In-vessel tritium inventory in ITER evaluated by deuterium retention of carbon dust

In order to estimate in-vessel tritium inventory of carbon dust, deuterium gas absorption and deuterium ion irradiation experiments were conducted for a carbon dust prepared by using electron beam evaporation for graphite. The retained amount of deuterium after the deuterium gas absorption was very low, D/C=10-3 in the atomic ratio. The retained amount of deuterium after the deuterium ion irradiation was very similar with that for graphite. The deuterium concentration becomes close to zero if the wall temperature at divertor wall region is higher than 1000 K. Co-deposited carbon dust was prepared by using a deuterium arc discharge apparatus with carbon electrodes at different gas pressure and substrate temperature. The co-deposited carbon dust had a largest deuterium concentration. In the ITER condition with gas pressure of 1 Pa and wall temperature of 573 K, the deuterium concentration in the atomic ratio becomes approximately D/C=0.2. In DT discharge, the tritium concentration in the atomic ratio becomes T/C=0.1. This value is presumed to be a highest concentration of carbon dust in ITER. The present result shows that the accumulation speed of in-vessel tritium inventory is lower than that predicted so far. (author)