The Impact of Inspection Uncertainties on the Estimation of the Flaw Growth Rate Distribution

Abstract of the technical presentation presented at:
Steam Generator Tube Integrity Research Program (TIP-6) Meeting
October 24-25, 2023

Prepared by:

M. Pandey
Professor, NSERC-UNENE Chair
University of Waterloo

B. Wasiluk and J. Riznic
Canadian Nuclear Safety Commission

Abstract:

Steam generator (SG) tubing is inspected during scheduled maintenance outages to detect and size existing flaws in the tubing. Using the flaw population sizing data collected during the outage, the condition and operational assessment are performed to demonstrate fitness for service of the SG tubing. Flaw growth rate is an important input to the operational assessment of SG tubing.

Tubing inspection primarily uses eddy current probes. Detection and sizing uncertainties associated with an inspection probe are represented by the probability of detection (POD) and sizing error curves, respectively. The POD and sizing error are greatly affected by internal deposits, variations in tube wall thickness, interference from support structure, and many other factors. Because of sizing errors, the measured flaw size is not identical to the actual flaw size, which poses a challenge to the flaw growth rate estimation.

A probabilistic approach was adopted to filter out the confounding influence of inspection uncertainties in the estimation of flaw growth rate. The proposed approach would provide a more realistic estimate of the growth rate distribution and increase the robustness of the operational assessment of SG tubing.

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