Fission Products Release from Irradiated FBR MOX Fuel during Transient Conditions.

Out-of-pile experiments on the release of fission products (FPs) under transient heating conditions were carried out for mixed oxide fuels. The fuels used in the experiments, the plutonium content of which was 30 wt%, were irradiated up to 65 GWd/t in the experimental fast reactor JOYO. The experiments consisted of two runs, FP-1 and FP-2. In FP-1, the fuel sample was first heated to 2,000degreesC and then up to 3,000degreesC. The holding time was 30 min at each temperature. In FP-2, the terminal temperatures were 1,500degreesC and 2,500degreesC, and the holding time was 30 min in the same manner. The release of Cs, a volatile FP, was detected as soon as the fuel sample was heated up. The release rate, after peaking in several minutes, decreased gradually via a diffusion process in the fuel matrix. The "gross" diffusion coefficient agreed well with the data reported in other experiments using LWR fuels. The release fractions were identical in both experiments, namely Cs similar to 100%, Sb similar to 100%, Ru similar to 10%, Ce similar to0% and Eu similar to0%.