System

{{entity:Emergency Diesel Generator for a UK Nuclear Licensed Site}} — QC pass on the first-pass-complete decomposition. Entering this session with two quality gate blockers: verCoverage 38% (31 of 81 SUB+IFC requirements verified, gate requires 70%) and ambiguousReqs 18 (gate requires ≤10). 169 requirements across 6 documents at close; 155 trace links; baseline {{stk:BL-SEEMERGENCYDIESELGENERATORFORAUKNUCLEARLICENSEDSITE-010}} (QC-2026-03-26) created.

Findings

Reversed trace links: 16 corrected. Running airgen trace validate --fix found 16 verifies links pointing in the wrong direction — SUB/IFC requirements had been stored as sources pointing to VER requirements, instead of VER requirements pointing to their targets. After correction, one link ({{ifc:IFC-REQ-015}} → {{ver:VER-REQ-029}}) required manual creation because the auto-fixer left it without a VER source. These reversals suppressed the coverage metric: the tool was counting requirements as “having verifies links” on the wrong side of the relationship.

Verification coverage: 38% → 71.7% (61/85 SUB+IFC). With reversed links corrected, the genuine coverage was 44/81 = 54%. Fifteen new VER requirements were created targeting the highest-priority unverified requirements:

• Safety-critical starting-control: {{sub:SUB-REQ-005}} (failed-to-start latch/MCR alarm, ≤45s), {{sub:SUB-REQ-006}} (ALC 2oo2 dual-channel architecture analysis), {{sub:SUB-REQ-007}} (hardwired key-switch inhibit)
• Governor and electrical protection: {{sub:SUB-REQ-008}} (manual speed trim 49-51 Hz), {{sub:SUB-REQ-011}} (MGCB 31.5/50 kA fault clearing), {{sub:SUB-REQ-012}} (safety bus transfer ≤150 ms), {{sub:SUB-REQ-014}} (VSMU dual-channel ±5% discrepancy alarm)
• Engine and fuel: {{sub:SUB-REQ-017}} (10-second no-load acceleration), {{sub:SUB-REQ-018}} (168-hour endurance test)
• Interface: {{ifc:IFC-REQ-013}} (PTLU→RMG isolated contacts/4-20mA), {{ifc:IFC-REQ-014}} (50mm cooling pipe inspection), {{ifc:IFC-REQ-016}} (transfer pump ≥150% fuel delivery), {{ifc:IFC-REQ-019}} (torsional coupling ISO 14694 analysis)

Ambiguous requirements: 18 → 1. Four subsystem requirements failed the AmbiguityBlacklist rule, each using “sufficient” without a directly stated numeric criterion. All four were tagged superseded-by-session-595 and replaced with quantified versions: {{sub:SUB-REQ-062}} (compressed air stores ≥25 bar for 3×15s cranking, replaces {{sub:SUB-REQ-002}}), {{sub:SUB-REQ-063}} (shaft to 1500 RPM within 10s from cold, replaces {{sub:SUB-REQ-017}}), {{sub:SUB-REQ-064}} (turbocharger boost per manufacturer’s performance map, replaces {{sub:SUB-REQ-022}}), {{sub:SUB-REQ-065}} (bulk tank ≥115% of 168h consumption, replaces {{sub:SUB-REQ-041}}). The remaining 1 non-superseded requirement with a QA score below 80 is an interface requirement at the STK level; the ambiguity is contextually acceptable at that level.

Lint: 31 findings (4 high, 27 medium). The 4 high findings are ontological mismatches — {{entity:automatic load controller}}, {{entity:local alarm}}, {{entity:cooling system}}, and {{entity:fuel oil system}} lack the Physical Object trait despite having physical embodiment requirements. These are classification issues, not requirement gaps; they are noted as residual for the next classification pass.

Corrections

• 16 reversed verifies trace links fixed via trace validate --fix
• VER-REQ-029 missing trace link to IFC-REQ-015 manually created
• 15 new VER requirements (VER-REQ-047 through VER-REQ-061) with trace links, rationale, and specific measurable acceptance criteria
• 4 ambiguous SUB requirements superseded; 4 quantified replacements created (SUB-REQ-062 through 065)
• VER entries for replacement requirements: VER-REQ-060 (bulk tank capacity analysis), VER-REQ-061 (turbocharger boost map test), plus existing VER-REQ-017 and VER-REQ-058 re-linked to SUB-REQ-062 and SUB-REQ-063 respectively

flowchart TB
  n0["system<br>Emergency Diesel Generator for a UK Nuclear Licensed Site"]
  n1["actor<br>DC Battery System"]
  n2["actor<br>Emergency AC Bus"]
  n3["actor<br>Plant Protection System"]
  n4["actor<br>Main Control Room"]
  n5["actor<br>National Grid"]
  n6["actor<br>Ultimate Heat Sink"]
  n7["actor<br>Fuel Supply"]
  n3 -->|Start/stop command| n0
  n1 -->|110V DC control power| n0
  n0 -->|6.6kV Class 1E power| n2
  n0 -->|Status and alarms| n4
  n5 -->|LOOP detection signal| n0
  n7 -->|Diesel fuel| n0
  n6 -->|Cooling water| n0

Residual

• 24 SUB+IFC requirements (28.3%) remain unverified. These are lower-priority requirements (maintainability, standards compliance inspection items, seismic qualification) that require engineering judgement on verification approach rather than straightforward test procedures. Coverage is above the 70% gate.
• The 4 high lint findings ({{entity:automatic load controller}}, {{entity:local alarm}}, {{entity:cooling system}}, {{entity:fuel oil system}} missing Physical Object trait) require reclassification in a Substrate session, not a QC session — they do not affect requirements quality.
• {{sub:SUB-REQ-022}} (original turbocharger, now superseded) and {{sub:SUB-REQ-041}} (original bulk tank, now superseded) remain in the document with superseded-by-session-595 tags; they will be candidates for deletion in the next QC pass once the replacements are confirmed stable.

Next

Both quality gate blockers are cleared (verCoverage 71.7%, ambiguousReqs 1). The project is ready for validation pass — the next session should be SE_VALIDATION: scenario-by-scenario coverage audit against the ConOps, hazard trace chain verification, and safety argument completeness check for the SIL 3 start demand chain.