FISSION PRODUCT RELEASE FROM UO$sub 2$ BY HIGH TEMPERATURE DIFFUSION AND MELTING IN HELIUM AND AIR

Experiments on the oxidation of UC/sub 2/ to U/sub 3/O/sub 8/ in air were found to result in the release of a large portion of the volatile fission products, although some anomalous behavior was exhibited in the temperature region of 600 to 900 deg C. Melting studies performed in helium and in air yielded similar, nearly quantitative, releases of Xe-Kr, iodine, tellurium, ruthenium, and cesium. Particles obtained from the vapors were composed of 0.02- to 0.2- mu -diameter crystals of U/sub 3/O/sub 8/ from melts obtained in air and of 0.0075- to 0.03- mu spheres of UC/sub 2/ from melts obtained in helium. High- temperature out-of-pile diffusion studies on sintered UC/sub 2/ compacts in high- purity flowing helium yielded rare-gas release rates similar to those obtained by other experimenters with vacuum type anneals. The energy of activation obtained from an average of all helium-diffusion experiments is 70 kcal/mole. Simultaneous measurements of the release of the principal fission products showed that two to three times as much iodine and tellurium diffuse out of UC/sub 2/ in helium as do the rare gases. Cesium and ruthenium diffuse somewhat less than the rare gases, and strontium diffuses much less than the rare gases.more » (auth)« less