Design and commissioning of the exhaust detritiation system for the Large Helical Device

The Large Helical Device (LHD) is the largest helical fusion test device with superconducting magnets. During deuterium plasma experiments using the LHD, tritium and neutrons are produced by the deuterium-deuterium reaction. Thus, an exhaust detritiation system (EDS) using conventional oxidation-adsorption tritium removal was designed and installed to ensure safe tritium handling and public acceptance. The EDS consisted of a vacuum exhaust gas processing system for deuterium plasma experiments and a maintenance purge gas processing system for LHD maintenance. The vacuum exhaust gas processing system used molecular sieves as the dryer unit, whereas the maintenance purge gas processing system used a polymer permeable membrane. The key technique for receiving the complex exhaust gas stream from the LHD was feedback control of the pressure in the piping line to keep the process flow constant. To validate the recovery performance and feedback control system for the EDS prior to using deuterium gas, we used hydrogen gas to simulate tritium gas and actual exhaust gas stream from the LHD. The specified hydrogen recovery rate of more than 95% was satisfied and the actual complex exhaust gas stream was received by the proposed feedback control system in the EDS.