Evaluation of the recovery annealing of the reactor pressure vessel of NPP Nord (Greifswald) Units 1 and 2 by means of subsize impact specimens

In 1988 and 1990, the reactor pressure vessels of Units 1 and 2, respectively, of the Greifswald nuclear power station were subjected to heat treatment at 475 C for annealing of irradiation effects. To demonstrate the effect of annealing and to evaluate a new postannealing transition temperature of vessel base metal and weld metal, boat samples were removed by means of electric discharge machining (EDM) from the (unclad) inner surface of the vessel. From these samples, micronotched bar impact test specimens were fabricated and tested at different temperature. Transition curves were evaluated from the results. By means of correlation tests, the transition temperatures evaluated from the micro-specimen tests are converted to standard Charpy-5 transition temperatures. Results are available for the weld metal of Unit 1 after annealing. The transition temperature Tk is lower than the value calculated by the designer of the plant. Specimens removed from Unit 2 before and after annealing are in preparation