Vacuum Vessel Integrity
The vacuum vessel is the primary structural boundary; its failure de-confines the plasma and ends the reaction inward.
The plasma burns inside a high-vacuum vessel that serves as the first structural confinement boundary. Its integrity matters for both operation and safety, but its failure mode is benign: a breach lets air in, which immediately cools and extinguishes the plasma. The vessel fails toward off, not toward release.
Roles of the vessel
- Vacuum boundary: maintains the low pressure the plasma requires.
- First confinement barrier: holds activated dust and any in-vessel tritium.
- Structural support: carries loads from the plasma-facing components and blanket.
- Neutron shield anchor: positions the blanket and shielding around the plasma.
An in-vessel leak (air ingress) is a self-terminating event for the plasma: the fragile burn conditions collapse the instant vacuum is lost. A leak the other direction is bounded by the small in-vessel radioactive inventory — activated dust and residual tritium — and is caught by the surrounding cryostat and building confinement. The vessel is one layer of defense in depth, not the sole barrier.
Integrity assurance
The vessel is designed, fabricated, and inspected to pressure-boundary standards, with leak testing and in-service monitoring. Because the pressures involved are modest and the internal energy is small, the structural demands are far lighter than for a high-pressure fission primary system. See confinement barriers.
A vacuum-vessel fault is contained by design and, for the reaction, self-correcting.