Fission product release and fuel behaviour in tests of LWR fuel under accident conditions

Experiments carried out at Oak Ridge National Laboratory have contributed to the understanding of fission product release and fuel degradation under LWR accident conditions and also to the identification of the chemical forms of the released species. This work, sponsored by the United States Nuclear Regulatory Commission, has emphasized tests of commercial LWR fuel, but has included tracer-level tests using specific fission product species. The fuel specimens were heated in an induction furnace in flowing steam for periods of approx. 20 min at temperatures up to 2000 deg. C. Released material was collected and analysed both on-line and after the test. The fractional releases of Kr, I and Cs varied with temperature, up to a maximum of approx. 55%; the release rates varied between 30 and 100% of published values. Release of tellurium was found to be strongly dependent on the extent of cladding oxidation, indicating the existence of a Zr-Te alloy or compound. Studies of the fuel and cladding microstructures showed a correlation between the amount of fuel porosity and the fractional release of volatile fission products. (author)