IMPACT OF INTERMETALLIC PRECIPITATES ON HYDROGEN DISTRIBUTION IN THE OXIDE LAYERS FORMED ON ZIRCONIUM ALLOYS IN A STEAM ATMOSPHERE - A D-2(HE-3,P)ALPHA NUCLEAR ANALYSIS STUDY IN MICROBEAM MODE

The aim of this study is to try and achieve a better understanding of the role of Zr(Fe,Cr)(2) and Zr-2(Fe,Ni) intermetallic precipitates in the hydrogen uptake mechanisms during aqueous corrosion of zirconium alleys at 400 degrees C. The deuterium distribution in the oxide layer s was studied by nuclear analysis using the D-2(He-3,p)alpha reaction in microbeam mode. The oxide thicknesses studied are between 0.7 and 1 .4 mu m. Preliminary results show that for oxide layers 0.7 mu m thick , the presence of a zirconium hydride is very often detected under the metal/oxide interface in the vicinity of a precipitate in the oxide. This correlation is not observed for oxide layers 1.4 pm thick. These results are interpreted as an indication of the role of precipitates a s hydrogen diffusion short-circuits through the zirconium layer, but o nly when these precipitates are metallic and still in contact with the metal, i.e., at the very early stages of oxidation. (C) 1998 Elsevier Science S.A.