GB1011348A - Improvements in or relating to nuclear fuel materials - Google Patents

Abstract

1,011,348. Nuclear fuel materials. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Oct. 26, 1964 [Oct. 28, 1963], No. 42407/63. Drawing to Specification. Heading G6C. A nuclear fuel particle comprises a hollow centre bounded by a wall of a refractory material in which fissile and/or fertile material is dispersed. A method of making such a particle in which the fuel material is UC 2 including ZrC as a diluent is to first form a pellet of 100 to 200 microns diameter from the mixed carbides and to coat this pellet with pyrolytic carbon by a conventional fluidized bed process, the coating comprising two layers separated by a discontinuity. If, by way of example, the initial layer is of laminar structure, then the outer layer may be of columnar structure. A number of such pellets are incorporated in a matrix of carbon granules by being mixed with powdered carbon and a binder, compacted by applying light pressure and sintered to form a coherent mass. The whole body is then placed in a graphite tube resistance furnace wherein an inert atmosphere is maintained and heated at a uniform rate up to 2400‹ C. whereupon the matrix, but not the pyrolytic carbon coatings, is graphitized. The temperature is then raised to above 3000‹ C. for half a minute, i.e. a temperature above the m.p. of the UC 2 but below that of the matrix. The UC 2 diffuses into the inner coating layer but the discontinuity between the inner and outer layers inhibits much, if not all, further outward diffusion of the UC 2 . The space left by the outward diffusing UC 2 becomes the hollow centre of the resulting particle. It is not necessary to incorporate the coated pellets in a matrix of carbon or graphite and the method described may alternatively be taken as far as the application of the two layers of pyrolytic carbon, whereupon other pellets are placed in a pot of refractory material, preferably carbon or graphite, and heated to above 3000‹ C. as before in a graphite tube resistance furnace. The particles so formed are preferably given a coating of pyrolytic carbon at low temperature by a conventional fluidized bed process and may then be incorporated in a fuel bearing component of any desired form. The invention is applicable to other fuel and refractory materials and, by way of example, pellets of UO 2 may be coated with Al 2 O 3 , BeO or Nb, possibly also further coated with carbon or other refractory materials, and then incorporated in a suitable refractory matrix material either before or after being heated to a temperature above the m.p. of the UO 2 .