Deterministic Vacuum Interlocks
PLC-enforced vacuum interlocks protect both machines' vessels by making unsafe valve and pump states physically unreachable.
Purpose
The breeder's spherical-tokamak vessel and the burner's tandem-mirror vessel operate under high vacuum. A wrong valve sequence — venting to atmosphere while hot, or isolating a running turbopump — can damage equipment or breach containment. Kronos's vacuum interlocks are deterministic PLC logic that permits only safe transitions and blocks the rest, independent of operator intent or higher-level software.
Permissive logic
Each actuator — gate valve, roughing valve, turbopump, gauge isolation — carries a permissive derived from pressure gauges, pump status, and neighboring valve states. A valve opens only when its permissive is true. The logic is combinational and latched where sequences matter, so the safe state is the default and unsafe commands are simply not issued.
Example interlock
| Pump running | Downstream P ok | Open high-vac valve |
|---|---|---|
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
The table shows a single high-vacuum gate valve permissive: it may open only when the backing pump is running and downstream pressure is within range. Every other combination holds the valve closed. Real interlocks compose many such conditions, but each remains a transparent boolean the PLC evaluates every scan.
Coupling to the fuel cycle
Vacuum interlocks are the substrate for gas delivery and pumping. The gas-puff servo valves and the fuel-cycle isotope handling both depend on a proven vacuum state; the PLC will not enable fueling actuators unless the vessel vacuum permissives hold. This keeps the fast fueling loops from ever acting into an unsafe plant state, on either machine.