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

Fractional release rates of relatively low volatility fission products from fuel have been measured at the Sascha facility at Karlsruhe, Federal Republivc of Germany, and elsewhere as a function of fuel temperature. A mass transfer model was developed to calculate these release rates. Of six materials (fission products or fission product oxides) analyzed at temperatures from 1800 to 24000C, favorable comparisons between experiments and theory were obtained for silver, antimony, ruthenium, BaO, and ZrO/sub 2/, while insufficient experimental data were available for SrO. The favorable comparison for the five materials provides a strong argument that vaporization mass transfer is controlling the release rate for certain low-volatility fission products