OXIDATION AND HYDROGEN UPTAKE OF ZR BASED NB ALLOYS AT 400-DEGREES-C UNDER 10 MPA H2O STEAM ATMOSPHERE

Abstract

Oxidation and hydrogen uptake of Zr based Nb alloys were studied as functions of Nb content and heat treatment in 400 degrees C H2O steam, and the results of the oxidation were compared to those obtained in 400 degrees C D2O steam. From the higher weight gain of the alloys in H2O steam than that in D2O steam, it is suggested that the oxidation rate of the alloys is controlled by cathodic reduction of the hydrogen ion. The changes of the weight gain and of percentage hydrogen uptake of the quenched and aged alloys with Nb content and heat treatment were discussed with respect to the aliovalent effects of Nb in matrix phase. The optimum alloy composition of the Zr-Nb binary system is proposed as the aged binary alloy less than 5 wt% Nb from the view points of weight gain, hydrogen uptake and microstructure.