Crevice corrosion has been observed since the early operation of CANDU power reactors, on the inner surface of pressure tubes where fuel bundle bearing pads sit. Traditionally, crevice corrosion flaws (CCFs) were assessed as planar against delayed hydride cracking (DHC) growth. However, with reactor ageing and associated increasing levels of corrosion induced hydrogen (deuterium) uptake, assessing these flaws as planar posed significant operational problems. A new assessment strategy has been pursued in which confirmed crevice corrosion flaws are assessed volumetrically using a proposed lower bound root radius. The paper explains what areas have been explored and what considerations have been given when assessing the acceptability of licensee's proposed new assessment strategy. It also describes measures and restrictions imposed by the regulatory authority to account for the uncertainties associated with the methodology in order to maintain the confidence on the structural integrity of the concerned components.
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