ML18213A082
| ML18213A082 | |
| 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: ML18213A082 (19) | |
Text
Module III - Fire Analysis Fire Fundamentals Introduction and Overview 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)
Scoping Fire Modeling Objectives The objectives of this module are:
Describe the process of screening ignition sources Describe the concept of zone of influence (ZOI)
Describe the recommended walkdown Review the walkdown forms Describe how to update the fire ignition frequencies calculated in Task 6 with the screening results 2
Scoping Fire Modeling Interfaces Inputs for this task
- PRA equipment list, Task 2
- List of ignition sources in each compartment, Task 6
- Room geometry
- Types of ignition sources and targets Output from this task
- Revised compartment fire ignition frequencies
- List of potential fire scenarios to be analyzed in Task 11 3
Scoping Fire Modeling Screening Ignition Sources Any ignition source can be screened if a postulated fire will not damage or ignite equipment in the compartment By screening the ignition source, its frequency contribution is eliminated, reducing the compartment frequency It is recommended to use the 98th percentile of the HRR probability distribution A walkdown is strongly recommended
- Related SRs: FSS-D10, D11 4
Scoping Fire Modeling The Zone of Influence (ZOI)
The zone of influence is the region in the compartment where a target will be damaged if exposed to fire conditions generated by a specific ignition source The ZOI has 5 distinct regions:
- Flames
- The fire plume
- The ceiling jet
- The hot gas layer
- Flame radiation region 5
Scoping Fire Modeling Task 8: Recommended Steps 5 steps for conducting Task 8
- 1. Preparation for walkdown
- 2. Plant walkdown and screen ignition sources
- 3. Verification of screened ignition sources
- 4. Calculation of severity factors
- 5. Calculation of revised fire frequency 6
Scoping Fire Modeling Step 1: Preparation for Walkdown It is recommended that walkdown forms be prepared for each compartment to be visited:
Create a list of ignition sources in each compartment
- Equipment counted in Task 6
- Flag equipment in the PRA equipment list created in Task 2
- Assigned a HRR to each ignition source (98th percentile of the pdf)
Collect damage criteria information for the equipment in the room
- Qualified/Unqualified cables, solid state equipment etc.
Develop and document zone of influences in each compartment Corresponding PRA Standard SRs: FSS-D10 and D11 7
Scoping Fire Modeling Step 1: Models for Zone of Influence Smoke or hot gas layer: MQH model 13 Q&2f T = Tamb + 6.85 A H h A o o k T k dm cp t < tp th 2 hk = t tp =
k 4 k th t tp (d m c p )
Input Parameters:
Tamb: Ambient temperature (oC)
Qf: Fire heat release rate (kW)
Ao: Opening area (or sum of opening areas) (m2)
Ho: Height of opening [m]
AT: Internal surface area of the room (not including opening area) (m2) k: Thermal conductivity of wall material (kW/m-oC) dm: Density of wall material (kg/m3) cp: Specific heat of wall material (kJ/kg-oC) th: Wall thickness (m) t: Time value (sec) 8
Scoping Fire Modeling Step 1: Example Calculation for Room Temperature MQH Temperature Correlation Inputs Ambient temperature [C] 20 13 Q&2f Duration [sec] 1200 T = Tamb + 6.85 Opening area [m2] 3 A H h A Height of opening [m] 3 o o k T Room length [m] 37 k dm cp Room width [m] 37 t < tp th 2 hk = t tp = Room height [m] 8 k
t tp 4 k ( ) Thermal conductivity [kW/mK] 0.0014 th d m c p Density [kg/m3] 2000 Specific heat [kJ/kg] 0.88 Wall thickness [m] 0.6 HRR [kW] 9500 Results Room Temp [C] 327 9
Scoping Fire Modeling Step 1: Models for Zone of Influence Flame height and fire plume: Heskestads models L = 0.235Q&f 5 1.02 D 2
Input Parameters:
Qf: Fire heat release rate (kW)
D: Fire diameter (m)
( )
53 k Q& (1 ) 2 5 T pl = Tamb + 25 f f r
((H p Fe ) zo )
z = 0.083Q& 5 1.02 D 2
o f Input Parameters:
Tamb: Ambient temperature (oC) kf: Fire location factor Qf: Fire heat release rate (kW)
Fe: Fire elevation (m)
Hp: Target height measured from the floor (m)
Xr: Irradiated fraction of the heat release rate (FIVE recommends 0.4)
D: Plume diameter (m) 10
Scoping Fire Modeling Step 1: Example Calcs for Flame Height and Plume Temp
( )
53 k Q& (1 ) 2 5
+ 25 f f r L = 0.235Q&f 2 T pl = Tamb 5 1.02 D ((H p Fe ) z o )
z o = 0.083Q&f 5 1.02 D 2
Heskestad's Plume Temperature Correlatio Heskdestad's Flame Height Correlation Inputs Ambient temperature [C] 20 Inputs Fire location factor 1 Fire diameter [m] 0.6 HRR [kW] 1375 HRR [kW] 250 Fire elevation [m] 0 Results [m] Target Elevation [m] 3.7 Flame height [m] 1.5 Radiation Fraction 0.40 Fire Diameter [m] 1 Results Plume Temp [C] 328 11
Scoping Fire Modeling Step 1: Models for Zone of Influence Flame Radiation: Point Source Model Q&f r
=
q&irr 4R 2 Input Parameters:
Qf: Fire heat release rate (kW)
R: Distance from flames (m)
Xr: Irradiated fraction of the heat release rate (FIVE recommends 0.4)
D: Fire diameter (m) 12
Scoping Fire Modeling Step 1: Example calculation for flame radiation Q&f r
=
q&irr 4R 2 Point Source Flame Radiation Model Inputs Fire heat release rate [kW] 317 Radiation fraction 0.40 Distance from flames [m] 1.5 Results Heat flux [kW/m2] 4.5 13
Scoping Fire Modeling Step 2: Walkdown (Screen Ignition Sources)
During the walkdown, equipment in the room is subjected to fire conditions from each ignition source using the ZOI.
Take the opportunity to verify & improve Task 6 counting Document location of ignition sources and reasons for screen/no-screen decisions If ignition sources are not screened, document location of affected equipment and which fire-generated condition affected it.
Do not screen:
- Oil fires
- Cables
- Interconnected cabinets 14
Scoping Fire Modeling Step 3: Verify Screened Ignition Sources It is important to verify that fire damage to the ignition source itself is not risk significant
- 1. Do not screen equipment in the PRA equipment list
- 2. If loss of the ignition source results in a trip (automatic or manual), but no equipment contributing to the CCDP is lost, compare the ignition source fire frequency with the random frequency of the trip it causes.
- 3. If loss of the ignition source results in both a trip (automatic or manual) and loss of one or more components contributing to the CCDP, add a fire-induced sequence using the ignition source fire frequency and the corresponding CCDP model with the damaged components set to fail (failure probability = 1.0).
15
Scoping Fire Modeling Task 8: Calculation of Severity Factors For each unscreened ignition source, calculate the severity factor using the appropriate probability distribution for peak HRR.
Determine the heat release rate required for damaging equipment This require information gathered during the walkdowns!
16
Scoping Fire Modeling Task 8: Calculation of Severity Factors Pr Gamma distribution Severity factor Q critical Q (kW)
HRR Gamma kW (Btu/s) Distribution Case Ignition Source HRR 98th Vertical cabinets with qualified cable, fire limited 1 69 211 0.84 59.3 to one cable bundle Vertical cabinets with qualified cable, fire in 2 211 702 0.7 216 more than one cable bundle Vertical cabinets with unqualified cable, fire 3 90 211 1.6 41.5 limited to one cable bundle Vertical cabinets with unqualified cable, fire in 4 232 464 2.6 67.8 more than one cable bundle closed doors Vertical cabinets with unqualified cable, fire in 5 232 1002 0.46 386 more than one cable bundle open doors 6 Pumps (electrical fires) 69 211 0.84 59.3 7 Motors 32 69 2 11.7 8 Transient Combustibles 142 317 1.8 57.4 17
Scoping Fire Modeling Task 8: Calculation of Revised Fire Frequency 18
Scoping Fire Modeling Concluding Remarks Task 8 is intended for screening fixed ignition sources. As a result of the screening, the compartment frequencies may be reduced, and a preliminary list of potential fire scenarios for detailed evaluation in Task 11 is developed.
A detailed walkdown is recommended Analysts should take the opportunity to review the equipment count made for Task 6 and/or improve it.
19