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High chromium nickel-based alloys(i.e.,Alloys 52 and 52M)are used extensively for repair and mitigation of dissimilar metal welds joining critical reactor coolant systems susceptible to primary water stress corrosion cracking(PWSCC).Alloy 52 and 52M are also specified for use in new PWR designs due to their high resistance to PWSCC.The industry,however,has experienced a number of challenges in welding with these alloys,including extensive in-process repair and rework,which has extended refueling outages and resulted in lost power generation.To address these issues,EPRIs Welding and Repair Technology Center has conducted a significant amount of research over the past several years and,while the story is not yet complete,substantial progress has been made.One example is the development of improved equations for heat input and power ratio to better characterize and control the welding process.The weldability and crack susceptibility of these alloys also varies significantly with minor variations within the alloy composition specifications,along with dilution by the base material and on welding process parameters in general.The influence of alloy chemistry,particularly minor elements like phosphorous,sulfur and silicon,has been assessed to establish acceptable ranges to achieve good welding results.Studies have also been performed to quantify the dilution of the high chromium alloys over a range of welding parameters.Finite element modeling and laboratory testing have been performed to establish guidance on weld bead layout and sequencing.As part of the overall effort in this area,several advanced welding processes are also being optimized and readied for deployment.Magnetic Stir Welding with gas tungsten arc welding(GTAW)is probably the most mature of these techniques,but efforts are also underway with laser welding for improved heat input control and laser hybrid welding for a combination of heat input control and control of weld residual stress.The potential for friction stir welding is also being actively pursued.