ABSTRACT
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 postulated faults at temperatures below 1000°C, the most severe are those involving air atmospheres. Under these conditions oxidation is rapid, the cubic UO2 lattice is converted to orthorhombic U3O8, resulting in the loss of structural integrity of the fuel and enhanced fission product release.
Apparatus has been constructed at the Harwell Laboratory capable of heating fuel in a variety of gaseous environments at temperatures up to 1600°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 analysed by gamma spectroscopy and beta counting techniques.
Fractional releases of fission products from Advanced Gas-cooled Reactor fuel, air oxidised to U3O8, in the temperature range 300–600°C have been determined. Current studies are investigating the release kinetics under the same conditions, with particular emphasis on the transport and plate-out characteristics of volatile ruthenium species.
