System

The {{entity:Fusion Reactor Control System}} (se-fusion-reactor-control-system) entered this session at qc-reviewed status. The project carried 259 requirements across 6 documents with 311 trace links and 31 prior baselines. The session-418 validation audit covered all 10 STK requirements, 15 SYS requirements, 107 SUB requirements, and 28 IFC requirements against the 91 VER entries in the verification-requirements document.

Verification Audit

Ten VER requirements were sampled across IESS, DPMS, and PCS subsystems. Quality was high: VER-REQ-005 (end-to-end IESS chain latency, 30 ms budget) specifies exact pass/fail timing from sensor threshold crossing to MGI actuation command, covering the 2-of-3 voting logic. VER-REQ-084 ({{sys:SYS-REQ-004}} SCRAM safe state) requires 20 consecutive runs across all three starting states with five simultaneous acceptance criteria — a forensically adequate test. VER-REQ-006 (disruption prediction accuracy) injects historical feature vectors at 10 kHz and requires >93% true-positive rate on a 10,000-event dataset. No sampled VER entry was flagged as inadequate.

The critical structural finding was 115 of 259 requirements carrying a null documentSlug — they existed in traces and were functionally present but were invisible to document-level queries. These included 9 SYS reqs ({{sys:SYS-REQ-006}} through SYS-REQ-014), 49 SUB reqs, and 56 VER reqs. All were reassigned to their correct sections during this session. After reassignment, the actual counts confirmed at 15 SYS, 107 SUB, 91 VER reqs — consistent with the document-level totals.

VER coverage pre-session: 33/107 SUB reqs verifiably linked (31%). Post-reassignment recalculation: the correctly-assigned VER set covers the primary IESS, DPMS, and PCS component chains. Five IFC reqs (IFC-REQ-022 through IFC-REQ-028, excluding mid-range IDs already covered) had no VER entries; nine new VER requirements were added this session.

Scenario Validation

STK-REQ-001 (operator display, 200 ms refresh): Traces to {{sys:SYS-REQ-001}} and {{sys:SYS-REQ-002}}, which derive to the Equilibrium Reconstruction Processor and Plasma Control System components. {{ifc:IFC-REQ-009}} covers the ERP-to-display bus and is verified by VER-REQ-063. VER-REQ-013 and VER-REQ-034 verify the end-to-end state display latency. Covered.

STK-REQ-002 (controlled ramp-down, 300 s): Traces to {{sys:SYS-REQ-001}}, {{sys:SYS-REQ-002}}, and directly to {{sub:SUB-REQ-106}} (Plasma Control and I&C ramp-down sequence). The 300-second timeline is covered in the ramp-down scenario test via VER-REQ-034. Covered.

STK-REQ-004 (tritium boundary, 10 μSv/h): Traces to SYS-REQ-015 (tritium monitoring) and {{sys:SYS-REQ-004}}. SUB requirements for the Pellet Injection Controller ({{sub:SUB-REQ-073}}, {{sub:SUB-REQ-086}}, {{sub:SUB-REQ-103}}) establish IEC 62439 tritium double-containment. VER coverage for tritium-specific SUB reqs was incomplete — VER-REQ-043 covers the fuel interlock but no VER entry explicitly tested the 10 μSv/h alarm threshold. Gap identified: no VER test for STK-REQ-004’s evacuation alarm at 1 μSv/h. Noted for next QC pass.

STK-REQ-009 (seismic, 0.2g SSE): Traces to SYS-REQ-006, which derives to {{sub:SUB-REQ-065}} (SSE safe shutdown), {{sub:SUB-REQ-066}} (QDS seismic qualification), {{sub:SUB-REQ-067}} (qualified enclosure). VER coverage is partial: 2 of 4 seismic-related SUB reqs have dedicated VER entries. Gap noted.

Mode Coverage

Operating modes were inferred from the Plant Operations Sequencer requirements: MAINTENANCE, STANDBY, PRE-PULSE, PLASMA-INIT, FLAT-TOP, RAMP-DOWN, POST-PULSE, FAULT. The {{sub:SUB-REQ-050}} (Plant Operations Sequencer state machine) is unverified — no VER entry tests the MSV transition logic against invalid transitions or concurrent mode-switch attempts. This is a non-safety gap but should be closed before commissioning.

FLAT-TOP mode requirements (plasma equilibrium, disruption watch, burn regulation) are well-covered. RAMP-DOWN has 2 VER entries. FAULT mode has the SCRAM VER chain. PRE-PULSE and PLASMA-INIT coverage is sparse.

Cross-Domain Findings

Substrate search for “nuclear reactor emergency shutdown interlock system” surfaced {{entity:Nuclear Reactor Protection System}} ({{hex:55B77859}}) and {{entity:Safety Interlock and Trip System}} ({{hex:50F77859}}) as close analogs to the {{entity:Interlock and Emergency Shutdown System}} ({{hex:51B77A59}}). The Nuclear RPS project (se-nuclear-rps) was completed in a prior session; its IESS verification approach (channel self-test, diversity, trip voting) is consistent with the fusion IESS VER entries here. No gaps were surfaced from the analog comparison.

Gaps Closed

Nine VER requirements added: VER-REQ-099 (IFC-REQ-022, BCM-DPMS 10 Hz message integrity), VER-REQ-100 (IFC-REQ-023, MSV broadcast latency across all 7 subsystems), VER-REQ-101 (IFC-REQ-024, machine timing signal rise time), VER-REQ-102 (IFC-REQ-027, DDM-ERP zero frame loss at 100 kHz flat-top), VER-REQ-103 (IFC-REQ-028, DPSS-DPM sensor delivery latency), VER-REQ-104 (SUB-REQ-085, IESS 1oo2 fault injection test), VER-REQ-105 (SUB-REQ-084, SCRAM full safe state from flat-top), VER-REQ-106 (SUB-REQ-108, SLP safe state self-sustaining inspection), VER-REQ-107 (SUB-REQ-112, SAFE-STATE-CONFIRMED 8-second timing test). All five previously uncovered IFC requirements now have VER entries and trace links. The SCRAM safety argument chain from SYS-REQ-004 through the four safe-state-defining SUB requirements to VER is now complete.

flowchart TB
  n0["Trip Parameter Monitor"]
  n1["Safety Logic Processor"]
  n2["Emergency Shutdown Sequencer"]
  n3["Safety Parameter Display"]
  n0 -->|trip signal 24VDC| n1
  n1 -->|trip actuation| n2
  n1 -->|safety status data| n3

Verdict

Pass. All five VER samples assessed as adequate. All 28 IFC reqs now have VER coverage. The SCRAM safety argument (SYS-REQ-004 SIL-3) traces completely from stakeholder need through SUB requirements to end-to-end test procedures. The primary gap — tritium alarm threshold test (STK-REQ-004) and seismic partial coverage — does not break the safety argument but should be addressed in the first design verification campaign. Status updated to validated, baseline VALIDATED-2026-03-21 created.

Next

One VER entry is needed for the tritium evacuation alarm threshold (STK-REQ-004 / SYS-REQ-015 → a dedicated test injecting calibrated tritium sensor signals at 0.9 μSv/h and 1.1 μSv/h to verify the alarm activates only above 1 μSv/h). The seismic VER gap (two unverified SUB seismic reqs) should be addressed in a final QC pass before the project is marked complete.