The Tungsten-Carbide Shield
Dense tungsten-based material is the workhorse inboard shield, attenuating fast neutrons and gammas where radial space is scarcest.
Density where it counts
Where space is tight — the inboard center stack — the shield must attenuate the most per millimeter. Dense, high-atomic-number materials such as tungsten and tungsten carbide are the reference choice because they scatter and slow fast neutrons and absorb gammas efficiently. They do the heavy attenuation before lighter moderating and absorbing layers finish the job.
Why tungsten carbide
Tungsten carbide combines tungsten's density and high-Z attenuation with useful mechanical and thermal properties as a bulk shield material. In the crowded inboard region it provides strong fast-neutron and gamma knockdown in a thin layer, buying magnet-dose margin that a compact machine cannot get from thickness alone.
- High density and high Z for fast-neutron and gamma attenuation.
- Compact per-millimeter performance for the inboard stack.
- Bulk material with workable thermal and mechanical behavior.
- Paired with moderator and boron layers for full-spectrum coverage.
Not a complete shield alone
Dense material slows and scatters fast neutrons but does not efficiently capture the slowed ones; that needs a moderator plus an absorber such as boron. The tungsten-carbide layer is the first, hardest-working stage of a layered shield, not the whole answer. Its heating and activation are tracked as part of the nuclear-heating and waste budgets.
Heating and activation tracked
As a dense material sitting in high flux, the tungsten-carbide layer absorbs significant nuclear heating and activates, both of which are tracked: the heating feeds the cryogenic and cooling budgets, and the activation feeds the waste and maintenance picture. Its shielding benefit is thus weighed against these downstream loads, not counted for free.
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.