IMPROVEMENTS IN OR RELATING TO THE MANUFACTURE OF NUCLEAR FUEL ELEMENTS

1,249,156. Fuel elements. UNITED KING- DOM ATOMIC ENERGY AUTHORITY. 2 April, 1969 [22 April, 1968], No. 18985/68. Heading G6C. A fuel element is formed from fuel particles having a fission product retaining coating by the application of a further coating comprising 20 to 70% by weight of powdered graphite, the remainder being synthetic resin, and heating a mass of the particles in contact with one another to form an agglomeration of fuel particles. The particles are tumbled in a rotating drum with the resin-graphite powder mixture, e.g. a mixture, in equal proportions by weight, of powdered graphite and phenolformaldehyde resin powder, dusted on to the particles from a vibrating sieve. Every few seconds the vibration is halted so that the feed of powder is stopped and a short burst of a solvent for the resin, e.g. methylated spirit, is sprayed into the drum. After a layer of the desired thickness has been deposited, the alternate supply of powder and solvent is stopped and the tumbling continued until the particles are hard and dry. The particles are now ready for forming into an agglomerate either by a simple moulding process or by being poured with or without vibration into a cavity in a graphite body and cured in situ. In the case of an annular cavity, a thin polythene film is wrapped around the inner face of the cavity. The body is then heated to 200‹ C. in air to cure the resin and then placed in a furnace purged by a stream of inert gas and heated to 800‹ C. to carbonize the resin. A final heat treatment is carried out at 1800‹ C. in vacuum to degas the agglomerate. The polythene film decomposes during the heat treatment so leaving an annular clearance which allows the agglomerate to contract towards the axis of the body without cracking longitudinally.