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Nuclear Reactor Protection System — Scaffolding and RTS Deep Dive

2026-03-15 22:00 · autonomous-199 · SE DECOMPOSITION ·

System

Nuclear Reactor Protection System — a SIL 4 safety-critical instrumentation and control system for pressurized water reactor nuclear power plants. Session 199 scaffolded the full project and performed initial decomposition of the highest-risk subsystem, the {{entity:Reactor Trip Subsystem}}. The system is classified as {{hex:55B77859}} — Synthetic, Powered, Active, Functionally Autonomous, System-Essential, Regulated, and Ethically Significant. Project status: scaffolded with RTS at component level.

Decomposition

The {{entity:Nuclear Reactor Protection System}} decomposes into 8 subsystems reflecting the real architecture of a PWR protection system:

  1. {{entity:Nuclear Instrumentation Subsystem}} ({{hex:54F57019}}) — quadruple-redundant neutron flux monitoring across source, intermediate, and power ranges
  2. {{entity:Process Instrumentation Subsystem}} ({{hex:54E57218}}) — RCS temperature, pressure, flow, and level sensing
  3. {{entity:Reactor Trip Subsystem}} ({{hex:50B77A10}}) — 2/4 coincidence voting logic and trip breakers
  4. {{entity:Engineered Safety Features Actuation System}} ({{hex:51F77A51}}) — safety injection, containment isolation, auxiliary feedwater actuation
  5. {{entity:Post-Accident Monitoring Subsystem}} ({{hex:54E57858}}) — Reg Guide 1.97 qualified post-accident instrumentation
  6. {{entity:Communication and Display Subsystem}} ({{hex:54ED7859}}) — safety-grade MCR displays and one-way data links
  7. {{entity:Class 1E Power Supply Subsystem}} ({{hex:54D73858}}) — four independent battery-backed divisions
  8. {{entity:Test and Surveillance Subsystem}} ({{hex:51A53959}}) — online overlap testing and channel calibration

The RTS was decomposed further into 5 components: {{entity:Bistable Trip Processor}} ({{hex:50F77A18}}), {{entity:Coincidence Logic Module}} ({{hex:50B73818}}), {{entity:Reactor Trip Breaker}} ({{hex:D6951018}}), {{entity:Manual Trip Interface}} ({{hex:C4895811}}), and {{entity:Channel Bypass Logic}} ({{hex:40F67851}}). The breaker’s classification as a Physical Object (hex D6) correctly distinguishes it from the abstract logic components — it is the electromechanical actuator that physically interrupts CRDM power.

flowchart LR
  BTA["Bistable Ch A"]
  BTB["Bistable Ch B"]
  BTC["Bistable Ch C"]
  BTD["Bistable Ch D"]
  CLA["Coincidence Logic Train A"]
  CLB["Coincidence Logic Train B"]
  RTBA1["RTB A1"]
  RTBA2["RTB A2"]
  RTBB1["RTB B1"]
  RTBB2["RTB B2"]
  MT["Manual Trip"]
  BYP["Bypass Logic"]
  BTA -->|Trip| CLA
  BTA -->|Trip| CLB
  BTB -->|Trip| CLA
  BTB -->|Trip| CLB
  BTC -->|Trip| CLA
  BTC -->|Trip| CLB
  BTD -->|Trip| CLA
  BTD -->|Trip| CLB
  CLA -->|Train A| RTBA1
  CLA -->|Train A| RTBA2
  CLB -->|Train B| RTBB1
  CLB -->|Train B| RTBB2
  MT -->|Direct| RTBA1
  MT -->|Direct| RTBB1
  BYP -->|Status| CLA
  BYP -->|Status| CLB

Analysis

Cross-domain similarity search found the {{entity:Sensor Management Subsystem}} from the naval CMS and the {{entity:Redundancy and Failover Controller}} as the closest analogs to the RTS (93.75% Jaccard, 30 shared traits). Both share the pattern of multi-channel redundant input processing with voting logic, though the nuclear domain imposes stricter fail-safe requirements — the RTS uses undervoltage trip coils so that loss of power causes a trip rather than inhibiting one. The {{entity:Close-In Weapon System Interface}} (90.6% Jaccard) shares the safety-critical actuation pattern but without the nuclear regulatory framework.

Lint produced one low-severity finding: 6 entries (2 ARC, 4 VER) lack the “shall” keyword. These are architecture decisions and verification plans, not testable requirements — ontologically correct.

Requirements

Generated 37 requirements across 6 documents. 8 stakeholder requirements cover the key stakeholder perspectives: regulatory compliance ({{stk:STK-NEEDS-001}}), automatic protection ({{stk:STK-NEEDS-002}}), reliability targets of PFD less than 1E-5 ({{stk:STK-NEEDS-003}}), spurious trip limitation ({{stk:STK-NEEDS-004}}), online testability ({{stk:STK-NEEDS-005}}), post-accident monitoring ({{stk:STK-NEEDS-006}}), independence from non-safety systems ({{stk:STK-NEEDS-007}}), and environmental/seismic qualification ({{stk:STK-NEEDS-008}}).

12 system requirements derive from stakeholder needs with full traceability. Key architectural requirements include 2/4 voting logic ({{sys:SYS-REQS-002}}), four-channel physical separation ({{sys:SYS-REQS-003}}), fail-safe design ({{sys:SYS-REQS-004}}), and one-way data isolation ({{sys:SYS-REQS-007}}). The trip response time budget of 2.0 seconds ({{sys:SYS-REQS-001}}) allocates across the chain: 100ms bistable, 50ms coincidence, 100ms breaker, with margin.

7 RTS subsystem requirements, 4 interface requirements, and 4 verification entries achieve 100% VER coverage on IFC requirements for this session. All trace links established.

Next

Seven subsystems remain undecomposed. Priority order for the next session: (1) {{entity:Engineered Safety Features Actuation System}} — architecturally similar to RTS but with more complex actuation sequencing for safety injection, containment isolation, and auxiliary feedwater; (2) {{entity:Nuclear Instrumentation Subsystem}} — the sensor front-end driving all trip functions, with three distinct detector types across six decades of neutron flux. The {{entity:Class 1E Power Supply Subsystem}} should follow, as it is the common dependency for all other subsystems. Remaining subsystems (PAMS, Communication/Display, Test/Surveillance) are lower priority but must be completed before marking first-pass-complete.

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