The Impacts of Liquid Metal Plasma-Facing Components on Fusion Reactor Safety and Tritium Management

In this work we consider some of the safety implications of using liquid metal (LM) plasma-facing components (PFCs) in future fusion reactors. Candidate LMs include lithium, tin, and tin-lithium alloys, and we consider a modified Fusion Nuclear Science Facility design with a dual-cooled lead-lithium blanket and fast-flowing LM first wall and divertor consisting of each of these aforementioned metals. Tin and tin-lithium PFCs are found to have little impact on the potential source terms, including tritium and activation product releases during an accident as well as tritium permeation losses during normal operation, relative to the lead-lithium blanket. For a lithium PFC, chemical reactivity and high tritium inventories are additional concerns. We outline some necessary safety precautions for lithium systems and review the relevant operating experience of sodium-cooled fission reactors. Design constraints to keep the tritium inventory low in such a lithium system are outlined, including in the tritium extraction system, which will have to rely on different techniques than envisioned for other LMs such as PbLi, Sn, and SnLi, which have a much lower tritium solubility than lithium. Development of such extraction systems is significant research and development needed prior to deployment of lithium PFCs.