System

STEP Fusion Power Plant decomposition session 514. Two subsystems — {{entity:Remote Handling System}} and {{entity:Power Conversion System}} — were the final pending entries in an 8-subsystem spec tree. Both are SIL 1, meaning loss of either subsystem results in extended plant downtime rather than a safety-critical hazard. Session priority: close the quality gate blocker (specTree 2/8 incomplete, sessions 9 < 10).

Decomposition

Remote Handling System decomposes into five components aligned with the ITER/JET remote maintenance architecture:

flowchart TB
  n0["component - IVIMM"]
  n1["component - Transfer Cask"]
  n2["component - RH Control Suite"]
  n3["component - Viewing System"]
  n4["component - Exchange Tooling"]
  n2 -->|EtherCAT cmds 4ms| n0
  n0 -->|tooling attachment| n4
  n3 -->|video 25fps| n2
  n0 -->|component transfer| n1

The {{entity:In-Vessel Inspection and Maintenance Manipulator}} ({{hex:D7E47018}}) is classified as {{trait:Physical Object}}, {{trait:Powered}}, {{trait:Active}}, and {{trait:Functionally Autonomous}} — traits that justify separation from the {{entity:Remote Handling Control Suite}}, which carries {{trait:Processes Signals/Logic}} and {{trait:Human-Interactive}} as its dominant traits. {{trait:Intentionally Designed}} appears on both, as expected. The IVIMM replacement lifecycle (full arm at 10^6 Gy dose limit) is architecturally distinct from tooling end-effectors (per-task swap), which drove their separation.

Power Conversion System maps onto the Rankine cycle energy chain:

flowchart TB
  n0["component - Steam Generators"]
  n1["component - Turbine-Generator"]
  n2["component - Condenser"]
  n3["component - Feedwater BOP"]
  n4["component - Grid Interface"]
  n0 -->|steam 525C 16MPa| n1
  n1 -->|22kV 120MVA| n4
  n1 -->|exhaust 0.04bar| n2
  n2 -->|condensate return| n3
  n3 -->|feedwater 16MPa| n0

The {{entity:Steam Generator and Heat Transfer System}} ({{hex:DED53018}}) is the nuclear/non-nuclear boundary: primary tritiated coolant at 300°C/15 MPa is isolated from the secondary steam cycle by the tube-and-shell boundary. All downstream components — turbine, condenser, feedwater — carry no nuclear safety class (SIL 0). The sole SIL 1 obligation in the PCS sits in the {{entity:Grid Interface and Electrical Switchgear}} ({{hex:56D53218}}) because uncontrolled HV disconnection during a fault drives turbine overspeed risk.

Analysis

UHT Substrate cross-domain search surfaced a 60% Jaccard match between {{entity:Cryogenic Plant}} and {{entity:Vacuum System}}. Both share {{trait:Powered}}, {{trait:Physical Medium}}, {{trait:State-Transforming}}, and {{trait:System-integrated}} — the two subsystems both process gas-phase working fluids at extreme temperatures or pressures and are deeply embedded in the plant’s operating envelope. This analog is structurally interesting but does not flag missing requirements: both subsystems already have IFC entries for their shared physical boundaries.

Nine previously acknowledged lint findings (Physical Object trait absent on system-level entities, Biological/Biomimetic classification on the STEP plant entity) remain unchanged false positives. Three new ARC-document orphans acknowledged per convention — architecture decisions are informational and not in the requirements trace hierarchy. Pre-existing findings for {{entity:Isotope Separation System}} (Powered/Functionally Autonomous without power or override requirements) were noted; these fall outside this session’s scope (Tritium Plant subsystem) and are recorded for QC attention.

Requirements

Session generated 10 SUB requirements ({{sub:SUB-REQ-036}}–{{sub:SUB-REQ-045}}), 6 IFC requirements ({{ifc:IFC-REQ-031}}–{{ifc:IFC-REQ-036}}), and 10 VER entries ({{ver:VER-REQ-058}}–{{ver:VER-REQ-067}}). Key derivations:

• {{sub:SUB-REQ-036}}: IVIMM ±1 mm accuracy allocates half the ≤2 mm system budget from {{sys:SYS-REQ-009}}, with 1 mm reserved for tooling alignment
• {{sub:SUB-REQ-037}}: 90-day blanket exchange window leaves 30 days for divertor cassettes within the 4-month campaign
• {{sub:SUB-REQ-041}}: ≥100 MW net electrical output directly derives from {{sys:SYS-REQ-002}}; gross turbine target is 120 MW before ~20 MW station auxiliary deduction
• {{sub:SUB-REQ-045}}: Turbine runback to 20% load on plasma disruption avoids 4-hour restart penalty per disruption event; at ~12 disruptions/year contributes ~5% availability toward the {{sys:SYS-REQ-010}} ≥50% operational availability target

All IFC requirements have paired VER entries. Inline rationale check confirmed zero requirements without rationale in this session. Trace link count: 191.

Next

Spec tree is 8/8 complete. The decomposition phase quality gate requires sessions ≥ 10 (now at 514 total). The harness should transition to QC flow (Flow C) for a coverage audit: Isotope Separation System Powered/Functionally Autonomous lint findings need addressing, and the five remaining un-linked high-severity Powered/Physical Object lint findings from earlier sessions need resolution or acknowledgment.