IMPROVEMENTS IN OR RELATING TO NUCLEAR FUEL COMPACTS OF COATED PARTICLE FUEL

1282454 Fuel material UNITED KINGDOM ATOMIC ENERGY AUTHORITY 13 April 1970 [11 July 1969] 35156/69 Heading G6C A nuclear fuel compact comprises a plurality of fuel particles, each having a fission product retaining coating, distributed in a firm matrix material incorporating a polymerized bonding agent. It is formed by applying to each of a number of coated particles an overcoating of the matrix material with its bending agent in an unpolymerized condition, placing the particles in a die cavity with a layer of matrix material containing unpolymerized bonding agent disposed against at least some surfaces of the cavity, such that the coated fuel particles adjacent these surfaces are separated from them by a layer of matrix material of a thickness greater than that of the overcoating on these particles, pressing the particles in the cavity whilst heating them to melt the bonding agent and maintaining the pressure whilst further heating the cavity contents to polymerize the bonding agent. The layer of matrix material may be in the form of a preformed coupon placed on one or more surfaces of the die cavity to reduce the effect of particles protruding through their overcoating. In the preferred embodiment, an annular coupon was placed in the base of an annular cylindrical die cavity and a second annular coupon between the particles in the cavity and an annular punch inserted into the die. The coupons were of the same material as the overcoating, e.g. graphite powder in admixture with phenolformaldehyde resin. The contents of the die were raised to 100‹ C., at which temperature the resin was plastic and subjected to a pressure of 2000 p.s.i. Then the temperature was raised to 180‹ C., at this pressure, to polymerize the resin. The buffer layer of matrix material may alternatively be provided by an extra thick overcoating on those coated particles lying adjacent the die cavity surfaces, or it may be provided by a layer of microspheres of matrix material, without fuel, disposed adjacent the die vavity surfaces. As a further alternative, a layer of powdered matrix material may be placed between the overcoated particles and the surfaces of the cavity. In all cases the buffer layer incorporates unpolymerized resin bonding and becomes a part of the formed compact.