Applicability of a cryogenic distillation system for D-T isotope rebalancing and protium removal in a DEMO power plant

Highlights: • A bleed and recycle stream is used to calculate how much exhaust gas separation from a fusion reactor is required. • Separating all torus exhaust gases is unnecessary and energy consuming. • Cryogenic distillation (CD) is shown to be a feasible separation technology within exhaust composition bounds. • Reference and alternative scenarios show that isotope imbalance is an important parameter. • Further work is necessary in comparing CD to other isotope separation methods. -- Abstract: The tritium plant at the future European DEMOnstration (DEMO) fusion power plant will require isotope separation systems for protium removal and isotopic rebalancing of the torus exhaust stream. Protium removal and isotopic rebalancing can occur within a single separation technology which is based upon the exploitation of isotopic effects; the minimum amount of exhaust gas processing can be calculated using a heuristic developed for this purpose. A model has been developed to quantify the size and separation ability of a cryogenic distillation system to perform the required separation duties. Comparison of a reference scenario and six alternative scenarios shows that the isotope imbalance ratio between deuterium and tritium has the largest effect on the size and separation ability of a cryogenic distillation system; provided that a trace amount of protium is acceptable within the gas introduction system into the torus. A cryogenic distillation system is found to be a suitable technology in terms of energy usage and isotope separation, but a single system size is not suitable to process a range of different compositions. This evaluation of the applicability of cryodistillation to isotope rebalancing and protium removal for a DEMO reactor, form a base case against which other hydrogen isotope separation technologies can be investigated and compared in terms of size, power requirements and safety.