Neutron Transport for Materials and Design
Neutron transport computes where neutrons go and what they do, the foundation for breeding, shielding, and materials damage predictions.
What transport computes
Neutrons born in the plasma stream outward, scattering and reacting with everything they meet. Neutron transport solves for the neutron flux everywhere in the machine as a function of energy and direction. From that flux come reaction rates: tritium production, material damage, heating, and activation.
Two solution families
- Monte Carlo methods trace individual neutron histories and average over many; accurate for complex geometry, expensive to converge.
- Deterministic methods solve the transport equation on a grid; fast for some problems, harder for complex geometry.
- Hybrids use one to accelerate the other, focusing effort where the answer matters.
Why it is demanding
A fusion neutron interacts differently at every energy, described by cross-section data spanning the full spectrum. Getting the answer right means detailed geometry, good nuclear data, and enough statistics in the regions that matter, which makes transport a heavy consumer of HPC.
Applied to Hyperion
For the Hyperion breeder, transport underpins the tritium breeding ratio of 1.8, the heating deposited in the blanket, and the dose reaching the magnets. Small geometry changes shift these numbers, so transport is run across candidate designs during shielding design.
The burner case
The D-3He burner has a neutron fraction of only 5.44 percent, far lower than a D-T machine, but that flux still requires transport to size shielding and predict activation honestly.
Verification
Transport results are checked against benchmarks and against each other across methods, part of verification and validation, so the breeding and dose numbers are defensible.