Tritium contamination and decontamination study on materials for ITER remote handling equipment

Several materials, lenses, dry bearings and cables were exposed to a tritiated moisture environment to study the behavior of tritium contamination on candidate materials for ITER remote handling equipment. To optimize the tritium removal procedure, decontamination experiments using a gas purge with three different moisture concentrations were also performed. The surface tritium concentrations of CeO2 containing alkaline barium glass (NB), CeO2 containing lead glass (LX) and synthetic quartz (Quartz) after the exposure experiments were 7.80, 10.94 and 0.67 Bq/cm2, respectively. It was found that the tritium concentration was influenced by the compositions of the materials. The concentrations of tritium on type 831 (solid lubrication material: graphite) and type 237 (solid lubrication material: tungsten disulfate) dry bearings after the exposure experiments were 89.80 and 31.78 Bq/cm2, respectively. The tritium concentration in an electric cable tested was 5014 Bq/g after HTO moisture exposure. The tritium concentrations of lenses, LX, as typical experimental results, decreased to 2.72, 4.42 and 3.89 Bq/cm2 by purging with the moist air, dry air and dry N2, respectively. The tritium concentrations of dry bearing, type 831 dropped to 6.61, 9.42 and 10.16 Bq/cm2 by the same three decontamination treatments, respectively. A large decontamination factor of 13.6 was achieved in the case of type 831 dry bearing with a moist air purge. The tritium concentration in the electric cable was 3236 Bq/g after a moist air purge, and the decontamination factor was as low as 1.6. Therefore, decontamination with a moist air purge is not so effective for the electric cable.