Estimation of tritium inventory in exhaust detritiation system for fusion test device in the initial tritium recovery operation

As one of the radiation safety issues at nuclear fusion facilities, the development of the tritium handling technique is indispensable. A small amount of tritium is produced by the deuterium plasma experiment in a large fusion test device and is exhausted from the vacuum vessel. From the viewpoint of radiation safety and public acceptance, tritium in the exhaust gas could be recovered by the exhaust detritiation system (EDS). Most of the tritium recovered by EDS is stored in the wastewater tanks as tritiated water. Then they are fractionated into the wastewater containers for delivery to the Japan Radioisotope Association once a year. However, some of the tritiated water would have remained in EDS. The residual tritium would be the issue of the dismantlement of EDS in the future. Thus, the amount of residual tritium in EDS was estimated in the initial tritium recovery operation. Since most of the wastewater containing tritium remains in the storage tanks, the residual wastewater was the main tritium inventory. Also, the tritium in the molecular sieve used in EDS was estimated to be less than 0.1 GBq. Thus, the decontamination of molecular sieves would be preferred when dismantling the EDS.