The effect of irradiation on the toughness of pressurized water reactor vessel steels under different service conditions

The different toughness tests performed on two pressure vessel steels with very different upper shelves served to make a number of observations concerning the shifts in the transition temperature due to the effect of irradiation, as well as changes in toughness with temperature in the ductile region. With respect to shifts in the transition temperature, the following was observed: the shift obtained with precracked charpy test specimens was narrower than with the others; the shift obtained with charpy V impact tests was substantially equal to that obtained with CT test specimens - wider in the case of steel A, but slightly narrower in that of steel H. With respect to toughness values in the ductile region: the toughness values obtained using precracked charpy test specimens are significantly higher than those obtained with CT test specimens for static tests; 25 and 12.5 mm thick CT test specimens display comparable variations in Jsub(1C) and dJ/da, but wide scattering; the effect of irradiation, if any, is of the same order of magnitude as the scattering of the results - however, a test temperature effect is observed; the variation in toughness with temperature is determined more easily by considering a J value corresponding to a stable crack propagation of 1 mm, so that Jsub(Δal)=Jsub(1C)+dJ/dax1; this variation of Jsub(Δal) with temperature is substantially the same for both steels, or about -30% at 70 or 800C, and -50% at 2900C. (orig.)