Within the research program “Integrity of Components,” reactor pressure vessel steels are irradiated in capsules in the swimming-pool-type research reactor FRG-2 at 290°C to different fluences of fast neutrons. Steel heats both conforming and not conforming to specifications with respect to chemical composition as well as to tensile and deformation properties are included.
So far, the results show that for the materials investigated the 41 J transition temperature shift from impact testing is always larger than the nil ductility transition (NDT) shift from drop-weight testing. This means that the mode of procedure of the regulatory rules leads to conservative values for the adjusted reference temperature even for material states near and beyond the specification limits.
From instrumentated Charpy tests, the arrest load was determined. It was found that the irradiation-induced shift of the arrest load versus temperature curve corresponds closely to the NDT shift. By evaluating Charpy surveillance specimens along this line, one has a supplementary criterion for assessing irradiation embrittlement at hand.
At low fluences, the 41 J transition temperature shifts are conservatively predicted by the trend curves of Regulatory Guide 1.99, whereas at high fluences—though a little beyond the validity limits—these shifts lie above the extrapolated trend curves.