module v – advanced fire modeling · module v – advanced fire modeling. example a: control room...

Joint EPRI/NRC-RES Fire PRA WorkshopAugust 13-17, 2018

Kevin McGrattan – NIST

Fred Mowrer – Cal. Poly State University

Module V – Advanced Fire Modeling

Example A: Control Room Fire

Example B: Switchgear Cabinet Room Fire

A Collaboration of the Electric Power Research Institute (EPRI) & U.S. NRC Office of Nuclear Regulatory Research (RES)

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Step 1. Define Fire Modeling Goals

Determine the length of time that the Main Control Room (MCR) remains habitable after the start of a fire within a low-voltage control cabinet. Follow guidance provided in Chapter 11 of NUREG/CR-6850

(EPRI 1011989), Volume 2, “Detailed Fire Modeling (Task 11).” Note that MCR fire scenarios are treated differently than fires

within other compartments, mainly because it is necessary to consider and evaluate forced abandonment in addition to equipment damage.

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Step 2. Characterize Fire Scenarios

General DescriptionGeometryMaterialsFire Protection SystemsVentilationFireHabitability and Human Factors

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Typical “open grate” ceiling

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Typical Control Room Cabinet

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Material Properties

For non-burning materials, the most important properties are thermal conductivity, k, density, ρ, and specific heat, cFor specified burning rates, you need:

– Heat Release Rate (HRR) or HRR Per Unit Area (HRRPUA)– Heat of Combustion – energy released per unit mass consumed

For predicting the burning rate, you need:– Heat of Vaporization (liquids)– Heat of Gasification (solids)– Kinetic constants for reaction rates– (typically not used for NPP applications)

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Typical material properties for common construction and cable materials

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Ventilation

25 Air Changes Per Hour (ACH) for purge modeTwo scenarios – purge mode or ventilation inoperativeLeakage – often the “leakage area” is the area of the crack

under the doorExact supply and exhaust location only important for CFDZone models usually only consider height of mechanical

ventilation injection and extraction grilles

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Fire

HRR taken from Appendix G, NUREG/CR 6850 (EPRI 1011989)

Note: This guidance has been replaced by RACELLE-FIRE

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New Guidance for Electrical Enclosure HRR

RACHELLE-FIRE (Refining And Characterizing Heat Release Rate from ElectricalEnclosures During Fire) NUREG-2178, EPRI 3002005578

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Fire

What is burning?

Cables made of polyethylene (C2H4) and neoprene (C4H5Cl)

Assume effective fuel: C3H4.5Cl0.5

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Habitability

Criteria for habitability (NUREG/CR-6850, Vol 2, Chap 11)• Gas Temperature 2 m off the floor is 95 °C• Heat Flux exceeds 1 kW/m2

• Optical Density exceeds 3 m-1

What is Optical Density?

Smoke Concentration (kg/m3)

Mass Extinction Coefficient (8700 m2/kg)

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Step 3. Select Fire Models

Algebraic Models: FPA algorithm in FIVE and FDTs provides estimate of HGL temperature within a closed, ventilated compartment. – FDTs do not allow for time-dependent HRR

Zone Models: CFAST includes smoke obscuration. MAGIC does not.CFD: Provides more detailed information at exact location of

operators

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Applicability of Validation

YesNUREG-1824, Supplement 1

0.2-9.1

YesNew Range

0.0-0.6

YesNew Range

0.3-8.0

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From: NUREG-1824, Supplement 1

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For the scenario with no ventilation, the classic definition of the Equivalence Ratio does not apply because there is no supply of oxygen in the room. However, it can be shown that there is sufficient oxygen in

the room to sustain the specified fire.

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Step 4. Calculate Fire-Generated Conditions

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Temperature in smoke purge scenario– Use FPA correlation in FIVE-rev1 or FDTs

Need equivalent length / width of non-rectangular rooms

Other input parameters

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CFAST Calculation

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FDS Simulation

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0

20

40

60

80

100

120

140

0 600 1200 1800 2400 3000 3600

Tem

pera

ture

(C)

Time (s)

Temperature near Operator

FPA (Purge)

CFAST (No Vent.)

CFAST (Purge)

FDS (No Vent.)

FDS (Purge)

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0

1

2

3

4

5

6

0 600 1200 1800 2400 3000 3600

Heig

ht (m

)

Time (s)

HGL Height

CFAST (No Ventilation)

FDS (No Ventilation)

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0.0

0.2

0.4

0.6

0.8

1.0

0 600 1200 1800 2400 3000 3600

Hea

t Flu

x (k

W/m

2 )

Time (s)

Heat Flux to Operator

FIVE (Purge)

CFAST (No Vent.)

CFAST (Purge)

FDS (No Vent.)

FDS (Purge)

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0.0

10.0

20.0

30.0

40.0

50.0

60.0

0 600 1200 1800 2400 3000 3600

Optic

al D

ensi

ty (1

/m)

Time (s)

Optical Density near Operator

SFPE (Purge)CFAST (No Vent.)CFAST (Purge)FDS (No Vent.)FDS (Purge)

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Step 5. Sensitivity and Uncertainty Analysis

Uncertainty Analysis quantifies the model uncertainty– List the predicted quantities and the critical values of these quantities

Sensitivity Analysis can be used to assess parameter uncertainty

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Step 6. Document the Analysis

Follow the steps; clearly explain the entire processAnswer the original questionReport model predictions with uncertainty and sensitivity

included Include all references

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Joint RES/EPRI Fire PRA Workshop

August, 2018

Rockville, Maryland

EPRI/NRC-RES FIRE PRA METHODOLOGY

Module 5Advanced Fire ModelingExample B: Switchgear Room Cabinet Fire

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Step 1. Define Fire Modeling Goals

Estimate the effects of fire in a cabinet in a Switchgear Room on nearby cable and cabinet targets. Switchgear Room contains safety-related equipment for both

Train A and Train B that are not separated as required by Appendix R. The purpose of the calculation is to analyze this condition

and determine whether these targets fail, and, if so, at what time failure occurs.Follow guidance provided in Chapter 11 of NUREG/CR-6850

(EPRI 1011989), Volume 2, “Detailed Fire Modeling (Task 11).”

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Step 2. Characterize Fire Scenarios

General DescriptionGeometryMaterialsVentilationFireFire Protection Systems

– None credited for this scenario

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Material Properties

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Ventilation

Design flowrate specified for each of three supply and return registers.Normal operation continues during the fire.Leakage – often the “leakage area” is the area of the crack

under the door.Exact supply and exhaust location only important for CFD.Zone models usually only consider height of ducts off floor

and orientation of the vent.

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Fire

HRR taken from Appendix G, NUREG/CR 6850 (EPRI 1011989)

Note: This guidance has been replaced by RACHELLE-FIRE

47

New Guidance for Electrical Enclosure HRR

RACHELLE-FIRE (Refining And Characterizing Heat Release Rate from ElectricalEnclosures During Fire) NUREG-2178, EPRI 3002005578

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Fire

• Original fire source is specified atop the central cabinet.

• FLASH-CAT model (NUREG/CR-7010, Volume 1) is used to determine the ignition, flame spread and extinction of the cables above the original fire source.

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Fire

What is burning?

Cables made of polyethylene (C2H4) and polyvinylchloride (C2H3Cl).

Assume effective fuel: C2H3.5Cl0.5

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Step 3. Select Fire Models

Algebraic Models: FPA algorithm in FIVE provides estimate of HGL temperature within a closed, ventilated compartment. FDTs do not allow for time-dependent HRR. Both FIVE and FDTs can estimate heat flux from a fire to a target.Zone Models: Both CFAST and MAGIC include algorithms

to estimate the heat flux to and temperature of cable targets.CFD: Typical application of FDS. The primary advantage of a

CFD model for this fire scenario is that the CFD model can predict local conditions at the specific location of the target cables and adjacent cabinet.

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0.2-9.1

0.0-1.6

0.0-8.3

0.0-0.6

0.6-8.3

0.3-8.0

Yes

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Should be 6.1 m

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CFAST Calculation

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FDS – Smokeview rendering of SWGR fire

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FDS – Smokeview rendering of SWGR fire

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Follow the steps; clearly explain the entire processAnswer the original questionReport model predictions with uncertainty and sensitivity

included Include all references

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module v – advanced fire modeling · module v – advanced fire modeling. example a: control room...

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