Search

In-pile release of 85mKr, 87Kr, 88Kr, 133Xe, 135Xe and 138Xe from natural graphite was measured over a temperature range of 100 to 950°C and that of 133I and 135I was estimated. The effects of fission rate and fission density on the fission gas release were examined. The β-decay process of iodine within and outside the graphite was observed to control the gross release of xenon. Possible mechanisms of an anomalous sink of 88Kr in the plot of log R B versus log λ were discussed. A new model for knock-out release was proposed on the basis of its temperature dependence found. These results were compared with those of post-irradiation experiments and explained by a mechanism whereby fission gas is trapped in defects created in graphite by fission and β-decay energy, and released through annealing of the defects.

Improvements made on the Fission Gas Release Loop from 1965 to 1970 are reported. These include the development and installation of a cartridge-type specimen chamber, an automatic flow controller and an automatic sampling-measuring equipment, as well as the installation of oxygen and water vapor analyzers. The performance of the safety systems during loop operation are also described.

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.