Overview of Modelling of Hydrogen Isotopes Ingress and Diffusion in Rolled Joint Area

Abstract

Hydrogen isotopes are present in CANDU® reactor pressure tubes as initial protium from manufacturing and through ingress during operation. Ingress is more prominent at the rolled joint connection at each end of the pressure tube such that concentration gradients cause inboard diffusion of the hydrogen. Ingress and diffusion modelling is applied to demonstrate that hydrogen equivalent concentration, [H_eq], remains eq within safe limits to ensure pressure tube integrity over the reactor operating interval.

This paper presents an overview of the rolled joint ingress and diffusion models used in the industry. Models used in the 1-D finite difference code RJDIM and the 2-D finite element code H3DMAP are presented. The use of probabilistic methods and recent developments in R&D are presented and discussed.