Fatigue Monitoring System and Post-Processing of Temperature Measurements: Surge Line Under Stratification Loading

The ageing management of power plants is nowadays a main issue for all nuclear industry actors: states, regulatory agencies, operators, designers or suppliers. Consequently, lots of operators have to deal with demanding safety requirements to ensure the operation of power plants particularly in the context of lifetime extension. With regard of the fatigue assessment of nuclear components, stringent safety standards are synonymous of new parameters to take into account in the fatigue analysis process such as for instance: new design of fatigue curves particularly for austenitic stainless steels, the consideration of environmentally assisted fatigue (EAF) and stratification effects. In this context AREVA developed within the integral approach AREVA Fatigue Concept (AFC) new tools and methods to live up to operators expectations. The last mentioned stratification issue will be focused on in the framework of this dedicated paper. Based on measured thermal loads, the Fast Fatigue Evaluation (FFE) process allows for highly-automated and reliable data processing to evaluate time-dependent cumulative usage factors of mechanical components. This method has recently been extended to the consideration of stratification loading with surge line application. The paper presents the latest AREVA research and development activities on the FFE method applied to a surge line under stratification thermal loading. An additional CFD analysis was performed in order to calculate realistic thermal loadings during start-up conditions of nuclear power plant conditions. The FFE methodology was used to calculate thermal stress at all relevant locations. This approach opens the possibility of a realistic CUF calculation. The methodology, the principle results and benefits are presented in the paper.