ABSTRACT
Zirconium alloys are widely used to make core components such as fuel cladding and pressure tubes in nuclear reactors where the rate of hydrogen uptake is largely controlled by the effectiveness of the oxide as a permeation barrier. The structure of the oxides formed on the CANDU reactor pressure tube material, Zr-2.5 wt%Nb, was investigated using electron microscopy and, following exposures both within and outside the reactor, SIMS was used to characterise the deuterium uptake profile in the oxide which it was found could be different from point to point. At regions of high bulk deuterium content, deuterium concentrations were high throughout the oxide on the outside surface of the pressure tube; conversely, where bulk alloy deuterium concentrations were low, much steeper diffusional profiles were observed in the oxide. The data obtained allowed a diffusion coefficient to be inferred for the low uptake regions and the implications of the results are discussed in relation to the different oxide structures seen in the scale.
