Deuterium diffusion in LiOH–water-corroded oxide layer of zirconium alloys

Abstract

In order to clarify the hydrogen diffusion mechanism in the oxide layer of zirconium alloys, in situ hydrogen isotope diffusion in the oxide layer has been examined. The zirconium alloys used were Zircaloy-2, GNF-Ziron (Zircaloy-2 type alloy with high iron content) and VB (zirconium-based alloy with high iron and chromium contents). They were corroded in 1 or 0.1M LiOH-containing water at 563K, producing oxide layers of 1.1–2.1μm in thickness. The diffusion experiments were carried out in the temperature range from 488 to 633K by using a combined technique of deuterium plasma exposure and nuclear reaction analysis for D (3He,p)4He reaction. From the transient deuterium profiles in the oxide layers, it was concluded the LiOH–water-corroded oxides had a single-layer structure, which was in contrast to the double-layer structure previously observed in steam-corroded oxide layers. The diffusion coefficients in the 1M LiOH–water-corroded oxides evaluated from the deuterium profiles were smaller in the order of Zircaloy-2>GNF-Ziron>VB at 573K. For the 0.1M LiOH–water-corroded oxide of GNF-Ziron, the diffusivity was lower than that of the 1M LiOH–water-corroded oxide by a factor of 1/4. The present diffusion coefficients of the 1M LiOH–water-corroded oxides of GNF-Ziron and VB were approximately 7 times larger than the previous data of the corresponding steam-corroded oxides. The deuterium diffusion properties in the oxides of the three alloys obtained in the in situ experiment were roughly consistent with their hydrogen absorption performances in the LiOH–water-corrosion tests, as well as in the previous steam corrosion tests.