ORNL STUDIES OF FISSION-PRODUCT RELEASE UNDER LWR SEVERE ACCIDENT CONDITIONS

The large inventories of radioactive fission products in irradiated fu el represent the principal personnel hazards from nuclear reactors. A large fraction of the existing fission-product release data has been c ollected from experiments at Oak Ridge National Laboratory (ORNL). Tes ts of high-burnup light-water-reactor fuel, and also simulated fuel wi th fission-product tracers, have been conducted in an induction furnac e at temperatures up to 2 700 K. In addition to the total releases, on -line release data for Kr-85 and Cs-137 at 1-min intervals throughout the tests provided release-rate values. The most volatile fission-prod uct elements-krypton, iodine, and cesium-are released almost totally a t the highest temperatures, with little effect of atmosphere, but the releases of fission product strontium, molybdenum, ruthenium, telluriu m, antimony, barium, and europium are sensitive to atmosphere. Data fo r krypton and cesium releases have been used to develop the ORNL Diffu sion Release Model, a simple, single-atom model that reliably predicts the release of volatile fission products. Studies of transport behavi or and the chemical forms of released elements, as well as fuel melt p rogression, have been included also.