IMPROVED TECHNIQUES FOR DISPERSING COATED FUEL PARTICLES IN CERAMIC BODIES

摘要

Coated fuel particles usually are oxidation resistant and retain fission products. The particles are normally dispersed within a ceramic matrix. A difficulty encountered in making dispersions is cracking of the coatings during blending and pressing. Two additional problems specific to oxide-base bodies are:(1) interference of the dispersed particles with densification of the matrix during sintering and (2) oxidative disruption of a body caused by progressive crack propagation through all particle coatings. These problems have been solved by use of a pelletizing technique. Each coated particle is over coated with a matrix material, either graphite or Al2O3. The spherical pellets are compacted and then heat treated. In oxide-base bodies, a burnout layer is incorporated into the pellet to allow room for matrix shrinkage on sintering, and to provide a void surrounding each particle. This void serves as a barrier to prevent a matrix crack from propagating into a particle coating, and also as a reservoir to contain the volume expansion associated with any oxidation of U02 to U308.