ML18213A085
| ML18213A085 | |
| 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: ML18213A085 (16) | |
Text
Module III - Fire Analysis Appendix E: Fire Severity 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)
Fire Severity Purpose A uniform methodology has been developed to define the severity of a fire.
- Severity factor concept
- Based on heat release rate
- Standardized cases Applicable SRs: FSS-C2, C3, C4, 2
Fire Severity Severity Factor Concept Severity Factor is . .
- A simplified, one parameter representation of a very complex phenomenon (i.e., fire) influenced by a large number of factors.
- Defined as the conditional probability that, given a fire has occurred, it is of certain severity (it is defined here through heat release rate).
- Quantified in combination with Non-Suppression Probability.
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Fire Severity Severity Factor Concept Probability fire Bin Bin # HRR (kW) is at least this Damage?
Probability big 1 11 0.445 1.000 No 2 36 0.219 0.555 No 3 61 0.129 0.336 No 4 87 0.078 0.207 No damage = Fire x 0.129 5 112 0.048 0.129 Yes 6 137 0.030 0.081 Yes 7 162 0.019 0.051 Yes 8 187 0.012 0.032 Yes 9 212 0.020 0.020 Yes Total 1 4
Fire Severity Severity Factor Concept Bin # HRR Bin Time available for suppression:
Probability Damage ts (min) PNS,i Pi
- PNS,i (i) (kW)
(Pi) ts = tdamage - tdetection 1 11 0.445 No 0 0 Net probability of damage:
2 36 0.219 No 0 0 PNSnet = (Pi
- PNS,i) 3 61 0.129 No 0 0 i=1,9 4 87 0.078 No 0 0 PNSnet = 0.011 5 112 0.048 Yes 28 0.03 0.0014 6 137 0.03 Yes 24 0.06 0.0018 7 162 0.019 Yes 20 0.09 0.0017 Frequency of damage:
8 187 0.012 Yes 16 0.15 0.0018 damage = IS,i x 0.011 9 212 0.02 Yes 13 0.21 0.0042 Net damage probability: 0.011 5
Fire Severity Probability of Damage Estimation Probability of damage before time t is estimated using complex fire spread and propagation models.
- Heat release rate is a key parameter of the analysis
- Assuming a known heat release rate, specific features of the compartment, ignition source, and target set configuration, time to damage can be calculated.
- Since heat release rate is expressed with a probability distribution, the time to damage can be expressed with a probability distribution Probability Density Probability Density Peak Heat Release Rate Time to Damage (t) 6
Fire Severity Heat Release Rate Distributions The heat release rate of the following equipment classes have been defined:
HRR (Btu/s)
Case Ignition Source 75th 98th 1 Vertical cabinets with qualified cable, fire limited to 65 200 one cable bundle 2 Vertical cabinets with qualified cable, fire in more 200 665 than one cable bundle 3 Vertical cabinets with unqualified cable, fire limited 85 200 to one cable bundle 4 Vertical cabinets with unqualified cable, fire in more 220 440 than one cable bundle closed doors 5 Vertical cabinets with unqualified cable, fire in more 220 950 than one cable bundle open doors 6 Pumps (electrical fires) 65 200 7 Motors 30 65 8 Transient Combustibles 135 300 7
Fire Severity Heat Release Rate Distributions Lets focus on one of these cases:
HRR (Btu/s)
Case Ignition Source 75th 98th 1 Vertical cabinets with qualified cable, fire limited to 65 200 one cable bundle 2 Vertical cabinets with qualified cable, fire in more 200 665 than one cable bundle 3 Vertical cabinets with unqualified cable, fire limited 85 200 to one cable bundle 4 Vertical cabinets with unqualified cable, fire in more 220 440 than one cable bundle closed doors 5 Vertical cabinets with unqualified cable, fire in more 220 950 than one cable bundle open doors 6 Pumps (electrical fires) 65 200 7 Motors 30 65 8 Transient Combustibles 135 300 8
Fire Severity Heat Release Rate Distribution - Example Table E-1 HRR Distribution for Vertical Cabinets with Qualified Cables, Fire Limited to One Cable Bundle Heat Release Rate (Btu/s) Severity Factor Bin Lower Upper Point Value (Pi) This is the 1 0 25 10.5 0.446 corresponding 2 25 50 36 0.219 distribution binning 3 50 75 61 0.129 table as presented in 4 75 100 87 0.078 the original report 5 100 125 112 0.048 which all contain an 6 125 150 137 0.030 error 7 150 175 162 0.019 8 175 200 187 0.012 9 200 225 212 0.007 The 98th 10 225 250 237 0.005 percentile value 11 250 275 262 0.003 should be the 12 275 300 287 0.002 largest fire 13 300 325 312 0.001 postulated 14 325 350 337 0.001 15 350 Infinity 405 0.001 9
Fire Severity Heat Release Rate Distribution - Example Table E MODIFIED This is the same table modified to reflect 98th HRR Distribution for Vertical Cabinets with Qualified Cables, Fire percentile value as Limited to One Cable Bundle largest bin (2% of Heat Release Rate (Btu/s) Severity Factor fires)
Bin Lower Upper Point Value (Pi) 1 0 25 10.5 0.446 Document, document, 2 25 50 36 0.219 document 3 50 75 61 0.129 4 75 100 87 0.078 5 100 125 112 0.048 6 125 150 137 0.030 7 150 175 162 0.019 8 175 200 187 0.012 9 200 Infinity 200 0.020 10
Fire Severity Severity Factor for General Pump Oil Fires Oil fire severities for general pumps are established from the following steps (per ML12171A583)
- 1. Determine the amount of oil that can be spilled in the room.
Determine the amount of oil available in the system for the large and very large oil spill fires. The pump oil fire plant-wide fire frequency remains unchanged.
- 2. Assign fire severity factors (split fractions) as follows:
Assign a severity factor of 0.05 (5%) to very large fires: scenarios involving 100% of the total oil inventory spilled and ignited.
Assign a severity factor of 0.07 (7%) to large fires: scenarios involving 10%
of the total oil inventory spilled and ignited.
Assign a severity factor of 0.88 (88%) for small fires: scenarios involving a leak that leads to a fire that only impacts the pump.
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FAQ 08-0044: MFW pump fires FAQ questioned application of pump fire guidance to MFW pumps
- Spill of very large oil volume led to unrealistic (high) frequency for very large oil fires Solution provides a new approach for MFW pumps:
- Determine the amount of oil available in the system for the large and very large oil spill fires. The MFW pump oil fire plant-wide fire frequency remains unchanged.
- Assign a severity factor of 0.0034 (0.34%) to very large fires: scenarios involving 100%
of the total oil inventory spilled and ignited.
- Assign a severity factor of 0.0306 (3.06%) to large fires: scenarios involving 10% of the total oil inventory spilled and ignited.
- Assign a severity factor of 0.966 (96.6%) for small fires: scenarios involving a leak that leads to a fire that only impacts the MFW pump.
Reference:
EPRI 1019259, Supplement 1 to NUREG/CR-6850 12
FAQ 14-009: Well Sealed MCCs The scope of this FAQ is limited to well-sealed, robustly-secured MCCs operating at 440V or greater, and does not apply to other electrical cabinets, notably those already covered by High Energy Arcing Fault (HEAF) analysis Factor of 0.23 can be used to represent the fraction of fires assumed to breach a well-sealed MCC cabinet Factor was derived from review of fire events data in EPRIs Fire Events Database The FAQ includes guidance for the application of severity factors to fires that breach the integrity of a well sealed MCC 13
Fire Severity Severity Factor for Other Ignition Sources The following notes address ignition sources not covered in the preceding discussions:
- Cable fires:
Heat release rate is established using fire propagation modeling Severity factor = 1.0 may be used where target damage can be ascertained
- High-energy arcing faults:
Severity factor = 1.0 within zone of influence
- Catastrophic transformer fires in the transformer yard:
Severity factor = 1.0 within zone of influence
- Non-catastrophic transformer fires in the transformer yard:
Generally not modeled, otherwise use severity factor = 1.0 within zone of influence
- Other fires in the transformer yard:
Depending on the item burning, the heat release rate of similar devices may be used.
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Fire Severity Frequency Bins and HRR Distributions Table 11-1 Recommended Severity Factors . . . for Ignition Sources in the Frequency Model ID Location Ignition Source HRR Distribution Category 1 Battery Room Batteries Electric motors 2 Containment Reactor coolant Pump Pumps (Electrical)/Oil spills (PWR) 4a Control Room Electrical cabinets Applicable electrical cabinet 4b Control Room Main control board See Appendix L 5 Control/Auxiliary/ Cable fires caused by Assume 1.0 Reactor Building welding and cutting 6 Control/Auxiliary/ Transient fires caused Transients Reactor Building by welding and cutting 21 Plant-Wide Pumps Pump (Electrical)/Oil spills Components 15
Fire Severity Concluding Remarks Severity Factor provides an adjustment to ignition frequency to account for the severity of the fire.
- It is tied to the heat release rate
- It is estimated in concert with probability of non-suppression
- Specific cases have been developed
- Guidance is provided for other cases 16