The Maintainable Fusion Pilot Plant – FY25 Updates

Abstract

The development of a fusion pilot plant will require robust solutions for maintenance and repair of plasma-facing components (PFCs) operating in an extreme radiation and thermal environment. Current reactor concepts anticipate frequent replacement of first wall and divertor components, driving complex remote-handling schemes and the need for very large, cost-prohibitive hot-cell facilities. To improve reactor availability and reduce lifecycle costs, in-situ repair strategies for first wall armor have emerged as a promising alternative to full component replacement. This project investigates an in-situ PFC repair concept based on remotely deployed metal additive manufacturing, with a focus on tungsten armor repair using TIG and plasma welding approaches. The approach targets localized damage to thin first wall armor caused by particle fluxes, radiation, and transient thermal events, while preserving neutron transparency and heat transfer to the breeding blanket. Radiation-hardened, embedded diagnostics are also being developed to assess armor condition and guide repair operations. During the first year of work, system components were selected and assembled, a multi-orientation deposition test stand was fabricated, and initial deposition trials were completed using stainless steel with both TIG and plasma torches and later using tungsten wire on tungsten plates. Subsequently, the second year of work focused on refining the tungsten material deposition and surface smoothing processes, characterizing the material properties of the resulting material and substrate, and evaluating the surface profile of both pre- and post-repaired areas. During the development for a viable deposition strategy for tungsten, many parameters are controlled and adjusted to refine the process, including plasma current, torch speed and standoff distance, wire feed rate, pre-heat temperature, and plasma and cover gas types and flowrates. The resulting depositions of tungsten wire on tungsten tiles produced mixed results including fractured tiles, porosity, surface cracks, and several successful, multi-bead deposits without detectable tile damage. The following sections detail the experimental results gained during the past year, as well as present proposals for future work in this area of research to further progress the feasibility of welding approaches for in-situ tungsten repair in fusion reactor environments.