Tritium Breeding Ratio Optimization
A D-T plant must breed more tritium than it burns; the breeding ratio is a computational optimization of blanket geometry and materials.
Why breeding is required
D-T fusion consumes tritium, which does not occur naturally in useful quantities. A plant must therefore breed its own by capturing fusion neutrons in a lithium-bearing blanket, where they produce tritium. The tritium breeding ratio, or TBR, is the tritium bred per tritium burned; it must exceed one, with margin for losses and startup inventory.
What sets the ratio
- Blanket material and lithium enrichment set how many neutrons produce tritium.
- Neutron multipliers increase the neutron budget before capture.
- Geometry and coverage set how many neutrons reach the blanket at all.
- Shielding and structure compete for the same neutrons.
The optimization
TBR is computed with neutron transport and optimized across blanket designs. Because the blanket, shield, and structure share space and neutrons, the optimization is coupled, and it is run over many candidate geometries rather than tuned by hand.
The Hyperion target
The Hyperion breeder is designed to a TBR of 1.8. That headroom above unity covers losses, radioactive decay, and the inventory needed to start later units. Kronos tracks the distinction between local and net breeding as an open reconciliation rather than asserting a single figure without conditions.
Materials coupling
Blanket materials must keep breeding under 14 MeV dose, so this work is tied to materials qualification; a material that breeds well but embrittles fast is not a solution.
Honesty
TBR predictions depend on nuclear data with real uncertainty, carried through uncertainty analysis so the design margin is genuine.