Fission product source terms for LOCAs and hypothetical core melt-down accidents

This paper describes two experimental projects for the study of fission product release at different boundary conditions. By the work done at Oak Ridge until now the temperature range of the loss-of-coolent accident (500-12000C) is covered; in additional experiments this range is extended to 16000C. The results obtanied are of special importance for the fission products Cs and I, for they mean to say that the release at 12000C is lower by the factors of 200 respectively 60 than assumed in the Rasmussen Report. For the calculation of the source term for these elements a semiempirical model was developed, well describing the experimental results from several series of experiments despite much different boundary conditions. In the PNS experimental program the release for hypothetical core melt-down accidents in the temperature range between 1200 and 27000C is studied. With the melt-down facility SASCHA, described in this paper, for the first time experiments can be performed at realistic boundary conditions with melted masses of up to at least 1 kg. Set up and development of the experimental technique taking several years, for the present there are not enough experimental data available for the calculation of the integral source term under core melt-down conditions. Nevertheless the release in air for about a dozen elements and melted masses of 30-300 g could be determined. (orig.)