R&D to lifetime management - ND-characterization of ageing phenomena

The contribution reports to R&D performed under the umbrella of the German Nuclear Safety Research Program in the last decade by the Fraunhofer-IZFP within the context of nondestructive materials characterization of materials ageing phenomena which can occur during the lifetime of a nuclear power plant. The Cu-rich low-alloy heat-resistant steel 15 NiCuMoNb 5 (WB 36, material number 1.6368) which is used as piping and vessel material in boiling water reactor (BWR) and pressurized water reactor (PWR) nuclear power plants in Germany was under special investigations. In all damage situations observed in plants, the operating temperature was between 320° and 350oC .and the damage was combined with a shift in the ductile-to-brittle-transition-temperature (ADBTT) of the notched-bar impact test to higher temperatures. Micromagnetic NDT techniques were applied to characterize the material degradation which is enhanced when low cycle fatigue loads are superimposed to the precipitation process of Cu-rich particles. As Cu-rich-precipitates play also an essential role in neutron embrittlement of pressure vessel material, the same NDT techniques were applied to predict ADBTT at irradiated Charpy specimen. Austenitic stainless steel A1S1 321 is used in German plants as surge- and spray-pipeline material which under service is exposed to cyclic thermo-mechanical loads. The contribution in the long Version will document the ability of ultrasonic time-of-flight measurements to sensitively characterize the whole fatigue life from the beginning to the end of life. As the experiments were performed at 300oC too, EMAT-transducers have been applied.