Statistical analysis of steam generator tube degradation

Statistical methods are investigated for use in evaluating and predicting the progression of steam generator tube degradation due to corrosion and other causes. It is found that the Weibull statistical distribution provides an easy to use and effective method for predicting damage progression. Other statistical functions, such as the log-normal, can also be used, often with essentially equivalent results. Statistical evaluations were performed of a variety of current degradation mechanisms. These evaluations covered: Intergranular attack/stress corrosion cracking (IGA/SCC) at tube supports, in tube sheet crevices, and in sludge piles of recirculating steam generators; primary water stress corrosion cracking (PWSCC) at roll transitions, U-bends and dents of recirculating steam generators; and erosion-corrosion in once-through steam generators. The statistical evaluations described in the report indicate that the progression of degradation often follows predictable patterns such that long term trends can be predicted. In addition, the behavior of plants experiencing degradation can provide insights regarding the potential behavior of other plants with similar design, materials, and operating conditions. Guidance is developed for use by utilities on application of statistical methods for evaluation of plant specific steam generator tube degradation. 17 refs., 30 figs., 3 tabs