Permeation of single gases and binary mixtures of hydrogen and helium through a MFI zeolite hollow fibres membrane for application in nuclear fusion

Abstract

Tritium Extraction Systems (TES) in future nuclear fusion power plants will recover tritium (radioactive hydrogen isotope) from the outlet stream of the breeder blanket, where tritium will be produced and purged out by a high flow rate of helium. This work presents an experimental assessment of the performance of a MFI zeolite hollow fibres membrane for the tritium removal and pre-concentration in the first stage of TES. A set-up was built for the permeation experiments of hydrogen and helium single gases and the separation experiments of binary mixtures of those gases. Numerous assays were performed for binary mixtures of H2 and He under various operating conditions (feed and permeate pressures, temperature, and feed composition) to assess the membrane separation performance. Optimal separations were achieved at the lowest temperatures (around room temperature) and the lowest hydrogen molar fraction (0.22). H2 and He permeances ranged 0.70–2.3 and 0.43–0.74μmolm−2Pa−1s−1, respectively, corresponding to membrane selectivities of H2 over He between 1.2 and 4.0. By regulating the feed pressure, hydrogen recovery factors around 50% were attained without compromising the maximum enrichment factor of 1.5. These preliminary data enable the design of a multi-stage separation process complying with the strict requirements for the tritium recovery and enrichment in a nuclear fusion power plant.