TRENDING INTEGRATED LEAKAGE-RATE TEST RESULTS

Abstract

Existing Canadian Nuclear Power Plants (NPPs) are aging, with 19 active reactors being in operation for 35 to 50 years. To ensure their leak tightness, concrete containment structures of NPPs shall be regularly leakage-rate tested in accordance with Integrated Leakage Rate Test (ILRT) requirements as detailed in CSA N287.7 and CNSC regulatory documents.

Concrete containment structures shall be subjected to ILRTs to ensure their leak tightness, either every 6 years or conforming to a performance-based test interval agreed upon between the licensee and the Authority Having Jurisdiction (AHJ), i.e. the CNSC. To establish a performance-based ILRT interval option, in addition to inspection, testing, and aging management requirements, demonstration shall be made to the AHJ that the leakage-rate trends, maintained from commissioning to the most recent outage ILRT, are stable over at least the two most recent (post- commissioning) outage tests. Stable is defined in CSA N287.7-17 as no statistically significant increase that would cause the acceptance leakage limit to be exceeded if it changed in a linear fashion over the next test interval.

The stability requirements mentioned above may be subject to interpretation. This paper discusses various options for trending leakage-rate test results and recommends a multi-step approach.