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.

Under German licensing rules, irradiation-induced embrittlement of a reactor pressure vessel (RPV) in the core belt region is taken into account basically by determining the shift of the 41-J transition temperature of the Charpy impact energy versus temperature curve and then adjusting either the exclusion line of the modified Porse diagram, or the KIR curve, by this 41-J shift. The accuracy limits of T 41 Jand Δ T 41 J determination are discussed and quantified. The transition temperature concept is shown to be conservative in the validity range of the respec-tive licensing rules because of the uncertainties in Δ T 41 J determination. Investigations with respect to irradiation effects on fracture toughness deserve high priority in current programs. Results from a A 533-B 2 steel (HSST03) are presented, and the shift of the KIC curve is evaluated for two fluence levels. Experiments related to the question of whether neutron flux density has an influence on embrittlement are briefly reported.

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