Andrew Bulla

University Of Oxford

I have completed my Bachelor’s and integrated Master’s degrees at the University of Oxford. For my fourth-year project, I investigated lithium uptake by aluminum oxide-coated steel, a candidate material for coolant tubes inside tritium breeder blankets. Currently, I am pursuing a DPhil entitled ‘Characterizing Lithium Corrosion for Fusion Applications,’ under the supervision of Prof. David Armstrong, Prof. Chris Grovenor, and Prof. Michael Moody at the University of Oxford.

The deuterium-tritium (D-T) fusion reaction, fundamental to all fusion power plants, requires a constant supply of tritium. Since tritium exists naturally only in trace amounts, it must be produced in situ. One proposed mechanism is through the fission of lithium isotopes using neutrons produced from D-T fusion, hence the term ‘breeding.’ The ideal breeder material, liquid lithium, incurs severe corrosion damage in most structural materials due to its very high reactivity. Over time, surface roughness, alongside a reduction in thickness, begins to appear in the breeder blanket. In extreme cases, this can lead to liquid lithium leakage through perforated components.

Vanadium alloys were initially proposed as structural materials for liquid metal cooling systems in the 1950s. However, breeder blanket designs for ITER were based on ferritic-martensitic steel, as it is commercially available and well-understood. Nevertheless, vanadium alloys demonstrate high resistance to lithium corrosion and irradiation embrittlement at high temperatures, making them the ideal candidate for breeder blanket designs using pure lithium as the breeder.

Although there is some current understanding of the corrosion behavior of vanadium alloys, these studies were hardly systematic, and parameters were often poorly quantified. The synergistic effect of irradiation and corrosion, as well as the effectiveness of a ceramic coating layer, has never been thoroughly investigated. My project will primarily use Atom Probe Tomography (APT) to provide atomic-scale spatial-chemical characterization of lithium. Additionally, I will use Secondary Ion Mass Spectroscopy (SIMS) and Scanning Electron Microscopy (SEM) to analyze lithium distribution and microstructural changes on a larger length scale. Different coating-substrate combinations, such as ZrC-tungsten, Er2O3-vanadium, and ZrO2-vanadium, will be analyzed in samples provided by industrial partners, and hopefully, proton-irradiated samples as well.