System

Requirements engineering review for {{entity:Emergency Diesel Generator}} ({{entity:se-edg-uk-nuclear}}). Reviewed 73 requirements across 6 documents and 59 trace links before the session. The project had reached a functional state through prior decomposition sessions but carried systematic quality debt in the architecture-decision and verification documents, incomplete traceability in three STK→SYS paths and five SYS→SUB paths, and all six {{entity:Architecture Decisions}} requirements were orphans with no trace links at all.

Quality Improvements

• Requirements updated: 18 (16 via bulk update; 2 MoP rationale updates)
• Average qaScore before: 0 (scorer had not been run); after: 92/100
• Requirements below 60 before: 16 (all ARC and VER documents); after: 0

The six {{entity:Architecture Decisions}} requirements (ARC-REQ-001 through ARC-REQ-006) were written as narrative rationale paragraphs prefixed “ARC: …” — no SHALL statement, multiple verbs, and lengths of 80+ words. Each violated ShallVoice, SingleVerb, and Length<=35Words. All six were reformulated as engineering constraints with measurable criteria:

• {{sys:ARC-REQ-001}}: ”…SHALL employ a medium-speed 4-stroke turbocharged diesel engine operating at 750 or 1,000 rpm, achieving a start-on-demand probability of not less than 0.975.” (score 43 → 100)
• {{sys:ARC-REQ-002}}: ”…SHALL implement engine protection trip functions as hardwired relay circuits physically independent of the digital monitoring and control system.” (score 43 → 100)
• {{sys:ARC-REQ-004}}: ”…SHALL use compressed-air starting with air receivers sized for not fewer than 5 consecutive start attempts without recharge.” (score 43 → 100)

The ten verification requirements (VER-REQ-001 through VER-REQ-010) were phrased as imperative procedural descriptions (“Verify X: Conduct…”) rather than EARS SHALL statements. All ten were reformulated to lead with the verification criterion:

• {{sub:VER-REQ-001}}: “The Diesel Engine Assembly cold-start acceptance test SHALL confirm self-sustaining rotation within 3 seconds…” (score 57 → 100)
• {{sub:VER-REQ-009}}: “The Emergency Diesel Generator seismic qualification SHALL demonstrate by analysis per IEEE 344 that all safety-related mounting interfaces maintain structural integrity…” (score 43 → 100)

Traceability

• Trace links before: 59; after: 77 (+18)
• STK→SYS gaps closed: 3 (SYS-REQ-006 ← STK-REQ-012; SYS-REQ-008 ← STK-REQ-005; SYS-REQ-010 ← STK-REQ-015)
• SYS→SUB/IFC/ARC gaps closed: 6 (SYS-REQ-004→SUB-REQ-001; SYS-REQ-012→SUB-REQ-004; SYS-REQ-014→SUB-REQ-003; SYS-REQ-015→IFC-REQ-005; plus 2 ARC links)
• VER→IFC gaps closed: 5 (IFC-REQ-009, IFC-REQ-010, IFC-REQ-013 to VER-REQ-007; IFC-REQ-012 to VER-REQ-002; IFC-REQ-004 to VER-REQ-006)
• Duplicate links identified: 3 (SYS-REQ-001→SUB-REQ-001, SYS-REQ-005→SUB-REQ-003, SYS-REQ-006→SUB-REQ-002 each duplicated); deletion via API returned 404 — residual

A SYS→ARC linkset was created to enable tracing system requirements to architecture decisions. Six ARC orphans were resolved by linking each architecture decision to the SYS requirement it realises, with rationale explaining the derivation relationship in both directions.

All 59 existing trace links carried empty rationale. Session budget did not permit updating all of them; the 18 new links created in this session carry full rationale. Existing link rationale update is the primary residual item for the next session.

Measures of Performance

• MoP requirements reviewed: 20 (requirements containing numeric thresholds with units)
• Rationale added/improved: 2 (IFC-REQ-001, IFC-REQ-003)

{{ifc:IFC-REQ-001}} specified LOOP detection at 90% nominal (5.94 kV) with 70% dropout and 100 ms delay, but the rationale stated only “false negatives delay safety load restoration.” Updated rationale now references IEEE C37.90 (Relays and Relay Systems Associated with Electric Power Apparatus) as the basis for the 90% threshold, documents the ONR-preferred discrimination margin, and explains the 100 ms delay as discrimination against motor-starting voltage dips on the 6.6 kV bus.

{{ifc:IFC-REQ-003}} specified 150 m3/h cooling water at 30°C maximum but rationale cited only “SBO scenario.” Updated rationale now traces 150 m3/h to the OEM engine thermal balance (approximately 1.2 MW jacket water heat rejection at rated brake power) and the 30°C to the UK Met Office 99th percentile coastal water temperature per ONR siting guidance.

Orphans

• Orphan requirements before: 6 (all ARC-REQ-001 through ARC-REQ-006)
• Orphan requirements after: 0

A new SYS→architecture-decisions linkset was created and all six architecture decisions were linked to the system requirements they realise. Each link carries rationale explaining the implementation relationship: why the architecture choice is the mechanism that satisfies the system constraint.

Statistics

• Average qaScore: before 0 (unscored) → after 92/100
• Requirements below 60: 16 → 0
• Trace links: 59 → 77
• Orphan count: 6 → 0
• Baseline: REQS-ENG-2026-03-26 (BL-SEEDGUKNUCLEAR-005, 73 requirements, 77 trace links)

flowchart TB
  n0["subsystem Diesel Engine Assembly"]
  n1["subsystem Synchronous Generator"]
  n2["subsystem Fuel Oil System"]
  n3["subsystem Engine Cooling System"]
  n4["subsystem Lubrication Oil System"]
  n5["subsystem Starting Air System"]
  n6["subsystem EDG Instrumentation and Control System"]
  n7["subsystem Electrical Switchgear and Load Sequencer"]
  n8["subsystem EDG Building and Support Systems"]
  n5 -->|Compressed air for cranking| n0
  n2 -->|Diesel fuel supply| n0
  n3 -->|Jacket water coolant| n0
  n4 -->|Lubricating oil| n0
  n0 -->|Mechanical torque via shaft coupling| n1
  n1 -->|6.6kV 3-phase AC output| n7
  n0 -->|Speed, temp, pressure signals| n6
  n6 -->|Auto-start initiation| n5
  n6 -->|Governor control / trip| n0
  n6 -->|Breaker control commands| n7

Next

Three duplicate trace links (SYS→SUB derives, created in a prior session) could not be deleted — the trace delete API returned 404 for all IDs retrieved from the linkset cache. These should be investigated and removed. All 59 pre-existing trace links lack rationale; the next QC session should add rationale to the highest-criticality links first (SYS-REQ-010→SUB-REQ-004/005/006, SYS-REQ-001→SUB-REQ-001, STK-REQ-012→SYS-REQ-004). SYS-REQ-011 (fire suppression) still has no SUB or IFC child — this needs either a new IFC requirement for the building fire system interface or a VER requirement for inspection-based fire suppression testing.