Study on retention of hydrogen isotopes and helium in nickel using tritium beam test apparatus

In fusion reactors, a membrane of some metals, such as nickel, may be employed to enhance the pumping efficiency for helium ash because of its capacity to retain helium. In the present study, retention behavior of helium and hydrogen isotopes including tritium in nickel was investigated by means of thermal desorption spectroscopy (TDS), using a new beam irradiation system which is capable of handling tritium. In the thermal desorption spectra of helium (He), at least two helium desorption peaks were observed at 490–555 K and 715–740 K, where hydrogen isotope irradiations after helium irradiations were found to enhance the helium release and shift the desorption peak temperature to lower temperatures. However, the peak temperatures of helium desorption in helium irradiations after hydrogen isotope irradiation showed little difference from that without hydrogen isotopes irradiations. In the tritium experiments, tritium was supplied either directly from an ampoule or from a sorption pump to the vacuum chamber pumped by a cryopump. An ion beam of hydrogen isotopes containing tritium was irradiated to nickel at room temperature and the TDS spectra for DT and T 2 were obtained. It was revealed that both DT and T 2 have at least two desorption peaks, appearing at 410–425 K and 600–650 K for the former and at 500–520 K and 650–670 K for the latter.