Liquid lithium corrosion studies for nuclear fusion reactor materials

As fusion devices push to become more compact and economical; higher-performance and smaller machines need to be developed. One potentially enabling technology is the use of liquid lithium-based plasma facing components (PFCs). The use of lithium as the plasma-facing surface can provide a myriad of benefits, including increased fusing volume, better fuel particle handling, and a reduction in damaging off-normal events. Increasing the fusing volume allows for more energy production per unit volume of reactor. Enhancing the fuel handling can lower the tritium inventory at the reactor site, making reactor licensing cheaper and quicker. A reduction in off-normal events means less down-time for reactor maintenance. However, the use of liquid lithium in these devices comes with a variety of challenges. The conductive fluid must be fully controlled in the system as it travels through spatially-varying magnetic fields. A full understanding of magnetohydrodynamics and wetting dynamics of the lithium in these systems is needed to describe this fluid flow, leading to a number of studies at the University of Illinois Urbana-Champaign (UIUC) and elsewhere. Additionally, the extraction of entrained fuel species from the liquid lithium is required for steady-state operation. The reactivity between lithium and atmospheric gases is quite high, requiring sophisticated safety measures to be put into place to prevent contact between the molten lithium and atmosphere. Lastly, and the focus of this work, is that the alkaline nature of lithium makes it highly corrosive to a wide array of materials. Understanding what materials can be used in contact with lithium is crucial to the continued development of a liquid lithium-based PFC. Lithium corrosion of materials has been studied fairly extensively in the literature, mostly in the nuclear fission context. However, these studies are often performed at high temperatures (>500◦C), which is not relevant for the use of liquid lithium in nuclear fusion. As such, studies need to be performed at fusion relevant temperatures for materials that will potentially be in contact with liquid lithium. In this work, a new experimental setup was created at the Center for Plasma-Material Interactions (CPMI) at UIUC to investigate the corrosion of seven fusion-relevant materials at 300◦C for 2000 hours (≈3 months). The seven materials were: tungsten, molybdenum, 304 stainless steel, 316 stainless steel, Inconel 625, silver plated 316 stainless steel, and aluminum bronze. These materials can be roughly split into three categories: refractory metals traditionally used as solid PFCs, structural materials used for supports, and bolt materials used for securing structures. Each material was submerged in a liquid lithium filled canister and analyzed with a suite of chemical and imaging techniques. After investigation, it was determined that all the refractory and structural materials had reasonable corrosion resistance to liquid lithium at 300 ◦C. Each of these materials had a corrosion rate of <1.0 μm/yr which will likely be an acceptable rate for future devices. However, both of the bolt materials (silver-plated 316 stainless steel and aluminum bronze) showed significant degradation over the course of the testing. Neither of these materials could be used in a liquid lithium environment. Further investigation is needed to test novel materials or coatings for use as bolts in a liquid lithium environment.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Nuclear, Plasma, Radiolgc Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Moynihan, Cody David

Contributors dc:contributor

• Ruzic, David N
• Andruczyk, Daniel

• Nuclear Fusion
• Liquid Lithium
• Corrosion

Statement dc:rights

• Copyright 2023 Cody Moynihan

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/120424

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F120424