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 temperatures. 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-V 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.

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This paper presents the results of a study on degradation due to irradiation occurring in WWER-440 reactor pressure vessel (RPV) steel, using subsize Charpy specimens (5×5×27.5 mm3). An application of subsize specimens for estimation of irradiation embrittlement of RPV steel has been substantiated. Comparison between ductile-to-brittle transition temperatures (DBTT) for full-size and subsize Charpy specimens has been carried out. The relation between these two values has been clarified. The results of testing trepans and templates cut out from WWER-440 reactor pressure vessels are considered. The main results of the program TACIS-91/1.1. are discussed.

The irradiation and recovery behavior of a nickel-chromium-molybdenum type weld metal with 0.27 weight percent copper was examined mainly with tension, impact, drop-weight, and fracture-mechanics specimens up to a thickness of 100 mm. After irradiation at about 6 × 1019 neutrons (n)/cm2 (E > 1 MeV) at 310°C, the impact tests show larger temperature shift than for the drop-weight and fracture-mechanics tests. Recovery annealing was done at 350 (only hardness measurements), 400, 450, 500, and 550°C. Reasonable recovery effects were observed after annealing for 60 h at 450°C. For complete recovery, annealing between 500 and 550°C is necessary. Direct transfer of the test results to light water reactors is not possible, as the irradiation temperature of the specimens was 30 K higher than the operating temperature of reactor pressure vessels.