Identify the composition of interface bubbles at the Ni–FLiBe boundary

Ascertain whether the bubbles nucleated at the Ni-200/FLiBe interface during metal-side charging in the HYPERION experiments are composed of pure H2 or a mixture of Ar and H2, in order to clarify the interfacial permeation barrier mechanism and its influence on measured fluxes.

Background

During metal-side charging, the authors observe oscillatory permeation signals consistent with bubble formation and detachment at the Ni–FLiBe interface, which can act as a permeation barrier and mask isotopic effects.

Understanding whether these bubbles are pure hydrogen or contain entrained argon from the downstream environment is critical to modeling interfacial transport and correcting measured permeation fluxes.

References

However, the nature of the bubbles in the present study remains unclear - specifically, whether the bubbles are formed of pure H2 or of Ar + H2.

— Permeation behaviour of hydrogen isotopes in molten FLiBe (2LiF-BeF2): Identifying sources of uncertainty and associated measurement challenges  (2603.28991 - Saraswat et al., 30 Mar 2026) in Section 3.2