NDT for Characterizing Ageing and Degradation of Nuclear Power Plant Materials - Fatigue and Irradiation

摘要

Following the design rules and considering the safety factors, the lifetime of nuclear power plants (NPP), worldwide is expected to be in the range of 40 years. Obviously, within such a lifespan the components and systems under heavy mechanical (static and dynamic pressure, vibration), thermic and irradiation loads, suffer ageing phenomena which are Thermal Ageing, Corrosion, Low Cycle Fatigue (LCF), High Cycle Fatigue(HCF), Very high Cycle Fatigue (VHCF) and Irradiation Damage due to neutrons - and the possible synergy of the phenomena together. However, the electrical power producing utilities as operators of the NPP, perform a `predictive maintenance', also called `retrofitting', by timely performing the replacement of especially stressed components. Examples for these replacement procedures are the change of heat-exchangers and parts of the main cooling pipes, like hot knees near heat-exchangers or components of the surge-line in pressurized-water NPP. As the components, which are replaced, always are manufactured according the newest technical state of the art, the retrofitting enhances inherently also the safety standard. In Germany, where due to the Atomic Law, the safety of the plants is asked for, this law - beside economic reasons of a higher technical availability - is the driver for replacement. The IAAEA has introduced safety standards for Ageing Management and according these documents, worldwide most of the atomic energy producing countries have adopted their national guidelines, newly introducing mainly fatigue condition monitoring. The proposed paper discusses, on one hand, the application of the 3MA-strategy (Micromagnetic, Multiparameter, Microstructure and Stress Analysis) on ferromagnetic components and Eddy-Current-based and Ultrasonic techniques on austenitic materials for early-characterizing fatigued microstructures - before cracking and, on the other hand, characterization of irradiation damage in pressure-vessel steels.