Deterministic Leak-Before-Break Treatment of Uncertainties: Part 2 – Example Application

Abstract The Canadian CANDU® Industry has developed and is implementing a composite analytical approach (CAA) to demonstrate, with high confidence, appropriate safety margins for deterministic nuclear safety analysis of large-break loss-of-coolant accident events in existing CANDU reactors. A key element of the CAA is the deterministic leak-before-break (CAA/DLBB) assessment for postulated through-wall cracks in all butt welds in the large-diameter primary heat transport system piping and reactor headers. The companion paper proposes an approach to integrate the uncertainties of the key leak-rate parameters into a single metric (a quantitative indicator of the uncertainty in the CAA/DLBB assessment, a.k.a., performance indicator). This approach ensures that the uncertainty in individual key parameters is not taken out of the context of the uncertainty of the other key parameters. This paper illustrates the application of this systematic approach for quantifying the uncertainty in the CAA/DLBB assessment to a specific postulated break location. The example application illustrates how the bounding values of the key leak-rate factors are quantified and how the uncertainties in the factors are integrated using the analytical and numerical approaches and discuss how the proposed approach provides an unbiased estimate of the leak-rate factor for the postulated break location that is assessed.