The Areva integrated and sustainable concept of fatigue design, monitoring and re-assessment

Avoiding fatigue-induced damage to components of nuclear power plant technology is an important prerequisite for maintaining plant safety and increasing availability. Fatigue monitoring is an integral part of plant aging and lifetime management. Against this background and changing framework conditions, such as design and construction of new nuclear power plants for 60 years of operation, life extension of existing plants, and the attention to be paid to media-induced effects, improving methods of detection is one of the main concerns of Areva's R and D work. The key objective is to determine more realistically the current degree of fatigue of power plant components. The integral and multi-step procedure proposed contributes to both cost optimization and inspection cycle minimization. Fatigue monitoring should start as early as in the commissioning phase, as the high loads and stresses arising at that stage already contribute significantly to the level of fatigue. Areva recommends using the FAMOS (Fatigue Monitoring System) system to determine the real transient loads and stresses and process them for purposes of a first quick fatigue assessment. On a medium-term basis, the current levels of fatigue are to be determined by means of a detailed code-based fatigue analysis. The input data in that case are the real loads and stresses measured, where the temperature transients are specified from the perspective of experts in systems technology. Fatigue is demonstrated on the basis of finite-element analyses taking into account transient temperature field loads and stresses affecting a component as well as primary loads and stresses. In this way, potential problem areas can be identified reliably which, in turn, helps reduce inspection cost. (orig.)