Measurement of hydrogen trapping in cold-work dislocations using synchrotron X-ray diffraction

Abstract

In water-cooled nuclear power plants containing zirconium alloys as the clad material, embrittlement of the cladding can occur from hydrides produced by the water-zirconium alloy interaction, thus limiting the life of the fuel assembly (Motta et al., 2019). The hydrogen produced at the water-zirconium interface can also be trapped in neutron irradiation-induced microstructural defects, reducing the amount of hydride present at any given time/temperature. Knowledge of the extent of hydrogen trapping by various microstructural features in zirconium and its alloys is therefore key for accurate predictions of hydride-induced embrittlement. A novel method for quantifying both trap capacity and trap binding energy using synchrotron X-ray diffraction is described and demonstrated for a cold-worked, Zircaloy-4 sample in which line dislocations provide an analogue for irradiation-induced dislocation loops as hydrogen trap sites. This study has experimentally determined the following parameters for cold-work dislocations: Thermal stability; Binding energy; Maximum capacity for hydrogen; Number of equivalent hydrogen trap sites. These parameters may be used in modelling hydrogen embrittlement of zirconium alloys, as experimental estimates for their analogue of irradiation-induced dislocation loops. More importantly, this pilot study has successfully demonstrated the methodology and results of a novel technique that may be applied generally to irradiated material to quantify hydrogen trapping at other irradiation-induced microstructural defects.