ML18213A087
| ML18213A087 | |
| 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: ML18213A087 (36) | |
Text
Module III - Fire Analysis Task 11a: Detailed Fire Modeling and Single Compartment Scenarios Joint EPRI/NRC-RES Fire PRA Workshop August 6-10, 2018 A Collaboration of the Electric Power Research Institute (EPRI) & U.S. NRC Office of Nuclear Regulatory Research (RES)
Objectives Describe the process of fire modeling for a single fire compartment The outcome of this activity is the extent and timing of fire damage within the compartment 2
Module III: Fire Modeling Role and Scope Fire modeling: An approach for predicting various aspects of fire generated conditions
- Requires idealization and/or simplifications of the physical processes involved
- Departure of the fire system from this idealization can affect the accuracy and validity Fire scenario: A set of elements representing a fire event
- Fire source/initiation
- Fire growth
- Fire propagation (room heating, HEAF, intervening combustibles, etc.)
- Active fire protection features, e.g., detection/suppression
- Passive fire protection features, e.g., fire stops
- Target sets (cables), habitability, etc.
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Module III: Process General Task Structure 4
Module III: Process Characterize Fire Compartment Information on compartment geometry that can impact fire growth
- Size and shape, e.g., ceiling soffit or beam pocket
- Boundary construction and material
- Ventilation Fire protection systems and features
- Fixed detection systems
- Fixed fire suppression systems, water or gaseous
- Manual detection
- Fire brigade
- Internal fire barriers and stops, e.g., ERFBS 5
Module III: Process Identify/Characterize Ignition Sources Location within the compartment, type, size, initial intensity, growth behavior, severity/likelihood relationship, etc.
Estimate frequency of ignition for the ignition source.
Example of fire events involving typical ignition sources
- Oil or liquid spill fires (Characterization described in Appendix G)
- Oil or flammable liquid spray fires (Characterization described in Appendix G)
- General fires involving electrical panels (Characterization described in Appendices G, L & S)
- High energy arcing faults events (Characterization described in Appendix M)
- Cable fires (Characterization described in Appendix R)
- Hydrogen fires (Characterization described in Appendix N)
- Transient fuel materials (Characterization described in Appendices G & S)
- Corresponding PRA Standard SR: FSS-A1, FSS-C1 through C4 6
Module III: Process Identify/Characterize Secondary (Intervening) Combustibles May include,
- Overhead raceways,
- Cable air-drops,
- Stored materials,
- Electrical panels,
- Construction materials, etc.
The information provided should describe:
- Relative proximity of the secondary combustibles to the fire ignition source
- Configuration of the secondary combustible 7
Module III: Process Identify/Characterize Target Sets Each target set should be a subset of the fire PRA components and circuits (i.e., cables) present in the compartment
- Target sets associated to PRA components can be identified by examining the associated CCDP, once damaged component failure probabilities are set to 1.0
- Those subgroups with very small CCDP may be ignored as insignificant contributors to fire risk
- Check for possibility of spurious actuations due to cable fires inside the compartment under analysis. Spurious actuations may generate the need of evaluating important scenarios Fire modeling should have information on target location within the compartment available
- If complete routing information is not available, the analyst must justify target selection process and the corresponding impacts in the Fire PRA model
- Routing by exclusion OK (from a compartment, from a set of raceways)
Identify failure modes of equipment due to fire damage to the equipment or associated circuits Corresponding PRA Standard SR: FSS-A2 through A4 8
Module III: Process Select Fire Scenarios Fire scenarios should take the following into consideration:
- Selected scenarios should reflect the objective of fire modeling, in this case impacting the components and circuits of interest to safety (targets)
- Selected scenarios should represent a complete set of fire conditions that are important to the objective
- Selected scenarios should challenge the conditions being estimated, e.g.,
scenarios that challenge habitability if manual action is of interest
- The list of postulated fire scenarios should include those involving fixed and transient ignition sources Corresponding PRA Standard SR: FSS-A5 9
Module III: Process Select Fire Scenarios (contd)
Approach to selection of fire scenarios is highly dependent on fire compartment hazard profile, i.e., location and amount of fire sources and combustibles and the location and number of potential targets. In general,
- In compartments with few fire sources and many target sets (e.g., a switchgear room), start with an ignition source, postulate potential growth and propagation to other combustibles and then postulate damage to the closest target set that may be exposed to the specific fire
- In compartments with many fire sources and few potential targets (e.g., a PWR turbine building), start with potential target sets
- In compartments with many fire sources and many potential targets (e.g., a PWR auxiliary building),
Nearby source/target combinations, and Always include that fire scenario most likely (all factors considered) to cause wide-spread damage (may be driven by fire source characteristics, fire spread potential, or by fire protection systems and features) 10
Module III: Process Conduct Fire Growth and Propagation Select fire modeling tool depending on the characteristics of each scenario
- Empirical rule sets
- Hand calculations
- Zone models
- Field models Analyze fire growth and spread to secondary combustibles Estimate resulting environmental conditions Estimate time to target set damage Corresponding PRA Standard SRs: FSS-C6, D1 through D6 11
Fire Modeling Fire modeling: an approach for predicting various aspects of fire generated conditions Compartment fire modeling: modeling fires inside a compartment Requires an idealization and/or simplification of the physical processes involved in fire events Any departure of the fire system from this idealization can seriously affect the accuracy and validity of the approach 12
Fire Modeling Capabilities Areas of application: Special models or areas for Thermal effects of plumes, future research:
ceiling jets and flame radiation Cable fires Room heat up, and hot gas Fire growth inside the main layer control board Elevated fires and oxygen Fire propagation between depletion control panels Multiple fires High energy arcing fault fires Multi-compartments: corridors Fire suppression and multi-levels Hydrogen or liquid spray fires Smoke generation and migration Partial barriers and shields Fire detection 13
The Fire Modeling Process (NUREG-1934/EPRI 1023259)
Fire Modeling Process:
- 1) Define goals and objectives
- 2) Characterize the fire scenarios
- 3) Select fire models
- 4) Calculate fire-generated conditions
- 5) Conduct sensitivity and uncertainty analyses
- 6) Document the analysis 14
Fire Models Hand calculations: Mathematical expressions that can be solved by hand with a relatively small computational effort
- Quasi steady conditions
- Usually semi-empirical correlations developed with data from experiments Zone models: Algorithms that solve conservation equations for energy and mass in usually two control volumes with uniform properties Field models: Algorithms that solve simplified versions of the Navier-Stokes equations. The room is divided into large number of cells and conservation equations are solved in each of them.
Special models: There are fire scenarios critical to NPP applications that are beyond capability of existing computational fire models
- Fire experiments,
- Operating experience, actual fire events
- Engineering judgment 15
Hand Calculations Heat release rate, flame height and flame radiation Fire plume velocity, temperature heat flux, and entrainment Ceiling jet velocity, temperature, and heat flux Overall room temperature Target temperature, and time to target damage 16
Example of Hand Calcs: FDTs FDTs are a series of Microsoft Excel spreadsheets issued with NUREG-1805, Quantitative Fire Hazard Analysis Methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program The primary goal of FDTs was to be a training tool to teach NRC Fire Protection Inspectors The secondary goal of FDTs was to be used in plant inspections and support other programs that required Fire Dynamics knowledge such as SDP and NFPA 805 17
Module III: Process Hand Calcs - NUREG-1805 02.1_Temperature_NV.xls 02.2_Temperature_FV.xls 02.3_Temperature_CC.xls 03_HRR_Flame_Height_Burning_Duration_Calculation.xls 04_Flame_Height_Calculations.xls 05.1_Heat_Flux_Calculations_Wind_Free.xls 05.2_Heat_Flux_Calculations_Wind.xls 05.3_Thermal_Radiation_From_Hydrocarbon_Fireballs.xls 06_Ignition_Time_Calculations.xls 07_Cable_HRR_Calculations.xls 09_Plume_Temperature_Calculations.xls 08_Burning_Duration_Soild.xls 10_Detector_Activation_Time.xls 09_Plume_Temperature_Calculations.xls 13_Compartment_ Flashover_Calculations.xls 14_Compartment_Over_Pressure_Calculations.xls 15_Explosion_Claculations.xls 16_Battery_Room_Flammable_Gas_Conc.xls 17.1_FR_Beams_Columns_Substitution_Correlation.xls 17.2_FR_Beams_Columns_Quasi_Steady_State_Spray_Insulated.xls 17.3_FR_Beams_Columns_Quasi_Steady_State_Board_Insulated.xls 17.4_FR_Beams_Columns_Quasi_Steady_State_Uninsulated.xls 18_Visibility_Through_Smoke.xls 18
Module III: Process Hand Calcs - NUREG-1805 19
Module III: Process Hand Calcs - FIVE-Rev2 EPRI version of the fire modeling equations
- Very similar to NRC FDTS EPRI 3002000830, published in 2014
- Spreadsheet based
- Programmed in VBA Contains most of the hand calculations in the original EPRI publication and some other models available in the fire protection engineering literature
- 4 stage heat release rate profile based on t2 growth
- Heskestads flame height model
- A radiation model from a cylindrical flame to targets
- Models for velocity of plume and ceiling jet flows
- Model for plume diameter as a function of height
- MQH model for room temperature
- Model for visibility through smoke 20
Module III: Process Hand Calcs - FIVE-Rev2 21
Zone Models
- Two zones
- Upper hot gas layer
- Lower layer with clear and colder air
- Mass and energy balance in the zones
- Entrainment
- Natural flows in and out
- Forced flows in and out
- Fire is treated as a point of heat release 22
Example of a Zone Model: MAGIC Duct Horizontal opening Fan
- Gaseous phase combustion, governed by Sprinkler system pyrolysis rate and oxygen availability
- Heat transfer between flame, gases and Vent smoke, walls and surrounding air, thermal Cables conduction in multi-layer walls, obstacles to Upper layer radiation
- Mass flow transfer: Fire-plumes, ceiling-jet, Plume Lower layer Target openings and vents Flame - Thermal behavior of targets and cables
- Secondary source ignition, unburned gas Obstacle Vertical opening management
- Multi-compartment, multi-fire, etc.
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CFAST Doorway Cable target loc ations and direc tions Liquid spray fire Burn room Target room Spec ified Leakage 110 kW gas burner fire Heptane Pan Fire Ceiling exhaust vent Com partm ent Vent Mec hanic al ventilation supply 1.2 m below c eiling Controlled gas fire Kerosene Pan Fire 24
MAGIC 25
Field Models
- Solve a simplified form of the Navier Stokes equations for low velocity flows
- Calculation time in the order of hours, days or weeks
- May help in modeling complex geometries 26
Example of Field Model: FDS Fire Dynamics Simulator Developed and maintained by NIST 27
Fire Dynamics Simulator (FDS) 28
Which Model to Choose?
NUREG-1934 (EPRI 1023259)
Hand calculations available
- Combustion - Heat release rates, flame heights
- Fire generated conditions Plume temperatures and velocities Ceiling jet temperatures and velocities Flow through vents Enclosure temperature Time and temperature to flashover Target temperature and time to target damage
- Heat transfer: irradiation from flames, plume and ceiling jet convective flux Analysts may need to go back and find additional parameters required 29
Verification and Validation (NUREG-1824/EPRI 1011999)
Verification: the process of determining that the implementation of a calculation method accurately represents the developers conceptual description of the calculation method and the solution to the calculation method. Is the Math right?
Validation: the process of determining the degree to which a calculation method is an accurate representation of the real world from the perspective of the intended uses of the calculation method. Is the Physics right?
See NUREG-1824 (EPRI 1011999) and Supplement 1 to NUREG-1824 (EPRI 3002002182) 30
Verification and Validation (NUREG-1824-Supplement 1) 31
Verification and Validation (NUREG 1824 Supplement 1)
Empirical CFAST MAGIC FDS Exp Correlations Output Quantity Corr.
HGL Temp. Rise, Natural MQH 1.17 0.15 1.21 0.38 1.13 0.33 1.02 0.07 0.07 Ventilation FPA 1.29 0.32 HGL Temp. Rise, Forced 1.13 0.23 1.04 0.15 1.14 0.20 0.07 Ventilation DB 1.18 0.25 HGL Temp. Rise, Beyler 1.04 0.37 0.99 0.24 1.07 0.16 1.16 0.11 0.07 No Ventilation HGL Depth ASET/YT - - 1.01 0.29 1.08 0.27 1.04 0.06 0.05 Ceiling Jet Temp. Rise Alpert 0.86 0.11 1.06 0.42 1.04 0.46 0.99 0.12 0.07 Heskestad 0.80 0.33 Plume Temp. Rise 1.09 0.29 1.03 0.19 1.12 0.21 0.07 McCaffrey 0.90 0.31 Oxygen Concentration N/A 1.08 0.28 1.01 0.22 0.99 0.13 0.08 Smoke Concentration N/A 3.42 0.68 3.71 0.66 2.63 0.60 0.19 Pressure Rise N/A 1.37 0.63 1.32 0.20 1.00 0.23 0.23 Target Temp. Rise Steel 1.29 0.45 1.25 0.49 1.04 0.38 0.99 0.17 0.07 Point Source 1.39 0.50 Target Heat Flux 1.04 0.59 0.85 0.66 0.97 0.26 0.11 Solid Flame 1.17 0.44 Surface Temp. Rise N/A 1.02 0.22 0.93 0.28 0.98 0.12 0.07 Surface Heat Flux N/A 0.94 0.26 0.76 0.33 0.89 0.17 0.11 Cable Failure Time THIEF 0.90 0.11 - - - - 1.10 0.16 0.12 Sprinkler Activation Time Sprinkler 1.11 0.41 1.01 0.20 0.91 0.20 0.93 0.15 0.06 32 Smoke Detector Act. Time Temp. Rise 1.07 0.58 1.77 0.39 1.44 0.38 1.22 0.34 0.34
Module III: Process Fire Detection/Suppression Analysis Assess fire detection timing Assess timing, reliability, and effectiveness of fixed fire suppression systems Assess manual fire brigade response Estimate probability of fire suppression as a function of time Corresponding PRA Standard SRs: FSS-D6, D7, D8 33
Module III: Process Calculate Severity Factor The time to target damage, and as a result the non-suppression probability, is a function of the postulated heat release rate The severity factor should be calculated in combination with the non-suppression probability Corresponding PRA Standard SRs: FSS-C4, D5 34
Use of Special Models There are fire scenarios critical to NPP applications that are beyond capability of existing computational fire models
- Cable fires
- High energy arcing faults and fires
- Fire growth inside the main control board
- Fire propagation between control panels
- The methods described here are documented in EPRI 1011989 &
NUREG/CR-6850, EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities.
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Module III: Process Document Analysis Results The first tier documentation should be sufficient in detail to allow for an independent reader to understand
- Scenarios postulated, the basis for their selection and analysis,
- The tools utilized in the analysis and basis for selection,
- The final results of the analysis The second tier documentation should provide the details of each individual analysis performed including:
- Details of scenario selection process,
- The fire modeling analyses performed All specific considerations and assumptions should be recorded clearly 36