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 an d 573 K. The oxide thickness and details in the D profile for 763 K sh ow considerable variation due to changes in surface preparation. Never theless, the D concentration in the central part of the oxide is withi n 0.002-0.005 D/Zr atomic ratio. At lower temperatures - 673 K and bel ow - the D concentration is somewhat higher: approximately 0.01 D/Zr. These concentrations are less than the 2-5% level observed with Zircal oy-2 after corrosion at 763 K. D distributions in O2-oxidized Zr-2.5 w t% 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 pr esented that two different diffusing species are responsible for the d ifferent D distributions measured in the oxide for the two types of ex posure.