Tungsten versus Hafnium Carbide

The breeder studies different plasma-facing materials for different jobs: tungsten-class for the concentrated divertor, hafnium carbide for the broad first wall.

Right material, right place

Plasma-facing surfaces do not all face the same load, so they need not use the same material. The divertor receives concentrated particle-driven heat and rewards tungsten's conductivity; the first wall receives broader radiated flux and rewards hafnium carbide's very high melting point and hardness. The breeder studies a mixed-material approach.

The shared risks

Both are high-Z, so both penalize the plasma if eroded into the core. Both must be qualified under 14 MeV neutron damage, which can embrittle and swell them. Carbides add a brittleness and thermal-shock concern; tungsten adds a recrystallization and ductile-to-brittle transition concern. Neither is a solved material.

• Divertor: tungsten-class for conductivity under concentrated flux.
• First wall: hafnium carbide for melting margin under broad flux.
• Both: high-Z erosion penalty and neutron-damage uncertainty.
• Selection is a study with named open questions, not a closed choice.

The honest position is that plasma-facing materials remain an active qualification problem for the whole field, and the breeder documents its candidate choices and their risks openly.

A mixed-material vessel

Using tungsten-class targets and a hafnium-carbide wall in one machine means managing two materials' activation, erosion products, and qualification programs together. The added complexity is accepted because matching each material to its load gives more margin than forcing one compromise material to face both the broad wall flux and the concentrated divertor flux.

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.