Fire Ignition Frequency (Task 6) - Revision history

User: /* Current FPRA Counting Guidance and Fire Ignition Frequencies */

2025-01-20T16:20:33Z

Current FPRA Counting Guidance and Fire Ignition Frequencies

User: /* Current FPRA Counting Guidance and Fire Ignition Frequencies */

2025-01-20T15:53:30Z

Current FPRA Counting Guidance and Fire Ignition Frequencies

User: /* Current FPRA Counting Guidance and Fire Ignition Frequencies */

2025-01-20T15:40:48Z

Current FPRA Counting Guidance and Fire Ignition Frequencies

User at 15:13, 20 January 2025

2025-01-20T15:13:25Z

User: /* Current FPRA Counting Guidance and Fire Ignition Frequencies */

2025-01-20T14:58:21Z

Current FPRA Counting Guidance and Fire Ignition Frequencies

User: /* Current FPRA Counting Guidance and Fire Ignition Frequencies */

2025-01-20T14:57:35Z

Current FPRA Counting Guidance and Fire Ignition Frequencies

User: /* Current FPRA Counting Guidance and Fire Ignition Frequencies */

2025-01-20T14:55:54Z

Current FPRA Counting Guidance and Fire Ignition Frequencies

User: /* Current FPRA Counting Guidance and Fire Ignition Frequencies */

2020-05-06T18:39:33Z

Current FPRA Counting Guidance and Fire Ignition Frequencies

User at 18:13, 22 April 2020

2020-04-22T18:13:29Z

User: /* Current FPRA Counting Guidance and Fire Ignition Frequencies */

2020-04-22T15:18:37Z

Current FPRA Counting Guidance and Fire Ignition Frequencies

@@ Line 239: / Line 239: @@
 | [https://www.epri.com/research/products/000000003002025942 EPRI 3002025942 / NUREG-2262]
 |-
-| 16.1
+| 16.1-1
 | Plant-Wide Components
-| HEAF for segmented bus ducts
+| HEAF for segmented (non-segregated) bus ducts (Zones BDUAT and BDSAT)
-| A bus duct where the bus bars are made up of multiple sections bolted together at regular intervals (transition points). Here, the bus bars are contained within open-ended sections of metal covers that are bolted together to form a continuous grounded enclosure running the full distance between termination points.
+| HEAFs associated with segmented bus ducts located in Zone BDUAT and Zone BDSAT.
-Note: This bin does not cover nonsegmented or continuous bus ducts or cable ducts. The arc faults for these two categories are inherently included in the treatment of the end device, and no further treatment is needed.
+Consistent with NUREG/CR-6850, Supplement 1, because NSBD (category 1) and cable ducts (category 3) have no transition points other than the termination at the end device, treatment of bus duct faults independent from the treatment of fire for the end device is not required. That is arc faults for categories 1 and 3 of bus ducts are inherently included in the treatment of the end device and no further treatment is needed.
-In 2023, new HEAF guidance was published. The prior guidance remains an acceptable approach. For prior HEAF bin descriptions, counting guidance, counting reference, fire ignition frequency, and fire ignition frequency reference please see [https://firepra.epri.com/index.php?title=FirePRA:Prior_HEAF_Guidance Prior HEAF counting guidance]
+Note: In 2023, new HEAF guidance was published. The prior guidance remains an acceptable approach. For prior HEAF bin descriptions, counting guidance, counting reference, fire ignition frequency, and fire ignition frequency reference please see [https://firepra.epri.com/index.php?title=FirePRA:Prior_HEAF_Guidance Prior HEAF counting guidance]
-| The analyst will need to choose between one of two recommended practices for counting segmented bus ducts as a fire ignition source. The choice will be dependent on whether or not the transition points can be identified based on an external visual inspection of the bus duct.
+| The analyst will need to choose between one of two counting practices; for known transition points (see Section 5.2.3.1 of NUREG-2262 for full details) or for unknown transition points (see Section 5.2.3.2 for full details). The choice will be dependent on whether or not the transition points can be identified.
-Counting approach 1: If the transition points along the length of the segmented bus duct can be identified by external visual inspection, or based on plant electrical construction drawings, then
+Counting approach 1 (For Known Transition Points): The counting is based on the total number of transition points within the bin (identified by external visual inspection or based on plant electrical construction drawings). Although transition points may not be generally known, certain locations may point to the presence of a transition point (e.g., geometric factors such as horizontal direction change or changes in elevation suggest the presence of a transition point).
-However, industry feedback indicates that the joints or junctions in the outer ducting surrounding a bus duct cannot be assumed to correspond to junctions in the bus bars themselves without
+Counting approach 2 (For Unknown Transition Points): Based on the total length of the segmented bus duct within the bin. A per-linear-foot frequency can then be estimated by dividing the plant-wide frequency by the total length of segmented bus duct within the bin.
-Counting approach 2: If the transition points cannot be identified based on external visual inspection, or by plant electrical construction drawings, then the partitioning of fire frequency to
+| [https://www.epri.com/research/products/000000003002025942 EPRI 3002025942 / NUREG-2262]
-a specific fire scenario is based on apportioning of the fire frequency equally along the length of the bus duct. Hence, the analysis must estimate the total length of segmented bus duct present in
+[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0035, Section 7 of Supplement 1]
-the plant under analysis. A “per linear foot” fire frequency can then be estimated by dividing the plant-wide fire frequency by the total length of segmented bus duct in the plant.
+| 2.61E-03
-That is, the fire frequency for a given fire scenario would be based on the ratio of the length of duct for which identified targets fall within the bus duct arc fault zone of influence to the total length of bus duct in the plant. A lower limit to the assumed fire frequency for any given fire scenario is also applied.
+Counting approach 2 (For Unknown Transition Points): Based on the total length of the segmented bus duct within the bin. A per-linear-foot frequency can then be estimated by dividing the plant-wide frequency by the total length of segmented bus duct within the bin.
 | [https://www.epri.com/research/products/000000003002025942 EPRI 3002025942 / NUREG-2262]
 [https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0035, Section 7 of Supplement 1]
-| 1.10E-03
+| 8.98E-04
 | [https://www.epri.com/research/products/000000003002025942 EPRI 3002025942 / NUREG-2262]
 |-

@@ Line 273: / Line 273: @@
 lower bound is based on the assumption that, lacking specific information on segment lengths, a nominal segment length of 12 feet should be assumed. Any single scenario is then assigned a fire
 frequency equivalent to that associated with one bus bar segment 12 feet in length (i.e., equivalent to one nominal transition point).
+| [https://www.epri.com/research/products/000000003002025942 EPRI 3002025942 / NUREG-2262]
-| [https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0035, Section 7 of Supplement 1]
+[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0035, Section 7 of Supplement 1]
 | 1.10E-03
-| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en  EPRI 3002002936 (NUREG-2169)]
+| [https://www.epri.com/research/products/000000003002025942 EPRI 3002025942 / NUREG-2262]
 |-
 | 16.2
 | Plant-Wide Components
 | HEAF for iso-phase bus ducts
-| A bus duct where the bus bars for each phase are separately enclosed in their own protective housing. The use of iso-phase buses is generally limited to the bus work connecting the main generator to the main transformer.
+| A bus duct where the bus bars for each phase are separately enclosed in their own protective housing (segregated bus ducts). The primary use of iso-phase buses is generally limited to the bus work connecting the main generator to the main and auxiliary transformers.
 In 2023, new HEAF guidance was published. The prior guidance remains an acceptable approach. For prior HEAF bin descriptions, counting guidance, counting reference, fire ignition frequency, and fire ignition frequency reference please see [https://firepra.epri.com/index.php?title=FirePRA:Prior_HEAF_Guidance Prior HEAF counting guidance]
 | There should generally be one iso-phase bus per unit (an iso-phase bus includes all three phases). If there is more than one iso-phase bus, simply count the total number of iso-phases buses per unit. For individual fire scenarios, the plant-wide frequency is applied (i.e. partitioned) equally to each end of each iso-phase bus duct counted.
-| [https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0035, Section 7 of Supplement 1]
+| [https://www.epri.com/research/products/000000003002025942 EPRI 3002025942 / NUREG-2262]
-| 5.91E-04
+[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0035, Section 7 of Supplement 1]
-| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en  EPRI 3002002936 (NUREG-2169)]
+| 1.01E-03
 |-
 | 17

@@ Line 214: / Line 214: @@
 | High-energy arcing faults are associated with load centers operating between 480 and 1000 Volts. Bin 16.a includes load centers at typical nominal system voltage ranging from 480 VAC to 1000 VAC but also includes system voltages down to 440 VAC.
-In 2023, new HEAF guidance was published. The prior guidance remains an acceptable approach. For prior HEAF bin descriptions, counting guidance, counting reference, fire ignition frequency, and fire ignition frequency reference please see [https://firepra.epri.com/index.php?title=FirePRA:Prior_HEAF_Guidance Prior HEAF counting guidance]
+Note: In 2023, new HEAF guidance was published. The prior guidance remains an acceptable approach. For prior HEAF bin descriptions, counting guidance, counting reference, fire ignition frequency, and fire ignition frequency reference please see [https://firepra.epri.com/index.php?title=FirePRA:Prior_HEAF_Guidance Prior HEAF counting guidance]
 | Only count load center supply circuit breakers for HEAF susceptibility - this is the most likely location of a load center HEAF. Do not assign a HEAF count to load centers without bus supply circuit breakers.
 | [https://www.epri.com/research/products/000000003002025942 EPRI 3002025942 / NUREG-2262]
@@ Line 223: / Line 223: @@
 | Plant-Wide Components
 | High Energy Arcing Faults - Medium Voltage Electrical Cabinets (>1000 V)
-| High-energy arcing faults are associated with switchgear and load centers. Switchyard transformers and isolation phase buses are not part of this bin. For this bin, similar to electrical cabinets, the vertical segments of the switchgear and load centers should be counted. Additionally, to cover potential explosive failure of oil filled transformers (those transformers that are associated with 4.16 or 6.9kV switchgear and load centers) may be included in vertical segment counts of the switchgear.
+| High-energy arcing faults associated with medium-voltage switchgear.
 In 2023, new HEAF guidance was published. The prior guidance remains an acceptable approach. For prior HEAF bin descriptions, counting guidance, counting reference, fire ignition frequency, and fire ignition frequency reference please see [https://firepra.epri.com/index.php?title=FirePRA:Prior_HEAF_Guidance Prior HEAF counting guidance]
-| Each vertical segment of the switchgear and load center for medium voltage (above 1000 V) electrical cabinets is counted separately.
+Note: In 2023, new HEAF guidance was published. The prior guidance remains an acceptable approach. For prior HEAF bin descriptions, counting guidance, counting reference, fire ignition frequency, and fire ignition frequency reference please see [https://firepra.epri.com/index.php?title=FirePRA:Prior_HEAF_Guidance Prior HEAF counting guidance]
-| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+| Each switchgear bank is counted as one.
-[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 06-0017, Section 4 of Supplement 1]
-| 2.13E-03
+Medium-voltage switchgear should be counted by the entire switchgear bank (e.g., an entire bank is counted as one.
-| [https://www.epri.com/#/pages/product/000000003002002936/?lang=en  EPRI 3002002936 (NUREG-2169)]
 |-
 | 16.1

@@ Line 212: / Line 212: @@
 | Plant-Wide Components
 | High Energy Arcing Faults - Low Voltage Electrical Cabinets (480-1000 V)
-| High-energy arcing faults are associated with switchgear and load centers operating between 480 and 1000 Volts.  For this bin, similar to electrical cabinets, the vertical segments of the switchgear and load centers should be counted.
+| High-energy arcing faults are associated with load centers operating between 480 and 1000 Volts. Bin 16.a includes load centers at typical nominal system voltage ranging from 480 VAC to 1000 VAC but also includes system voltages down to 440 VAC.
 In 2023, new HEAF guidance was published. The prior guidance remains an acceptable approach. For prior HEAF bin descriptions, counting guidance, counting reference, fire ignition frequency, and fire ignition frequency reference please see [https://firepra.epri.com/index.php?title=FirePRA:Prior_HEAF_Guidance Prior HEAF counting guidance]
-| Each vertical segment of the switchgear and load center for low voltage (480-1000 V) electrical cabinets is counted separately. MCCs are not included, unless the MCC is associated with switchgear that is used directly to operate equipment such as load centers.
+| Only count load center supply circuit breakers for HEAF susceptibility - this is the most likely location of a load center HEAF. Do not assign a HEAF count to load centers without bus supply circuit breakers.
-| [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
+| [https://www.epri.com/research/products/000000003002025942 EPRI 3002025942 / NUREG-2262]
-[https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 06-0017, Section 4 of Supplement 1]
+| 5.32E-04
-| 1.52E-04
+| [https://www.epri.com/research/products/000000003002025942 EPRI 3002025942 / NUREG-2262]
 |-
 | 16.b

@@ Line 244: / Line 244: @@
 Note: This bin does not cover nonsegmented or continuous bus ducts or cable ducts. The arc faults for these two categories are inherently included in the treatment of the end device, and no further treatment is needed.
 | The analyst will need to choose between one of two recommended practices for counting segmented bus ducts as a fire ignition source. The choice will be dependent on whether or not the transition points can be identified based on an external visual inspection of the bus duct.
@@ Line 273: / Line 275: @@
 | HEAF for iso-phase bus ducts
 | A bus duct where the bus bars for each phase are separately enclosed in their own protective housing. The use of iso-phase buses is generally limited to the bus work connecting the main generator to the main transformer.
 | There should generally be one iso-phase bus per unit (an iso-phase bus includes all three phases). If there is more than one iso-phase bus, simply count the total number of iso-phases buses per unit. For individual fire scenarios, the plant-wide frequency is applied (i.e. partitioned) equally to each end of each iso-phase bus duct counted.
 | [https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0035, Section 7 of Supplement 1]

@@ Line 80: / Line 80: @@
 [https://www.nrc.gov/docs/ML1419/ML14190B307.pdf FAQ 14-0008]
 | 2.05E-3
-|  [https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Vol 2 / EPRI 3002016052]
+| [https://www.epri.com/#/pages/product/000000003002016052/ NUREG-2178 Vol 2 / EPRI 3002016052]
 |-
 | 5
@@ Line 322: / Line 322: @@
 | This bin includes pumps and large hydraulic valves. Due to a lack of sufficient statistical data, a separate bin was not defined for large valves that include hydraulic fluid powered mechanisms. It is recommended such valves (e.g. Main Steam Isolation Valves, and Turbine Stop Valves) be counted and included in the pump bin.
 | Each pump with a rating greater than 5 hp should be counted separately (do not count pumps with a horsepower rating of 5 hp or below).
 | [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
 [https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0031, Section 6 of Supplement 1]
@@ Line 330: / Line 332: @@
 [https://epri.box.com/s/0v6yxom7rjun3f6abvct0ww0sul87964 Panel Decision (NRC Recent Fire PRA Methods Review Panel Decisions - Attachment 6)]
 | 2.72E-02
 | [https://www.epri.com/#/pages/product/000000003002002936/?lang=en  EPRI 3002002936 (NUREG-2169)]
@@ Line 392: / Line 396: @@
 | This category includes components such as air conditioning units, chillers, fan motors, air filters, dampers, etc.  A fan motor and compressor housed in the same component are counted as one component.  Do not count ventilation fans if the drive motor is 5 hp or less.
 | Each component with a rating greater than 5 HP should be counted separately.
 | [https://www.epri.com/#/pages/product/000000000001011989/?lang=en-US EPRI 1011989 / NUREG/CR-6850]
 [https://www.epri.com/#/pages/product/000000000001019259/?lang=en-US FAQ 07-0031, Section 6 of Supplement 1]
 | 1.64E-02
 | [https://www.epri.com/#/pages/product/000000003002002936/?lang=en  EPRI 3002002936 (NUREG-2169)]

@@ Line 196: / Line 196: @@
 | Electrical Cabinets
 | Electrical cabinets represent such items as switchgears, motor control centers, DC distribution panels, relay cabinets, control and switch panels (excluding panels that are part of machinery), fire protection panels, etc.
-| <div id="Bin15"></div>Electrical cabinets in a nuclear power plant vary significantly in size, configuration, and voltage. Size variation range from small-wall mounted units to large walk-through vertical control cabinets, which can be 20’ to 30’ long. The configuration can vary based on number of components that contribute to ignition, such as relays and circuit cards, and combustible loading, which also affects the fire frequency. Voltages in electrical cabinets vary from low voltage (120 V) panels to 6.9 kV switchgear. Even though it is expected that these features affect the likelihood of fire ignition, from a simple analysis of the event data involving the electrical cabinets, it was determined that the variation by cabinet type did not warrant separate frequency evaluation. Therefore, one fire frequency was estimated for the electrical cabinets.
+| <div id="IgnBin15"></div>Electrical cabinets in a nuclear power plant vary significantly in size, configuration, and voltage. Size variation range from small-wall mounted units to large walk-through vertical control cabinets, which can be 20’ to 30’ long. The configuration can vary based on number of components that contribute to ignition, such as relays and circuit cards, and combustible loading, which also affects the fire frequency. Voltages in electrical cabinets vary from low voltage (120 V) panels to 6.9 kV switchgear. Even though it is expected that these features affect the likelihood of fire ignition, from a simple analysis of the event data involving the electrical cabinets, it was determined that the variation by cabinet type did not warrant separate frequency evaluation. Therefore, one fire frequency was estimated for the electrical cabinets.
 The following rules should be used for counting electrical cabinets: