System

STEP Fusion Power Plant ({{entity:STEP Fusion Power Plant}}, {{hex:5AF5121D}}) — 9-subsystem fusion energy project at the close of its first QC pass. Entry state: 149 requirements, 124 trace links, 1 orphan, 7 baselines, DECOMPOSITION_STATUS concept-defined. Exit state: 162 requirements, 161 trace links, 0 orphans, 8 baselines, status qc-reviewed.

System decomposition across 9 subsystems: {{entity:Plasma Control System}}, {{entity:Tokamak Core Assembly}}, {{entity:Superconducting Magnet System}}, {{entity:Cryogenic Plant}}, {{entity:Tritium Plant}}, {{entity:Power Conversion System}}, {{entity:Remote Handling System}}, {{entity:Vacuum System}}, {{entity:Radiation Protection System}}.

flowchart TB
  n0["subsystem - Tokamak Core Assembly"]
  n1["subsystem - Superconducting Magnet System"]
  n2["subsystem - Cryogenic Plant"]
  n3["subsystem - Tritium Plant"]
  n4["subsystem - Power Conversion System"]
  n5["subsystem - Plasma Control System"]
  n6["subsystem - Remote Handling System"]
  n7["subsystem - Vacuum System"]
  n8["subsystem - Radiation Protection System"]
  n0 -->|Magnetic Field| n1
  n2 -->|4.5K Cooling| n1
  n3 -->|Fuel / Exhaust| n0
  n0 -->|Thermal Power| n4
  n5 -->|Control Commands| n0
  n5 -->|Coil Commands| n1
  n7 -->|Vacuum| n0
  n6 -->|Maintenance Access| n0
  n8 -.->|Shielding| n0

Findings

Verification coverage gaps were the dominant deficiency. Entry state showed 49 VER entries against 57 SUB+IFC requirements with measurable criteria. Trace link analysis revealed 23 cases where VER entries had been created in prior sessions but the IFC→VER and SUB→VER trace links had not been added, making them invisible to the verify matrix and orphan reports.

Specifically: IFC-REQ-010 through IFC-REQ-020, IFC-REQ-023 (12 requirements) each had corresponding VER-REQ-025 through VER-REQ-035 and VER-REQ-041 — created in sessions 507–511 — but no trace links. Similarly, SUB-REQ-003, 004, 006, 007, 008, 009, 010, 011, 012, 013, 014 (11 requirements) had VER entries VER-REQ-014 through VER-REQ-024 that were disconnected from their source requirements. These 23 disconnected links were the primary cause of the apparent low verification coverage.

Seven SUB requirements had no VER entries at all: {{sub:SUB-REQ-019}} (ISS DT purity), {{sub:SUB-REQ-020}} (TSDS fuel delivery), {{sub:SUB-REQ-021}} (BTES extraction rate), {{sub:SUB-REQ-024}} (CS flux swing), {{sub:SUB-REQ-026}} (magnet power supply ramp), {{sub:SUB-REQ-028}} (TF coil thermal margin), {{sub:SUB-REQ-030}} (pressure monitoring accuracy and interlock). Two IFC requirements also lacked VER entries: {{ifc:IFC-REQ-024}} (quench interlock 1 ms timing) and {{ifc:IFC-REQ-027}} (pressure monitoring to PCS interface, 10 Hz / 50 ms Ethernet plus hardwired interlock).

Lint high-severity findings (10 total): The two most actionable were the absence of redundancy/failover requirements for {{entity:Tritium Plant}} (classified {{hex:52953218}}, System-Essential, bit 16) and the absence of safety override and watchdog requirements for the {{entity:isotope separation system}} ({{hex:55973219}}, Functionally Autonomous, bit 15). The remaining 8 high findings relate to Physical Object trait classification mismatches for software-dominant subsystems — consistent with the false-positive pattern noted for software subsystems in prior sessions and correctly dismissed.

Structural issues: ARC-REQ-008 (Vacuum System three-component topology) was the sole orphan requirement — no trace link to any SYS requirement. Two pairs of duplicate diagrams: TCA Internal Components (diagram-1774361478017 empty, diagram-1774361484210 populated) and SMS Internal Components (diagram-1774363345725 populated, diagram-1774363350619 populated with different component ordering).

Spray pattern check: no SYS requirement showed 5+ SUB links. Link rationale coverage was complete for all existing links examined.

Corrections

23 missing SUB/IFC→VER trace links created: 11 SUB→VER links (SUB-003 through SUB-014), 12 IFC→VER links (IFC-010 through IFC-020, IFC-023). These connected pre-existing VER entries to their source requirements.

9 new VER entries created and linked:

• {{ifc:IFC-REQ-024}} → VER-039: oscilloscope-based 1 ms quench interlock signal propagation test
• {{ifc:IFC-REQ-027}} → VER-040: combined Ethernet latency and hardwired interlock path verification
• {{sub:SUB-REQ-019}} → VER-042: residual gas analyser ISS DT purity ≥99.9 mol% and throughput
• {{sub:SUB-REQ-020}} → VER-043: TSDS containment integrity and 60-second fuel delivery response
• {{sub:SUB-REQ-021}} → VER-041: calorimetric BTES tritium hold-up ≤1 g accountability
• {{sub:SUB-REQ-024}} → VER-045: CS flux swing integration and ramp rate measurement
• {{sub:SUB-REQ-026}} → VER-047: magnet power supply ramp time and 10 ppm current ripple test
• {{sub:SUB-REQ-028}} → VER-044: Cernox sensor winding-pack temperature and thermal margin calculation
• {{sub:SUB-REQ-030}} → VER-046: PMS six-decade accuracy and 200 ms interlock response test

2 new SUB requirements to address lint gaps:

• SUB-023: Tritium Plant single-component failure tolerance at ≥50% throughput with 30-second automatic isolation — linked to {{sys:SYS-REQ-005}} and verified by VER-049
• SUB-024: ISS hardwired manual override (10-second valve closure) and 60-second watchdog — linked to {{sys:SYS-REQ-005}} and verified by VER-048

ARC-REQ-008 orphan fixed: trace link added to {{sys:SYS-REQ-008}} (ultra-high vacuum integrity).

2 duplicate diagrams deleted: empty TCA Internal Components (diagram-1774361478017) and duplicate-ordered SMS Internal Components (diagram-1774363350619). Populated versions retained.

Residual

45 medium-severity lint findings remain. These split into two groups: (a) Physical Object trait mismatches for software-dominant subsystems (PCS, Plasma Control) — correctly dismissed as false positives for non-physical entities; (b) STK coverage gaps where stakeholder concepts (national grid notification, environmental permitting, fusion research data sharing) have not been decomposed to SYS-level requirements. These are legitimate gaps but require engineering judgement about scope and are deferred to a validation session.

No SUB requirements contain “degraded” or “graceful” language — degraded-mode verbiage check passed. No requirements without rationale or verification fields — both at 0/162 missing.

Next

Verification coverage is now 60 VER entries across 162 requirements (37%), with 32 SUB and 27 IFC requirements each having at least one VER trace link. The STK coverage gaps identified by lint (items 42–55: national grid connection, environmental permitting, fusion research data sharing, safety assessment principles) should be addressed in the next decomposition or validation session by creating SYS-level requirements for the most safety-critical gaps. The next session qualifies as session 8 of 10 toward the sessions gate and should focus on validation rather than further decomposition.