Source-term platform implementation status

Tracking issue: #3860. Implementation scope as of 2026-09-23; this does not confer qualification or replace domain review.

Delivered foundations

Architecture proposal #3861 is merged. Physics #3867, exchange contract #3868, and live integration #3870 reached master through merge commit b08d8bb59a95cf52e0565fab5c368c5548a9f27f. The latter two merged into the physics branch first.

The current implementation includes:

• Opt-in homogeneous-equilibrium short-opening physics, immutable inputs/results, explicit thermodynamic stations and required closure checks.
• Versioned deterministic JSON, NDJSON and reduced CSV, bundled JSON Schema, source identity, provenance and machine-readable failure/lifecycle states.
• Steady runs, external capture and native dynamic stepping for ProcessSystem and ProcessModel, including real separator dynamics in tests.
• Weighted uncertainty ensembles, retaining failures and refusing unconditional statistics for incomplete ensembles, with schema-compatible case frames.
• Explicit ideal-gas and legacy-screening adapters. The ideal-gas path has no silent property defaults; the compatibility path reports SCREENING_ONLY and unresolved station semantics.
• Coupled inventory depletion through native process dynamics, with component/energy/volume closure, atomic unit updates, receiving-pressure event location, timestep-refinement evidence and schema-validated frames from both process containers. The compatibility API remains single-gas; an explicit phase-selected API supports equilibrium gas, oil, generic-liquid and aqueous withdrawal without inferring entrainment or phase fallback.
• Analytical gas limits, dense-fluid conservation and flashing, multicomponent, lifecycle and contract regressions in focused CI.
• Guarded same-EOS continuation for the previously unresolved propane/butane entropy root, with nine nearby mixture cases, a separate saturation-path comparison, inventory scaling, back-pressure sensitivity and retained schema/benchmark evidence. Model version 1.2.0 preserves the acoustic warning and UNQUALIFIED evidence boundary.
• Mixture-specific, fail-closed equilibrium-solid and hydrate applicability assessment at the resolved upstream, throat and ambient-expanded stations. Detected risk is UNSUPPORTED; an unresolved required assessment is INVALID. This does not add solid-bearing flow physics.
• A separate ideal-gas Fanno model for quasi-steady, one-sided full-bore release through a constant-area pipe with explicit length and specified Darcy friction. The same immutable geometry reaches steady/live process frames and coupled inventory depletion; short-opening models reject it rather than ignoring it.
• Immutable per-model evidence manifests now retain stable applicability and limitation codes, typed analytical/conservation/numerical/experimental references, and an explicit independent- evidence flag in schema-validated frames. Current built-in manifests truthfully remain UNQUALIFIED; no successful calculation promotes its own evidence level.
• The executed NeqSim-Colab safety source-term demonstration is merged through EvenSol/NeqSim-Colab #176, with retained outputs, rendered-equation/figure inspection, catalog entry and repository validation.

Legacy LeakModel behavior is preserved. The new interface now has homogeneous-equilibrium, analytical ideal-gas and explicit legacy-screening implementations. Model selection remains caller-owned; no phase-count rule silently changes the requested physics.

Remaining work before the whole issue can close

Work item	Current boundary	Completion evidence required
Broader transient inventory regimes	Rigid adiabatic equilibrium inventory supports explicit phase-selected withdrawal, caller-declared ordered phase-exhaustion transitions, conservative receiving-pressure events, and balance/refinement tests.	Assessed phase-level/geometry, entrainment/slip and finite-rate interfacial transfer beyond the current well-mixed equilibrium boundary.
Full-bore/long-pipe and non-equilibrium regimes	A bounded ideal-gas Fanno model covers quasi-steady one-sided constant-area pipe flow with specified Darcy friction and analytical validation.	Real-gas/transient decompression and separate non-equilibrium multiphase models, applicability controls and independent validation data.
Independent qualification and dense-fluid accuracy	Machine-readable model evidence records now distinguish applicability, limitations, evidence type and independence; current records are analytical/conservation/numerical and frames remain UNQUALIFIED.	Add independently sourced datasets with error/range analysis, record them without self-promotion, and obtain domain review.
Solid-formation applicability	Mixture-specific solid/hydrate station assessment now fails closed and retains machine-readable diagnostics.	Assessed solid-bearing release physics where supported, plus independent mixture validation.
Multicomponent flashing qualification	The documented 80/20 propane/butane entropy root and nearby cases now close with guarded continuation; a separate same-EOS saturation path checks the maximum. Acoustic warnings remain explicit.	Independent experimental benchmarks and domain review; broader mixtures are not qualified by the regression matrix.
Colab demonstration	Executed, output-retaining demonstration merged in NeqSim-Colab #176 with rendering, catalog and validation-ledger checks.	No remaining implementation item; broader physical qualification remains governed by the rows above.

Do not close #3860 merely because initial PRs merged or focused CI passes. The NRC retains design intent; current guidance is in physics, contract, live sessions and uncertainty.