission products and embedded in a matrix of graphite, incorporates radium 226 which may be included in the binder for the rains of the fuel. During the manufacturing process, the integrity of the pyrolytic carbon coating can be checked before irradiation in a reactor by circulating an inert gas such as argon over the particles at a temperature in excess of 8000C. This may be carried out in the final carbonization step during manufacture or immediately before vacuum degassing. The inert gas after passing over the particles is checked for the presence of radon 222, for example by passing the gas into a decay chamber having a filter in its outlet to collect radioactive solid daughters of radon and counting the alpha particles emitted by the material collected by the filter. It is thus possible to test the integrity of the pyrolytic carbon coating before the fuel is irradiated