Tritium permeation through Inconel 600 under high temperature, high pressure water environment: Influence of oxidation of coexisting materials and gas addition

• The permeation of tritium through an Inconel 600 sample was examined under exposure to tritiated water at 280 °C and 6.4 MPa. • The presence of a metallic material with high oxidation rate in the system resulted in high tritium permeation rate via generation of H 2 and HT molecules. • The permeation rate significantly increased with H 2 gas addition and decreased by O 2 gas addition. • The control of partial pressures of H 2 and HT gases is a key to control tritium permeation rate. Tritium (T) permeation through steam generator piping from the primary to the secondary side of a water-cooled breeding blanket system increases a risk of exposure of workers and members of the public. From this viewpoint, the T permeation through Inconel 600, a candidate material of steam generator piping, under exposure to tritiated water was examined at 280 °C and 6.4 MPa by focusing attention on the influence of oxidation of coexisting materials and that of H 2 and O 2 gas addition. The T permeation rate through Inconel 600 sample was sensitively dependent on the oxidation rate of coexisting material, and a high permeation rate was observed with a material with high oxidation rate. The H 2 gas addition also resulted in a remarkable increase in T permeation rate, while the O 2 gas addition led to clear reduction. These observations indicated that HT generated by the oxidation of coexisting material by HTO and the isotope exchange reaction between HTO and H 2 gas (HTO + H 2 → H 2 O + HT) contributed to the permeation. Reduction in T permeation in a steam generator appears possible by minimizing oxidation of coexisting materials in the primary loop and/or continuous O 2 gas supply.