Fission product release during the air oxidation of irradiated uranium dioxide

The ability to predict accurately the fractional release of fission products from nuclear reactor fuel during severe faults is important when assessing safety implications for the nuclear industry. Of the postulate faults at temperatures below 1000 degrees C, the most severe are those involving air atmospheres. Under these conditions oxidation is rapid, the cubic UO2 lattice is converted to orthorhombic U3 O8, resulting in the loss of structural integrity of the fuel and enhanced fission product release. Apparatus has been constructed capable of heating fuel in a variety of gaseous environments at temperatures up to 1600 degrees C. The furnace and associated glassware can accommodate approximately 100g of highly irradiated fuel, either as bare fragments or clad pellets. Volatile fission products are collected on thermal gradient tubes, particulate filters and traps which are subsequently quantitatively analyzed by gamma spectroscopy and beta counting techniques. Fractional released of fission products from advanced gas-cooled reactor fuel, air oxidized to U3 O8, in the temperature range 300-600 degrees C have been determined