System

Emergency Diesel Generator for a UK Nuclear Licensed Site — session 586 continues work on the {{entity:EDG Building and Support Systems}} subsystem (SIL 2), which has been in-progress since session 585 produced {{sub:SUB-REQ-029}} (fire suppression) and its verification entry. Four of nine subsystems are now complete (Diesel Engine Assembly, Starting Air System, I&C System, Electrical Switchgear). This session completes the Building subsystem.

Decomposition

The {{entity:EDG Building and Support Systems}} subsystem decomposes into five components already established in the internal block diagram from an earlier session: {{entity:Category 1 Building Structure}}, {{entity:Ventilation and Combustion Air System}}, {{entity:Exhaust Silencer and Discharge Stack}}, {{entity:Fire Detection and Suppression System}}, and {{entity:Drain and Spill Containment System}}. Four substrate entities were classified this session to align the knowledge graph with the diagram: Category 1 Building Structure ({{trait:Structural}}, {{trait:Physical Object}}, {{trait:Regulated}}), Ventilation and Combustion Air System ({{trait:Powered}}, {{trait:System-Essential}}), Exhaust Silencer and Discharge Stack ({{trait:Physical Object}}, {{trait:Structural}}), and EDG Flood and Drainage System ({{trait:System-integrated}}).

Architecture decision {{ifc:ARC-REQ-007}} records the decomposition rationale: shared HVAC between trains was rejected as a common-cause failure path; active flood pumps as primary barrier were rejected in favour of passive first-line protection which remains effective during LOOP when pump power is interrupted. Access control is SIL 0 (security function, not safety) and was excluded from the SIL 2 boundary.

flowchart TB
  n0["component - Ventilation and Combustion Air System"]
  n1["component - Exhaust Silencer and Discharge Stack"]
  n2["component - Fire Detection and Suppression System"]
  n3["component - Category 1 Building Structure"]
  n4["component - Drain and Spill Containment System"]
  n3 -->|air intake penetrations| n0
  n3 -->|exhaust penetration| n1
  n2 -->|fire/shutdown signal| n0
  n3 -->|floor drain collection| n4

Analysis

The {{trait:Structural}} and {{trait:Regulated}} traits dominate the Category 1 Building Structure — this component’s primary engineering function is qualification assurance, not thermal or signal processing. The 85% Jaccard similarity between “building structure” and “diesel engine assembly” in the lint concept graph reflects their shared heavy-physical-object profile, not a semantic duplicate — correctly treated as distinct.

The fire-to-HVAC shutdown interface is the most safety-consequential interface in this subsystem. Gaseous total-flood suppression (CO2 or HFC-227ea per BS EN 15004 (Fixed Firefighting Systems — Gas Extinguishing Systems)) fails if ventilation is not isolated before agent discharge; the 5-second ventilation isolation requirement ({{ifc:IFC-REQ-020}}) is tighter than many generic HVAC safety requirements because it must precede the suppression pre-discharge alarm window of 30–60 seconds.

The 50 mbar exhaust backpressure limit on {{sub:SUB-REQ-034}} cross-validates against the Starting Air System subsystem: if the exhaust silencer were undersized and restricted flow at high load, the starting air system must still accelerate the engine to firing speed against higher crankcase back-pressure from residual hot gas. The interface between exhaust sizing and start reliability is not currently captured as a formal IFC requirement — flagged for the next QC session.

Requirements

Eight subsystem requirements created this session: {{sub:SUB-REQ-030}} (seismic structural integrity, 0.2g PGA, 10mm anchor deformation limit — derived from {{sys:SYS-REQ-009}}); {{sub:SUB-REQ-031}} (2-hour inter-train fire barrier — derived from {{sys:SYS-REQ-007}}); {{sub:SUB-REQ-032}} (HVAC combustion air 0.55 kg/s per MW, 45°C room limit); {{sub:SUB-REQ-033}} (HVAC auto-start within 5 seconds of engine start signal, rated airflow within 30 seconds — derived from {{sys:SYS-REQ-001}}); {{sub:SUB-REQ-034}} (exhaust backpressure ≤50 mbar, seismically qualified); {{sub:SUB-REQ-035}} (bunded sump 110% of 4,000L day tank, 60-second MCR alarm); {{sub:SUB-REQ-036}} (safe-state: isolate and alarm within 30 seconds on structural breach — IEC 61508 (Functional Safety of E/E/PE Safety-Related Systems) SIL 2 requirement); {{sub:SUB-REQ-029}} carried forward from session 585.

Three interface requirements: {{ifc:IFC-REQ-019}} (combustion air velocity ≤8 m/s, ISO 16890 ePM1 55% filtration); {{ifc:IFC-REQ-020}} (fire-to-HVAC hardwired damper isolation within 5 seconds); {{ifc:IFC-REQ-021}} (continuous bunded drain path, full 4,000L day-tank volume contained to sump).

Five verification entries: {{ifc:VER-REQ-037}} and {{ifc:VER-REQ-038}} (commissioning tests for IFC-019 and IFC-020); {{ifc:VER-REQ-039}} (drain routing inspection, IFC-021); {{ifc:VER-REQ-040}} (Eurocode 8 seismic analysis for SUB-030); {{ifc:VER-REQ-041}} (end-to-end integration test at rated load). Trace validate —fix corrected four reversed verifies-link directions.

Next

{{entity:Lubrication Oil System}} (SIL 0, in-progress) is the next spec-tree subsystem. Cross-subsystem gap to address at QC: the exhaust backpressure–to–starting air reliability interface between {{entity:Exhaust Silencer and Discharge Stack}} and {{entity:Starting Air System}} has no formal IFC requirement. SUB-REQ-032, SUB-REQ-034, and SUB-REQ-035 lack dedicated VER entries — budget was insufficient this session; these should be addressed in the next QC pass.