A MODEL FOR NONVOLATILE FISSION-PRODUCT RELEASE DURING REACTOR ACCIDENT CONDITIONS

An analytical model has been developed to describe the release kinetic s of nonvolatile fission products (e.g., molybdenum, cerium, ruthenium , and barium) from uranium dioxide fuel under severe reactor accident conditions. This treatment considers the rate-controlling process of r elease in accordance with diffusional transport in the fuel matrix and fission product vaporization from the fuel surface into the surroundi ng gas atmosphere. The effect of the oxygen potential in the gas atmos phere on the chemical form and volatility of the fission product is co nsidered. A correlation is also developed to account for the trapping effects of antimony and tellurium in the Zircaloy cladding. This model interprets the release behavior of fission products observed in Commi ssariat a l'Engerie Atomique experiments conducted in the HEVA/VERCORS facility at high temperature in a hydrogen and steam atmosphere.