Technology Development for Isotope Rebalancing and Protium Removal in the EU-DEMO Fuel Cycle

One of the main design drivers of the EU-DEMO fuel cycle is to avoid unnecessary hydrogen isotope separation. In the tritium plant, this implies a novel functionality for isotope rebalancing (IR) and protium removal (PR). The task of IR is to adjust the deuterium-tritium ratio by several percent gradually over time in order to establish the required fuel mixture composition before reinjection into the torus. The PR is needed to process and separate protium, which inevitably enters the system via outgassing or replacement reactions. The candidate technology for the IR/PR function is temperature swing absorption, which is based on anticyclical operation of two absorption columns with reversed isotope effects. In order to characterize the separation process, a new test rig has been designed and is currently being assembled. This paper describes the principle idea of the process, develops a model to predict the performance, and presents simulation results for a DEMO-relevant gas composition. Palladium and vanadium have been selected for the modeling. It is shown that at the end of one column tritium could be separated with 92.5% purity. At the other column, protium with 46.4% and deuterium with 44.8% purity could be removed. A subsequent parameter study showed that the ideal gas supply would be 40% of the total length of the column and that 22 was the optimal number of cycles before extraction.