Developers using deuterium–tritium fuel should disclose the assumptions that connect startup inventory, breeding, processing, losses and deployment scale.
Fusion schedules are often published as if fuel appears when the machine is ready. For deuterium–tritium systems, that assumption is not good enough. Tritium is radioactive, scarce in civil inventories and expected to be bred inside future plants. The time between those facts is an engineering and deployment constraint.
A serious ledger begins before first plasma. It states the startup inventory, the source and timing of that inventory, the quantity held in processing systems and components, the expected breeding margin, extraction time, losses and decay. It then asks whether the same assumptions still work when one plant becomes several.
The minimum public tritium account
| Ledger item | Question to answer |
|---|---|
| Startup inventory | How much tritium is required before breeding begins, and from where? |
| Breeding margin | What plant-wide ratio is assumed after extraction and processing losses? |
| Residence time | How long is tritium held in blankets, components and processing loops? |
| Losses and decay | What inventory is unavailable through leakage, retention and radioactive decay? |
| Scale-up | Can available inventory start the second and subsequent plants? |
| Verification | Which experiments or facilities will validate each assumption? |
Fleet sequencing makes the account harder. The first plant may consume the available startup inventory while commissioning takes longer than expected, and a second may need fuel before the first has established a reliable surplus. A deployment forecast should therefore show inventory through time for the whole proposed fleet, including commissioning periods, reserve requirements, staggered starts and plausible delays between expected and actual surplus.
None of this is an argument against D–T fusion. It is an argument for treating fuel-cycle closure as part of the machine rather than a later procurement task. The IAEA describes tritium self-sufficiency as a key commercial challenge. Developers should make their pathway testable.
Commercial confidentiality is not a blanket excuse. Companies need not publish every proprietary process parameter to disclose system boundaries, key assumptions and the evidence required to improve them. Investors, regulators and prospective customers should ask for at least that much.
Dates acquire credibility when ledgers close. Until then, a D–T timetable is a scenario contingent on an unpublished fuel model.