PROBABILISTIC TECHNIQUES FOR THE ASSESSMENT OF PRESSURE TUBE HYDRIDE BLISTERING IN CANDU REACTOR CORES

The integrity of pressure tubes in CANDU reactors can be threatened if there is contact with the surrounding calandria tube and hydride blisters form in the pressure tube. In order to assess the state of a reactor core in which such contacts can occur, a probabilistic assessment technique based upon Monte Carlo methods has been developed. This approach was required due to the distributed nature of many of the factors required for such an assessment. The computer code embodies the results of an extensive research program into the growth and fracture characteristics of hydride blisters in pressure tube material. A single assessment generates distributions of the times to first blister formation and first blister cracking in the reactor core as well as the expected number of blistered tubes as a function of time. Multiple assessments can be used to explore the dependence of the assessment on variation in input assumptions. The result is a powerful tool for making key decisions on reactor maintenance requirements.