Deuterium buildup in the rolled joint regions of operating CANDU pressure tubes

Deuterium uptake by operating pressure tube material is usually enhanced at the rolled joint regions relative to the ingress into the main body of the tube. Predicting the concentration of hydrogen isotopes in the rolled joint regions as a function of reactor operating time is important in structural integrity evaluations such as flaw assessments and end of life predictions. A model, accounting for the ingress and changing distribution due to diffusion and precipitation, has been developed, and updated over the past few years, to make predictions of the axial profile of the hydrogen isotope concentration in the rolled joint regions of operating pressure tubes as a function of reactor operating time. The updates included several improvements such as the introduction of the effect of an initial thermal spike (at the inlet of inner zone channels at Bruce A) on the solubility of hydrogen that improved the accuracy of the predictions. As non-linear (with time) models were developed for deuterium ingress due to corrosion in the body of the tube, the rolled joint model was modified to incorporate the observed non-linear behaviour. (author)