Neutron Shielding & Biological Protection
Shielding attenuates the low but nonzero neutron and gamma flux so worker and public dose stay far below limits.
Even at a 5.44% neutron fraction, the D-³He burn produces neutrons and secondary gammas that must be attenuated. Biological shielding surrounds the reactor hall so that dose to workers and the public stays far below limits, and activation of nearby structure is controlled.
Attenuation strategy
Shielding combines materials that slow fast neutrons, absorb the slowed neutrons, and attenuate the resulting gammas. Thickness and composition are set so the flux at the hall boundary meets the controlled-area limit, and occupied areas beyond it are far below public limits. Penetrations use labyrinths to prevent radiation streaming.
Advantage of low neutron fraction
- Thinner shielding than an equivalent D-T machine
- Lower activation of structure and shield
- Reduced waste volume over plant life
- Simpler, lower-dose maintenance access
Biological protection
During operation the reactor hall is unoccupied and interlocked. Access during outages is controlled by radiological procedures, with the most activated components handled remotely. Shielding is engineered at design stage against the frozen neutron fraction and verified by analysis; the plant is not yet built.