INTRODUCTION F

摘要

A single session under this topic includes three technical papers and one technical presentation. Two technical papers and a technical presentation are devoted to the subject of uncertainty analysis in probabilistic fitness-for-service evaluations of Zr-2.5Nb pressure tubes in CANDU nuclear reactors. A recently developed annex to the Canadian Nuclear Standard CSA N285.8, "Technical requirements for in-service evaluation of zirconium alloy pressure tubes in CANDU reactors", is intended to provide guidelines for uncertainty analysis in probabilistic evaluations performed within the scope of this Standard, such as the probabilistic evaluations of leak-before-break. The first presentation in this Session provides an overview of the developed annex, where the general approach to uncertainty analysis is comprised of three major activities: identification of influential variables, characterization of uncertainties in influential variables, and propagation of uncertainties through the evaluation framework or code. The application of the proposed guidelines has been exercised by performing a pilot study for the probabilistic evaluation of leak-before-break based on a postulated through-wall crack. The approaches used and the results obtained in the first stage (identification of influential variables) and in the second stage (characterization of uncertainties in influential variables) of this pilot study have been summarized in two technical papers presented in this Session.