Counter-current isotope swamping in a membrane reactor: The PERMCAT process and its applications in fusion technology

Abstract

A PERMCAT reactor is a catalytic membrane reactor that combines a Pd/Ag membrane and a catalyst bed. It has been developed to ensure very high tritium recovery from the unspent fuel of fusion machines using deuterium tritium mixtures. The PERMCAT process takes advantage of simultaneously unlocking chemically bound tritium via heterogeneously catalysed isotope exchange reactions and removing tritium via its selective permeation through the membrane. The PERMCAT reactor operated in the counter-current isotope swamping mode allows a very low tritium activity at the outlet of the component to be maintained. Two main issues have been solved to achieve efficient and reliable PERMCAT operation. Firstly, the mechanical design has to cope with the elongation and deformation of the membrane resulting from thermal expansion and lattice parameter increase under operation with hydrogen. Secondly, the catalyst material has to be chosen in order to promote isotope exchange reactions while minimising the numerous side reactions that occur especially when the mixture contains carbon oxides. This paper presents a general overview of the R&D performed at the Tritium Laboratory Karlsruhe for PERMCAT technology. Technical solutions to solve both issues together with relevant experimental results including processing tests with tritium are discussed.