Materials ageing in nuclear power plants: Surveillance programmes and some mitigation strategies to enhance operational reliability and safety

Some aspects concerning the detection and monitoring of Nuclear Power Plant (NPP) materials ageing in components that could be relevant to safety are presented. Various materials ageing mechanisms are also discussed and strategies for the early recognition, control, mitigation and management of degradation are described. Emphasis is given to the importance of maintaining inherent safety levels of components that may age sufficiently under service conditions to reduce the design-base safety margins. Arguments are given for the inception and implementation of a comprehensive, component ageing surveillance programme. These must be based on operational experience, relevant data bases, current knowledge and state of the science and technology and the remaining operational life requirement. The paper restricts itself to light water nuclear power plants of western design, namely the Pressurised Water Reactor (PWR) and the Boiling Water Reactor (BWR).