Probabilistic Evaluations of Rolled Joint Deuterium Uptake

Abstract

To ensure the integrity of the CANDU® pressure tubes (PT), the ingress and redistribution of hydrogen isotopes requires monitoring and evaluation. RJDIM is the computer code that deterministically predicts the axial distribution of hydrogen equivalent concentration [H_eq] as a function of operating time in the rolled joint (RJ) region of pressure tubes. Due to the stochastic nature of the phenomenon, it is not possible to select a set of deterministic inputs that will conservatively describe [H_eq] at all axial RJ locations. In addition, a wide range of [H_eq] profiles have been observed, which can give the impression that the deterministic method is not always in good agreement with measurements.

The Monte-Carlo probabilistic method is more suitable for describing the PT RJ deuterium ingress phenomenon. It samples the key input parameters from statistical distributions, which include the rolled joint deuterium uptake, body-of-the-tube deuterium uptake, initial hydrogen, diffusivity, terminal solid solubility (TSS), etc. The range of [H_eq] at each axial RJ location is estimated as well as the likelihood of exceeding TSS or CSA limits [][] at any time during the operation of the reactor. Examples are used to show that the probabilistic method is better at describing the different possible outcomes in [H_eq] profiles.