System

Radiochemistry Laboratory for a UK Nuclear Dockyard v2 (se-radiochem-lab-v2). Second decomposition session — the first session scaffolded the project with 13 subsystems and decomposed the {{entity:Active Ventilation and Containment System}}. This session tackles the {{entity:Radiation Protection and Health Physics Monitoring System}} ({{hex:54F57A59}}), selected as the highest safety-criticality subsystem: it interfaces with every laboratory space, drives ONR licence condition compliance, and its failure modes directly affect personnel dose.

Decomposition

The RP subsystem decomposes into six components reflecting the real instrumentation and data architecture of a nuclear dockyard radiochemistry facility:

• {{entity:Continuous Air Monitor Network}} ({{hex:54E57251}}) — Alpha-in-air and beta-gamma CAMs at each classified zone, PIPS detectors, 150 L/min sampling, three-level DAC-fraction alarm cascade
• {{entity:Area Gamma Dose Rate Monitoring Array}} ({{hex:54C57050}}) — Energy-compensated GM tubes across all classified areas, dual-path output (4-20mA hardwired + Modbus digital)
• {{entity:Contamination Monitoring Stations}} ({{hex:D4ED5050}}) — Hand-foot-clothing monitors at zone exits, portal monitors at controlled area boundary, bench-top alpha/beta meters
• {{entity:Personal Dosimetry and Dose Record System}} ({{hex:54F57B59}}) — EPD dispensing with real-time dose tracking, TLD as legal dose of record, CADOR integration, dose constraint enforcement
• {{entity:Health Physics Central Alarm and Display System}} ({{hex:50F57B58}}) — SIL 1 centralised SCADA with mimic display, alarm management, 10-year historian, statutory returns generation, active-standby redundancy
• {{entity:Radioactive Source Inventory and Calibration System}} ({{hex:44A57A58}}) — Sealed source register, barcode tracking, leak test scheduling, NPL-traceable calibration jig

The architecture follows a star topology with {{entity:Health Physics Central Alarm and Display System}} as the single aggregation point ({{arc:ARC-REQ-004}}). This is driven by ONR SAP EKP.3 requiring single-point alarm awareness for the Radiation Protection Supervisor. Each instrument retains local audible/visual alarm capability as defence-in-depth — loss of the central system degrades trending and recording but does not eliminate immediate warnings.

flowchart TB
  CAM["Continuous Air Monitor Network"]
  GAMMA["Area Gamma Dose Rate Monitoring Array"]
  CONTAM["Contamination Monitoring Stations"]
  DOSIM["Personal Dosimetry and Dose Record System"]
  HPCAD["HP Central Alarm and Display System"]
  SOURCE["Source Inventory and Calibration"]
  CAM -->|RS-485 Modbus: DAC readings, alarms| HPCAD
  GAMMA -->|4-20mA + Modbus: dose rates, alarms| HPCAD
  CONTAM -->|Ethernet: pass/fail, contamination data| HPCAD
  DOSIM -->|OPC-UA: EPD dose data, constraints| HPCAD
  SOURCE -.->|Calibration references| GAMMA
  SOURCE -.->|Calibration references| CAM
  HPCAD -->|OPC-UA read: zone status| LIMS["LIMS"]
  HPCAD -->|Hardwired relay: evacuation alarm| SAFETY["Facility Safety System"]

Analysis

The {{entity:Health Physics Central Alarm and Display System}} shares an architectural pattern with {{entity:Combat Direction Central}} ({{hex:D6FD7951}}) — both are centralised sensor-fusion and alarm hubs for safety-critical distributed monitoring. The naval CMS analog reinforces the design choice of hardwired relay paths for the most critical alarm function (evacuation), independent of digital network availability. This is the same diversity principle applied in naval combat systems where weapons release authority bypasses the digital combat management network.

Lint found 3 findings: one HIGH from the prior session (Active Ventilation physical object trait mismatch on {{sys:SYS-REQ-008}}), one MEDIUM on {{ifc:IFC-REQ-003}} statistical parameters (also prior session), and one LOW noting that architecture decisions and verification entries do not use SHALL — which is correct by convention for those document types.

Requirements

12 subsystem requirements ({{sub:SUB-REQ-010}} through {{sub:SUB-REQ-021}}) covering detection sensitivity, alarm cascades, measurement ranges, contamination clearance levels, dose constraint management, CADOR integration, system availability, UPS resilience, and source inventory management. Every requirement includes EARS-pattern SHALL statements with quantified thresholds and engineering rationale.

6 interface requirements ({{ifc:IFC-REQ-007}} through {{ifc:IFC-REQ-012}}) defining data paths: RS-485 Modbus for CAMs, dual-path 4-20mA/Modbus for gamma monitors, Ethernet for contamination and dosimetry, OPC-UA for LIMS integration, and hardwired relay for the safety-critical evacuation interface to {{entity:Facility Safety and Emergency Response System}}.

6 verification entries ({{ver:VER-REQ-007}} through {{ver:VER-REQ-012}}) including an end-to-end system integration test using Tc-99m aerosol release to exercise the complete detection-alarm-display chain. 13 trace links created with selective derivation rationale. All subsystem and interface requirements from this session are now traced.

Next

12 of 13 subsystems remain undecomposed. Next priority should be the {{entity:Facility Safety and Emergency Response System}} — it receives the hardwired evacuation relay from the RP subsystem and is the second-highest safety criticality subsystem. Alternatively, the {{entity:Sample Receipt, Registration and Preparation Facility}} is architecturally central as the entry point for all samples and drives workflow through every analytical laboratory. The prior-session lint finding on {{sys:SYS-REQ-008}} physical embodiment should be addressed during QC.