A risk-informed approach to assessment of DHC initiation in pressure tubes of CANDU reactors

Abstract

The delayed hydride cracking (DHC) of flaws and cracks in pressure tubes is a serious form of degradation in the reactor core. CSA standard N285.8 (2005) recommends deterministic and probabilistic procedures for assessing the potential of DHC initiation from flaws that are generated by fretting or any other mechanism. Although the deterministic method is simple, it lacks a quantitative risk-informed basis for the assessment. On the other hand, a full probabilistic method based on simulation is tedious to implement. This paper presents an efficient, reliability-based approach that bridges the gap between a simple deterministic analysis and full Monte Carlo simulations. In the proposed method, a deterministic DHC initiation criterion is calibrated to specified target probability levels. The main advantage of the proposed approach is that it provides a practical, risk-informed basis for DHC initiation assessment while retaining the simplicity of the deterministic method.