Neutron Transport Codes for Fusion
Neutron transport codes track fusion neutrons through the blanket and structure to predict heating, breeding, and shielding.
Following the neutrons
Deuterium-tritium fusion releases 14 MeV neutrons that carry most of the energy and are unconfined by the magnetic field. Neutron transport codes follow these neutrons through the surrounding materials, computing where they deposit energy, how many are absorbed to breed tritium, and how effectively shielding protects the magnets and personnel. This is the neutronics foundation of blanket and shield design.
The transport equation, the Boltzmann equation for neutrons, is solved either by Monte Carlo particle tracking or by deterministic discretization of angle, energy, and space.
Monte Carlo and deterministic branches
Monte Carlo codes sample neutron histories through collision physics in exact geometry, giving high fidelity at the price of statistical noise controlled by variance reduction. Deterministic codes discretize the phase space and solve the resulting equations directly, giving noise-free global fields but requiring careful treatment of geometry and angular resolution. The two are cross-checked.
Nuclear data
Results depend on evaluated nuclear cross-section libraries for scattering, absorption, and (n,2n) reactions. Uncertainty in these data propagates into breeding and shielding predictions and is a recognized contributor to the overall uncertainty budget.
Design relevance
For the Hyperion breeder, neutron transport computes the tritium breeding ratio, targeted at 1.8, the nuclear heating of the blanket, and the shielding that protects the superconducting magnets from the 14 MeV flux. Its output feeds the activation and dose analysis. All results are simulation-stage ahead of construction.
- Tracks 14 MeV neutrons through materials
- Predicts breeding, heating, and shielding
- Monte Carlo vs deterministic methods
- Depends on evaluated nuclear data