In-pile release of fission gas from graphite

In-pile release of fission krypton, xenon and iodine from graphite was measured and the release mechanism is discussed in detail compared with the data of post-irradiation experiments. No temperature-independent release of fission gases and iodine was observed in the temperature range from 100 to 640 °C. After reactor shutdown with the specimen temperature constant, only xenon was released from the specimen and not krypton and iodine. To explain this phenomenon, a hypothesis is proposed that fission gas releases are induced by β-decay of precursor halogens trapped in defects in the specimen. By the hypothesis, the release behavior of fission gases and iodine can be explained satisfactorily.