System

Emergency Diesel Generator for a UK nuclear licensed site — project se-edg-uk-nuclear. The project was scaffolded in session 570 with 46 requirements created but all homeless (not assigned to documents). This session corrected that housekeeping issue first, then executed the first subsystem decomposition: the {{entity:Diesel Engine Assembly}} at {{trait:Regulated}} SIL 3, the architectural foundation upon which all other subsystems depend.

Starting position: 46 requirements across STK/SYS/ARC/IFC, all unassigned. Ending position: 67 requirements across all six documents, baseline DECOMP-2026-03-26 created.

Decomposition

All 46 existing requirements were reassigned to their correct documents via reqs reassign: 18 to stakeholder-requirements (now STK-REQ-001 to 018), 15 to system-requirements (SYS-REQ-001 to 015), 6 to architecture-decisions, and 7 to interface-requirements. Refs updated to document-prefix format.

The {{entity:Diesel Engine Assembly}} was decomposed into seven components:

• {{entity:Diesel Engine Block and Crankcase}} ({{hex:DE851018}}) — {{trait:Structural}} main casting, crankshaft, piston assemblies
• {{entity:Diesel Fuel Injection System}} ({{hex:D6D53218}}) — cam-driven injection pump, high-pressure lines to 1,500 bar, injector nozzles
• {{entity:Diesel Engine Turbocharger}} ({{hex:C6C51018}}) — exhaust-gas centrifugal, 20,000–40,000 rpm, bearing oil from main gallery
• {{entity:Engine Governor and Speed Control Unit}} ({{hex:D5F73A18}}) — isochronous governor maintaining 50 Hz ±2%, mechanical overspeed trip at 115% rated speed
• {{entity:Engine Protection Relay Package}} ({{hex:D6B73858}}) — hardwired relay channels for overspeed, high coolant temperature, low oil pressure, overcurrent; physically separate from digital I&C per ARC-REQ-002
• {{entity:Engine Exhaust System}} ({{hex:CEC51018}}) — manifold, expansion bellows, silencer, seismically qualified stack
• {{entity:Crankshaft and Flexible Shaft Coupling}} — forged alloy steel crankshaft with flexible coupling accommodating ±0.3 mm parallel offset to generator shaft

flowchart TB
  n0["Engine Block and Crankcase"]
  n1["Fuel Injection System"]
  n2["Turbocharger"]
  n3["Governor and Speed Control"]
  n4["Engine Protection Relays"]
  n5["Exhaust System"]
  n6["Crankshaft and Coupling"]
  n1 -->|fuel charge| n0
  n2 -->|compressed air| n0
  n0 -->|exhaust gas| n2
  n0 -->|exhaust gas| n5
  n3 -->|fuel rack signal| n1
  n0 -->|mechanical power| n6
  n4 -->|trip signal| n0
  n0 -->|speed feedback| n3

Analysis

UHT lint flagged 27 high-severity findings, of which the substantive engineering ones are: the {{entity:Diesel Fuel Injection System}} ({{hex:D6D53218}}) is classified {{trait:Powered}} but has no power source requirements — the injection pump is mechanically driven, but the electronic governor overlay draws 24VDC Class 1E; a power budget requirement is needed when the I&C subsystem is decomposed. The digital monitoring and control system ({{hex:51F77B1D}}) is classified {{trait:Functionally Autonomous}} without a watchdog or fail-safe override requirement — this gap will be addressed during the EDG I&C System decomposition. Two findings were acknowledged as ontological artifacts: the “protection separation” concept extracted from ARC-REQ-002 was misclassified, and the “interface between the diesel engine assembly” correctly lacks the {{trait:Physical Object}} trait since it represents a connection protocol rather than a physical assembly.

Cross-domain search against the Factory corpus surfaced a {{entity:Safety Interlock and Trip System}} ({{hex:50F77859}}) described as hardwired relay-based for a UK nuclear site — Jaccard similarity with the Engine Protection Relay Package suggests checking whether 2oo3 voting logic is expected. IEEE Std 741 for nuclear EDGs requires single-channel hardwired trips; 2oo3 is used in reactor protection but would be disproportionate complexity here. No gap raised.

Requirements

Nine subsystem requirements created for the Diesel Engine Assembly ({{sub:SUB-REQ-001}} through {{sub:SUB-REQ-009}}): start self-sustain within 3 seconds, speed stability ±1.5 rpm steady-state, 720-hour endurance between overhauls, overspeed trip at 863 rpm within 1 second, low oil pressure trip at 2.0 bar within 2 seconds, high coolant temperature trip at 90°C within 2 seconds, fuel injection cylinder-to-cylinder balance ±3%, Seismic Category I at 0.2g PGA, and safe-state transition to standstill within 5 seconds. Six interface requirements defined the DEA’s boundaries with the Fuel Oil System, Engine Cooling System, Lubrication Oil System, Starting Air System, I&C System, and Synchronous Generator ({{ifc:IFC-REQ-008}} through {{ifc:IFC-REQ-013}}). Six verification entries were created including a critical end-to-end start-chain integration test ({{sub:VER-REQ-006}}) covering all five milestones from LOOP detection to safety load connection.

All 9 SUB requirements and 6 IFC-DEA requirements carry rationale. Three STK→SYS trace links were established to begin reducing 35 orphaned pre-existing requirements.

Next

The Diesel Engine Assembly is marked complete in the spec tree. Eight subsystems remain pending, all at SIL 3 or SIL 2: highest priority next session is the {{entity:EDG Instrumentation and Control System}} (SIL 3) — it integrates the hardwired protection relay outputs, the digital governor interface, the Main Control Room signals, and the PPS LOOP start path. The interface between the I&C system and the Engine Protection Relay Package ({{ifc:IFC-REQ-012}}) requires elaboration into full signal-level requirements. The 32 remaining orphaned requirements (STK and system-level IFC-REQ-001 to 007) need trace chain work — this should be done during the I&C decomposition session since many STK requirements map to I&C functions.