In-situ repair of eroded tungsten plasma facing components using wire arc directed energy deposition

Within existing conceptual studies, it is assumed a fusion reactor will require replacement of its divertor every 2 years and the blanket module every 5 to 6 years. The complexity of this replacement operation requires advanced remote-handling technologies and generates a large rad-waste stream. Keeping these challenges in mind, the in-situ repair of plasma-facing components has been proposed to extend their working life and reduce required reactor downtime. This work explores the application of wire arc deposition to in-situ repair of tungsten PFCs with both gas tungsten arc welding and plasma arc welding systems. Additive manufacturing technologies have been previously explored to allow for in-situ repair, but many of these technologies cannot be adapted to the requirements of the reactor environment. We develop a methodology that allows for the crack-free deposition of pure tungsten onto tungsten substrates by preheating the substrates with the welding torch. This methodology is then extended to filling simulated erosions in the tungsten substrate, and a surface correction process is developed to ensure a uniform surface finish on repaired tiles. A comparison between pure tungsten and tungsten-rhenium alloy substrates was conducted to evaluate their relative compatibility with the wire arc repair process. Extensive material characterization was also performed on the deposited tungsten material to establish its properties relative to the manufactured substrate. Collectively, these results form the foundation to develop a robust PFC repair methodology using wire arc deposition.