Evaluation of the effect of chemical composition on the irradiation sensitivity of reactor vessel weld metal

The effects of weld metal alloying constituents on the irradiation response of reactor vessel weld metal were evaluated to determine why vessel welds tend to be more sensitive to irradiation damage than parent plate material. Weld data, collected from published reports, were compared on the basis of neutron radiation exposure; subsequent nil-ductility transition temperature (NDTT) shift (measured at the Charpy 30 ft . lb energy fix); chemical composition; postweld heat treatment, and microstructure. The data comparison produced a correlation between NDTT shift with irradiation and a ratio of a weld's major alloying elements. The alloy ratio is designated A/B where the element content of the weld, by weight percent, is expressed: A/B = (Ni + Si)/(Mn + Cr + Mo). As the ratio increases for a weld, higher NDTT shifts with irradiation can be expected. Effects of postweld heat treatment and microstructure are also related to the NDTT shift-A/B correlation. The known effects of copper content on NDTT shift with irradiation were found to be separate from the effects of the A/B ratio. Both copper and A/B effects, however, contribute to the total NDTT shift experienced by the weld with irradiation