Tritium Breeding Simulation
Neutronics codes compute the tritium breeding ratio of a blanket, the key figure of merit for a self-sufficient deuterium-tritium fuel cycle.
Why breeding must be simulated
A deuterium-tritium plasma consumes tritium, which does not occur naturally in useful quantities. It must be bred by capturing fusion neutrons in a lithium-bearing blanket, where lithium-6 and lithium-7 react to produce tritium. The tritium breeding ratio (TBR), tritons produced per fusion neutron, must exceed one for self-sufficiency once losses are accounted for.
What the calculation involves
A Monte-Carlo neutronics model represents the plasma neutron source, the blanket geometry and composition, the structure, and any neutron multiplier such as beryllium or lead. The code tallies the tritium-producing reaction rate in the lithium, integrated over the blanket, and divides by the source rate to get the TBR.
Levers on breeding
- Lithium-6 enrichment, which raises the low-energy breeding cross-section
- Neutron multipliers that boost the neutron population before capture
- Blanket coverage fraction, reduced by ports and gaps
- Structural and coolant materials that parasitically absorb neutrons
Local versus net breeding
A local TBR computed for an idealized blanket segment overstates what a real machine achieves. Penetrations, diagnostic ports, and heating access reduce coverage, and some bred tritium is lost in processing. Credible design tracks the difference between an idealized local ratio and the achievable net ratio.
Kronos context
The Hyperion breeder is designed around a target breeding ratio of 1.8 to provide margin over unity. Neutronics simulation is how that target is evaluated against realistic geometry, and the distinction between local and net breeding is treated as an open reconciliation to be closed with detailed modeling, not assumed away.
Breeding results are always paired with the neutron source model, cross-section library, and coverage assumptions so the number can be interpreted correctly.