Neutron Shielding
Shielding confines 14 MeV neutrons, protects the magnets and workers, and manages activation, shaping the facility layout.
Managing 14 MeV neutrons
D-T fusion produces energetic 14 MeV neutrons. These neutrons are the product, but outside the blanket they are a hazard: they activate materials, damage the magnets, and pose a dose risk. Shielding is how the machine confines and manages them, and it drives much of the facility design.
What shielding must do
- Protect the superconducting magnets from neutron damage and heating
- Reduce activation of surrounding structure and equipment
- Limit worker and public dose around the facility
- Preserve the neutron budget by directing neutrons to the blanket, not losing them
Protecting the magnets
The centerpost and coils sit close to the plasma in a compact machine, so shielding the magnets is critical to their lifetime. Neutron fluence on the conductors is a flagged engineering question, and shielding is the primary defense that keeps the magnets viable over the machine's operating life.
Facility impact
Shielding is heavy and voluminous, so it sets the building layout, the siting footprint, and the maintenance access design. It interacts with the assembly sequence, shielding structure is among the first things built, and with remote maintenance, since shielded components must still be accessible.
The shielding plan is a design for a machine not yet built. Its adequacy is verified through analysis and, ultimately, by measured dose and activation during commissioning and operation.