Study of diffusion processes in the oxide layer of zirconium alloys

In the active zone of a nuclear reactor where zirconium alloys are used as a coating material, this material is subject to various harmful impacts. During water decomposition reactions, hydrogen and oxygen are evolved that may diffuse through the oxidic layer either through zirconium dioxide (ZrO₂) crystals or along ZrO₂ grains. The diffusion mechanism can be studied using the Ion Beam Analysis (IBA) method where nuclear reaction ¹⁸O(p,α)¹⁵N is used. A tube made of zirconium alloy E110 (with 1 wt. % of Nb) was used for making samples that were pre-exposed in UJP PRAHA a.s. and subsequently exposed to isotopically cleansed environment of H₂¹⁸O medium in an autoclave. The samples were analysed with gravimetric methods and IBA methods performed at the electrostatic particle accelerator Tandetron 4130 MC in the Nucler Physics Institute of the CAS, Řež. With IBA methods, the overall thicknesses of corrosion layers on the samples, element composition of the alloy and distribution of oxygen isotope ¹⁸O in the corrosion layer and its penetration in the alloy were identified. The retrieved data shows at the oxygen diffusion along ZrO₂ grains because there are two peaks of ¹⁸O isotope concentrations in the corrosion layer. These peaks occur at the environment-oxide and oxide-metal interface. The element analysis identified the presence of undesirable hafnium.