Fission Product Release During UO2 Oxidation

Abstract

As part of a general program on fission product source term research we have measured the release of fission products from UO₂ oxidized in air. Three types of measurement were made: volatile fission products carried in the gas stream, condensible fission products deposited in the thermal gradient of the furnace tube, and direct measurement of non-volatile fission products which remained with the oxidized UO₂.

Xenon, cesium and iodine were detected in the gas stream. Cesium and iodine also deposited in the thermal gradient of the furnace tube. They were released from the fuel independently, not as CsI. Ruthenium was also deposited, as an oxide, within the thermal gradient. Release was strongly dependent on the oxidation temperature and by 1100°C 100% of these fission products were released.

Reactive elements such as barium and the rare earths did not move from the fuel, probably because they reacted with oxygen to form highly stable, high melting point, oxides.