Observations of the Gas Stream from the Large Helical Device for the Design of an Exhaust Detritiation System

A small amount of tritium is produced by deuterium-deuterium reactions in the core plasma during deuterium plasma experiments conducted in the Large Helical Device (LHD). From the viewpoints of tritium safety handling and public acceptance, any waste gas streams arising from the vacuum vessel of the LHD and Neutral Beam Injection (NBI) system will be treated by an exhaust detritiation system (EDS). The exhaust gas stream produced during the 18th cycle of LHD plasma experiments was observed to design the EDS. The rough pumping gas streams from the LHD and NBIs produced a high flow rate of 300 Nm3/h. The vacuum exhaust gas stream from the LHD had a high hydrogen concentration more than 7% and a flow rate of less than 5 Nm3/h during plasma experiments. The regeneration gas stream of the cryopump systems had a flow rate of more than 5 Nm3/h. Based on these observations, the proposed EDS utilizes two types of tritium recovery system. One comprises two types of catalyst and dual absorbent beds. Other comprises an oxidation catalyst and polymer membrane system.