Role of hydrides on the oxidation and deuterium pickup of Zr-2.5Nb in D2O at 573 K

This study was initiated to determine the role of hydrides on the oxidation and D-pickup rates of Zr-2.5Nb pressure tubes used in CANDU®1reactors. Coupons of Zr-2.5Nb pressure tube material were charged to H concentrations ranging from 5 to 800 mg H/kg metal. A continuous layer of hydride was also introduced on the surface of some coupons. Tests were conducted in lithiated D2O at 573 K for about 4 years. The coupons were removed at certain intervals for oxide thickness, D-pickup and various other evaluations such as metallography. All the coupons, except those with a surface hydride layer, showed comparable oxidation and D-pickup rates. The coupons with a surface hydride layer showed oxidation and D-pickup rates of about a factor of two higher than the other coupons. These findings, as well as results from the other examinations are reported in this paper.