ML18213A083
| ML18213A083 | |
| Person / Time | |
|---|---|
| Issue date: | 07/31/2018 |
| From: | Tammie Rivera NRC/RES/DRA/FRB, Electric Power Research Institute |
| To: | |
| Shared Package | |
| ML18213A072 | List: |
| References | |
| Download: ML18213A083 (21) | |
Text
Joint RES/EPRI Fire PRAWorkshopAugust 6-10, 2018Module III
-FireAnalysisFire Fundamentals:Appendix G
-HeatRelease RatesA Collaboration of the Electric Power Research Institute (EPRI) & U.S. NRC Office of Nuclear Regulatory Research (RES) 2Heat Release RatesObjectivesThe objectives of this module are:
1.Define heat release rate and heat release rate profile 2.Review the recommended peak heat release rate values for typical ignition sources in NPPs 3.Describe the method provided for developing heat release rate profiles for fixed and transient ignition sources in NPPsNOTE: Appendix G recommends values for ignition sourcesonly. Heat release rates associated with fires propagatingoutside of the ignition source have to be evaluatedaccordingly.
3Heat Release RatesDefinition Definition: Heat generated by a burning object per unit time. BTU/sec or KWm" is burning rate [kg/s
-m 2], H cis heat of comb [kJ/kg], A is area [m 2]Equivalent terms: energy release rate, fire intensity, fire powerHRR profile describes fire intensity as a function of time Q&A H m Q c&&IncipientGrowthFully DevelopedDecayPeakTime 4Heat Release RatesFire Growth in Electrical Cabinets The t 2function is recommended for modeling the growth phase of the fire:2 , t Q QMin t Qpeakpeak&&&Heat Release Rate 0 5 10 15 20Time [min]
kWPeak HRR= time to peak 5Heat Release RatesHRR ProfileThe HRR profile can be expressed as a constant or as afunction of time: Incipient stage: Not recommended to be moeled-Duration and intensity are uncertainGrowth: Depends on the fuel and geometry of the scenario
-Based on engineering judgment and/or experimental observationsFully developed: Usually after the fire reaches its peak intensity
-Also known as steady burning
-Starts at ignition if the growth period is not considered
-A constant fire intensity should be the peak heat release rate of the profileDecay: In general, less hazardous conditions than the growth and fully developed stage 6FAQ 08-0052: Transient FiresManual Suppression CurveFire Growth Time:
-Common trash can (refuse in a trash receptacle):Can be associated with a t 2fire growth that grows from zero to peak in approximately 8 minutes.
-Common trash bag (refuse in plastic bags not in a receptacle):Can be associated with a t 2fire growth that grows from zero to peak in approximately 2 minutes.
-Flammable or combustible liquid spills:Negligible growth time (near infinite growth rate)Assume peak heat release rate for the spill through the entire duration of the fire (ignition through burnout) 7Heat Release RatesFixed Ignition SourcesThe methodology recommends heat release rate values forvarious fixed ignition sourcesVertical cabinets
-Open/closed
-Qualified/unqualified cablesPumps (electrical fires)Electric motorsHRR for flammable liquid fires should be calculatedusing the equationSeparate guidance for cables, pressurized oil, and hydrogen fires A H m Q c&&
8Heat Release RatesRecommended Peak HRR ValuesRecommended peak HRR values were developed based on expert judgment (Table G
-1)Panel included EPRI and NRC representatives with expertise in fire behavior/phenomena and PRA.Values are expressed as probability distributions. The panel identified the 75thand 98thpercentiles of the distribution for peak HRR.Primary sources of information included NUREG/CR
-4527 and VTT publicationsGamma distribution selected:
-Only positive values starting at 0 kW
-Values in the same order of magnitudeCorresponding PRA Standard SR: FSS
-D5, E3 9Heat Release RatesRecommended Peak HRR ValuesExample distribution developedby the expert panel75 th= 232 kW98 th = 464 kW= 2.6= 67.8 0 500 1000Peak HRR DistributionHRR 10Heat Release RatesRecommended Peak HRR Values (Table G
-1)*See report for footnotesIgnition Sources HRRkW/ (Btu/s)Gamma Distribution75 th98 thVertical cabinets with qualified cable, fire limited to one cable bundle69 1(65)211 2(200)0.84(0.83)59.3(56.6)Vertical cabinets with qualified cable, fire in more than one cable bundle211 2(200)702 3(665)0.7(0.7)216(204)Vertical cabinets with unqualified cable, fire limited to one cable bundle90 4(85)211 2(200)1.6(1.6)41.5(39.5)Vertical cabinets with unqualified cable, fire in more than one cable bundle closed doors232 5(220)464 6(440)2.6(2.6)67.8(64.3)Vertical cabinets with unqualified cable, fire in more than one cable bundle open doors232 5(220)1002 7(950)0.46(0.45)386(366)Pumps (electrical fires) 869(65)211 2(200)0.84(0.83)59.3(56.6)Motors 832(30)69(65)2.0(2.0)11.7(11.1)Transient Combustibles 9142(134)317(300)1.8(1.9)57.4(53.7) 11Heat Release RatesFire Growth in Electrical CabinetsThe methodology suggests a firegrowth rate for electrical cabinetfiresThe fire grows to its peak HRR in approximately 12 minThe fire burns at its peak HRR for approximately 8 minBased on experiments reported in NUREG/CR
-4527 12Heat Release RatesAssigning HRR Values to Electrical CabinetsVisual examination of cabinet interior is recommendedIdentify openings in the cabinet wallsIdentify type of cable: qualified/unqualifiedIdentify cable bundles Qualitatively determine if a fire can propagate from one bundle to anotherSelect the appropriate peak HRR probability distribution 13Heat Release RatesExamplesMore than one cable bundleAssuming qualified cable, select distribution with percentiles:
-75 th= 211 kW-98 th= 702 kW 14Heat Release RatesExamplesOnly one cable bundleAssuming qualified cable, select distribution with percentiles:
-75 th= 69 kW-98 th= 211 kW 15FAQ 08-0042: "Fire Propagation From Electrical Cabinets"Purpose & Scope
-Provide clarification on conflicting language in NUREG/CR
-6850 related to the description of fire propagation from unvented cabinetsGuidance in Appendix G is in conflict with the guidance in chapters 6 and 11 of NUREG/CR
-6850-The scope of this FAQ is limited to the clarification of the conflicting guidance provided in NUREG/CR
-6850 related to fire propagation outside unvented cabinets.-
Reference:
EPRI 1019259, Supplement 1 to NUREG/CR
-6850 16FAQ 08-0042: SolutionChapter 11 of NUREG/CR
-6850 provides the consensus position on fire propagation outside of unvented cabinets
-The following, from the second paragraph on section G.3.3 should be disregarded:
17FAQ 08-0042: SolutionModified language includes description of electrical cabinet features that should be present to prevent fire propagation outside the cabinet
-Fire sealed (not fire rated) at cable entry points
-No vents-Robustly secured 18FAQ 08-0043: "Location of Fires Within Electrical Cabinets"Purpose & Scope
-This FAQ provides clarification on the location of fires within an electrical cabinet.
-The scope of this FAQ is limited to describing the location of a fire postulated in an electrical cabinet in a Fire PRA.
Reference:
-EPRI 1019259, Supplement 1 to NUREG/CR
-6850 19FAQ 08-0043: SolutionFor cabinets with no vents, the fire should be postulated approximately 1' below the top of the cabinetAnalysts should inspect cabinets to determine vent location or the possibility of door openings.
-For vented cabinets, fires should be postulated at the location of the vents-Fire should be postulated at the top of open doors 20Heat Release RatesTransient Ignition SourcesThe peak HRR for transient fires is also characterized with agamma probability distributionGamma distribution percentiles:
-75th= 142 kW, 98th= 317 kW-= 1.9, = 53.7Applicable only to localized transient combustibles (trash cans, etc.)Not applicable to flammable liquid transient fires 21Heat Release RatesConcluding RemarksPeak HRR values are recommended for some typical fixedand transient ignition sources in NPP fire scenariosValues are for localized ignition source (not for fires propagating outside the ignition source)HRR for flammable liquid fires can be calculated from fundamental equationsHRR for "solid" ignition sources are generally expressed as probability distributions based on experimental data and expert judgmentRevised HRRs for electrical cabinets are discussed in a separate presentation