FUEL ELEMENT DEVELOPMENT PROGRAM FOR THE PEBBLE BED REACTOR. Quarterly Progress Report for November 1, 1959 to January 31, 1960

A variety of spherical uranium--graphite fuel elements for the Pebble Bed Reactor (PBR) was fabricated. Poor results with sintered alumina coated UO/ sub 2/ particles led to the development of slumina coating by vspor deposition, for which good results have been obtained. A variety of sub-surface metal, metal carbide, and ceramic coatings located between an unfueled graphite shell and the fueled core of a PBR fuel element was prepared and examined. Most of the materials and processes showed poor results. Excellent metal recoveries were achieved from the metal oxide--graphite system using the grind-leach technique of reprocessing. Test results on Si-- SiC coated fuel elements showed good fission product retention in neutron activation tests, a self-welding tendency between adjacent spheres at 2500 deg F surface temperature, and no evidence of failure when an interanl gas pressure of 300 psi was applied. Fission product release rates from a pyrolytic carbon coated specimen under low-level irradiation were obtained at 150 to 1900 deg F. The design of the in-pile loop to study the behavior of fission products escaping from PBR fuel elements wss established. (C.J.G.