Changing Mechanisms of High-Temperature Oxidation of Zr-1%Nb Alloy in Air and Steam by Surface Modification with Charged Particles

The Zr-1%Nb alloy is widely used as a structural material for nuclear fuel assemblies of light water reactors. One of its key properties is the behavior upon a possible loss-of-coolant accident (LOCA) that can be changed by the surface modification procedures. This paper presents the research results on the effects of both high-intense pulsed ion beam (HIPIB) irradiation and high-current pulsed electron beam (HCPEB) processing on the kinetics of its oxidation at 1200 degrees C in air and steam, similar to the LOCA conditions. HIPIB irradiation led to more uniform reliefs on the sample surfaces but did not change their phase composition. However, both a and c lattice parameters decreased slightly with a simultaneous increase in microstrains. After HCPEB processing, the general patterns of changes in the modified surface layers were similar, but microcracks were found in some areas. In all studied cases, weight gains were greater after oxidation in air than those in steam. Nevertheless, diffusion of oxygen and the formation of scales occurred more slowly in the modified surface layers due to their distorted crystal lattices. The main reason for the variations was different physical processes that had occurred when the surfaces had been modified with charged ions and electrons.