RNP-RA/15-0006, Response (120-Day) to Request for Additional Information Associated with License Amendment to Adopt National Fire Protection Association (NFPA) Standard 805

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Response (120-Day) to Request for Additional Information Associated with License Amendment to Adopt National Fire Protection Association (NFPA) Standard 805
ML15036A059
Person / Time
Site: Robinson Duke Energy icon.png
Issue date: 01/22/2015
From: Glover R
Duke Energy Carolinas, Duke Energy Progress
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
RNP-RA/15-0006, TAC MF2746
Download: ML15036A059 (24)
v • d • e


Text

R. Michael Glover DUKE H. B. Robinson Steam Electric PlantUnit 2 Site Vice President Duke Energy Progress 3581 West Entrance Road Hartsville, SC 29550 0:843 857 1704 F: 843 857 1319 Mike. Glov'ertduke-energiv.conm Serial: RNP-RA/15-0006 JAN 2 2 2015 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 DOCKET NO. 50-261 / RENEWED LICENSE NO. DPR-23 RESPONSE (120-DAY) TO REQUEST FOR ADDITIONAL INFORMATION ASSOCIATED WITH LICENSE AMENDMENT REQUEST TO ADOPT NATIONAL FIRE PROTECTION ASSOCIATION (NFPA) STANDARD 805

REFERENCES:

1. Letter from W. R. Gideon (Duke Energy Progress) to U. S. Nuclear Regulatory Commission (USNRC) (Serial: RNP-RA/1 3-0090), License Amendment Request (LAR) to Adopt NFPA 805 Performance-BasedStandard for Fire Protection for Light Water Reactor Generating Plants (2001 Edition), dated September 16, 2013, ADAMS Accession No. ML13267A211
2. Letter from Martha Barillas (USNRC) to Site Vice President, H. B. Robinson Steam Electric Plant (Duke Energy Progress), H. B. Robinson Steam Electric Plant, Unit 2 - Request for Additional Information on License Amendment Request to Adopt NationalFire Protection Association Standard805, Performance-BasedStandard for Fire Protection (TAC No.

MF2746), dated October 23, 2014, ADAMS Accession No. ML14289A260

3. Letter from R. Michael Glover (Duke Energy Progress) to U. S. Nuclear Regulatory Commission (USNRC) (Serial: RNP-RA/14-0122), Response (60-Day)to Request for Additional Information Associated with License Amendment Request to Adopt National Fire ProtectionAssociation (NFPA) Standard 805, dated November 24, 2014
4. Letter from R. Michael Glover (Duke Energy Progress) to U. S. Nuclear Regulatory Commission (USNRC) (Serial: RNP-RA/14-0134), Response (90-Day)to Request for Additional Information Associated with License Amendment Request to Adopt National Fire ProtectionAssociation (NFPA) Standard805, dated December 22, 2014

Dear Sir/Madam:

By letter dated September 16, 2013 (Reference 1) Duke Energy Progress, Inc. submitted a license amendment request to adopt a new risk-informed performance-based fire protection licensing basis for the H. B. Robinson Steam Electric Plant, Unit No. 2 (HBRSEP2).

During the week of September 22, 2014, the NRC conducted an audit at HBRSEP2 to support development of questions regarding the license amendment request. On October 23, 2014 the NRC provided a set of requests for additional information regarding the license amendment request (Reference 2). That letter divided the requests for additional information into 60-day, 90-day, and 120-day required responses. The Duke Energy Progress 60-Day responses and 90-Day Ao(-(c

U. S. Nuclear Regulatory Commission Serial: RNP-RAI1 5-0006 Page 2 responses were conveyed to the NRC Document Control Desk via letters from R. Michael Glover on November 24, 2014 (Reference 3) and December 22, 2014 (Reference 4), respectively.

Enclosed as agreed are the Duke Energy Progress responses to the 120-day requests for additional information.

Please address any comments or questions regarding this matter to Mr. Richard Hightower, Manager - Nuclear Regulatory Affairs at (843) 857-1329.

There are no new regulatory commitments made in this letter.

I declare under penalty of perjury that the foregoing is true and correct. Executed on January 2, 2015.

Since R. Michael Glover Site Vice President RMG/jmw Enclosure cc: Mr. V. M. McCree, NRC, Region II Ms. Martha C. Barillas, NRC Project Manager, NRR NRC Resident Inspector, HBRSEP2 Ms. S. E. Jenkins, Manager, Infectious and Radioactive Waste Management Section (SC)

U. S. Nuclear Regulatory Commission Enclosure to Serial: RNP-RA/15-0006 22 Pages (including this cover page)

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING VOLUNTARY FIRE PROTECTION RISK INITIATIVE

REQUEST FOR ADDITIONAL INFORMATION VOLUNTARY FIRE PROTECTION RISK INITIATIVE DUKE ENERGY PROGRESS H. B ROBINSON STEAM ELECTRIC PLANT. UNIT NO. 2 DOCKET NO. 50-261 Safe Shutdown Analysis (SSA) Request for Additional Information (RAI) 03 LAR Attachment G, Table G-1, appears to have inconsistencies with the VFDR dispositions provided in LAR Attachment C. For examples, in LAR Attachment C, Fire Area A15, components LI-474 and LI-476 are dispositioned with a recovery action (RA) to monitor S/G A level using local instruments, but neither of these RAs is identified in Table G-1. However, in LAR Attachment C, Fire Area A16, components LI-474, LI-476, and LT-477 are dispositioned with RA-DIDs and each of these are identified as RAs in LAR Attachment G, Table G-1. Provide a clarification for these inconsistencies.

Response

In example discussed above, the recovery actions discussed in Attachment C for Fire Area A15 to monitor steam generator level locally are included in Attachment G. The actions in question are identified in Attachment C for LI-474, LI-476, and LT-477. However, only the LT-477 entry was included in Attachment G, Table G-1. With no specific entry in Table G-1 for LI-474 and LI-476. It was not clear that the recovery actions discussed in Attachment C for these components were in fact included in Attachment G.

To clarify this and other apparent discrepancies and inconsistencies between Attachments C and G, updates to these attachments, including updated VFDR lists and revised dispositions, will be provided with the response to PRA-RAI-3.

SSA RAI 09 There are inconsistencies between LAR Attachment S, Table S-2, and the VFDR dispositions and Fire Area Overview provided in LAR Attachment C.

Examples:

1. In LAR Attachment C, Fire Areas A3, A1S, A16, A18 and C have many VFDRs that are dispositioned using the Reactor Coolant Pump (RCP) Shutdown Seal modification. However, this modification is not referenced in the overview of the subject fire areas.

Page 2 of 22

2. LAR Attachment S, Table S-2, Modification Item 5 ensures the intumastic meets the minimum 10-minute fire delay time in the Cable Spreading Room and the El/E2 Switchgear Room (as identified in response to Section V, F&O [Facts and Observations] FSS-H2-O1). However, this modification is not discussed in LAR Attachment C, Fire Area A15 and A16, either as a required modification or as a credited fire protection feature [also see FPE RAI 7].

Reconcile the inconsistencies between LAR Attachment C and LAR Attachment S, Table S-2, as appropriate.

Response

For example (1), the Reactor Coolant Pump (RCP) Shutdown Seal modification is being installed to reduce overall plant risk and not to address any specific VFDR. However, Attachment C will be updated as appropriate to indicate where this modification is credited to remove the reliance on recovery actions.

For example (2), see the response to FPE RAI-04 submitted with the 90 day responses.

Updates to Attachments C and S, including Table 5-2, will be provided with the response to RAI-PRA-3.

The revised Attachment C will include applicable updates to the VFDRs for each area, along with the credited fire protection features.

Fire Modeling (FM) Request for Additional Information (RAI) 01.q NFPA 805, Section 2.4.3.3, states that "the PSA [probabilistic safety assessment] approach, methods, and data shall be acceptable to the AHJ [authority having jurisdiction] ...

The NRC staff noted that fire modeling comprised the following:

- Fire Dynamics Tools (FDTs) were used for zone of influence (ZOI) calculations of cabinets, pumps, motors, oil fires and transient fire sources, and to evaluate the development and timing of Hot Gas Layer (HGL) conditions in selected compartments.

- The Consolidated Fire Growth and Smoke Transport (CFAST) model was used to calculate MCR abandonment times and to determine HGL temperature, optical density and Halon system activation time for a specific analysis in Fire Zone 20.

- The FLASH-CAT model was used to calculate the fire propagation in a vertical stack of horizontal cable trays in Fire Zone 20.

- The Generic Fire Modeling Treatments (GFMTs) were used to determine 'initial' severity factors.

LAR Section 4.5.1.2, "Fire PRA," states that fire modeling was performed as part of the FPRA development (NFPA 805 Section 4.2.4.2). Reference is made to LAR Attachment J, "Fire Modeling V&V

[verification and validation]," for a discussion of the acceptability of the fire models that were used.

Page 3 of 22

Specifically, regarding the acceptability of CFAST for the event timing analysis study for Fire Zone 20:

q. The objective of this detailed fire modeling is to compare the calculated HGL temperature with the smoke detector activation time, which will activate a Halon suppression system after a 30-second delay. Provide the technical justification for using the zone fire model CFAST for this purpose.

Response

q. CFAST is selected because it is capable of determining the room-wide (or average zone) temperature and optical density conditions. The room hot gas layer temperature is used to determine the timing of hot gas layer exposure damage based on the rules prescribed in NUREG/CR-6850. The use of CFAST for this purpose has been verified and validated in NUREG-1824, provided the model input parameters are within the stated valid ranges. The Optical Density (OD) output parameter can be linked to the actuation of an ionization type smoke detector as reported by Geiman and Gottuk ("Alarm Thresholds for Smoke Detector Modeling,"

FireSafety Science: Proceedingsof the 7th InternationalSymposium, International Association for Fire Safety Science, pp 197-208., Hemisphere Publishing Corporation, 2002). The method is considered conservative because it is based on room-wide OD levels, which are a parameter that CFAST has been verified and validated to calculate per NUREG-1824. This approach does not credit localized plume and ceiling jet conditions at the detector, and the actuation of the device is considered to be conservatively bound using a room wide average value.

FM RAI 01.r NFPA 805, Section 2.4.3.3, states that "the PSA [probabilistic safety assessment] approach, methods, and data shall be acceptable to the AHJ [authority having jurisdiction] ...

The NRC staff noted that fire modeling comprised the following:

- Fire Dynamics Tools (FDTs) were used for zone of influence (ZOI) calculations of cabinets, pumps, motors, oil fires and transient fire sources, and to evaluate the development and timing of Hot Gas Layer (HGL) conditions in selected compartments.

- The Consolidated Fire Growth and Smoke Transport (CFAST) model was used to calculate MCR abandonment times and to determine HGL temperature, optical density and Halon system activation time for a specific analysis in Fire Zone 20.

- The FLASH-CAT model was used to calculate the fire propagation in a vertical stack of horizontal cable trays in Fire Zone 20.

- The Generic Fire Modeling Treatments (GFMTs) were used to determine 'initial' severity factors.

LAR Section 4.5.1.2, "Fire PRA," states that fire modeling was performed as part of the FPRA development (NFPA 805 Section 4.2.4.2). Reference is made to LAR Attachment J, "Fire Modeling V&V

[verification and validation]," for a discussion of the acceptability of the fire models that were used.

Page 4 of 22

Specifically regarding the acceptability of the detailed fire modeling analysis performed for Fire Zone 20:

r. It is stated in the analysis that the assumed ambient temperature of 32°C is not bounding, but is consistent with the ambient temperatures present during testing to determine damage threshold times. Provide the technical justification for not using a bounding ambient temperature in the fire modeling analysis, or show that the value used is consistent with actual plant conditions.

Response

r. The initial ambient temperature for Fire Zone 20 is assumed to be 32°C (90°F), which represents an elevated temperature in the space relative to normal operating conditions. Although this is not necessarily a bounding value, it is consistent with the initial conditions under which the threshold temperatures for cables were obtained. The design basis temperature for the space is 40°C (104°F) per RNP-M-HVAC-1069, "El/E2 Room Loss of HVAC Model," Revision 1. Model sensitivity to the baseline ambient temperature assumption is evaluated in Revision 2 of the Damage Timing Analysis for Fire Zone 20 (Attachment 8) with ambient temperature up to 40°C (104°F), demonstrating that the model output parameters are not sensitive to this assumption.

FM RAI 01.s NFPA 805, Section 2.4.3.3, states that "the PSA [probabilistic safety assessment] approach, methods, and data shall be acceptable to the AHJ [authority having jurisdiction] ...

The NRC staff noted that fire modeling comprised the following:

- Fire Dynamics Tools (FDTs) were used for zone of influence (ZOI) calculations of cabinets, pumps, motors, oil fires and transient fire sources, and to evaluate the development and timing of Hot Gas Layer (HGL) conditions in selected compartments.

- The Consolidated Fire Growth and Smoke Transport (CFAST) model was used to calculate MCR abandonment times and to determine HGL temperature, optical density and Halon system activation time for a specific analysis in Fire Zone 20.

- The FLASH-CAT model was used to calculate the fire propagation in a vertical stack of horizontal cable trays in Fire Zone 20.

- The Generic Fire Modeling Treatments (GFMTs) were used to determine 'initial' severity factors.

LAR Section 4.5.1.2, "Fire PRA," states that fire modeling was performed as part of the FPRA development (NFPA 805 Section 4.2.4.2). Reference is made to LAR Attachment J, "Fire Modeling V&V

[verification and validation]," for a discussion of the acceptability of the fire models that were used.

Page 5 of 22

Specifically regarding the acceptability of the detailed fire modeling analysis performed for Fire Zone 20:

s. Given that CFAST often significantly overestimates the soot concentration in the HGL, provide the technical justification for assuming that the use of the HGL optical density, as calculated by CFAST, is representative or otherwise bounding.

Response

s. The calculation was updated in Revision 2 of the Damage Timing Analysis for Fire Zone 20 to include the soot yield in the parameter sensitivity analysis (Attachment 8). It was found that the original results were sensitive to the assumed soot yield and were revised in the updated calculation accordingly. The sensitivity analysis demonstrates that the revised soot yields produce conservative detection timing or that the results are not sensitive, depending on the particular case. Furthermore, a model uncertainty analysis has also been performed in Revision 2 of the Damage Timing Analysis for Fire Zone 20 (Attachment 8) based on the guidance of NUREG-1934. The model uncertainty analysis is designed to evaluate the probability that the model (CFAST) over-estimation of optical density can have an adverse impact on the evaluated risk relative to the expected actual performance of the system. Based on the combined results of the model sensitivity and uncertainty analysis evaluation performed in Revision 2 of the Damage Timing Analysis, the revised detector timing was found to be adequate. The revised analysis provides justification that the detector timing is adequately representative or otherwise bounding the anticipated actual performance of the system given the model sensitivity to the soot yield and uncertainty in predicting the optical density.

FM RAI 01.t NFPA 805, Section 2.4.3.3, states that "the PSA [probabilistic safety assessment] approach, methods, and data shall be acceptable to the AHJ [authority having jurisdiction] ...

The NRC staff noted that fire modeling comprised the following:

- Fire Dynamics Tools (FDTs) were used for zone of influence (ZOI) calculations of cabinets, pumps, motors, oil fires and transient fire sources, and to evaluate the development and timing of Hot Gas Layer (HGL) conditions in selected compartments.

- The Consolidated Fire Growth and Smoke Transport (CFAST) model was used to calculate MCR abandonment times and to determine HGL temperature, optical density and Halon system activation time for a specific analysis in Fire Zone 20.

- The FLASH-CAT model was used to calculate the fire propagation in a vertical stack of horizontal cable trays in Fire Zone 20.

- The Generic Fire Modeling Treatments (GFMTs) were used to determine 'initial' severity factors.

LAR Section 4.5.1.2, "Fire PRA," states that fire modeling was performed as part of the FPRA development (NFPA 805 Section 4.2.4.2). Reference is made to LAR Attachment J, "Fire Modeling V&V

[verification and validation]," for a discussion of the acceptability of the fire models that were used.

Page 6 of 22

Specifically regarding the acceptability of the detailed fire modeling analysis performed for Fire Zone 20:

t. The heat of combustion and soot yield of cables specified in the CFAST calculations for this analysis are reported to be based on the data for PE/PVC cables in Tewarson's Chapter of the SFPE Handbook. It is stated that the heat of combustion is the lower bound value for PE/PVC cables and that the yield of other products is the upper bound for PE/PVC cables. Provide the technical justification for these bounding assumptions, in the context of calculating a conservative (longest) smoke detector activation time.

Response

t. The calculation was updated in Revision 2 of the Damage Timing Analysis for Fire Zone 20 to include the soot yield and heat of combustion in the parameter sensitivity analysis (Attachment 8). It was found that the original results were not sensitive to the assumed heat of combustion.

However, it was found that the original results were sensitive to the assumed soot yield and were revised in the updated calculation accordingly. The sensitivity analysis demonstrates that the revised soot yields produce conservative detection timing or that the results are not sensitive, depending on the particular case. Furthermore, a model uncertainty analysis has also been performed in Revision 2 of the Damage Timing Analysis for Fire Zone 20 (Attachment 8) based on the guidance of NUREG-1934. The model uncertainty analysis is designed to evaluate the probability that the model (CFAST) over-estimation of optical density can have an adverse impact on the evaluated risk relative to the expected actual performance of the system. Based on the results of the model uncertainty analysis evaluation performed in Revision 2 of the damage timing analysis, the revised detector timing was found to be adequate. The revised analysis provides adequate justification that the revised detector timing is representative or otherwise bounding the anticipated actual performance of the system given the expected variability in fuel properties.

FM RAI 01.u NFPA 805, Section 2.4.3.3, states that "the PSA [probabilistic safety assessment] approach, methods, and data shall be acceptable to the AHJ [authority having jurisdiction] ...

The NRC staff noted that fire modeling comprised the following:

- Fire Dynamics Tools (FDTs) were used for zone of influence (ZOI) calculations of cabinets, pumps, motors, oil fires and transient fire sources, and to evaluate the development and timing of Hot Gas Layer (HGL) conditions in selected compartments.

- The Consolidated Fire Growth and Smoke Transport (CFAST) model was used to calculate MCR abandonment times and to determine HGL temperature, optical density and Halon system activation time for a specific analysis in Fire Zone 20.

- The FLASH-CAT model was used to calculate the fire propagation in a vertical stack of horizontal cable trays in Fire Zone 20.

Page 7 of 22

- The Generic Fire Modeling Treatments (GFMTs) were used to determine 'initial' severity factors.

LAR Section 4.5.1.2, "Fire PRA," states that fire modeling was performed as part of the FPRA development (NFPA 805 Section 4.2.4.2). Reference is made to LAR Attachment J, "Fire Modeling V&V

[verification and validation]," for a discussion of the acceptability of the fire models that were used.

Specifically regarding the acceptability of the detailed fire modeling analysis performed for Fire Zone 20:

u. In the discussion of the uncertainty of this specific calculation, it is stated that the two key parameters, with respect to uncertainty are the HRR and the ventilation. It is understood that that these two parameters are important and that the analysis has considered bounding ventilation configurations and HRRs, which are prescribed in NUREG/CR-6850. However, the analysis does not describe the uncertainty of the key parameter that drives the calculation of smoke detector activation (i.e., soot yield). Explain how the uncertainty of this calculation is affected by not assuming the most conservative fuel properties or provide the technical justification for the properties used.

Response

u. Model uncertainty analysis has been performed in Revision 2 of the Detector Timing Analysis for Fire Zone 20 (Attachment 8) based on the guidance of NUREG-1934. The model uncertainty analysis is designed to evaluate the probability that the model (CFAST) over-estimation of optical density can have an adverse impact on the evaluated risk relative to the expected actual performance of the system. Model sensitivity analysis of the predicted detector timing has also been performed in Revision 2 to evaluate the effects of changes in the soot yield. Based on the combined results of the model sensitivity and uncertainty analysis evaluation performed in Revision 2 of the damage timing analysis, the detector timing has been revised. The revised analysis provides adequate justification that the revised detector timing is representative or otherwise bounding the anticipated actual performance of the system given the expected variability in fuel properties.

FM RAI 01.v NFPA 805, Section 2.4.3.3, states that "the PSA [probabilistic safety assessment] approach, methods, and data shall be acceptable to the AHJ [authority having jurisdiction]..."

The NRC staff noted that fire modeling comprised the following:

- Fire Dynamics Tools (FDTs) were used for zone of influence (ZOI) calculations of cabinets, pumps, motors, oil fires and transient fire sources, and to evaluate the development and timing of Hot Gas Layer (HGL) conditions in selected compartments.

- The Consolidated Fire Growth and Smoke Transport (CFAST) model was used to calculate MCR abandonment times and to determine HGL temperature, optical density and Halon system activation time for a specific analysis in Fire Zone 20.

Page 8 of 22

- The FLASH-CAT model was used to calculate the fire propagation in a vertical stack of horizontal cable trays in Fire Zone 20.

- The Generic Fire Modeling Treatments (GFMTs) were used to determine 'initial' severity factors.

LAR Section 4.5.1.2, "Fire PRA," states that fire modeling was performed as part of the FPRA development (NFPA 805 Section 4.2.4.2). Reference is made to LAR Attachment J, "Fire Modeling V&V

[verification and validation]," for a discussion of the acceptability of the fire models that were used.

Specifically regarding the acceptability of the detailed fire modeling analysis performed for Fire Zone 20:

v. One of the stated limitations of the analysis is that no high energy arcing fault (HEAF) is postulated. However, in the walkdown sheets that were used to build the fire scenarios, multiple scenarios were annotated with the comment that a HEAF should be postulated. Clarify if any alternative analysis (e.g., ZOI, PRA, etc.) considered HEAF events in this Fire Zone and justify not postulating a HEAF as part of this specific analysis in Fire Zone 20.

Response

v. The FPRA considers bus duct HEAF scenarios within Fire Zone 20. The PRA does not consider electrical panel HEAF scenarios in Fire Zone 20 per the evaluation in EC 92253.

The impact of a bus duct HEAF scenario in Fire Zone 20 can be compared to the existing analysis for the electrical cabinet fires evaluated in Fire Zone 20. The zone of influence for a bus duct HEAF is defined as instantly igniting any cables or combustibles immediately adjacent to the bus duct in NUREG/CR-6850, Appendix M and section 7 of Supplement 1. Given the arrangement of cable trays in Fire Zone 20, it is assumed that a bus duct HEAF will ignite between 1 and 4 adjacent cable trays. The impact of the bus duct scenarios can be compared to the existing electrical panel fire scenarios examined in Fire Zone 20. Four bus duct fire scenarios developed using FLASH-CAT with an ignition delay of zero seconds for all ignited trays are provided in Figure 1 below. Figure 1 also includes two electrical panel scenarios from Revision 2 of the Damage Timing Analysis for Fire Zone 20, corresponding to the maximum and minimum heat release rates evaluated.

Page 9 of 22

8000 7000

-Electrical Panel Minimum 6000 Fire scenario 5 (Intumastic 285 credited)

Electrical Panel Maximum 5000 Fire scenario 2 (Intumastic 285 not credited)

- - - Bus Duct HEAF 4000 1 Tray Ss S-- - - Bus Duct HEAF 3000 1 2 Trays

- - - Bus Duct HEAF 3 Trays 2000

-BusDuct HEAF

-- - 4Trays 1000 0

0 10 20 30 40 50 60 Time (min)

Figure 1: Heat Release Rate Comparison of Evaluated Electrical Panel Fires and Possible Bus Duct HEAF Fires The heat release rate profiles in Figure 1 demonstrate two key behaviors of the bus duct fire relative to the evaluated electrical panel fires. The first behavior is in the first 3 to 4 minutes of the fire growth period, in which the optical density smoke detection is predicted to occur.

Within this initial growth period, the fire spread over the ignited cable trays occurs faster than the fire growth of the electrical panel ignition sources. This result suggests that a bus duct HEAF fire will produce more smoke in the initial stages of fire growth, and therefore shorter smoke detection timing. The second behavior is in the 11 to 25 minute time range, in which the hot gas layer temperature damage is predicted for the electrical panel fires. In the 11 to 25 minute time range, it can be seen that the bus duct HEAF scenarios are either bound by or are within the range of the specified electrical panel scenarios. This result suggests that a bus duct HEAF fire will result in a damaging hot gas layer within a similar time as those reported for the electrical panel fires or longer.

Since the anticipated behavior of the bus duct HEAF fire is to produce shorter smoke detection, and longer hot gas layer damage relative to an evaluated electrical panel fire, the results of the bounding electrical panel fire can be conservatively applied to the bus duct HEAF fires in the FPRA.

Page 10 of 22

Probabilistic Risk Assessment (PRA) RAI 01.a Section 2.4.3.3 of NFPA 805 states that the PSA (PSA is also referred to as PRA) approach, methods, and data shall be acceptable to the AHJ, which is the U.S. Nuclear Regulatory Commission (NRC). RG 1.205, "Risk-Informed, Performance-Based Fire Protection for Existing Light-Water Nuclear Power Plants,"

Revision 1, December 2009 (ADAMS Accession No. ML092730314), identifies NUREG/CR-6850 as documenting a methodology for conducting a fire PRA and endorses, with exceptions and clarifications, NEI 04-02, Revision 2, as providing methods acceptable to the staff for adopting a fire protection program consistent with NFPA-805. RG 1.200, "An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk Informed Activities," Revision 2, March 2009 (ADAMS Accession No. ML090410014), describes a peer review process utilizing an associated American Society of Mechanical Engineers/American Nuclear Society (ASME/ANS) standard (currently ASME/ANS-RA-Sa-2009, "Addenda to ASME/ANS RA-S-2008, Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications") as one acceptable approach for determining the technical adequacy of the PRA once acceptable consensus approaches or models have been established for evaluations that could influence the regulatory decision. The primary results of a peer review are the F&Os recorded by the peer review and the subsequent resolution of these F&Os.

Clarify the following dispositions to the fire F&Os and Supporting Requirement (SR) assessments identified in LAR Attachment V that have the potential to impact the fire PRA results and do not appear to be fully resolved:

a. CF-A2-01 and FSS-El-01 (State of knowledge correlation (SOKC))

The dispositions to F&O CF-A2-01 and F&O FSS-E1-01 state that uncertainty analysis does not impact mean risk results. Mean CDF and LERF values can be affected by SOKC and should be accounted for as part of statistical uncertainty analysis. It is not clear to what extent statistical analysis of uncertainty required by SR FSS-E1 was performed or whether SOKC was taken into account. SR QU-A3 (referenced by FQ-A4) requires that CDF be estimated accounting for the SOKC between event probabilities. Clarify whether SOKC was taken into account for hot short probabilities and other Fire PRA parameters (i.e., fire ignition frequency, non-suppression probabilities, and component type failure mode probabilities). If CDF was estimated without accounting for the SOKC for these parameters, then account for SOKC for these parameters in the integrated analysis performed in response to PRA RAI 3.

Response

a. Fire ignition frequency, non-suppression probability, and hot short probability parametric uncertainty and SOKC concerns were not explicitly addressed in the Fire PRA that supported the LAR submittal. They will be taken into account, as needed, for parametric uncertainty and mean value SOKC concerns for CDF and LERF in the integrated analysis performed in response to PRA RAI 3.

Page 11 of 22

PRA RAI 01.k Section 2.4.3.3 of NFPA 805 states that the PSA (PSA is also referred to as PRA) approach, methods, and data shall be acceptable to the AHJ, which is the U.S. Nuclear Regulatory Commission (NRC). RG 1.205, "Risk-Informed, Performance-Based Fire Protection for Existing Light-Water Nuclear Power Plants,"

Revision 1, December 2009 (ADAMS Accession No. ML092730314), identifies NUREG/CR-6850 as documenting a methodology for conducting a fire PRA and endorses, with exceptions and clarifications, NEI 04-02, Revision 2, as providing methods acceptable to the staff for adopting a fire protection program consistent with NFPA-805. RG 1.200, "An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk Informed Activities," Revision 2, March 2009 (ADAMS Accession No. ML090410014), describes a peer review process utilizing an associated ASME/ANS standard (currently ASME/ANS-RA-Sa-2009, "Addenda to ASME/ANS RA-S-2008, Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications") as one acceptable approach for determining the technical adequacy of the PRA once acceptable consensus approaches or models have been established for evaluations that could influence the regulatory decision. The primary result of a peer review are the facts and observations (F&Os) recorded by the peer review and the subsequent resolution of these F&Os.

Clarify the following dispositions to the fire F&Os and Supporting Requirement (SR) assessments identified in LAR Attachment V that have the potential to impact the fire PRA results and do not appear to be fully resolved:

k) PRM-B11-01 (Credit for MCR abandonment actions)

The disposition to this F&O explains that human failure events associated with MCR abandonment are not modeled directly in the Fire PRA. Table W-3 of the LAR presents MCR abandonment failure as a single scenario, and it appears that a single conditional core damage probability/conditional large early release probability (CCDP/CLERP) value was used in a single scenario to represent a range of possible MCR abandonment scenarios. The analysis provides discussion of MCR abandonment, but from this discussion it is not completely clear how MCR abandonment was treated in the Fire PRA. In particular, it is not clear how potential fire-induced failures resulting from fires leading to MCR abandonment were addressed, or how the scenario frequency for MCR abandonment was determined. Therefore, provide the following:

Describe how MCR abandonment was modeled for loss of habitability in both the post-transition and the compliant plant. Include identification of the actions required to execute safe alternate shutdown and how they are modeled in the Fire PRA, including actions that must be performed before leaving the MCR. Also, include an explanation of how the CCDPs and CLERPs are estimated for fires that lead to MCR abandonment.

ii. Explain how the CCDPs and CLERPs estimated for fires that lead to abandonment due to loss of habitability address various possible fire-induced failures. Specifically include in this explanation, discussion of how the following scenarios are addressed:

a. Scenarios where fire fails only a few functions aside from forcing MCR abandonment and successful alternate shutdown is straightforward; Page 12 of 22
b. Scenarios where fire could cause some recoverable functional failures or spurious operations that complicate the shutdown, but successful alternate shutdown is likely; and,
c. Scenarios where the fire-induced failures cause great difficulty for shutdown by failing multiple functions and/or complex spurious operations that make successful shutdown unlikely.

iii. Explain how the abandonment scenario frequency due to loss of habitability was determined. Include explanation of how the fire ignition frequencies and non-suppression probabilities contributing to this scenario were addressed.

iv. It appears that 0.1 was used to estimate CLERP since the MCR abandonment scenario from Tables W-3 and W-4 presents a CDF of 4E-6/year and a CLERP of 4E-7/year, respectively. Explain and justify how the apparent CLERP of 0.1 was derived.

Response

The method for analyzing Main Control Room (MCR) abandonment scenarios is separate from other scenarios in the Fire PRA. Within the Fire PRA, MCR abandonment scenarios are treated as a single point value that assumes the worst-case scenario. The CCDP/CLERP value used in the Fire PRA was generated as part of an analysis of the DSP-002 procedures. DSP-002 was written to address MCR abandonment.

L CCDP/CLERP values for MCR abandonment caused by loss of habitability are calculated the same in both post-transition and compliant models. A worst-case scenario value was applied in both models. To calculate the CCDP and LERP used in the Fire PRA, the human error probabilities (HEP) for abandonment actions are developed and summed to determine the worst-case scenario. The worst-case scenario CCDP and LERP are based on analysis of the DSP-002 procedures. The sequence of actions leading to hot standby in the worst-case scenario are as follows:

1. Operator successfully trips the reactor prior to evacuating the control room. Action leading to failure to maintain the plant in hot standby:
  • Operator fails to trip reactor prior to abandoning control room.
2. Operator successfully maintains RCS inventory and pressurizer level. Actions leading to failure to maintain the plant in hot standby:

" Failure to place pressurizer PORVs in the isolated position prior to evacuation.

" Failure to deenergize Auxiliary Panels "D-C" and "G-C", pressurizer PORVs PCV-456 and PCV-455C, and safeguard trains A and B from distribution panels A and B.

3. Operator successfully re-energizes the DS bus if power to both the emergency buses is lost.

Actions leading to failure to maintain the plant in hot standby:

" Failure to maintain DS bus voltage.

  • Failure to transfer loads from El/E2 bus to the DS bus.
4. Operator successfully maintains steam generator pressure. Actions leading to failure to maintain the plant in hot standby:

" Failure to establish AFW flow to the SG.

" Failure to establish steam line PORV control.

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5. Operator successfully maintains long-term primary and secondary inventory. Actions leading to failure to maintain the plant in hot standby:

" Failure to maintain natural circulation using the steam line PORVs.

" Failure to monitor CST level and align SW backup to the SDAFW pump suction.

" Failure to ensure the RWST does not inadvertently drain into the containment vessel sump.

" Failure to maintain pressurizer level long term by controlling the charging pump speed, dumping steam on the secondary, and starting and stopping the charging pump as required.

This response does not prohibit the addition or deletion of operator actions that will be credited in the Fire PRA as per the response to be developed for PRA RAI 3.

ii. The CCDP/CLERP values were only calculated based on the worst-case scenario; these different scenarios are bounded by the current modeling results. The worst-case scenario is determined by failure of any operator actions as discussed in the previous section. Scenarios in which operators succeed in any capacity are bounded by the worst-case scenario result. MCB scenarios that do not lead to MCR abandonment caused by loss of habitability remain as quantified scenarios in the Fire PRA.

iii. The frequency for MCR abandonment is based on the source ignition frequency and the probability that the fire is not suppressed prior to habitability thresholds being reached. The ignition frequencies of the sources are calculated per the method of Task 6 in NUREG/CR-6850.

The time to reach the habitability thresholds is determined for each applicable ignition source type (e.g. Main Control Board or Electrical Cabinet). For this analysis, it is assumed that the HVAC will not be in pressurization mode, as radiological conditions in the MCR should not change immediately because of a fire in the MCR. Therefore, all doors are assumed closed, multiple cable bundles in the MCB and panels, and including propagation. Cases with ventilation operable and inoperable were considered for the calculated risk. The probability that the fire is not suppressed before abandonment occurs is calculated at the time when habitability thresholds are reached with a floor value of 0.001.

The total frequency of MCR abandonment is determined by summing the product of the source ignition frequency, severity factor, split fraction for operability of control room ventilation and the non-suppression probability at loss of habitability for each source.

iv. The CDF for MCR abandonment caused by loss of habitability was calculated using the aforementioned approach. LERF was reasonably assumed to be one order of magnitude lower than CDF. This is consistent with the internal events order of magnitude values.

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PRA RAI06 Section 2.4.3.3 of NFPA 805 states that the PRA approach, methods, and data shall be acceptable to the NRC. RG 1.205 identifies NUREG/CR-6850 as documenting a methodology for conducting a fire PRA and endorses, with exceptions and clarifications, NEI 04-02, Revision 2, as providing methods acceptable to the staff for adopting a fire protection program consistent with NFPA-805. In letter dated July 12, 2006, to NEI (ADAMS Accession No. ML061660105), the NRC established the ongoing FAQ process where official agency positions regarding acceptable methods can be documented until they can be included in revisions to RG 1.205 or NEI 04-02. Methods that have not been determined to be acceptable by the NRC staff or acceptable methods that appear to have been applied differently than described require additional justification to allow the NRC staff to complete its review of the proposed method.

NRC staff could not identify in the LAR or licensee's analysis a description of how potential fire damage to sensitive electronics was modeled or how the licensee's approach of using Generic Modeling Treatment addressed damage to sensitive electronics. Though the treatment of sensitive electronics may be consistent with recent guidance on modeling sensitive electronics, Appendix H of the LAR does not cite FAQ 13-0004 (Clarifications on Treatment of Sensitive Electronics, issued December 3, 2013, ADAMS Accession No. ML13322A085), as one of the FAQ guidance documents used to support the Fire PRA. Describe the approach to modeling sensitive electronics. Explain whether the treatment of sensitive electronics performed for the Fire PRA is consistent with the guidance in FAQ 13-0004, including the caveats about configurations that can invalidate the approach (i.e., sensitive electronics mounted on the surface of cabinets or in the presence of louver or vents). Justify the treatment of sensitive electronics used in the Fire PRA, and if the approach cannot be justified using available NRC guidance, then replace the current approach with an acceptable approach and describe this change to the Fire PRA, or address the impact of your proposed method as part of the integrated analysis performed in response to PRA RAI 3.

Response

Sensitive electronics were not modeled in the Fire PRA but will be incorporated into the Fire PRA consistent with the guidance in Fire PRA FAQ 13-0004, "Clarifications on Treatment of Sensitive Electronics," and the results will be included in the response to PRA RAI 3.

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PRA RAI 10 Section 2.4.3.3 of NFPA 805 states that the PRA approach, methods, and data shall be acceptable to the NRC. RG 1.205 identifies NUREG/CR-6850 as documenting a methodology for conducting a fire PRA and endorses, with exceptions and clarifications, NEI 04-02, Revision 2, as providing methods acceptable to the staff for adopting a fire protection program consistent with NFPA-805. In letter dated July 12, 2006, to NEI (ADAMS Accession No. ML061660105), the NRC established the ongoing FAQ process where official agency positions regarding acceptable methods can be documented until they can be included in revisions to RG 1.205 or NEI 04-02. Methods that have not been determined to be acceptable by the NRC staff or acceptable methods that appear to have been applied differently than described require additional justification to allow the NRC staff to complete its review of the proposed method.

The licensee's analysis states that because junction boxes can be considered a well-sealed non-propagating ignition source, ignition frequency determination is not needed. FAQ 13-0006, "Modeling Junction Box Scenarios in a Fire PRA," indicates that the risk from failure of cables within each junction box needs to be estimated and that, unlike electrical cabinets, there is no exclusion of a junction box from counting because it is robustly secured and well-sealed. Thus, junction boxes that route Fire PRA target cables that can contribute to fire risk should not be excluded as ignition sources. Justify the approach to evaluating junction boxes using NRC guidance or address the impact of your proposed method as part of the integrated analysis performed in response to PRA RAI 3.

Response

FAQ 13-0006, "Modeling Junction Box Scenarios in a Fire PRA," will be utilized to incorporate junction box scenarios into the fire PRA model and the results will be included in the response to PRA RAI 3.

PRA RAI 12 Section 2.4.3.3 of NFPA 805 states that the PRA approach, methods, and data shall be acceptable to the NRC. RG 1.205 identifies NUREG/CR-6850 as documenting a methodology for conducting a fire PRA and endorses, with exceptions and clarifications, NEI 04-02, Revision 2, as providing methods acceptable to the staff for adopting a fire protection program consistent with NFPA-805. In letter dated July 12, 2006, to NEI (ADAMS Accession No. ML061660105), the NRC established the ongoing FAQ process where official agency positions regarding acceptable methods can be documented until they can be included in revisions to RG 1.205 or NEI 04-02. Methods that have not been determined to be acceptable by the NRC staff or acceptable methods that appear to have been applied differently than described require additional justification to allow the NRC staff to complete its review of the proposed method.

The licensee's analysis states that bus ducts were typically treated as HEAFs "without secondary combustibles fire scenarios." NUREG/CR-6850, Supplement 1 (i.e., FAQ-08-0035), provides guidance for determining a zone of influence (ZOI) from bus duct fires, stating that exposed combustible or flammable material within the ZOI should be assumed to ignite. The basis for not propagating fire from bus ducts is not clear. Justify the treatment of bus duct fires in the Fire PRA. Include explanation of how guidance in FAQ-08-0035 was addressed. If treatment of bus ducts cannot be shown to be consistent of NRC guidance then model the excluded bus duct fire scenarios in the integrated analysis provided in response to RAI 3.

Response

Guidance found in Fire FAQ-13-0005 supports the treatment of bus duct HEAF fires in the RNP Fire PRA.

The cables within the initial HEAF ZOI are assumed to be damaged and ignite. Following the initial HEAF Page 16 of 22

event it was determined that the heat generated by the ignited cables would be insufficient to support continued propagation to other trays. This is especially applicable for the cables beneath the HEAF in the ZOI created by the falling slag. These secondary combustible targets are potentially exposed to molten material produced by the HEAF; however this material is treated in the same way as molten slag from cutting or welding.

Test results documented in FAQ-13-0005 state that a relatively small quantity of molten slag resulting from cutting or welding does not have the necessary heat capacity to sustain a minimum critical heat flux over a large enough area for a long enough period of time to establish sustained combustion. This is in comparison to a gas burner or liquid fuel fire that is typically used as an ignition source in cable fire experiments. Similarly, the relatively small flames resulting from a single over-heated cable cannot transfer enough heat to surrounding cables to propagate a substantial fire. The test demonstrated that a fire within a single tray containing unqualified thermoplastic cables does not radiate enough energy to the unburned portion of the cables within the tray to initiate fire spread beyond the point of origin.

These results demonstrate that a substantial energy source is required to cause sustained combustion.

The guidance found in FAQ-08-0035 states that the molten material generated from the HEAF will ignite the exposed combustibles, however based on the test results documented in FAQ-13-0005 the ignition is not sustained and the fire is extinguished. Consequently the modeling of secondary combustible fire scenarios as a result of bus duct HEAFs is not necessary.

PRA RAI 16 Section 2.4.3.3 of NFPA 805 states that the PRA approach, methods, and data shall be acceptable to the NRC. RG 1.205 identifies NUREG/CR-6850 as documenting a methodology for conducting a fire PRA and endorses, with exceptions and clarifications, NEI 04-02, Revision 2, as providing methods acceptable to the staff for adopting a fire protection program consistent with NFPA-805. In letter dated July 12, 2006, to NEI (ADAMS Accession No. ML061660105), the NRC established the ongoing FAQ process where official agency positions regarding acceptable methods can be documented until they can be included in revisions to RG 1.205 or NEI 04-02.

LAR Attachment S, Table S-2 indicates that incipient detection systems (i.e., VEWFDS) are credited in the Fire PRA and will be installed in MCR cabinets; in Safeguards, Hagan Room, turbine supervisory, and Rod Control room cabinets; and the CSR as wide-area detection. Though LAR Attachment S, Table S-2 provides some comments about how incipient detection was modelled in the Fire PRA more explanation is needed to fully understand how incipient detection was credited. NRC staff notes that results of sensitivity studies presented in Sections 4.8.3.2.4, 4.8.3.2.5, and 4.8.3.2.6 of the LAR that remove credit for incipient detection and replace it with credit for other detection systems, show an increase in ACDF and ALERF as high as 18%. Existing guidance (e.g., FAQ 08-0046) does not credit incipient detection in the MCR because detection credit is already realized when non-suppression probabilities are applied in an area continuously occupied. Also, existing guidance does not credit incipient detection as a very early warning fire detection system for area-wide applications. Explain and justify how area-wide incipient detection is credited in the Fire PRA results presented in Attachment W of the LAR. For VEWFDS credit that followed FAQ 08-0046, describe any departures from guidance in FAQ 08-0046. If incipient detection is credited in the Fire PRA for very early warning in the MCR or in wide area application, or is credited beyond what is allowed by FAQ 08-0046, then remove this credit or incorporate acceptable credit as part of the integrated analysis performed in response to RAI 3.

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Response

Area-Wide Incipient Detection Credit The area-wide incipient detection, which is to be installed in fire compartment 190 ("Unit 2 Cable Spreading Room") as a Very Early Warning Fire Detector System (VEWFDS) as defined in NFPA 76, was credited in the Fire PRA as a high-sensitivity smoke detection system in addition to other existing automatic detection and suppression, consistent with the guidance in Appendix P, Section P.1.3, of NUREG/CR-6850. FAQ 08-0046 is not applicable to this credit, as the discussion in FAQ 08-0046 pertains to the incipient fire detection systems installed in electrical cabinets. Therefore, only Appendix P of NUREG/CR-6850 was used in the development of the non-suppression probability for fire compartment 190 scenarios with area-wide incipient detection credit.

The prompt detection/suppression variables of the detection-suppression event tree in Appendix P for non-suppression probability of scenarios in fire compartment 190 were developed based on the following:

" Prompt detection (PD) was assigned a value of 0.99, based on an assumed unavailability rate of 0.5% and an assumed failure rate of 0.5%. This is consistent with Appendix P of NUREG/CR-6850 as the failure probability of high-sensitivity smoke detection systems should be considered for the value of PD

  • Prompt suppression (PS) was assigned a value based on the non-suppression curve, Pr(T > t) = e-At, with X=0.33 for a fire in the Main Control Room (MCR) and an additional five minutes credited for the incipient stage. Use of the MCR non-suppression curve was justified because the detection of a fire during the incipient stage by an area-wide incipient detection system is expected to prompt an operator response to act as a continuous fire watch in fire compartment 190 until the incipient alarm is resolved. This situation would resemble an MCR scenario. The addition of five minutes was conservatively based on operating experience at HNP where the incipient alarm permitted the fire brigade to arrive significantly before the actual fire event, which occurred several hours after the alarm.

As the area-wide incipient detection credit is acceptable based on NUREG/CR-6850 guidance, no changes are proposed for the treatment of area-wide incipient detection credit for the integrated analysis in response to PRA RAI 3.

Main Control Room (MCR) IncipientDetection Credit No credit to the non-suppression probability was applied as a result of incipient detection available in the MCB. For fires scenarios in the MCB, the non-suppression probability was developed solely using Appendix L of NUREG/CR-6850 with no credit or changes in the methodology regarding incipient fire detection systems. FAQ 08-0046 is not used for the MCB scenarios as this FAQ pertains to non-suppression probability for incipient fire detection systems installed in electrical cabinets only.

However, incipient detection provided credit for fire prevention in the MCR for reducing the fire event frequency of main control board (MCB) scenariosonly. The reduction of the event frequency for main control board (MCB) scenarios was based on the product of assumed factors for incipient phase detectability, detector system availability and reliability, success of operator response, and success of the technician to prevent the fire from occurring (technician success is based on a detailed human reliability analysis [HRA]). These factors are similar to those described in FAQ 08-0046; however, no failure rates associated with fire suppression were incorporated into the reduction of the event Page 18 of 22

frequency. The resulting product of these factors yields an applied reduction factor of approximately 0.127 to the event frequency for MCB scenarios.

As the incipient detection credit in the MCR does not violate what is permissible by current guidance, no changes are proposed for the treatment of incipient detection credit in the MCR for the integrated analysis in response to PRA RAI 3.

In-cabinet IncipientDetection Credit Outside of the Main Control Room, in-cabinet incipient detection was applied in the Safeguards cabinets, the Hagan Room cabinets, the Turbine Supervisory and Rod Control Room cabinets per FAQ 08-0046, with credit for technician response based on a detailed HRA.

PRA RAI 23a Section 2.4.3.3 of NFPA 805 states that the PRA approach, methods, and data shall be acceptable to the NRC. Section 2.4.4.1 of NFPA-805 further states that the change in public health risk arising from transition from the current fire protection program to an NFPA-805 based program, and all future plant changes to the program, shall be acceptable to the NRC. RG 1.174 provides quantitative guidelines on CDF, LERF, and identifies acceptable changes to these frequencies that result from proposed changes to the plant's licensing basis and describes a general framework to determine the acceptability of risk-informed changes. The NRC staff review of the information in the LAR has identified the following information that is required to fully characterize the risk estimates.

Section W.2.1 of the LAR provides some description of how the change-in-risk and the additional risk of recovery actions associated with VFDRs is determined but not enough detail to make the approach completely understood. Provide the following:

a) A detailed definition of both the post-transition and compliant plant models used to calculate the reported change-in-risk, including any special calculations for the MCR. Include description of the model adjustments made to remove VFDRs from the compliant plant model, such as adding events or logic, or use of surrogate events. Also include explanation of how VFDR and non-VFDR modifications are addressed for both the post-transition and compliant plant models.

Include explanation of whether the approach is consistent with guidance in FAQ 08-0054, "Demonstrating Compliance with Chapter 4 of NFPA 805" and FAQ 07-0030, "Establishing Recovery Actions."

Response

The post-transition model is developed using the as-built, as-operated and maintained plant configuration with additional procedure changes and modifications identified in Attachment S of the H. B Robinson Steam Electric Plant Transition to 10 CFR 50.48(c) LAR submittal. The NFPA 805 compliant Fire PRA model is developed based on the post-transition model and removes Variances From Deterministic Requirements (VFDRs) by excluding basic events that are related to cables identified with deterministically required equipment as per Attachment C of the LAR.

Recovery actions, defined in the Fire PRA as operator actions taken outside of the main control room and primary control stations (PCS), that are not considered Defense-In-Depth (DID) are set to have a failure rate of zero in the compliant plant model. Table G-1 of Attachment G of the LAR provides the recovery actions for each fire area (denoted as "RA" in the "RA/RADID/PCS" column).

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Special consideration is made for Main Control Room (MCR) abandonment in the post-transition and compliant plant models. Planned changes to MCR abandonment procedure (DSP-002, "HOT SHUTDOWN WITH A FIRE IN THE CONTROL ROOM/HAGAN ROOM") are to be addressed in the response to PRA RAI 3.

For the compliant case, critical actions that occur outside of a PCS in the updated MCR abandonment procedure will be set to always succeed as these would be considered recovery actions. However, the planned changes to the MCR abandonment procedure will not include critical actions that occur outside of a PCS. Therefore, it is currently assumed that MCR abandonment will not differ between the compliant and variant models for calculating reported change-in-risk as part of the response to PRA RAI 3.

Plant modifications that have been completed or committed to be performed are defined in Tables S-1 and S-2 of Attachment S of the LAR. For calculation of the risk associated for both the post-transition and compliant case, all completed and committed plant modifications are included in each FPRA model.

This response has been evaluated against the guidance provided in FAQ 08-0054, "Demonstrating Compliance with Chapter 4 of NFPA 805" and FAQ 07-0030, "Establishing Recovery Actions." The modeling practices of the post-transition and compliant models are consistent with both models.

This response does not preclude the addition or reduction of recovery actions that will be credited in the Fire PRA as per the response to be developed for PRA RAI 3.

PRA RAI 23b Section 2.4.3.3 of NFPA 805 states that the PRA approach, methods, and data shall be acceptable to the NRC. Section 2.4.4.1 of NFPA-805 further states that the change in public health risk arising from transition from the current fire protection program to an NFPA-805 based program, and all future plant changes to the program, shall be acceptable to the NRC. RG 1.174 provides quantitative guidelines on CDF, LERF, and identifies acceptable changes to these frequencies that result from proposed changes to the plant's licensing basis and describes a general framework to determine the acceptability of risk-informed changes. The NRC staff review of the information in the LAR has identified the following information that is required to fully characterize the risk estimates.

Section W.2.1 of the LAR provides some description of how the change-in-risk and the additional risk of recovery actions associated with VFDRs is determined but not enough detail to make the approach completely understood. Provide the following:

b) A description of how the reported additional risk of recovery actions was calculated, including any special calculations performed for the MCR.

Response

As per FAQ 08-0054, "Demonstrating Compliance with Chapter 4 of NFPA 805," the additional risk of recovery actions was calculated by finding the ACDF and ALERF values between the post-transition model CDF/LERF values and the CDF/LERF values of the post-transition model with the recovery actions assumed to always succeed (recovery actions defined as "RA" in Attachment G). Similarly, the additional risk of recovery actions for any scenarios leading to Main Control Room (MCR) abandonment was calculated by finding the difference in risk between the baseline post-transition case and the risk of the post-transition case where any actions that occurred outside of the MCR or Primary Control Stations (PCS) were set to always succeed.

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This response does not preclude the addition or reduction of recovery actions that will be credited in the Fire PRA as per the response to be developed for PRA RAI 3.

PRA RAI 23c Section 2.4.3.3 of NFPA 805 states that the PRA approach, methods, and data shall be acceptable to the NRC. Section 2.4.4.1 of NFPA-805 further states that the change in public health risk arising from transition from the current fire protection program to an NFPA-805 based program, and all future plant changes to the program, shall be acceptable to the NRC. RG 1.174 provides quantitative guidelines on CDF, LERF, and identifies acceptable changes to these frequencies that result from proposed changes to the plant's licensing basis and describes a general framework to determine the acceptability of risk-informed changes. The NRC staff review of the information in the LAR has identified the following information that is required to fully characterize the risk estimates.

Section W.2.1 of the LAR provides some description of how the change-in-risk and the additional risk of recovery actions associated with VFDRs is determined but not enough detail to make the approach completely understood. Provide the following:

c) An explanation of any major changes made to the Fire PRA model or data for the purpose of evaluating VFDRs.

Response

Changes made to the Fire PRA for the purposes of evaluating the VFDRs are discussed in sections (a) and (b) of this response.

PRA RAI 25a Section 2.4.3.3 of NFPA 805 states that the PRA approach, methods, and data shall be acceptable to the NRC. Section 2.4.4.1 of NFPA-805 further states that the change in public health risk arising from transition from the current fire protection program to an NFPA-805 based program, and all future plant changes to the program, shall be acceptable to the NRC. RG 1.174 provides quantitative guidelines on CDF, LERF, and identifies acceptable changes to these frequencies that result from proposed changes to the plant's licensing basis and describes a general framework to determine the acceptability of risk-informed changes. The NRC staff review of the information in the LAR has identified the following information that is required to fully characterize the risk estimates.

Regarding Fire Risk Evaluations, address the following:

a. Step 5, "Evaluate the Reliability of Recovery Actions," of LAR Attachment G states that "For the bounding reliability treatment see results in Attachment W." Explain what this bounding treatment is for the recovery actions.

Response

The statement in Step 5 of Attachment G of the LAR was intended to convey that the Defense In Depth (DID) recovery actions were not modeled in the PRA and therefore did not contribute any additional delta risk. If they were modeled, the risk of the recovery actions would be less than the VFDR without Page 21 of 22

the recovery applied. The response to PRA RAI 3 will include a revision of Attachment W. Any risk from recovery actions will be stated explicitly.

PRA RAI 25b Section 2.4.3.3 of NFPA 805 states that the PRA approach, methods, and data shall be acceptable to the NRC. Section 2.4.4.1 of NFPA-805 further states that the change in public health risk arising from transition from the current fire protection program to an NFPA-805 based program, and all future plant changes to the program, shall be acceptable to the NRC. RG 1.174 provides quantitative guidelines on CDF, LERF, and identifies acceptable changes to these frequencies that result from proposed changes to the plant's licensing basis and describes a general framework to determine the acceptability of risk-informed changes. The NRC staff review of the information in the LAR has identified the following information that is required to fully characterize the risk estimates.

Regarding Fire Risk Evaluations, address the following:

b) Explain whether previously approved recovery actions being transitioned are included in the additional risk from recovery action values presented in Attachment W. If they are not included, add them or explain why they are not included.

Response

The additional risk of previously approved recovery actions performed for control room abandonment is included in the risk for control room abandonment.

The risk from previously approved non-control room abandonment recovery actions is included in the risk delta between the compliant and variant case for the VFDR condition included in Attachment W.

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