A microstructural examination of irradiated reactor pressure vessel weld samples

An important contribution to the life extension of Magnox nuclear power sta tions comes from the assessment of microstructural changes in reactor press ure vessel (RPV) weld metal after extended in-service exposure to a neutron Aux. A project was undertaken to remove through-thickness weld samples fro m an RPV at a power station undergoing decommissioning. Sampling was carrie d out in a region of the reactor where the RPV was exposed to a high fast n eutron irradiation dose at a low operating temperature. Each sample was cut into several specimens for mechanical tests to establish fracture toughnes s, chemical analysis and dosimetry data. This paper describes some of the preliminary results obtained from a micros tructural characterisation programme. Samples were cut in various positions along the weld and at different depths through the vessel wall. These samp les were examined by a number of techniques to evaluate the macro and micro structure after different amounts of neutron irradiation. In-situ micro-ana lysis and fractography was carried out on specimens after mechanical testin g. (C) 2000 Published by Elsevier Science Ltd.