Research progress and prospects of ODS steel welding technology for nuclear fuel element cladding

Oxide dispersion strengthened steel (ODS steel) is considered as one of the most promising candidate materials for the next-generation nuclear reactor cladding due to its excellent high-temperature mechanical properties, irradiation resistance, and thermal creep resistance. The excellent performance of ODS steel is mainly attributed to the dispersed nano oxide particles in the matrix. Inhibiting and avoiding the precipitation, growth, and agglomeration of nano oxides during the welding process is the most important basis for selecting welding methods. However, the current ODS steel structure for nuclear fuel elements (large aspect ratio cladding) and extreme service conditions (high temperature, high pressure, strong irradiation) requires higher technical indicators for welding methods. Currently, welding technology has become the most important factor restricting ODS steel as a cladding material for nuclear fuel elements. Based on this, the characteristics of different welding methods including fusion welding, brazing, and pressure welding, as well as the evolution of the microstructure, especially nano oxide particles, and mechanical properties of welded joints when using different welding methods to weld ODS steel, are elaborated in detail in this paper. Through comparison and summary, it is found that although both fusion welding and brazing are suitable for welding ultra long thin-walled pipe fittings, fusion welding can easily lead to grain growth and aggregation of nano oxides at the joint, while in brazing welding, the heterogeneous interface formed by the introduction of brazing material will crack under neutron irradiation. In comparison, pressure welding can obtain welded joints with higher strength. Finally, the future development direction of welding methods is also discussed in the paper.