Loading...
Palladium-based metal foil pumps for direct internal recycling of hydrogen isotopes in the fusion fuel cycle
Li, Chao
Li, Chao
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2024
Date Submitted
Collections
Files
Loading...
Li_mines_0052E_12899.pdf
Adobe PDF, 5.55 MB
Research Projects
Organizational Units
Journal Issue
Embargo Expires
2025-11-26
Abstract
In deuterium-tritium (D-T) fusion, about 1% of the injected fuel is converted into helium, making efficient recovery of unburnt D-T essential. Direct internal recycling (DIR) processes ex-tract pure DT from the plasma exhaust and return it directly to the fueling system. Metal foil pumps (MFPs) are the enabling technology that operate through superpermeation, where plasma-generated H/H+ absorb directly into the metal, bypassing the dissociative adsorption step in pressure-driven permeation. This enables effective pumping and purification at the low pressures expected at the plasma exhaust.
This thesis systematically investigated MFPs comprised of palladium and its alloys (PdAg, PdCu). A sputter cleaning process was developed that enabled instant and stable high flux. Performance increased as temperature was reduced, suggesting that absorption of superthermal H is the primary rate-limiting step. Among the alloys, PdCu produced the highest flux reported to date. Composite MFPs, formed by applying thin coatings of Pd and PdCu to vanadium foils, demonstrated that the superiority of PdCu derived from its excellent ability to both absorb superthermal H upstream and desorb molecular hydrogen downstream. High flux was maintained while compressing hydrogen from 10 to >1000 Pa, which offers simplifications to the downstream pump train. Fundamental measurements of pressure-driven permeation at comparable conditions were used to construct pump curves and estimate maximum compression ratios that matched experimental results with high fidelity.
Parametric studies of DIR target 80-90% recovery of the hydrogen feed, which results in significant helium enrichment. A study of helium enrichment (0-100%) on plasma-driven permeation revealed that flux scaled with H2 partial pressure, but brief exposure to high He levels significantly attenuated flux due to low-energy He ion implantation. This previously unrecognized issue has major implications for MFP durability, but its impact is greatly mitigated under low-temperature operation. These insights were leveraged to demonstrate the first continuous DIR process, with stable flux achieved for DIR fractions exceeding 90% from a 1% He feed. Additionally, a semi-batch process was designed and demonstrated to efficiently extract nearly 100% hydrogen. The findings of this thesis offer valuable insights into the design and implementation of practical DIR systems.
Associated Publications
Rights
Copyright of the original work is retained by the author.