Material Surveillance Program Regulatory Guidance for Steam Generator Tubes Extracted From Canadian CANDU Reactors

The Canadian Nuclear Standard, CSA N285.4, requires periodic extraction of steam generator tubes for metallurgical examination; however, the Standard does not specify detailed program requirements. Therefore, Canadian Nuclear Safety Commission (CNSC) staff has recently brought forth a set of guidelines to clarify the regulatory expectations for steam generator tube material surveillance programs. This paper introduces the material surveillance program required by CSA N285.4, and provides a discussion of the CNSC staff proposed guidelines, to explain the technical basis behind the expectations for tube removal and examination. The objectives of the steam generator tube material surveillance program include evaluating inspection tool capabilities, confirming tube material performance over the life of the plant and assessing the operating environment’s potential contribution to tube degradation. The knowledge acquired from the program can reduce uncertainties associated with the non-destructive inspection practices, and can provide data for steam generator aging management programs. Over the life of a plant, CSA N285.4 requires that only a few tubes be extracted for examination. However, each tube removal is costly and represents significant personnel dose. The tube removal and examination guidelines will aid in maximizing the value of each tube extracted for metallurgical examination.