Role of surface vaporization in low-volatility fission product release experiments

Source term analysis requires models for the release of relatively low-volatility fission products such as barium, strontium, ruthenium, etc. from fuel that may be present in debris beds following fuel melting. The objective of this paper is to provide a comparison between the fission product release rates obtained experimentally by Albrecht et al. at the SASCHA Facility at Karlsruhe with values calculated from a mass transfer model. Also, available data from the HI test described by Lorenz at Oak Ridge National Laboratory and one result from the relative volatility study are included in the comparison. This comparison may serve as a basis for determining the extent to which vaporization can be supported as the rate-controlling mechanism in the release of certain fission products from fuel particles. It is recommended that mass transfer correlations appropriate to the fuel or fuel debris geometry be used to calculate fission product release rates from such material in a severe reactor accident.