Surveillance of Defects in Reactor Pressure Vessel and Pipes Under Cyclic Thermal and Mechanical Load (German HDR-Reactor-Safety-Program)

During thermal and mechanical loading, NDT techniques were applied on pipe nozzles and in the cylindric pressure vessel (e.g. 15NiCuMoNb5; WB36) wall. With the acoustic emission, macroscopic crack growth at the tube could be detected. After an analysis of the energy and amplitude of the signals, criteria for a prewarning of the failure of the tube line could be defined. For the thermal shock test on nozzles and in the cylindric wall, small initiating cracks could be indicated with the acoustic emission analysis in the cladding. It was possible to differentiate between crack growth and crack surface friction noise. For online quantification of crack growth at some cracks, stationary potential drop probes were applied. A resolution of crack growth of approx 0.5 mm could be reached. In off-line mode, small defects in crack fields could be detected. With the ALOK procedure, defects of > 3 mm depth and 5 mm length in the crack fields could be detected and resolved. With electro-dynamic exited SH-waves, all defects > 10 mm depth could be detected. With the potential drop technique, an exact characterization of the crack profile is possible, if the cladding thickness is known.