System

The {{entity:STEP Fusion Power Plant}} — a 100 MW net spherical tokamak D-T fusion facility — entered this session at DECOMP_STATUS validated with 246 requirements, 348 trace links, and 10 subsystem diagrams. This session addressed residual trace gaps identified in the previous validation pass: 13 missing VER→SUB links, 4 homeless VER requirements, absent ARC→SYS trace rationale, and a direct SYS-level verification gap on the net power requirement. Session 526 ran Flow D (SE_VALIDATION) on project se-step-fusion-power-plant.

Verification Audit

Ten VER requirements were sampled spanning plasma control, cryogenics, tritium processing, remote handling, and infrastructure. All sampled entries specify test setup, step-by-step procedure, and binary pass/fail criteria with quantified thresholds. The single Analysis verification in the sample — {{sub:VER-REQ-037}} (MCNP6 neutronics for TBR ≥ 1.1) — is appropriate: the {{sub:SUB-REQ-016}} requirement itself specifies neutronics analysis as the measurement method and direct in-situ measurement is impractical at scale. The Analysis VER correctly specifies the code (MCNP6), validation benchmark (ITER tritium production data), and Monte Carlo uncertainty limit (< 3%).

One adequacy gap was found: {{sys:SYS-REQ-002}} (≥ 100 MW net electrical, ≥ 25% efficiency) had no direct VER trace despite being the primary performance output requirement. {{sub:VER-REQ-065}} (first full-power commissioning, 100 MW net power measurement at 400 kV metering point) fully verifies this requirement; the missing trace link was added.

Trace count corrected: 348 → 367 links across 19 new trace relationships.

Trace gaps repaired (13 VER→SUB): {{sub:VER-REQ-017}} → {{sub:SUB-REQ-007}} (divertor heat load), {{sub:VER-REQ-018}} → {{sub:SUB-REQ-008}} (TF coil field strength), {{sub:VER-REQ-019}} → {{sub:SUB-REQ-010}} (tritium processing throughput), {{sub:VER-REQ-020}} → {{sub:SUB-REQ-009}} (cryogenic cooling capacity), {{sub:VER-REQ-021}} → {{sub:SUB-REQ-011}} (net electrical output at subsystem level), {{sub:VER-REQ-022}} → {{sub:SUB-REQ-012}} (remote handling dexterity), {{sub:VER-REQ-023}} → {{sub:SUB-REQ-013}} (vacuum base pressure), and {{sub:VER-REQ-084}} through {{sub:VER-REQ-089}} for SUB-REQ-049 to 054 (ISS power, PPS isolation command, structural building reqs, vacuum penetration count).

Four homeless VER requirements (REQ-SESTEPFUSIONPOWERPLANT-060 to -063) were reassigned to the verification-requirements document. Their existing traces to {{sub:SUB-REQ-014}} (radiation zone classification), {{sub:SUB-REQ-037}}, {{sub:SUB-REQ-042}}, and {{sys:SYS-REQ-001}} were already correct.

Inspection method for structural reqs (VER-REQ-086–089): These use Inspection for civil/structural building requirements (floor load ratings, seismic construction grade, building dimensions). Inspection by a certified structural engineer against design drawings is the standard nuclear facility verification method for these — appropriate despite SIL tags inherited from tritium and cryogenic plant safety functions.

Scenario Validation

S-001 Full-Power Burn (Q≥5, 6-hour pulse, 100 MW net to grid): COVERED. Chain: {{stk:STK-REQ-009}} → {{sys:SYS-REQ-001}} + {{sys:SYS-REQ-002}} → {{sub:SUB-REQ-019}}/024/025/026 (PCS burn control, cryogenic steady-state, tritium fuel cycle, power conversion) → VER-REQ-065 (100 MW net commissioning demonstration). VER-REQ-065 extended to cover SYS-REQ-002 directly this session.

S-002 Disruption and Recovery (locked mode, SPI within 10 ms, 4-hour turnaround): COVERED. Chain: {{stk:STK-REQ-002}} → {{sys:SYS-REQ-004}} → {{sub:SUB-REQ-002}} (precursor detection) + {{sub:SUB-REQ-017}} (runaway electron mitigation) → {{sub:VER-REQ-090}} (SPI test bench, timing measurement to 1 ms resolution, <10 ms pass criterion). The turnaround target is implicit in maintenance campaign reqs rather than a standalone requirement — acceptable for a non-safety metric.

S-003 Tritium Processing Malfunction (< 0.1 g release, auto isolation, remote repair): COVERED. Chain: {{stk:STK-REQ-008}} → {{sys:SYS-REQ-005}} → Tritium Plant SUB reqs (automatic isolation, double-barrier) → {{sub:VER-REQ-091}} (end-to-end tritium containment commissioning test). The 0.1 g release limit is captured indirectly via regulatory discharge limit reqs rather than a standalone scenario threshold — this is acceptable since the regulatory limit is more conservative.

S-004 Seismic Emergency (0.1g OBE, fast shutdown <100 ms, 2–4 week recovery): COVERED. Chain: {{stk:STK-REQ-003}} → {{sys:SYS-REQ-011}} → {{sub:VER-REQ-094}} (shake-table + PPS trip timing, 100 ms shutdown signal + 10 s full safe-state pass criteria). The 2–4 week recovery window is a non-safety operational metric not requiring a separate VER.

S-005 Planned Maintenance Campaign (4-month divertor replacement, re-commissioning): COVERED. Chain: {{stk:STK-REQ-005}} → {{sys:SYS-REQ-009}} → RHS + divertor SUB reqs → {{sub:VER-REQ-061}} (full RHS integration test, cassette exchange) + {{sub:VER-REQ-066}} (full blanket module exchange trial). Minor gap: no explicit VER for commissioning hydrogen plasma mode entry/exit as precursor to first D-T — noted but not blocking.

Mode Coverage

Six operating modes identified in the concept phase were checked:

• Plasma Startup: Entry interlocks (cryogenics at 4 K, vacuum < 1×10⁻⁶ Pa) covered by {{sub:SUB-REQ-006}} (PCS interlock logic) and {{sub:SUB-REQ-013}}/{{sub:VER-REQ-023}}. Mode exit (plasma reaches burn conditions) covered by {{sys:SYS-REQ-001}}/VER chain. ADEQUATE.
• Steady-State Burn: Sustained operation reqs (Q ≥ 5, TBR ≥ 1.1, 100 MW net) covered. ADEQUATE.
• Planned Shutdown: Operator command → current ramp-down covered by PCS reqs. No explicit timed ramp-down VER — acceptable since 10–30 s is within PCS control loop capability verified in other tests. ADEQUATE.
• Emergency Shutdown: Covered by {{sub:VER-REQ-090}} (disruption) and {{sub:VER-REQ-094}} (seismic). ADEQUATE.
• Remote Maintenance: Plasma terminated, vessel cooled, tritium removed → covered by maintenance campaign reqs. ADEQUATE.
• Commissioning: Hydrogen/deuterium plasma mode has no dedicated VER; only D-T commissioning tests exist. MINOR GAP — not blocking since commissioning mode is primarily a procedural matter; all subsystem acceptance tests (VER-REQ-017 to VER-REQ-023) are conducted pre-first-plasma.

Cross-Domain Findings

The seismic trip logic ({{sys:SYS-REQ-011}}, 100 ms trip) is analogous to {{entity:Nuclear Reactor Protection System}} trip logic — existing nuclear RPS patterns in the Factory corpus confirm that 100 ms is conservative for a hardwired trip system (typical RPS < 20 ms). No gap surfaced.

The tritium double-barrier ({{sys:SYS-REQ-005}}) is analogous to offshore oil platform secondary containment patterns. The VER approach (integrated commissioning test) matches offshore secondary barrier testing methods.

Gaps Closed

1. 13 VER→SUB trace links created for SUB-REQ-007 to SUB-REQ-013 and SUB-REQ-049 to SUB-REQ-054.
2. 4 homeless VER requirements reassigned to verification-requirements document.
3. VER-REQ-065 → SYS-REQ-002 trace added: net 100 MW net power now has direct system-level verification.
4. 5 ARC→SYS trace links created: ARC-REQ-001 (ST geometry) → SYS-REQ-001; ARC-REQ-002 (SMS/cryo separation) → SYS-REQ-006; ARC-REQ-003 (PCS separation) → SYS-REQ-001; ARC-REQ-004 (PCS thermal grouping) → SYS-REQ-002; ARC-REQ-005 (tritium plant isolation) → SYS-REQ-005.
5. Validation baseline BL-SESTEPFUSIONPOWERPLANT-016 created at 246 requirements, 367 trace links.

Verdict

PASS. All five ConOps scenarios are covered by complete STK→SYS→SUB/IFC→VER trace chains. Safety argument for H-001, H-002, H-003, H-006, and H-009 is structurally complete with SIL-appropriate Test verifications. Residual observations: (a) H-001 disruption mitigation has single-channel detection architecture (PCS-only) which a SIL-3 allocation would normally address through redundancy — this is an architectural finding for a future review session, not a VER gap; (b) the commissioning hydrogen plasma mode lacks a dedicated VER but this does not affect safety or D-T operational scenario coverage.

Next

Run SE_REVIEW (Flow E) to check holistic coherence before marking the system complete. Priority checks: confirm no requirement duplication between old-style REQ-SESTEPFUSIONPOWERPLANT refs and renamed VER/SUB/IFC refs; check the SIL-1 allocation on H-010 (neutron streaming) versus the Test verification adequacy of VER-REQ-095; and assess whether the single-channel disruption detection gap warrants a new SUB requirement.