Fuel-Cycle Isotope Balancing

L1 coordinates real-time fuel delivery against isotope inventory, keeping the breeder's D-T mix and the burner's D-3He mix on target as fueling actuators fire.

Fueling meets inventory

Fueling is not just flow control; it draws from and returns to an isotope inventory. The breeder runs D-T and breeds tritium; the burner runs D-3He. L1's fueling actuators — gas valves and pellet injectors — must deliver the correct isotopic mixture, and the plant's fuel-cycle logic must keep the running inventory balanced against what the plasma consumes and the exhaust returns.

Real-time balancing

L1 (with the PLC fuel-cycle layer) tracks isotope accounting: fuel delivered, fusion consumption inferred from neutron/reaction rates, and species recovered by pumping and processing. Fueling setpoints are conditioned on this balance so the plasma composition stays on target and inventory is neither depleted nor over-accumulated. This is an operational balance, framed in kilograms and rates, never economics.

Per machine

• Breeder: D-T fueling with tritium breeding; products in the ~4 kg/yr tritium class plus ~1.97 kg/yr helium-3 and 14 MeV neutrons.
• Breeder lever: tritium breeding ratio treated across 1.1 / 1.5 / 1.8 in design studies.
• Burner: D-3He fueling, low-neutron (neutron fraction 5.44%), not aneutronic.

The tritium breeding ratio is a design lever, not a fixed constant: whether the blanket returns 1.1, 1.5, or 1.8 tritons per fusion changes the inventory dynamics the fuel-cycle control must manage. L1's role is to make delivery track whichever operating assumption is in force, deterministically.

Safety coupling

Fueling actuators are gated by vacuum and tritium-handling permissives; the PLC will not enable delivery outside a proven plant state. The fast gas and pellet loops execute the delivery, while the fuel-cycle logic maintains the slower inventory balance around them.