Irradiation embrittlement of a variety of RPV steel plates and weldments

A variety of reactor pressure vessel plate and weldment Charpy specimens in the water quenched and tempered condition were irradiated in experimental assemblies in the Dido, Pluto and Herald materials test reactors at a temperature of 523+-5K. The shift in the nil ductility transition temperature (ΔNDTT) was then determined by a series of Charpy impact tests to ASTM, E-23 standards and because the relationship between ΔNDTT and neutron dose varied between different batches of specimens, the ΔNDTT values were normalized to neutron doses of 8 and 10x1018 n.cm2(E>1MeV). These results were correlated with the chemical composition of the specimens using the Varsik and Byrne method. The normalized ΔNDTT results plotted against the log of the Varsik and Byrne Chemistry Relation, showed good agreement with a straight line fit and confirmed that sensitivity to neutron irradiation increases primarily with the copper content and with two exceptions all the results considered here could have been described on the basis of copper content alone. The two exceptions occurred in specimens where a high nickel content is combined with a high copper content. Therefore, a high nickel content does need to be considered in its effect on radiation sensitivity. It does appear, however, on limited data that at this irradiation temperature, the beneficial effect of nickel is not lost when the copper content is low