Permeation behaviour of hydrogen isotopes in molten FLiBe (2LiF-BeF2): Identifying sources of uncertainty and associated measurement challenges

TL;DR

This study systematically investigates hydrogen isotope permeation in molten FLiBe, addressing uncertainties and measurement challenges to improve understanding of transport parameters relevant for nuclear applications.

Contribution

It introduces experimental methods to clarify permeation behavior and sources of scatter in previous measurements, especially regarding interface effects and charging techniques.

Findings

Permeability can be significantly affected by bubble-laden Ni-FLiBe interfaces.

Salt-side charging can suppress isotopic transport behavior.

Results challenge earlier assumptions and highlight measurement uncertainties.

Abstract

This paper presents results from systematic investigations conducted in the HYPERION facility to quantify permeabilities of hydrogen isotopes in FLiBe over a temperature range of 773K - 973K. To address the knowledge gap resulting from widely scattered transport parameters reported in the earlier studies, HYPERION experiments incorporate specific provisions to probe unsubstantiated assumptions, including a one-dimensional permeation, membrane surface coverage by the salt, and ideal wettability of the salt-metal interface. Suppression of the isotopic transport behaviour for metal-side charging highlights the permeation barrier characteristics of a bubble-laden Ni-FLiBe interface, impacting permeability by up to 77%. This work attempts to resolve this issue via salt-side charging and informs constraints on the permeant charging methodology for future studies. The initial insights from HYPERION experiments call into question the design choices and estimated transport properties in earlier works. This study provides a plausible explanation for the observed scatter in H/D/T transport in FLiBe.