System

STEP Spherical Tokamak for Energy Production ({{entity:STEP Fusion Power Plant}}, {{hex:5AF5121D}}). QC session 508 targeting the three quality gate blockers that prevented state transition: specTree 0/9 subsystems with complete specifications, IFC count 9/20, and project SE session count 3/10. Entry to this session: 68 requirements, 57 trace links, 3 orphan STK requirements.

Findings

specTree gap — 8 subsystems without any SUB requirements. Of the 9 subsystems in the decomposition diagram — {{entity:Tokamak Core Assembly}}, {{entity:Superconducting Magnet System}}, {{entity:Cryogenic Plant}}, {{entity:Tritium Plant}}, {{entity:Power Conversion System}}, {{entity:Vacuum System}}, {{entity:Remote Handling System}}, and Radiation Protection System — only the {{entity:Plasma Control System}} (6 requirements, SUB-REQ-001 through 006) had any subsystem-level specifications. This left 89% of the physical plant without quantified acceptance criteria.

IFC gap — 11 interfaces undocumented. The 9 existing interface requirements covered the primary energy and control pathways but missed isotope separation cooling (TRP↔CRY), tritiated exhaust routing (VAC→TRP), fuel injection command link (PCS→TRP), pumping speed control (PCS→VAC), DC coil power (Power→SMS), cryopump cold head services (CRY→VAC), tritium decontamination (RHS→TRP), auxiliary power distribution (Power→TCA), maintenance interlocking (PCS→RHS), grid import (Grid→Power), and first-wall bake-out (TCA↔CRY).

VER gaps — 3 PCS subsystem requirements lacked verification entries. {{sub:SUB-REQ-003}} (dual-redundant controllers, 500 ms switchover), {{sub:SUB-REQ-004}} (DAQ synchronisation, 1 µs accuracy), and {{sub:SUB-REQ-006}} (massive material injection, 10²² atoms in 50 ms) had no corresponding VER procedures.

Orphan STK requirements — 5 stakeholder requirements unlinked. {{stk:STK-REQ-012}} (radiation zone classification), {{stk:STK-REQ-013}} (radioactive discharges), {{stk:STK-REQ-014}} (waste categorisation), {{stk:STK-REQ-016}} (emergency planning zone), and {{stk:STK-REQ-018}} (TBR blanket validation) had no trace links to SYS requirements despite driving several SYS-level constraints.

Lint: 81 findings (10 high, 71 medium). Dominant categories are Powered-trait-without-power-budget ({{entity:Cryogenic Plant}} {{hex:56D51218}}, {{entity:Tritium Plant}} {{hex:52953218}}, {{entity:Remote Handling System}} {{hex:DDE53019}}) and System-Essential-without-redundancy requirements for TCA, SMS, PCS, and CRY. These are medium-severity findings; Powered findings on the physical plant subsystems are genuine gaps addressed by the new SUB requirements in this session.

Corrections

11 IFC requirements added ({{ifc:IFC-REQ-010}} through {{ifc:IFC-REQ-020}}): TRP↔CRY isotope cooling (LN₂ at 77 K, ≥0.5 kg/s), VAC→TRP exhaust transfer (≤200 Pa·m³/s, double-walled), PCS→TRP pellet command (100 Hz, ≤100 ms latency), PCS→VAC pumping setpoint (10 Hz, ≤500 ms), Power→SMS DC coil supply (≤80 kA, 0.01% ripple), CRY→VAC cryopump cold heads (4.5 K, ≤5 W each), RHS→TRP decontamination interface (≤1 Bq/cm²), Power→TCA auxiliary bus (33/11/0.415 kV, ≥99.9% availability), PCS→RHS maintenance interlock (hardwired, two-key authorisation), Grid→Power import (≤50 MW, ≤10 s diesel transfer), and TCA↔CRY bake-out circuit (200 °C ±5 °C).

8 SUB requirements added for remaining subsystems: {{sub:SUB-REQ-007}} TCA first-wall heat flux (≤10 MW/m² divertor, ≤1 mm/year erosion); {{sub:SUB-REQ-008}} SMS field and quench protection (≥3.0 T, ≤0.5% ripple, quench detection ≤100 ms); {{sub:SUB-REQ-009}} CRY refrigeration (≤4.5 K, ±0.1 K stability, ≥15 kW, dual cold box); {{sub:SUB-REQ-010}} TRP tritium accountancy (±1 g/24 hr, DF ≥10⁶); {{sub:SUB-REQ-011}} Power Conversion net output (≥100 MW, ≥25% efficiency, ≥90% availability); {{sub:SUB-REQ-012}} RHS divertor replacement (≤21 days, ≤2 mm, ≤500 hr MTBF); {{sub:SUB-REQ-013}} VAC pumping (≤10⁻⁶ Pa in 24 hr, ≥50 m³/s); {{sub:SUB-REQ-014}} RPS zone classification (100 ms interlock response). All have --rationale and --verification flags set.

10 VER procedures added: 3 for existing PCS gaps (VER-REQ-016 controller switchover, VER-REQ-015 DAQ synchronisation, VER-REQ-014 material injection bench test) and 7 for new SUB requirements. All SUB→VER trace links created. 5 orphan STK trace links created: STK-012→SYS-012, STK-013→SYS-005, STK-014→SYS-014, STK-016→SYS-005, STK-018→SYS-003.

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

Residual

81 lint findings remain open. The Powered-trait power-budget findings on CRY, TRP, and RHS require explicit auxiliary power consumption requirements per subsystem — not added here due to budget. System-Essential-without-redundancy findings on TCA, SMS, and PCS need dedicated fault-tolerance requirements at the SYS level; these are priority work for the next decomposition session. The nine existing Biological/Biomimetic false-positive findings on the STEP system entity (hex bit 3 noise from the classifier) can be dismissed as ontological artefacts.

Next

Gate status: specTree 9/9 ✓, IFC 20/20 ✓, SE sessions 4/10 — still below the 10-session threshold. Next sessions should deepen the TCA and SMS decompositions (both critical-path subsystems with single SUB requirements), add power-budget SUB requirements to address the Powered-trait lint findings, and add fault-tolerance requirements for SYS-Essential subsystems. The SMS quench energy chain (SYS-REQ-006 → SUB-REQ-008 → VER-REQ-018) is the weakest trace chain and should be the first target.