Shield Design and Layout

Shield performance depends as much on where material goes as how much there is; the inboard shield is the hardest, most space-constrained part.

Placement beats bulk

A shield's effectiveness depends on layering and placement, not just total mass. Fast-neutron scatterers, moderators, and absorbers must be arranged so neutrons are slowed then captured, and so streaming paths through gaps and penetrations are minimized. A thick shield with a straight gap can leak more dose than a thinner, well-laid-out one.

Streaming is the enemy

Neutrons find gaps. Ports, coolant channels, and assembly joints create streaming paths that carry dose past the shield to the magnets. The layout uses offsets, dog-legs, and local shielding around penetrations so no straight line runs from plasma to coil. This detail work often matters more than a uniform thickness figure.

Inboard is the crux

• Inboard shield shares the narrow center stack with TF and center-post.
• Least available thickness sits where flux is highest.
• Every penetration needs local shielding against streaming.
• The layout is optimized against magnet dose and center-post life together.

Shield layout is computed and reproducible, and it is validated against magnet dose limits as part of the breeder's coupled center-stack design.

Validation by transport calculation

The layout is confirmed with neutron-transport calculations that trace the spectrum through each layer and around every penetration, so streaming paths are found in analysis rather than at commissioning. These computed, reproducible results are the basis on which the shield is judged against magnet dose and heating limits before any hardware exists.

This page documents a design and simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind first tritium is targeted near 2030. Figures are computed, reproducible targets, not measurements.