Leak-before-break assessment of CANDU pressure tube considering leak detection capability

The leak before break (LBB) concept is employed as defense in depth in CANDU reactors in order to avoid an unstable failure in pressure tubes. The LBB in pressure tubes can be ensured when detection, confirmation and location of the leak are carried out and the reactor is placed in a depressurized condition before the crack exceeds critical crack length. Leak detection and location is provided by the annulus gas system (AGS). Therefore, the evaluation parameters for LBB assessment, such as leak detection and leak location capabilities, should be made available through AGS performance test. Recently, the AGS in-situ tests with a simulated moisture injection were carried out in one of the CANDU reactors in Korea. This paper presents the LBB assessment performed taking into account the leak detection capability and the modification of operating procedure therefrom. (orig.)