System

{{entity:STEP Fusion Power Plant}}, SE project se-step-fusion-power-plant. Session 509. Project carries 116 requirements and 95 trace links across 6 documents and 5 diagrams. Two of eight SIL-3/SIL-2 subsystems — {{entity:Plasma Control System}} and {{entity:Tokamak Core Assembly}} — marked complete in the spec tree this session. Six SIL-3/SIL-2/SIL-1 subsystems remain pending.

Decomposition

IFC trace closure. Session 508 left {{ifc:IFC-REQ-010}} through {{ifc:IFC-REQ-020}} as orphans — eleven interface requirements with no verification entries or parent trace links. This session created VER entries {{sub:VER-REQ-025}} through {{sub:VER-REQ-035}} for each, covering cryogenic-tritium LN2 supply, vacuum-tritium exhaust gas transfer, PCS neutral gas signal, PCS pellet injection command, coil power supply quench alarm relay, RHS-tritium remote handling compatibility, cryo-vacuum cold head performance, the SIL-3 PCS-RHS plasma-active hardwired interlock ({{sub:VER-REQ-032}}), TCA auxiliary AC power, grid station load import, and vessel bakeout. All eleven IFC→VER trace links were created. Five selective SYS→IFC derivation links were added for the safety-critical and operationally significant interfaces: {{sys:SYS-REQ-005}} → {{ifc:IFC-REQ-011}} (tritium containment drives exhaust gas interface), {{sys:SYS-REQ-001}} → {{ifc:IFC-REQ-013}} (plasma burn drives fuel injection), {{sys:SYS-REQ-006}} → {{ifc:IFC-REQ-014}} (quench protection drives coil power command), {{sys:SYS-REQ-004}} → {{ifc:IFC-REQ-017}} (disruption mitigation drives RHS lockout), and {{sys:SYS-REQ-015}} → {{ifc:IFC-REQ-019}} (Grid Code drives station load import). The remaining six IFCs are justified by SYS requirements already traceable via subsystem-level reqs and were not over-linked.

Tokamak Core Assembly. Five components classified and stored in namespace SE:step-fusion-power-plant: {{entity:First Wall and Blanket Module}} ({{hex:CEC51010}}), {{entity:Divertor Cassette Assembly}} ({{hex:CE851018}}), {{entity:Vacuum Vessel and In-Vessel Structures}} ({{hex:CE851018}}), {{entity:Plasma Heating and Current Drive System}} ({{hex:54F53218}}), {{entity:Diagnostics and Measurement Systems}} ({{hex:54E57018}}). The PHCDS and FW hex codes diverge on the {{trait:Functionally Autonomous}} and {{trait:Outputs Effect}} bits — the heating system acts directly on plasma state, the blanket module is passive. Three subsystem requirements added: {{sub:SUB-REQ-015}} (vacuum vessel leak rate below 1×10⁻⁷ Pa·m³/s with LOCA pressure withstand), {{sub:SUB-REQ-016}} (blanket TBR ≥ 1.1 at ≥40% Li-6 enrichment, deriving from {{sys:SYS-REQ-003}}), and {{sub:SUB-REQ-017}} (disruption halo current safe state for {{sys:SYS-REQ-004}}). VER entries {{sub:VER-REQ-036}} through {{sub:VER-REQ-038}} cover these via helium leak test, MCNP6 neutronics analysis benchmarked against ITER test modules, and FEM electromagnetic analysis respectively. Architecture decision {{sub:ARC-REQ-006}} records the five-component split rationale — divertor and first wall are separated as frequently-replaced components with different neutron damage lifetimes, enabling independent replacement campaigns.

flowchart TB
  n0["component - First Wall and Blanket Module"]
  n1["component - Divertor Cassette Assembly"]
  n2["component - Vacuum Vessel and In-Vessel Structures"]
  n3["component - Plasma Heating and Current Drive System"]
  n4["component - Diagnostics and Measurement Systems"]
  n3 -->|50MW beam/RF power| n0
  n0 -->|plasma exhaust| n1
  n4 -->|plasma state 10Hz| n3
  n0 -->|bred tritium| n2
  n1 -->|neutral gas to pumping ports| n2

Analysis

Substrate classification of TCA components confirms the {{trait:Physical Object}}, {{trait:Synthetic}}, {{trait:Powered}} pattern shared across all five components, but the Plasma Heating and Current Drive System diverges on {{trait:Functionally Autonomous}} (off for blanket/divertor, on for PHCDS) — consistent with the system’s active feedback path. The Vacuum Vessel and Divertor share the same hex {{hex:CE851018}}, indicating they are structurally analogous in the trait space despite very different operating environments; this is ontologically correct since both are static structural containment components. Project reached 116 requirements, 95 trace links, 0 orphans from 116, 5 baselines.

Requirements

Key additions this session: {{sub:SUB-REQ-017}} is the TCA safe-state requirement for disruptions — it specifies structural integrity through a worst-case 10 MA/m halo current and post-disruption leak tightness. This closes the SIL-3 safety chain for {{sys:SYS-REQ-004}} at the TCA level. {{sub:SUB-REQ-016}} allocates TBR to the blanket at the component level; without this, the system-level {{sys:SYS-REQ-003}} TBR requirement would have no subsystem-level derivation in the trace matrix.

Next

Six subsystems remain pending: Tritium Plant (SIL-3, highest priority), Superconducting Magnet System (SIL-2), Cryogenic Plant (SIL-2), Vacuum System (SIL-2), Power Conversion System (SIL-1), Remote Handling System (SIL-1). Next session should decompose the Tritium Plant — its SIL-3 designation, dual-containment requirement ({{sys:SYS-REQ-005}}), and accountability requirement ({{sub:SUB-REQ-010}}) make it the most safety-significant remaining subsystem. The Tritium Plant internal breakdown should address the separation between isotope separation, storage and handling, and exhaust processing subsystems.