Tritium retention behavior in tungsten exposed to off-normal plasma condition

A first series of experiments concerning off-normal plasma event were performed under the US-Japan collaboration program. The off-normal plasma event was simulated by introducing nitrogen gas into DT plasma. Tritium retention amount and thermal desorption behavior of tritium from tungsten exposed pure DT plasma and nitrogen introduced DT plasma was investigated as a function of nitrogen flow rate. As a result, it was found that tritium retention increased and tritium release temperature rose with increasing nitrogen flow rate. Surface analysis by XPS was also carried out for tungsten specimens after the thermal desorption. Effective chemical change on the surface chemical composition or chemical state was not observed between DT and nitrogen introduced DT plasma.