CFAST Validation (NUREG 1934 Appendix A)
CFAST Validation (NUREG 1934 Appendix A)
FRI3D generates CFAST input decks from the same 3D plant model used for FDS generation — compartments, natural and mechanical vents, leakage, thermal boundaries, and fire sources. The generation pipeline is validated against the U.S. NRC NUREG-1934 (EPRI 1023259), Appendix A — Main Control Room (MCR) reference scenario: the published NRC CFAST model is run unmodified as the baseline, the FRI3D-generated deck for the same room is run with the same CFAST build, and the two are compared input-by-input and output-by-output over the full 3600 s simulation.
Reference case
A 702 kW electrical cabinet fire (NUREG/CR-6850 t² profile, XPE/Neoprene fuel, CO yield 0.082, soot yield 0.175, radiative fraction 0.53) in the nominally sealed MCR, with two return vents (6.71 m³/s each) and six supply vents (2.24 m³/s each) stepping from normal flow to full smoke-purge flow at t = 120 s, and wall/floor leakage ratios of 0.0002 / 0.0001. Simulation duration 3600 s.
Input deck comparison
Every input group of the FRI3D-generated deck was compared field-by-field against the NRC model: simulation controls, ambient conditions, compartment geometry and leakage, thermal properties (ceiling/wall/floor materials), wall vents, mechanical ventilation (flow rates, elevations, filter and dropoff settings, flow-fraction ramps), and the fire specification (chemistry, heat of combustion, HRR curve, yields). All fields match, with two understood differences:
- Compartment footprint. The MCR is not rectangular, so both models flatten it to an equivalent box: NRC conserved room volume and surface area (27.1 × 13.8 × 5.2 m), while FRI3D conserves volume (24.04 × 15.83 × 5.08 m). Same volume, slightly different footprint.
- Vent sill/soffit round-off at the millimeter level from vent positioning in the FRI3D 3D model; vent dimensions are identical.
Results
Matched-time comparison over the 3600 s run (FRI3D-generated deck vs NRC baseline):
| t (s) | HRR (kW) FRI3D / NRC | Upper layer temp (°C) FRI3D / NRC | Layer height (m) FRI3D / NRC | Upper layer O₂ (%) FRI3D / NRC |
|---|---|---|---|---|
| 300 | 122.9 / 122.9 | 26.5 / 25.9 | 4.91 / 4.91 | 19.86 / 19.93 |
| 600 | 489.1 / 489.1 | 41.4 / 40.6 | 4.90 / 4.90 | 18.30 / 18.39 |
| 900 | 702.0 / 702.0 | 51.4 / 51.1 | 4.90 / 4.90 | 17.39 / 17.39 |
| 1200 | 702.0 / 702.0 | 52.8 / 52.8 | 4.90 / 4.90 | 17.39 / 17.39 |
| 1800 | 332.5 / 332.5 | 41.4 / 41.9 | 4.91 / 4.91 | 18.73 / 18.69 |
| 3600 | 0.0 / 0.0 | 25.0 / 25.1 | 4.94 / 4.94 | 20.30 / 20.19 |
Peak / extreme values over the full run:
| Quantity | FRI3D | NRC | Difference |
|---|---|---|---|
| Peak upper layer temperature | 52.8 °C | 52.8 °C | +0.1 % |
| Minimum layer height | 4.90 m | 4.90 m | −0.1 % |
| Peak compartment pressure | 38.0 Pa | 37.0 Pa | +2.7 % |
| Peak HRR | 702 kW | 702 kW | 0 % |
| Minimum upper layer O₂ | 17.39 % | 17.39 % | 0 % |
| Peak upper layer CO₂ | 1.805 % | 1.805 % | 0 % |
| Peak upper layer optical density | 13.28 /m | 13.27 /m | +0.1 % |
FRI3D generated CFAST deck vs NRC CFAST baseline — smoke purge
Across the transient, the maximum instantaneous relative differences on the primary quantities are 4 % (upper layer temperature), 2.3 % (layer height), and 6 % (compartment pressure), attributable to the volume-equivalent footprint difference described above; larger relative excursions appear only on quantities near zero magnitude, where relative measures are not meaningful.
Conclusion
The FRI3D-generated CFAST deck reproduces the NRC NUREG-1934 MCR baseline to within a few percent on all layer, pressure, and species quantities, with peak values matching essentially exactly. The only systematic modeling difference — the volume-equivalent compartment footprint — is documented and its effect is bounded by the percentages above.
Reference
- NUREG-1934 / EPRI 1023259, Nuclear Power Plant Fire Modeling Analysis Guidelines, Appendix A: Main Control Room.
- NUREG-1824 / EPRI 1011999, Verification and Validation of Selected Fire Models for Nuclear Power Plant Applications (CFAST volume).