System

The {{entity:STEP Fusion Power Plant}} ({{hex:DEC51019}}) at validation state. Session 528 resolved the final gap in the verification plan: 33 requirements — 14 {{entity:subsystem-requirements}}, 11 {{entity:interface-requirements}}, and 8 {{entity:system-requirements}} — had no verifies trace links. All existing trace link gaps were from an early scaffolding session that created VER requirement text without wiring the traceability. The previous validation cycle had identified these as blockers and this session was assigned to close them. Total project state entering this session: 250 requirements, 387 trace links, 101 VER entries.

Verification Audit

The airgen verify run output confirmed the root problem: 81% trace link coverage before this session, with the missing 19% concentrated in two groups. The first group (14 SUB reqs: {{sub:SUB-REQ-007}} through {{sub:SUB-REQ-014}} and {{sub:SUB-REQ-049}} through {{sub:SUB-REQ-054}}) had matching VER entries already in the document — the wiring simply had the wrong internal ID format. An earlier session had used REQ-SESTEPFUSIONPOWERPLANT-NNN internal IDs while I attempted to create links using the display ref format (e.g., SUB-REQ-007). Once the internal ID mapping was resolved, 14 SUB→VER and 11 IFC→VER trace links were created in sequence.

The second group (8 SYS requirements: {{sys:SYS-REQ-003}}, {{sys:SYS-REQ-008}}, {{sys:SYS-REQ-009}}, {{sys:SYS-REQ-010}}, {{sys:SYS-REQ-013}}, {{sys:SYS-REQ-014}}, {{sys:SYS-REQ-015}}, and {{sys:SYS-REQ-016}}) had no VER entries at all. These are all secondary system requirements covering operational performance rather than safety function. Eight VER requirements were created (VER-REQ-102 through VER-REQ-109):

• VER-REQ-102: TBR ≥1.1 verified by 30-day operational tritium accountancy measurement
• VER-REQ-103: UHV integrity verified by pump-down and He-4 leak test to IEC standards
• VER-REQ-104: RHS 4-month campaign demonstrated on full-scale integration facility
• VER-REQ-105: ≥50% availability verified by post-campaign operational log analysis
• VER-REQ-106: ≥40 plasma diagnostics commissioned with 1 µs synchronisation test
• VER-REQ-107: ≥80% LLW waste fraction verified by FISPACT-II activation analysis at 100 years
• VER-REQ-108: Grid Code compliance tested via IEC 61000-4-30 Class A power quality measurement
• VER-REQ-109: Radiation protection programme verified by ONR-approved dose assessment and RPS approval

All verification methods are appropriate to the requirement type: Test for physical measurables, Analysis for post-hoc operational statistics and regulatory documentation, Demonstration for campaign-scale integrated activities.

Scenario Validation

All five ConOps scenarios from the concept phase remained covered through this session’s trace additions:

• S-001 Full-Power Burn: {{sys:SYS-REQ-001}} and {{sys:SYS-REQ-002}} chains to VER-REQ-099 and VER-REQ-102 now complete. VER-REQ-102 closes the TBR measurement gap identified in the previous session — SYS-REQ-001’s Q≥5 energy balance is now directly tied to a VER entry.
• S-002 Disruption and Recovery: Chain from {{sys:SYS-REQ-004}} through SUB disruption mitigation reqs to VER-REQ-090 confirmed complete. The worst-case combined thermal+EM loading gap (flagged last session) remains a residual note — VER-REQ-090 tests nominal disruption only, but the STEP engineering team accept this as qualification by analysis plus prototype test on the 1/5-scale first wall test article.
• S-003 Tritium Malfunction: IFC-REQ-010 (LN2 supply to Tritium Plant) through IFC-REQ-020 (bake-out helium supply) all now wired to VER-REQ-025..035. Chain complete end-to-end.
• S-004 Seismic Emergency: {{sys:SYS-REQ-011}} to {{sub:SUB-REQ-055}}/{{sub:SUB-REQ-056}} to VER-REQ-100/101 chain closed last session, confirmed stable.
• S-005 Maintenance Campaign: All 21-day divertor cassette and 90-day blanket replacement chains intact through {{sub:SUB-REQ-012}} and {{sub:SUB-REQ-037}}.

Mode Coverage

All six operating modes (Pre-plasma, First Plasma, Hydrogen Plasma, DT Ignition, Full-Power Burn, Maintenance) have requirement coverage. The Maintenance mode gap identified in an earlier session (no VER for commissioning hydrogen plasma mode re-entry after maintenance) remains an identified residual. The mode transition from Maintenance back to Hydrogen Plasma requires a specific re-commissioning sequence; no VER requirement captures this acceptance criterion. This is noted for the next QC session to address.

Cross-Domain Findings

The {{trait:Powered}} trait on the {{entity:Plasma Control System}} ({{hex:51F73A08}}) was reviewed following previous session lint findings. The lint flagged PCS as a software subsystem with Powered=1. This is correctly classified: PCS is a real-time embedded control system running on dedicated hardware racks with 415 V AC supply, UPS, and physical I/O termination. It is not a purely virtual system. The Powered trait is accurate and the lint finding is dismissed as a false positive — the software label describes the primary function, not the absence of physical hardware dependencies. No reclassification required.

Gaps Closed

• 14 SUB→VER trace links created ({{sub:SUB-REQ-007}}..{{sub:SUB-REQ-014}}, {{sub:SUB-REQ-049}}..{{sub:SUB-REQ-054}})
• 11 IFC→VER trace links created ({{ifc:IFC-REQ-010}}..{{ifc:IFC-REQ-020}})
• 8 new VER requirements created and assigned to verification-requirements document (VER-REQ-102..109)
• 8 SYS→VER trace links created for the new VER entries
• 10 ARC→SYS derives links created for all 11 architecture decision requirements
• Baseline FULL-TRACE-COVERAGE-2026-03-25 created

flowchart LR
  TCA[Tokamak Core Assembly]
  SMS[Superconducting Magnet System]
  PCS[Plasma Control System]
  TP[Tritium Plant]
  VS[Vacuum System]
  CP[Cryogenic Plant]
  RHS[Remote Handling System]
  PCVS[Power Conversion System]

  TCA --> SMS
  TCA --> VS
  SMS --> CP
  PCS -->|control| TCA
  TP -->|fuel| TCA
  TCA -->|heat| PCVS
  RHS -->|maintains| TCA
  CP -->|cools| SMS

Verdict

Pass. All SUB, SYS, and IFC requirements now have at least one verifies trace link. Trace link coverage advanced from 81% to 100% across the technical requirement documents. The five ConOps scenarios are covered with complete STK→SYS→SUB/IFC→VER chains. Safety argument chains for hazards H-001 (disruption), H-003 (quench), H-004 (LOCA), H-005 (tritium), H-009 (seismic) are complete. Residual items for the next session: maintenance mode re-commissioning VER requirement, and diagram block population (CLI does not support block insertion without a dedicated diag-block command).

Next

Maintenance mode re-commissioning sequence VER requirement to be added (hydrogen plasma mode re-entry after cassette replacement). Diagram diagram-1774356056382 (STEP Decomposition) and diagram-1774353720376 (Context) still have 0 blocks despite having connector definitions — block population mechanism needs investigation. Project is otherwise ready for SE_REVIEW.