In Situ Structural Repair and Protection of LWR Components Using Cold Spray

A major problem facing the existing U.S. fleet of Light Water Reactor facilities is stress corrosion cracking of austenitic nickel and iron alloys, which comprise the bulk of wetted components in LWR facilities; up to 70% of wetted non-fuel areas in a typical facility, making this problem particularly widespread and especially prevalent with extended service life. Cold spray technology offers an effective solution to repair corrosion damage that can be applied at low temperature, therefore minimizing substrate heating, maintaining dimensional stability, and avoiding unwanted thermal effects (HAZ, thermal stresses, dilution layer formation, etc.). The repair will arrest crack growth, protect from further corrosion damage, and fully restore load carrying capacity of the component, and can be applied in-situ, eliminating the otherwise necessary component removal process. In phase I, the project team down-selected appropriate cold spray-able nickel powder materials, established baseline processing parameters, optimized the cold spray material deposition process, evaluated the structural properties of the repair, analyzed the corrosion resistance of the cold spray material, optimized the cold spray material through the development of post-deposition heat treatment, established working relationships with a LWR manufacturer, a DOE National Laboratory, and a large owner / operator, identified several target components for repair, established long term transition targets, and designed equipment modifications to enable in-situ repair within the LWR facility. The cold spray repair process can be applied at low temperatures, resulting in a material with exceptional structural properties that is more noble than 304L Stainless Steel or Alloy 600, which minimizes galvanic effects and prevents further corrosion at the repair site, making cold spray an ideal solution for structural repair in corrosive environments. The phase II project will implement design modifications allowing in situ repair, further develop cold spray processing parameters, surface preparation techniques, and repair geometry effects, and develop statistically assured material property data for future structural implementation efforts. Additional cold spray materials will be investigated for feasibility and applicability, and the cold spray material will be analyzed in greater detail, using elemental analysis, advanced mechanical testing techniques, and stress corrosion crack testing under relevant conditions. Finally, phase II will demonstrate a cold spray repair on a component supplied by a large owner / operator. This effort advances the state of the art in cold spray repair and develops the foundation for ASME code consideration, directly in line with the DOE’s need for in situ mitigation and repair of corrosion damage in LWR’s, offering owners / operators a cost-effective means of plant sustainment and reducing the overall maintenance burden of aging reactor components. This repair approach also improves the safety of LWR facilities, which provides both a benefit to the plant owner / operator, as well as the general public.