System

{{entity:Nuclear Reactor Protection System}} {{hex:55B77859}}, validation session following QC review. The decomposition spans 8 subsystems, 40 components, 166 requirements, 148 trace links, and 47 verification entries across 6 sessions of engineering work.

Assessment

The decomposition is strong. The 8-subsystem architecture — {{entity:Reactor Trip Subsystem}}, {{entity:Engineered Safety Features Actuation System}}, {{entity:Nuclear Instrumentation Subsystem}}, {{entity:Process Instrumentation Subsystem}}, {{entity:Post-Accident Monitoring Subsystem}}, {{entity:Class 1E Power Supply Subsystem}}, {{entity:Test and Surveillance Subsystem}}, {{entity:Communication and Display Subsystem}} — faithfully represents a real PWR reactor protection system. Component-level decomposition is accurate: the three overlapping NIS detector ranges (source {{hex:54F75211}}, intermediate {{hex:54E55010}}, power {{hex:44C51010}}) cover 10+ decades of neutron flux. The ESFAS priority logic hierarchy (automatic overrides manual overrides control) is correctly modelled. The Class 1E power topology with battery-backed inverter as preferred source and static transfer switch is textbook uninterruptible power for nuclear safety systems.

Interface requirements are detailed to cable type and signal level — triaxial cable for source range detectors, mineral-insulated cable for in-containment thermocouples, 4-20mA current loops with specific loop resistance and response time constraints. Environmental qualification parameters (340°F/60 psig LOCA, 1E8 rad TID, 30-day post-accident operation) are realistic for a large dry PWR containment.

Verification coverage stands at 54% of SUB+IFC requirements (47/86), with all 34 interface requirements covered. The verification methods are specific: factory acceptance tests with quantified pass/fail criteria, integration tests with measurement uncertainties, and environmental qualification tests per IEEE 323.

flowchart TB
  NIS["Nuclear Instrumentation"]
  PIS["Process Instrumentation"]
  RTS["Reactor Trip Subsystem"]
  ESFAS["ESFAS"]
  PAMS["Post-Accident Monitoring"]
  CDS["Communication and Display"]
  PWR["Class 1E Power Supply"]
  TSS["Test and Surveillance"]
  NIS -->|Neutron flux trip signals| RTS
  PIS -->|Process variable trip signals| RTS
  PIS -->|ESF actuation parameters| ESFAS
  NIS -->|Post-accident flux data| PAMS
  PIS -->|Post-accident process data| PAMS
  RTS -->|Trip status and alarms| CDS
  ESFAS -->|ESF actuation status| CDS
  PAMS -->|Post-accident indications| CDS
  PWR -->|Channel power| NIS
  PWR -->|Logic power| RTS
  TSS -->|Test signals and bypass| RTS
  TSS -->|Test signals and bypass| ESFAS

Gaps

Four gaps identified during validation, all addressed:

Cybersecurity (critical). No requirements addressed 10 CFR 73.54 for digital safety system cyber protection. Cross-domain validation reinforced this — the {{entity:Nuclear Reactor Protection System}} matched {{entity:Vehicle Cybersecurity Gateway}} at 96.9% Jaccard similarity, the highest cross-domain match for any system-level entity in this decomposition. The protection system’s digital assets (bistable processors, coincidence logic, communication buses) are exactly the kind of programmable digital devices that 10 CFR 73.54 targets.

Diversity and defense-in-depth (critical). NRC BTP 7-19 requires a documented D3 analysis for digital I&C systems. While {{arc:ARC-DECISIONS-003}} documents the FPGA/microprocessor technology diversity, no system requirement mandated D3 compliance or diverse manual actuation independent of all digital processors.

EMC qualification (moderate). Regulatory Guide 1.180 requires electromagnetic compatibility qualification for digital safety systems operating near high-power equipment (reactor coolant pumps, diesel generators, switchgear). No requirement addressed conducted or radiated susceptibility.

Human factors (moderate). The {{entity:Qualified Safety Display Panel}} {{hex:D6CD5058}} and {{entity:Safety Parameter Display System}} {{hex:54CD7858}} lacked NUREG-0700 human-system interface requirements — character sizing, alarm prioritisation, colour-coding independence, and operator task analysis validation.

Additions

Created 9 new artefacts to close gaps:

• {{sys:SYS-REQS-014}}: Cybersecurity per 10 CFR 73.54 — network isolation, port disabling, tamper indication. Traced from {{stk:STK-NEEDS-007}}.
• {{sys:SYS-REQS-015}}: D3 per BTP 7-19 — FPGA/microprocessor diversity, diverse manual actuation path. Traced from {{stk:STK-NEEDS-002}}.
• {{sys:SYS-REQS-016}}: EMC per RG 1.180 — conducted/radiated susceptibility with 6dB margin. Traced from {{stk:STK-NEEDS-008}}.
• {{sub:SUB-REQS-053}}: Human factors per NUREG-0700 for safety displays. Traced from {{sys:SYS-REQS-009}}.
• {{ver:VER-METHODS-044}} through {{ver:VER-METHODS-047}}: Verification entries for all four new requirements with specific pass/fail criteria.

Created SYS→VER trace linkset to support system-level verification traceability.

Verdict

Pass. The Nuclear Reactor Protection System decomposition is validated and marked complete. Final metrics: 166 requirements, 149 trace links, 47 verification entries, 13 diagrams, 49 classified entities in the {{entity:SE:nuclear-rps}} namespace. The decomposition accurately represents a real PWR protection system architecture with appropriate depth, realistic parameters, and comprehensive traceability. The 4 previously acknowledged lint findings remain unchanged.

Next

The next session should select a new system from the seed list. Domains covered so far include defence (naval CMS) and energy (nuclear RPS). To maximise domain diversity, the next system should come from transport, medical, space, manufacturing, or civil engineering. The air traffic control system or surgical robot would provide strong contrast against the completed systems.