TRITIUM PERMEATION, CONTAMINATION AND DECONTAMINATION

The objective of this study is to gain an understanding of tritium (T)-material interactions to minimize uncontrolled tritium emissions from fusion reactors. The main chemical forms of T permeating steel pipes are HT and HTO, and the latter has a far higher risk of internal exposure. We found that the fraction of HTO was able to be reduced by reducing surface coverage of Fe hydroxides. Developments of wet-chemical methods to prepare ceramic permeation barrier coatings enabled reduction in permeation rate to 1/104. Retention of T in tungsten being a leading candidate of plasma-facing material was found to increase significantly with neutron irradiations. Important parameters for assessment of T inventory in a reactor core such as binding energy between T and radiation defects were quantitatively evaluated. Heat treatments under the presence of H and/or D were proposed for efficient decontamination of neutron-irradiated tungsten.