HYDROGEN INGRESS INTO OXIDIZED ZR-2.5NB

Deuterium (D) distributions in D2O-corroded Zr-2.5 wt% Nb samples have been measured for three different corrosion temperatures: 763, 673 and 573 K. The oxide thickness and details in the D profile for 763 K show considerable variation due to changes in surface preparation. Nevertheless, the D concentration in the central part of the oxide is within 0.002-0.005 D/Zr atomic ratio. At lower temperatures - 673 K and below - the D concentration is somewhat higher: approximately 0.01 D/Zr. These concentrations are less than the 2-5% level observed with Zircaloy-2 after corrosion at 763 K. D distributions in O2-oxidized Zr-2.5 wt% Nb have been measured following a subsequent exposure to either D2 or D2O exposure at 573 K. D ingress into the metal is enhanced with D2 compared to D2O, supporting the expectation that reducing conditions (D2) may lead to a degradation of the protective oxide. Evidence is presented that two different diffusing species are responsible for the different D distributions measured in the oxide for the two types of exposure.