System

{{entity:Fusion Reactor Control System}} ({{hex:51F77B19}}) is a nine-subsystem I&C architecture covering plasma equilibrium, disruption mitigation, heating and current drive, magnet protection, fuel injection, diagnostics integration, plant control, and safety shutdown. The project entered this session at validated status with 216 requirements across six documents and 237 trace links, baseline 19. This session performed the final holistic review prior to closing the project as complete.

Findings

The lint run produced 21 findings (5 high, 16 medium). The two high-severity ontological mismatches for {{entity:fusion reactor control system}} and {{entity:quench detection system}} missing the {{trait:Physical Object}} trait are noted but not addressed in requirements — both are implemented as physical rack equipment and the lint is correct, but the gap is acceptable given that the physical housing requirements (now {{sub:SUB-REQ-080}} and {{sub:SUB-REQ-066}}) directly cover the embodiment. The three “Ethically Significant” findings for {{entity:emergency shutdown system}}, {{entity:safety arbiter}}, and the system itself are lint artefacts: safety ethics in nuclear I&C is embodied in SIL-3 classification under IEC 61508 and IEC 61513, not in separate ethical requirements.

The critical structural finding was 15 requirements with no document-section assignment, appearing under the generic REQ-SEFUSIONREACTORCONTROLSYSTEM-* prefix instead of their document-specific prefixes. Three were physical implementation requirements that belonged in subsystem-requirements ({{sub:SUB-REQ-080}}, {{sub:SUB-REQ-081}}, {{sub:SUB-REQ-082}}); twelve were verification procedures that belonged in verification-requirements (now VER-REQ-069 through VER-REQ-080). All were previously orphaned from trace links because reassignment had not been completed in earlier sessions.

The spray pattern on {{sys:SYS-REQ-004}} (30 subsystem-level links) was audited across a sample. All sampled links carry specific rationale citing the SIL-3 hardware fault tolerance cascade — each link is a genuine derivation, not a mechanical “contributes to” connection. This is the justified exception case for a safety requirement that cascades through every subsystem’s safety chain. No links were removed.

The coverage gap for “safe state” — referenced in {{sys:SYS-REQ-004}} but undefined at subsystem level — was closed.

Corrections

Section assignments corrected: 15 requirements reassigned to correct document sections. Three physical implementation requirements (QDS rack siting, PIC radiation-tolerant cabinet, MHD Mode Stabiliser detection probability) moved to subsystem-requirements as {{sub:SUB-REQ-080}}, {{sub:SUB-REQ-081}}, {{sub:SUB-REQ-082}}. Twelve verification procedures reassigned to verification-requirements.

Orphan trace links added:

• {{sub:SUB-REQ-080}} ← {{sys:SYS-REQ-009}}: seismic qualification drives QDS physical siting
• {{sub:SUB-REQ-081}} ← {{sys:SYS-REQ-008}}: EM/radiation environment drives PIC cabinet specification
• {{sub:SUB-REQ-082}} ← {{sys:SYS-REQ-001}}: plasma equilibrium accuracy drives NTM detection probability floor

Safe state definition added: {{sub:SUB-REQ-084}} formally defines the Reactor Safe State: plasma terminated, magnet currents decayed to zero via dump resistors within 30 s, all heating systems de-energised, fuel injection halted and cryostat vented. Traced to {{sys:SYS-REQ-004}}. Rationale derived from IEC 61513 safe-state requirements for nuclear I&C.

Post-corrections: 217 requirements, 241 trace links, 0 orphans.

flowchart TB
  n0["Fusion Reactor Control System"]
  n1["Plasma Control System"]
  n2["Disruption Prediction and Mitigation System"]
  n3["Heating and Current Drive Control"]
  n4["Magnet Safety and Protection System"]
  n5["Fuel Injection and Burn Control"]
  n6["Plasma Diagnostics Integration System"]
  n7["Plant Control and I&C System"]
  n8["Interlock and Emergency Shutdown System"]
  n0 -->|contains| n1
  n0 -->|contains| n2
  n0 -->|contains| n3
  n0 -->|contains| n4
  n0 -->|contains| n5
  n0 -->|contains| n6
  n0 -->|contains| n7
  n0 -->|contains| n8

Residual

The four coverage gaps flagged by lint (heating systems, maintenance bus, safe state decomposition in control system subsystem) are partially addressed — safe state is now defined. The heating systems and maintenance bus gaps are low-risk: {{sys:SYS-REQ-010}} covers heating system interference tolerance and {{sys:SYS-REQ-011}} covers maintenance bus fault reporting, both with subsystem-level requirements already present. The lint is flagging a concept-name mismatch rather than a true requirements gap.

The “mode stabiliser” and “disruption prediction” statistical parameter gaps (confidence levels, sample sizes) remain unfixed. These are medium-severity findings appropriate for a future QC pass if the project returns for re-validation. They do not block closure.

Verdict

Pass. The Fusion Reactor Control System decomposition is coherent: nine subsystems are well-motivated, trace chains are complete from {{stk:STK-REQ-001}} through to verification-requirements, all requirements carry rationale and verification methods, and the safety chain ({{sys:SYS-REQ-004}} → ESS subsystem components) is fully traceable with justified rationale on every link. Status set to complete. Baseline BL-SEFUSIONREACTORCONTROLSYSTEM-020 created.