CANDU Plant Life Extension: Steam Generator Considerations

Abstract

Life Management planning and its effective implementation is essential for reliable and competitive power plant operation. Lack of timely implementation of plant life management (PLIM) in many Nuclear Power plants worldwide, particularly for steam generators, has forced many operators into a remedial repair mode, and sometimes steam generator replacement, particularly steam generators with Alloy 600 tubing. Maintaining economically competitive nuclear power plant operation requires high capacity factors. This requires a high degree of component reliability and an innovative approach to maintenance and outage planning. If these are achieved NPPs offer a competitive and environmentally sound product, making the option of plant life extension (PLEX) an attractive one. Point Lepreau Generating Station (PLGS) has been in operation since 1983, with an average lifetime capacity factor to date of 84% and a good safety track record. Hence the option of extending its service life can be considered. The viability of PLEX depends heavily on the state of key systems, structures and components (SCCs). Steam generators (SGs) are one key component while considering the PLEX option. For CANDU 6 PLEX decisions, the timing of a potential fuel channel replacement is also a primary decision-making activity, and steam generator replacement or may need to tit with any fuel channel replacement activity. This paper presents some of the aspects currently under consideration for a life extension of CANDU 6 steam generators to a 50 year life (design life is 30 years), and makes recommendations to address these aspects. Tube bundle life, although a significant factor, may not be the most important factor in determining the probability of achieving 50 year life. Steam generator internal structures, for instance, present a challenge in estimating current condition as well as future life. The life assurance of the internal structures needs to be assessed with an appropriate inspection program. The excellent corrosion resistance of the PLGS (and Alloy 800M world-wide) tube bundles so far requires a novel approach to predicting future performance. This approach is based on extensive laboratory data and involves defining a minimal set of tubes that can be predicted to be susceptible to degradation