In general, PWR reactor vessels are made of low alloy nickel manganese molybdenum steel. The behavior of this material under neutron irradiation is now relatively well known. On the other hand, the weld metals used for these vessels, which are also irradiated, exhibit a wide range of metallurgical structures and trace element contents, and further studies are necessary to gain a better understanding of their behavior under irradiation. Fourteen weld deposits were irradiated with a fluence of 5×10¹⁹ n/cm² (E > 1 MeV) at 288°C. The results of the corresponding Charpy V-notch impact tests are presented. Emphasis is given to the roles of copper and nickel. The effects of the different welding processes (shielded metal arc and submerged are welding) are also studied. The consumable products used were either of commercial origin or made specially in order to obtain copper contents between 0.02 and 0.18 % and nickel contents between 0.07 and 1.85 %. The results indicate that nickel strongly enhances irradiation damage in the same way as copper, but the effects of the nickel contents seem to be very dependent on the copper contents. The roles of these two elements (and also that of phosphorus) in the brittle-ductile transition temperature shift is quantitatively expressed in a formula which takes the irradiation damage of these 14 welds into account, together with that of 16 further base metal samples irradiated under Lidentical conditions in the same laboratory. Meanwhile irradiation damage did not appear to be related to the particular welding process used.