Nuclear Fuel Coated Particle Development in the Reactor Fuel Element Laboratories of the U.K. Atomic Energy Authority

Abstract

The objectives of the coated particle development program at the Reactor Fuel Element Laboratories (RFL) have been to define the essentials of a production route for the manufacture of nuclear fuel kernels and coated particles and to identify the important process parameters that determine the particle properties and hence the irradiation performance. Detailed characterization assessments of the various components of the coated particles have enabled a number of advanced coated particle designs to be optimized. The versatility of the RFL powder agglomeration process for the fabrication of highly spherical carbide or oxide kernels is exemplified by its ability to produce virtually monosized kernels in the range from 200 to 1000 ..mu..m in diameter, with controlled porosities in the range from 5 to 20 percent and the facility with which solid fission product and oxygen getters may be incorporated. The principles of the RFL pyrocarbon (PyC) and silicon carbide (SiC) coating processes, together with the experience of coating particles on a large--kernel batch sizes up to 25 kg--have been delineated. The understanding of the important parameters controlling deposition processes has led to optimum specifications for coater design and process route such that high sphericity is maintained throughout coating with a minimummore » spread in coat properties. More recent detailed investigations of process variables have identified the factors controlling PyC microstructure and the effect that coat defects and substrate shapes have on the ability of SiC to contain the gaseous fission products released by the fuel kernel during in-reactor operation. The proportion of defective particles is reduced by establishing process specifications to minimize coating-kernel bonding and misshapen kernels.« less