1. 1.6 FIRE MODELING IN SUPPORT OF FIRE PRA An Educational Program to Improve the Level of Teaching Risk-Informed, Performance- based Fire Protection Engineering Assessment Methods 1

2. 1.6 Fire Modeling in Support of Fire PRA Fire PRA primarily applies fire modeling in the fire scenario development and analysis process. A fire scenario in a Fire PRA is often modeled as a progression of damage states over time, which is initiated by a postulated fire involving an ignition source. Each damage state is characterized by a time and a set of targets damaged within that time. Fire modeling is used to determine the targets affected in each damage state and the associated time at which this occurs. 2

3. 1.6 Fire Modeling in Support of Fire PRA An example of scenario progression through five damage states 3

4. 1.6 Fire Modeling in Support of Fire PRA The first damage state usually consists of damage only to the ignition source itself. Depending on the characteristics and configuration of the scenario, the last damage state may consist of an HGL formation that leads to a full room burnout. Damage states between the first and final states capture target sets compromised as the fire propagates through intervening combustibles. 4

5. 1.6 Fire Modeling in Support of Fire PRA The initiating event (ignition) is characterized by the ignition source frequency. The first damage state captures the event in which damage is limited to the ignition source itself. The second and third damage states capture additional targets as the fire continues to grow or propagate through intervening combustibles. 5

6. 1.6 Fire Modeling in Support of Fire PRA The time t1 (as well as any subsequent time milestones in the progression) at which this damage is postulated can be determined using fire modeling tools used to determine which targets are damaged. Each scenario progression postulated in a Fire PRA is quantified to determine its contribution to fire risk. The fire risk metrics are Core Damage Frequency (CDF) and Large Early Release Frequency (LERF). 6

7. Conceptual representation of the severity factor 7

8. 1.7 MSO FIRE MODELING APPLICATIONS An Educational Program to Improve the Level of Teaching Risk-Informed, Performance- based Fire Protection Engineering Assessment Methods 8

9. 1.7 MSO Fire Modeling Applications Multiple Spurious Operation (MSO) interactions is another type of fire modeling application frequently encountered in commercial NPPs. MSOs involve one or more fire-induced component failures that include spurious operation due to hot shorts as a result of fire damage to electrical control cables. The consideration of MSOs arises from the post-fire safe shutdown circuit analysis. 9

10. 1.7 MSO Fire Modeling Applications Key aspects of the MSO analysis process are: –Ignition sources are characterized by the 98th percentile severity fire as defined in NUREG/CR-6850 –Transient combustible materials are assumed anywhere in the plant unless it is physically impossible –Fire modeling tools should be verified and validated for the application –Fire modeling should be performed in a manner consistent with the methods described in NUREG/CR- 6850 –The analysis should include an assessment of model sensitivity to uncertainty 10

11. 1.8 Organization of the Guide Chapter 2 - a qualitative overview of the process for conducting fire modeling Chapter 3 - guidance on selecting models to address typical scenarios in commercial nuclear power plants Chapter 4 - information on determining the sensitivity and uncertainty associated with fire modeling calculations Chapter 5 - Lists Appendices A through H with example fire modeling analyses 11

12. Appendix A – Cabinet Fire in Main Control Room Appendix B – Cabinet Fire in Switchgear Room Appendix C – Lubricating Oil Fire in Pump Compartment Appendix D – Motor Control Center Fire in Switchgear Room Appendix E – Trash Fire in Cable Spreading Room Appendix F – Lubricating Oil Fire in Turbine Room Appendix G – Transient Fire in Multi-Compartment Corridor Appendix H – Cable Tray Fire 12

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