MetroVolt caps per-site tritium inventory below one kilogram and consumes bred tritium internally as fuel-cycle feedstock. That single design rule reshapes safety analysis, licensing posture, and neighborhood conversations alike.
D-T plants must breed, extract, purify, and store tritium at multi-kilogram site inventories — the defining radiological source term of mainstream fusion. MetroVolt's D-³He cycle produces tritium only as a D-D side product; the staged fuel management burns it (catalysed operation) or holds it briefly as it decays into the very helium-3 the plant wants. The sub-kilogram cap is a designed operating rule of the fuel cycle, enforced by its own mass-balance ledger, deposited and plotted.
Less inventory means smaller source terms in accident analyses, lighter confinement engineering, and a licensing conversation about a bounded trace species rather than a bulk process stream.
Communities and regulators price the worst case. A plant whose entire site inventory of the mobile radioisotope is bounded below a kilogram — and falls with time by decay into fuel — starts that conversation from a categorically different place than a breeding-blanket plant. Tritium-lean is not just physics elegance; it is time-to-permit.
| Per-site tritium cap | < 1 kg (design rule) |
| Breeding blanket | none — no bulk tritium process stream |
| Bred tritium fate | burned / decays to ³He fuel |
| Basis | fuel-cycle mass balance, deposited |
| Licensing posture | trace-species source term |