Modeling fuel cycle dynamics beyond 50:50 deuterium–tritium operation

Fusion Power Plant operation requires tight coupling between plasma and fuel cycle: the plasma sets exhaust flows and injection requirements, while the fuel cycle determines the availability of the fuel necessary to sustain operation. Dynamic fuel cycle models have largely been adopted to address startup inventory, tritium self- sufficiency, and safety, often under the assumption of 50:50 DT operation. For operation with a generic mixture, these assumptions no longer suffice because multiple atomic species evolve simultaneously and can drive transients both in the plasma and fuel cycle inventories. A lumped parameters, dynamic model is presented, coupling 0D multispecies plasma particle balances to a Residence Time method fuel cycle representation. The coupled state evolves deuterium, tritium, helium-3 and helium-4 in the plasma and in inner fuel cycle, outer fuel cycle and storage inventories, with interconnecting flows characterized by finite residence times. The model is then applied across different scenarios: 50:50 DT, tritium-lean and D3He operation quantifying the resulting plasma composition evolution and fuel cycle inventory transients.