Exposure to Tritiated Moisture and Decontamination of Components for ITER Remote Maintenance Equipment

Typical materials and elements such as carbon steel, grease lubricant, electric cable and AC servomotor for the ITER remote maintenance equipment were exposed to a tritiated moisture environment to choose the appropriate materials from the viewpoint of tritium contamination / decontamination and to contribute to the structural and maintenance design of the remote maintenance equipment. After the test samples were exposed, the concentrations of tritium adsorbed on the samples were measured and decontamination experiments using gas purges with three different moisture concentrations were performed. It was found that metallic oxidized layer (Fe₃O₄ coated on S45C, slightly rusted SS400, rusted Cu of electric connector of the AC servomotor) adsorbs larger amount of tritiated moisture. Grease lubricant was highly contaminated in proportion to the exposed surface area of the pasted layer. Cable jacket (cross-linked polyethylene) was also highly contaminated in spite of hydrophobicity. This is probably because the jacket contains the filler “white carbon (SiO₂·nH₂O)” which adsorbs large amount of moisture. Internal parts of the AC servomotor were contaminated in the same level as the outer surface, because tritiated moisture goes into the inside through the sealing gap between casing and brackets.