System

The {{entity:Emergency Diesel Generator System for UK Nuclear Licensed Site}} ({{hex:D7F73A59}}) project se-edg-uk-nuclear entered this session at state qc-reviewed with 171 requirements, 158 trace links, and 11 diagrams across 6 documents. Two subsystems — the {{entity:Lubrication and Bearing System}} and the {{entity:Synchronous Generator Assembly}} — had internal decomposition diagrams but no subsystem-level requirements. Twelve requirements had no trace links. The session objective was to close both gaps.

Decomposition

The {{entity:Lubrication and Bearing System}} ({{hex:46D53218}}) received six subsystem requirements. The critical path runs from the {{trait:Functionally Autonomous}} {{entity:Pre-Lube and Post-Lube Pump}} establishing 1.5 bar gallery pressure before the air start valve opens, through the {{trait:Engine-Driven Lube Oil Pump}} maintaining 3.5–5.5 bar at rated speed, to the post-shutdown 10-minute lubrication cycle that purges residual heat from the turbocharger bearing cartridge. The low-lube-oil-pressure trip setpoint (2.0 bar, 500 ms) is traced directly to {{sys:SYS-REQ-010}} hardwired engine protection.

flowchart TB
  n0["component<br>Engine Lube Oil Sump"]
  n1["component<br>Engine-Driven Lube Oil Pump"]
  n2["component<br>Pre-Lube and Post-Lube Pump"]
  n3["component<br>Lube Oil Cooler"]
  n4["component<br>Lube Oil Filter and Strainer"]
  n0 -->|oil draw| n1
  n1 -->|pressurised oil| n3
  n3 -->|cooled oil| n4
  n2 -->|pre/post-lube flow| n0

The {{entity:Synchronous Generator Assembly}} ({{hex:DEC51018}}) received five requirements. The {{entity:Generator Stator Winding and Thermal Protection}} ({{hex:D6953018}}) chain is covered by the Generator Cooling Fan auto-start at 50 rpm and 5-minute coasting period, both derived from {{sys:SYS-REQ-005}}. The Automatic Voltage Regulator is specified to ±1% steady-state regulation and a 1.5-second block-load transient recovery window — the latter is the binding constraint for Class 1E motor contactor immunity during load sequencer steps. The Generator Neutral Earthing Unit limits earth fault current to 5 A (high-impedance earthing), consistent with {{entity:Generator Protection Relay}} ({{hex:D5F77858}}) differential scheme requirements in {{sub:SUB-REQ-027}}.

flowchart TB
  n0["component<br>Stator and Stator Winding Assembly"]
  n1["component<br>Rotor and Field Winding"]
  n2["component<br>Automatic Voltage Regulator"]
  n3["component<br>Generator Neutral Earthing Unit"]
  n4["component<br>Generator Cooling Fan"]
  n2 -->|excitation current| n1
  n1 -->|rotating magnetic field| n0
  n0 -->|neutral connection| n3
  n4 -->|cooling airflow| n0
  n0 -->|terminal voltage feedback| n2

Analysis

Eight previously homeless VER requirements (covering the Engine Cooling System and Fuel Oil System interfaces written in a prior session) were reassigned to the verification-requirements document and linked to their parent {{ifc:IFC-REQ-022}} through {{ifc:IFC-REQ-028}} and {{sub:SUB-REQ-037}}, {{sub:SUB-REQ-039}}, {{sub:SUB-REQ-044}}, {{sub:SUB-REQ-047}} requirements. Four residual orphan SUB requirements — the Thermostatic Control Valve ({{sub:SUB-REQ-042}}), Fuel Transfer Pump trigger ({{sub:SUB-REQ-048}}), Fuel Oil System standards compliance ({{sub:SUB-REQ-050}}), and Generator Cooling Fan — were linked to their parent {{sys:SYS-REQ-005}} and {{sys:SYS-REQ-008}} entries.

The {{trait:Regulated}} trait in the AVR Class 1E requirement (IEC 60780, IEEE Std 603, IEEE Std 344) directly maps the ONR ENSREG seismic design basis to a testable qualification document scope, producing a verification requirement (qualification file inspection) that is deterministically auditable against the safety case.

Requirements

18 requirements were created: 11 SUB and 7 VER. 37 trace links were added. Project state at close: 189 requirements, 195 trace links, 0 orphans (reduced from 12). All 11 subsystems in the decomposition diagram now have at least one traced and verified subsystem requirement. The AVR transient recovery requirement (1.5s, ±3%) and the pre-lube pressure timing (20s, 1.5 bar) are the two requirements most likely to drive acceptance test specification during commissioning.

Next

The two new subsystems lack {{trait:Observable}} degraded-mode requirements: the Lubrication Oil System has no filter-bypass alarm response procedure requirement, and the Generator has no AVR manual/automatic changeover fallback for AVR failure. A follow-on decomposition session should address these, along with the remaining unlinked interface definitions between the Lubrication Oil System and the Engine Protection Relay Package.