The Bounding Accident Source Term
The most that any accident can release is set by the site tritium inventory — a small, well-characterized quantity.
A source term is the amount and form of radioactive material that could be released in an accident. It is the input to any dose or evacuation analysis. For a fusion plant the source term is dominated by tritium, and it is bounded from above by a simple fact: you cannot release more than the site holds, and the site holds little.
What is — and is not — in the source term
- In: a fraction of the mobile tritium inventory, mostly as HTO.
- In: small amounts of activated dust or corrosion products.
- Not in: volatile fission products — there are none.
- Not in: long-lived actinides — there is no fissile fuel.
Because tritium disperses and clears from the body quickly, and because the releasable fraction of an already-small inventory is limited by the barrier system, the resulting off-site dose in a bounding accident stays low. This is what underpins the case for right-sized emergency planning.
Why the analysis is tractable
With one dominant radionuclide, a known chemical behavior, and an inventory cap, the source-term analysis is far simpler than for a fission plant with hundreds of nuclides. The result is a bounded, defensible worst case rather than an open-ended severe-accident spectrum. See maximum credible accident.
The burner's near-absence of a large tritium inventory makes its source term smaller still.