L-PI-12-117, Supplement to License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactors - Response to Acceptance Review Questions

Supplement to License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactors - Response to Acceptance Review Questions

ML12354A464
Person / Time
Site:	Prairie Island
Issue date:	12/18/2012
From:	Jeffery Lynch Xcel Energy, Northern States Power Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
L-PI-12-117, TAC ME9734, TAC ME9735
Download: ML12354A464 (47)

Text

Prairie Island Nuclear Generating Plant 1717 Wakonade Drive East Welch, MN 55089 December 18,2012 L-PI-12-117 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Units 1 and 2 Dockets 50-282 and 50-306 Renewed License Nos. DPR-42 and DPR-60 Supplement to License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactors - Response to Acceptance Review Questions (TAC Nos. ME9734 and ME97351

References:

1. NSPM letter, J.P. Sorensen to NRC Document Control Desk, License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactors, L-PI-12-089, dated September 28, 2012, ADAMS Accession No. MLI 2278A405.

2. NSPM letter, J.E. Lynch to NRC Document Control Desk, Supplement to License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactors - Submittal of Internal Flooding Peer Review Results and Revised Total Plant Risk Values, L-PI-12-102, dated November 8, 2012, ADAMS Accession No. ML12314A144.

3. NRC e-mail, T. Wengert to S. Chesnutt, Prairie lsland NGP -

Acceptance Review Questions Regarding NFPA 805 License Amendment Request (TAC Nos. ME9734 and ME9735), dated November 29,2012, ADAMS Accession No. ML12335A183.

This letter provides supplemental information for the License Amendment Request (LAR) that was submitted in Reference 1 and supplemented in Reference 2 by the Northern States Power Company, a Minnesota Corporation (NSPM), doing business as Xcel Energy. The subject LAR requested approval to transition the fire protection

Document Control Desk Page 2 program for the Prairie Island Nuclear Generating Plant (PINGP), Units 1 and 2, to a Risk-Informed, PerFormance-Based alternative in accordance with 10 CFR 50.48(c),

which incorporates by reference National Fire Protection Association Standard 805 (NFPA 805).

During the initial review of the subject LAR, the Nuclear Regulatory Commission (NRC) staff identified five questions that were discussed during a telephone conference on November 28, 2012, and were transmitted via Reference 3. Additional telephone discussions were held on December II, 2012. Enclosure 1 to this letter provides NSPM responses to the questions in Reference 3. Enclosure 2 to this letter provides a revision to Attachment W, Fire PR4 Insights, to reflect changes described in Enclosure

1. The enclosed revision to Attachment W supersedes in its entirety the information previously provided in Attachment W to the subject LAR (Reference 1).

This supplement is submitted in accordance with 10 CFR 50.90. The supplemental information provided in this letter does not impact the conclusions of the No Significant Hazards Evaluation or Environmental Considerations Evaluation presented in the Reference Isubmittal.

In accordance with 10 CFR 50.91, NSPM is notifying the State of Minnesota of this LAR supplement by transmitting a copy of this letter to the designated State Official.

If there are any questions or if additional information is needed, please contact Gene Eckholt at 651-388-1121 x4137.

Summary of Commitments This letter contains no new commitments and no revisions to existing commitments.

9 .

I declare under penalty of perjury that the foregoing is true and correct.

Executed on December 18,2012 6??L James . Lynch Site Vice president, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosures cc: Administrator, Region Ill, USNRC NRR Project Manager, PINGP, USNRC Resident Inspector, PINGP, USNRC Minnesota Department of Commerce

ENCLOSURE 1 Supplement to License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactors Response to Acceptance Review Questions This enclosure includes responses from the Northern States Power Company, a Minnesota Corporation (NSPM) doing business as Xcel Energy, to questions identified by the Nuclear Regulatory Commission (NRC) in an e-mail dated November 29, 2012 (Reference 3). These questions were identified during the NRC staffs initial review of a License Amendment Request (LAR) submitted September 28, 2012 (ADAMS Accession number ML12278A405, Reference 1) and supplemented on November 8, 2012 (ADAMS Accession number ML12314A144, Reference 2). The subject LAR requested approval to transition the fire protection program for the Prairie Island Nuclear Generating Plant (PINGP), Units 1 and 2, to a Risk-Informed, Performance-Based approach in accordance with 10 CFR 50.48(c), which incorporates by reference National Fire Protection Association Standard 805 (NFPA 805).

This enclosure provides each question in italics, followed by the NSPM response.

Referenced documents are identified at the end of the discussions in this enclosure.

NRC Question 1:

Modifications described in Table S-2, Items 1-4, address separation of Train A and B equipment in Fire Areas 31 and 32, which contain auxiliary feedwater components, remote shutdown panels, and other redundant train equipment. Each of these modifications is described similarly as follows: modify equipment in FA 31 (or 32) to ensure that Train A (or B) equipment is available for fire safe shutdown. It is unclear from these descriptions what specifically the modification will be and, thus, it is unclear if the final plant configuration has been determined. The plant modifications need to be developed to the level of detail that can support an independent review of the efficacy of the proposed plant changes (e.g., re-route cables from specific fire areas, what equipment will be installed, etc.). Furthermore, these modifications are risk-ranked High, and are modeled in the FPRA, and are relied upon to yield an acceptable change in risk. Therefore, these modifications for transition need to be described and, as appropriate, modeled in the PRA to properly estimate the change in risk associated with transition.

Provide a more explicit description of modifications identified in Attachment S of the LAR as items 1, 2, 3, and 4, and how these modifications are treated in the PRA.

Page 1 of 12 NSPM Response to Acceptance Review Questions - NFPA 805 LAR NSPM Response to Question 1:

The modifications identified as items 1, 2, 3, and 4 in Table S-2 in Attachment S of the LAR provide train separation for safe shutdown (SSD) equipment in the Hot Shutdown Panel / Auxiliary Feedwater (AFW) pump rooms, Fire Areas (FA) 31 and 32. Currently, these fire areas each include equipment and controls for SSD equipment for both Train A and Train B, so that a fire in one of these areas could affect both trains. PINGP has an exemption from Appendix R requirements in these areas, and cables for AFW discharge control valves are protected up to the Hot Shutdown Panels. However, in each fire area, the panel itself is not protected with a fire barrier. This condition has been identified in the NFPA 805 transition process as a variance from deterministic requirements (VFDR) that will be resolved through modifications.

In general, the proposed modifications will provide SSD train separation by relocating AFW controls, cables, and associated MCC power supplies, and providing fire barriers on certain cables. These modifications will ensure that a fire in Fire Area 31 which houses the AFW pumps for Train B, will not affect the controls, power supplies, and other equipment for Train A. In the same manner, modifications will ensure that a fire in Fire Area 32 which houses the AFW pumps for Train A, will not affect the controls, power supplies, and other equipment for Train B.

The proposed modifications were incorporated into the Fire PRA model by re-assigning the affected cables and equipment to the new post-modification Fire Area location.

Items 1 through 4 in Table S-2 are similar because they describe Units 1 and 2, Train A and B, and Fire Areas 31 and 32. Specific modifications for each of the items identified in Table S-2 include the following:

Item 1:

Current configuration:

Fire Area 31 contains the following equipment related to the AFW VFDR:

• Unit 1, Train B Motor Driven Auxiliary Feedwater Pump (12 MDAFWP)

• Controls and associated cables for Unit 1, Train A AFW pump (AFWP) discharge valves Proposed modification:

The controls and associated cables for the Unit 1 Train A AFWP discharge valves will be moved to Fire Area 32 so they are not damaged by a fire in Fire Area 31.

Page 2 of 12 NSPM Response to Acceptance Review Questions - NFPA 805 LAR Item 2:

Current configuration:

Fire Area 31 contains the following equipment related to the AFW VFDR:

• Unit 2, Train B Turbine Driven Auxiliary Feedwater Pump (22 TDAFWP)

• Unit 2, Train A motor operated valves which discharge from the 21 MDAFWP to the 21 and 22 Steam Generators

• Controls, MCC power supply, and associated cables for Unit 2, Train A AFWP discharge and suction valves Proposed modification:

The controls, MCC power supply, and associated cables for the Unit 2 Train A AFWP discharge and suction valves will be moved to Fire Area 32 so they are not damaged by a fire in Fire Area 31. The cables going to Unit 2 Train A AFWP discharge valves will be protected from fire damage so that they will not spuriously close due to a fire in Fire Area 31.

Item 3:

Current configuration:

Fire Area 32 contains the following equipment related to the AFW VFDR:

• Unit 1, Train A Turbine Driven Auxiliary Feedwater Pump (11 TDAFWP)

• Unit 1, Train B motor operated valves which discharge from the 12 MDAFWP to the 11 and 12 Steam Generators.

• Controls, MCC power supply, and associated cables for Unit 1, Train B AFWP discharge and suction valves Proposed modification:

The controls, MCC power supply, and associated cables for the Unit 1 Train B AFWP discharge and suction valves will be moved to Fire Area 31 so they are not damaged by a fire in Fire Area 32. The cables going to Unit 1 Train B AFWP discharge valves will be protected from fire damage so that they will not spuriously close due to a fire in Fire Area 32.

Item 4:

Current configuration:

Fire Area 32 contains the following equipment related to the AFW VFDR:

• Unit 2, Train A Motor Driven Auxiliary Feedwater Pump (21 MDAFWP)

• Controls and associated cables for Unit 2, Train B AFWP discharge valves Proposed modification:

The controls and associated cables for the Unit 2 Train B AFWP discharge valves will be moved to Fire Area 31 so they are not damaged by a fire in Fire Area 32.

Page 3 of 12 NSPM Response to Acceptance Review Questions - NFPA 805 LAR Clarification of Risk Informed Characterization information provided in Table S-2 of the LAR:

In Table S-2 of the LAR, NSPM stated that the modifications proposed by Items 1 through 4 will reduce risk by modifying Fire Areas 31 and 32 to ensure that each Fire Area has either Train A or Train B related AFW equipment. The Risk Informed Characterization discussions in Table S-2 for Items 1 through 4 are clarified to state that the modifications proposed by Items 1 through 4 will reduce risk by modifying Fire Areas 31 and 32 to ensure that each Fire Area has either Train A or Train B related AFW equipment unaffected by a fire. As described above, cables to the discharge valves from the MDAFWPs will be protected to ensure that a fire will not result in spurious closure of these valves, although the valves are physically located in the Fire Areas that include the AFW pumps for the opposite train.

NRC Question 2:

The impact on the PRA results of implementing incipient detection (very early warning fire detection system - VEWFDS) in the Relay Room and Shutdown Reactor Coolant Pump seals is presented as a sensitivity study in Section W.2 of the LAR as a risk reduction of about 2.50E-04/yr (Unit 1) and 2.41E-04/yr (Unit 2) for CDF and 2.35E-05/yr (Unit 1) and 3.10E-05/yr (Unit 2) for LERF, which implies current risk levels at or above these values.

Describe how this risk reduction is calculated. If the results are correctly presented, 1) describe what additional compensatory actions have been implemented to lower the risks to acceptable ranges prior to the installation of the two modifications, and 2) discuss why the risk reduction is greater than the remaining CDF and LERF from all hazards.

NSPM Response to Question 2:

SUMMARY

OF ISSUE As described in Section W.2 of the License Amendment Request (LAR), two (2) modifications were credited to offset the additional risk associated with Recovery Actions credited for compliance with NFPA 805. The two modifications credited in the sensitivity analysis were the Shutdown Reactor Coolant Pump (RCP) seals and incipient detection (very early warning fire detection system (VEWFDS)).

During a review of the sensitivity analysis that supported the LAR, an error was identified. An updated sensitivity analysis has been performed and the values were found to be slightly lower than those calculated in the original sensitivity analysis, as follows:

Page 4 of 12 NSPM Response to Acceptance Review Questions - NFPA 805 LAR Risk benefit values reported in LAR:

• 2.50E-04/rx-yr / 2.35E-05/rx-yr, respectively for Unit 1 CDF and LERF

• 2.41E-04/rx-yr / 3.10E-05/rx-yr, respectively for Unit 2 CDF and LERF Corrected risk benefit values:

• 2.02E-04/rx-yr / 9.76E-06/rx-yr, respectively for Unit 1 CDF and LERF

• 1.43E-04/rx-yr / 1.23E-05/rx-yr, respectively for Unit 2 CDF and LERF Note that risk benefit of the modifications is greater than the risk increase of the Fire Recovery Action reported in Attachment W of the LAR, and the acceptance guidelines of Regulatory Guide 1.174 continue to be met.

DESCRIBE HOW THE RISK REDUCTION IS CALCULATED The risk reduction of the incipient detection and the Shutdown RCP seals was calculated by comparing the results of the base fire PRA model to the results of a fire PRA model that did not credit either modification. The resulting differences in CDF and LERF represent the risk benefit of both modifications.

DISCUSSION OF SENSITIVITY RESULTS The large calculated reduction in risk provided by these two modifications implies that the internal fires CDF and LERF risk metrics for the current, unmodified plant may be high. Conservatisms in the Fire PRA model contribute to this conclusion, and therefore, it is believed that these values overstate the actual (numerical) risk benefit of the modifications. These conservatisms represent expected reductions in the baseline CDF/LERF, and also in the sensitivity case delta-CDF/LERF values because they reduce the number of risk-significant sequences that can be impacted by the proposed modifications. For example, fires initiated in the Unit 1 Turbine Building account for approximately 70% of the Unit 1 modification risk reduction. All initiators located in the current Fire Area 69 are postulated to damage all fire PRA targets. This area is a large, multi-level compartment where the target set includes all targets regardless of the actual location of the initiating source. In addition, limited credit was given in the model for detection and manual suppression of fires in this compartment.

Another example of an area where the sensitivity analysis showed a large risk benefit was the Mezzanine level of the Auxiliary Building. Fires initiated in the Mezzanine level account for approximately 41% of the Unit 2 modification risk reduction. Detailed fire modeling was performed in this area; however, there are some conservatisms that contribute to the large risk benefit of the Shutdown Reactor Coolant Pumps Seal modification. For example, although the buses are not located in the area, some fires in this area affect the normal offsite source and its source breaker to one of the two 4kV safeguards buses; for these fires, manual action to restore power from an available alternate source is not credited.

There are other conservatisms in the fire PRA that, if credited, would result in an overall risk-reduction. Some examples include: 1) developing detailed growth models for each Page 5 of 12 NSPM Response to Acceptance Review Questions - NFPA 805 LAR fire initiator, 2) crediting prompt detection and suppression for all transient fires caused by welding and cutting, and 3) crediting plant-installed detection and suppression systems for every fire area where the equipment is available.

However, there are some areas where the large risk-benefit of the modifications is due to the high risk-significance of the equipment failed by the fire. For example, the results of the sensitivity analysis showed that the 4.16 kV Safeguards Switchgear Rooms benefited from the Shutdown Reactor Coolant Pump Seals. The risk-benefit was expected because the current fire analysis assumes all initiators located in each bus room damage all fire PRA targets. With one train of equipment damaged, any random equipment failures important to RCP Seal Cooling increase the risk of an RCP Seal LOCA.

Another example of an area where the sensitivity analysis showed a risk benefit was the Relay Room. Since the Relay Room contains cables associated with both units and both trains of equipment, it was expected that this room would show a risk-benefit from both modifications. The incipient detection modification provides a risk benefit because the system is designed to detect a fire prior to ignition, while the Shutdown RCP Seal modification provides a risk benefit by reducing the risk-significance of an RCP Seal LOCA in an area where a lot of equipment important to RCP seal cooling can be damaged.

INTERIM COMPENSATORY MEASURES Table S-2 of the LAR describes compensatory measures that are credited in the current fire protection licensing basis and are provided for the Fire Area affected by each modification. Compensatory measures identified for the Incipient Detection modification (Table S-2, item 5) include hourly fire watches and operator recovery actions.

Compensatory measures identified for the Shutdown Reactor Coolant Pump (RCP) seal modification (Table S-2, item 18) include hourly fire watches.

To reduce plant risks until these two modifications can be installed, NSPM is implementing additional risk-informed interim measures at PINGP. Using the guidance in RIS 2005-07, interim measures have been identified that will be more effective at reducing risk than continuous fire watches, which were discussed during an informal telephone conference with the NRC reviewers on December 11, 2012. NSPM has completed a Fire Protection Engineering Evaluation (FPEE) to identify these risk-informed interim measures. This FPEE:

• Identifies high risk areas of the plant,

• Identifies the type of fire initiators that contribute to these high risk values (e.g.,

transient combustibles, electrical cabinets, pumps),

• Identifies the risk significant operator manual actions that can recover equipment affected by a fire, and

• Defines the appropriate risk-informed interim measures that address the high risk contributors in each high risk area.

Examples of these risk-informed interim measures include the following:

Page 6 of 12 NSPM Response to Acceptance Review Questions - NFPA 805 LAR

• Protection of redundant equipment if Hot Work is required in the vicinity of risk significant Fire PRA targets.

• Additional restrictions on storage of transient combustible materials in the vicinity of risk significant Fire PRA targets.

• Operator Manual Actions not credited in the Fire PRA that recover equipment affected by a fire (e.g., manually repositioning a motor operated valve that lost power).

• Communications and training for operators and other plant personnel to enhance awareness of high risk areas and risk significant operator response actions.

The interim measures to reduce risk for the two modifications described in the LAR are being performed and completed as actions identified in the PINGP Corrective Action Program.

NRC Question 3:

Inconsistencies were identified between scenario-specific CDF/LERF results reported in Tables W-1 through W-4 and the fire area CDF/LERF results reported in Tables W-5 and W-6 which are potentially significant: (1) Table W-1, Fire Scenario U1FDS-41GRP, reports a CDF of 6.25E-07, whereas Table W-5 reports a CDF of epsilon for Fire Area 41; (2) Table W-3 provides the CDF for 5 fire scenarios for Fire Area 59 that sum to a total CDF of 5.8E-06, which is greater than the CDF of 1.24E-06 for Fire Area 59 reported in Table W-6; (3) similarly, Table W-4 provides the LERF for 11 fire scenarios for Fire Area 59 that sum to a total LERF of 1.4E-06, which is greater than the LERF of 1.9E-07 for Fire Area 59 reported in Table W-6).

Clarify the discrepancies between the scenario-specific CDF/LERF results provided in Tables W-1 through W-4 and the fire area CDF/LERF results provided in Tables W-5 and W-6. Provide revised tables if necessary.

NSPM Response to Question 3:

The apparent inconsistencies between information presented in the tables in Attachment W of the LAR are due to several factors. In Item 1, as explained in greater detail below, there are differences between the Fire Compartments (FCs) included in the Fire Initiating Events (Fire Scenario) tables (Tables W-1 through W-4) and the Fire Areas (FAs) included in the Fire Area Risk Summary tables (Tables W-5 and W-6). In Item 2 and other instances explained below, NSPM has identified a number of errors in the information presented in Attachment W. As described below, these errors were associated with the presentation of results of analyses, and not with the analyses themselves.

Page 7 of 12 NSPM Response to Acceptance Review Questions - NFPA 805 LAR Attachment W of the LAR provides fire PRA insights, primarily in six (6) different tables.

Tables W-1 through W-4 consist of dominant risk contributors for both Units CDF and LERF values that represent >1% to the calculated fire risk. The values listed in Tables W-1 through W-4 are based on specific fire scenarios that typically include FCs or groups of FCs whose boundaries do not necessarily reflect defined FAs. Tables W-5 and W-6 provide risk values for each FA. Tables W-5 and W-6 also provide the overall risk associated with the Recovery Actions that were credited in the Fire Risk Evaluations (FREs).

The specific issues identified in Question 3 are addressed as follows:

Item 1: The values listed in Tables W-1 and W-5 for Fire Scenario U1FDS-41GRP and Fire Area 41 are reported correctly. In Table W-1, Fire Scenario U1FDS-41GRP reports values for a specific Fire Scenario. The Fire Areas and Fire Compartments applicable to this item include the following:

• Fire Area 41, Screenhouse - General Area; Table W-5 correctly identifies FA 41 CDF/LERF values.

• Fire Area 41B, Screenhouse Basement Below Grade (this also includes Fire Compartment 41B-1).

• Fire Compartment 41GRP includes Fire Areas 41 and 41B, but does not include a portion of Fire Area 41B which was partitioned into Fire Compartment 41B-1.

Items 2 and 3: The CDF and LERF values identified in Tables W-3 and W-4 for FA 59 are correct, but the values listed in Table W-6 for FA 59 were found to be in error. The Table W-6 values for CDF and LERF for FA 59 are revised as follows:

LAR Table W-6 Correction FA 59 (page W-30) CDF/LERF Existing values in LAR 1.24E-06 / 1.90E-07 Corrected CDF/LERF 1.29E-05 / 1.86E-06 The quantification calculations that determined the total CDF/LERF values for all Fire Areas, as presented in the LAR, already reflected these corrected values for FA 59.

Therefore, the total CDF/LERF values presented in Table W-6 of the LAR are not affected by this change and are correct as stated.

In addition, the CDF/LERF values for FA 59 were found to be in error. The Table W-6 values for CDF and LERF for FA 59 are revised as follows:

LAR Table W-6 Correction FA 59 (page W-30) CDF/LERF Existing values in LAR 1.50E-07 / 2.43E-08 Corrected CDF/LERF /

Page 8 of 12 NSPM Response to Acceptance Review Questions - NFPA 805 LAR The CDF/LERF values for FA 59 are also identified as Additional Risk of RAs values in Table W-6. This correction for FA 59 affects the total Unit 2 Additional Risk of RAs values which are identified in two places in the LAR, Table W-6 and Section W.2. Table W-6 Additional Risk of RAs values are revised as follows:

LAR Table W-6 Correction Total for Unit 2 (page W-32) Additional Risk of RAs Existing values in LAR 8.87E-06 / 9.57E-07 Corrected risk values 8.72E-06 / 9.32E-07 This same correction is made to the total additional risk values due to recovery actions presented in the Delta CDF and Delta LERF discussion in Section W.2 of the LAR, at the top of page W-3. No changes are required to the values presented for Unit 1.

Other Corrections to Attachment W - Tables W-1 through W-4 In Tables W-1 through W-4, NSPM identified a number of inconsistencies in the Ignition Frequency (IF), Conditional Core Damage Probability (CCDP), and Conditional Large Early Release Probability (CLERP) values. None of these inconsistencies affect the reported CDF or LERF values and they are all correct in the Attachment W submitted with the LAR. For completeness, revised Tables W-1 through W-4 with corrected IF, CCDP, and CLERP values are identified in a revision to Attachment W that is provided in Enclosure 2 to this letter. This revised Attachment W supersedes in its entirety the information previously provided in Attachment W to the LAR (Reference 1). These changes are due to a calculation change that uses a method consistent with the rest of Attachment W for calculating the CCDP and CLERP values, and this change has no effect on the conclusions drawn from the tables.

Other Corrections to Attachment W - Table W-5, FA-94 During review of other information in Attachment W, NSPM identified an error in Table W-5, in the CDF/LERF values for Fire Area 94. The Table W-5 values for CDF and LERF for FA 94 (LAR page W-26) should be revised as follows:

LAR Table W-5 Correction FA 94 (page W-26) CDF/LERF Existing values in LAR 9.81E-08 / 3.10E-09 Corrected CDF/LERF 3.84E-07 / 1.04E-08 The quantification calculations that determine total CDF/LERF values for all Fire Areas already reflected these corrected values for FA 94. Therefore, the total CDF/LERF values presented in Table W-5 of the LAR are not affected by this change and are correct as stated.

Summary The apparent inconsistency for FA 41 results identified in Question 3, item 1, is due to the difference between plant areas included in the Fire Compartment 41GRP Fire Page 9 of 12 NSPM Response to Acceptance Review Questions - NFPA 805 LAR Scenario results presented in Table W-1 and the Fire Area 41 results presented in Table W-5. The information presented in the LAR is correct.

The inconsistency of FA 59 results identified in Question 3, items 2 and 3, is due to an error in Table W-6. During the review of this error, an additional error was identified in information presented in Table W-5 for FA 94. In addition, an inconsistency in the method for calculating CCDP and CLERP values was identified. Resolution of this inconsistency does not change the CDF or LERF values in Attachment W, but it does change a number of CCDP, IF, and CLERP values in Tables W-1 through W-4. provides a revised Attachment W that corrects the identified errors and inconsistencies. The identified errors were associated with the presentation of results of analyses, and not with the analyses themselves. The conclusions that PINGP risk values meet the Regulatory Guide 1.174 acceptance guidelines as presented in the LAR are not affected by these corrections.

NRC Question 4:

The resolutions to peer review Findings for SRs CS-B1 (self assessed as CC-I) and CS-C4 (self assessed as Not Met) in Table V-2 of the LAR describe that these Findings cannot be completely addressed until a breaker coordination study is completed and that the PRA assumes that there are no coordination issues. It is noted that Implementation Item #34 in Table S-3 of the LAR is to complete the breaker fuse coordination study and Modification #20 in Table S-2 of the LAR is to install appropriate fuses and/or breaker to fix issues identified in the study. Engineering analyses needed to support the LAR and fire PRA should be completed prior to LAR submittal since the final results from such studies/analyses could impact the risk results presented in the LAR.

Provide justification for why the LAR is acceptable without a completed breaker fuse coordination study.

NSPM Response to Question 4:

The PINGP Fire PRA assumes that all power supplies are coordinated. A breaker fuse coordination study was in progress at the time of LAR submittal to identify power supplies that currently do not coordinate and that will require modifications to support this assumption. Modification Item 20 in Table S-2 of the LAR requires installation of appropriate fuses and/or breakers to resolve issues identified in the breaker fuse coordination study. In addition, Implementation Item 34 in Table S-3 of the LAR will revise applicable Design calculations to support conclusions within the final breaker fuse coordination study.

Page 10 of 12 NSPM Response to Acceptance Review Questions - NFPA 805 LAR Subsequent to submittal of the LAR, the final breaker fuse coordination study has been completed, consistent with the recommended resolution for Peer Review Finding CS-B1 in Table V-1 of the LAR. The breaker fuse coordination study evaluated existing coordination studies to determine which power supplies in the Fire PRA were uncoordinated. The study identified 22 Fire PRA Credited Power Supplies that do not coordinate and will therefore be modified in accordance with Table S-2, Item 20 of Attachment S of the LAR.

A list of the PINGP power supplies that will be modified to ensure breaker coordination as assumed in the Fire PRA is as follows:

BUS-180 MCC-2EB2 MCC-1B1 PNL-117 MCC-1BB1 PNL-136 MCC-1E1 PNL-137 MCC-1E2 PNL-148 MCC-1EB1 PNL-171 MCC-1EB2 PNL-181 MCC-1U2 PNL-1RPA23 MCC-2E1 PNL-217 MCC-2E2 PNL-271 MCC-2EB1 PNL-281 NRC Question 5:

The resolution to the peer review Finding for SR PRM-A1-01 in Table V-1 of the LAR concludes, for fire scenarios that damage only the component from which the fire originates, that loss of the component and any resulting plant transient (including a reactor trip) is encompassed by the internal events PRA and are therefore appropriately screened from the fire PRA.

Describe the analysis performed to draw this conclusion. Also discuss whether NUREG/CR-6850 guidance in Section 8.5.3 Step 3: Verification of Screened Fixed Ignition Sources was considered.

Page 11 of 12 NSPM Response to Acceptance Review Questions - NFPA 805 LAR NSPM Response to Question 5:

Each component that was not screened during Task 6 of NUREG/CR-6850 (Fire Ignition Frequency) was reviewed using the information collected during the initial plant walkdowns and was modeled with the applicable NUREG 1805 spreadsheets to determine fire propagation and severity. When initiators were identified as non-propagating, they were no longer considered. The exceptions to this are the relay racks located in FC 18 and some MCCs throughout the plant. The guidance of Section 8.5.3 Step 3 in NUREG/CR-6850 was completed for these MCCs and relay racks. When a fire would not propagate beyond the initiator, fire scenarios were created where only damage to the component was considered.

As the Fire PRA is built on top of the internal events PRA model, fire ignition sources that are not the specified MCCs or relay racks, which damage only themselves, and do not propagate beyond the ignition source, will have the same Conditional Core Damage Probability as they do in the internal events model. Fire induced failure or unavailability is already incorporated into the component modeling in the internal events PRA. Fire induced failure or unavailability is a subset of the failure and unavailability data for these components and is based on historical data.

Complete analysis of all ignition sources could not be confirmed so a review of all screened ignition sources was performed against the specific guidance of NUREG/CR-6850, Section 8.5.3 Step 3. This was done to ensure that the non-propagating ignition sources were appropriately screened. The results of this review show that all ignition sources were appropriately screened.

References

1. NSPM letter, J.P. Sorensen to NRC Document Control Desk, License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactors, L-PI-12-089, dated September 28, 2012, ADAMS Accession No. ML12278A405.

2. NSPM letter, J.E. Lynch to NRC Document Control Desk, Supplement to License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactors - Submittal of Internal Flooding Peer Review Results and Revised Total Plant Risk Values, L-PI-12-102, dated November 8, 2012, ADAMS Accession No. ML12314A144.

3. NRC e-mail, T. Wengert to S. Chesnutt, Prairie Island NGP - Acceptance Review Questions Regarding NFPA 805 License Amendment Request (TAC Nos. ME9734 and ME9735), dated November 29, 2012, ADAMS Accession No. ML12335A183.

Page 12 of 12

ENCLOSURE 2 Attachment W - Fire PRA Insights (Revised) 32 pages follow

Northern States Power - Minnesota Attachment W - Fire PRA Insights W. Fire PRA Insights 31 Pages Attached PINGP Page W-1 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights W.1 Fire PRA Overall Risk Insights Risk insights were documented as part of the development of the Fire PRA. The total plant fire CDF/LERF was derived using the NUREG/CR-6850 methodology for Fire PRA development, and is useful in identifying the areas of the plant where fire risk is greatest. The risk insights generated were useful in identifying areas where specific contributors might be mitigated via modification. A detailed description of significant risk sequences associated with the fire initiating events that individually represent any sequences contributing more than 1% of the calculated fire risk for the plant was prepared for the purposes of gaining these insights which included the contribution from MSO combinations. These insights are provided in Tables W-1 through W-4.

Fire scenarios were selected based on the definition of significant accident sequence from RG 1.200, Revision 2:

Significant accident sequence: A significant sequence is one of the set of sequences, defined at the functional or systemic level that, when ranked, compose 95% of the CDF or the LERF/LRF, or that individually contribute more than ~1% to the CDF or LERF/LRF.

There are 38 fire scenarios comprising 71% of the total Unit 1 fire CDF that contribute more than 1% to the total on an individual basis. These scenarios are presented in Table W-1. There are 12 fire scenarios comprising 63% of the total Unit 1 fire LERF that contribute more than 1% to the total on an individual basis. These scenarios are presented in Table W-2. There are 28 fire scenarios comprising 56% of the total Unit 2 fire CDF that contribute more than 1% to the total on an individual basis. These scenarios are presented in Table W-3. There are 28 fire scenarios comprising 72% of the total Unit 2 fire LERF that contribute more than 1% to the total on an individual basis. These scenarios are presented in Table W-4. For each scenario, Tables W-1 through W-4 identify a Conditional Core Damage Probability (CCDP) and Conditional Large Early Release Probability (CLERP) which are combined with a Fire Ignition Frequency (IF) to determine CDF and LERF values.

W.2 Risk Change Due to NFPA 805 Transition In accordance with the guidance in Regulatory Position 2.2.4.2 of RG 1.205 Revision 1:

The total increase or decrease in risk associated with the implementation of NFPA 805 for the overall plant should be calculated by summing the risk increases and decreases for each fire area (including any risk increases resulting from previously approved recovery actions). The total risk increase should be consistent with the acceptance guidelines in Regulatory Guide 1.174. Note that the acceptance guidelines of Regulatory Guide 1.174 may require the total CDF, LERF, or both, to evaluate changes where the risk impact exceeds specific guidelines. If the additional risk associated with previously approved recovery actions is greater than the acceptance guidelines in Regulatory Guide 1.174, then the net change in total plant risk incurred by any proposed alternatives to the deterministic criteria in NFPA 805, Chapter 4 (other than the previously approved recovery actions), should be risk-neutral or represent a risk decrease.

PINGP Page W-2 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights The PINGP fire area risk summary is provided in Tables W-5 (Unit 1) and W-6 (Unit 2).

Delta CDF and Delta LERF From Tables W-5 and W-6, the total additional risk due to recovery actions is:

• 9.00E-06/rx-yr / 8.69E-07/rx-yr, respectively for Unit 1 CDF and LERF

• 8.72E-06/rx-yr / 9.32E-07/rx-yr, respectively for Unit 2 CDF and LERF This risk increase due to Recovery Actions shown above is below the threshold for Region II of RG 1.174, Revision 2 Figures 4 and 5, which are 1E-5/rx-yr (CDF) and 1E-6/rx-yr (LERF). In addition, plant modifications were identified that reduce the cumulative CDF and LERF. The credit for these modifications is included in both variant and compliant cases in Tables W-5 and W-6. These modifications were incorporated into the Fire PRA Model to reduce the overall risk. Incorporation of these modifications also eliminated much of the risk impact for several Variances from Deterministic Requirements (VFDRs). The risk benefit from these modifications can be used to offset the additional risk due to recovery actions shown above. The risk benefit was estimated within a sensitivity study by eliminating two modifications (low leakage RCP seals and incipient detection for cabinets in the Relay Room (FA18)) from the variant case. The resulting risk reduction due to including these modifications is shown below:

• 2.02E-04/rx-yr / 9.76E-06/rx-yr, respectively for Unit 1 CDF and LERF

• 1.43E-04/rx-yr / 1.23E-05/rx-yr, respectively for Unit 2 CDF and LERF When risk reduction from these modifications is combined with the additional risk due to recovery actions, the result is a net risk decrease associated with the transition to NFPA 805. Therefore, the total change in risk associated with the transition to NFPA 805 represents a risk decrease, and the acceptance criteria of RG 1.174 are met.

Total CDF and LERF Although not required for a net risk decrease, total plant risk is estimated in order to provide additional perspective.

The total plant risk is lower than the RG 1.174 limits for total plant risk of 1E-04/yr for CDF or 1E-05/yr for LERF. More specifically, the total plant risk estimated by summing the contributions from internal events (including internal floods), fires, and estimates for external events yield a total plant CDF and LERF of approximately 8.43E-05/rx-yr /

4.00E-06/rx-yr, respectively for Unit 1 and 9.84E-05/rx-yr / 7.15E-06/rx-yr, respectively for Unit 2. These numbers are below the 1E-04/yr and 1E-05/yr thresholds for CDF and LERF, respectively.

Both the internal events and internal flooding contribution to total plant risk are values from a sensitivity study that credits a plant modification and procedure changes that are listed in Attachment S. These changes include installation of Shutdown Reactor Coolant Pump seals, development of a process to depressurize the Reactor Coolant PINGP Page W-3 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights System and use alternate low pressure makeup sources. Without crediting these described changes, the total plant risk would exceed the RG 1.174 limits noted above.

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Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-1 Fire Initiating Events for Unit 1 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF Full compartment burn of FA 69; initiator results in damage to cables supporting Unit 1 4kV Bus 16 and both offsite supplies Turbine Building Ground to both Bus 15 and 16, 12 MDAFW pump. Dominant U1FDS-8GRP-FA69 Floor & Mezzanine Floors 10.05% sequences include failure of D1 EDG and failure of operator 1.93E-04 2.70E-02 5.20E-06 Unit 1 695, 715 action to cross-tie Unit 2 4kV buses to Unit 1 (SBO), followed by failure of operator action to trip the RCPs and failure of the RCP shutdown seal to successfully actuate.

Fire initiated in MCR Panel 1PLP that is successfully suppressed but that fails all panel equipment; includes failure U1-MCR-FS-EC Main Control Room - of SG pressure instrumentation supporting AFW manual start 6.07% 2.55E-02 1.23E-04 3.14E-06 CDF Electrical Cabinet - 14 and control; core damage occurs with operator failure to initiate bleed and feed RCS cooling or to perform transfer to high head recirculation.

Full compartment burn of FC 22; initiator results in loss of 480V AC Buses 121 and 122 as well as loss of 12 CC pump and 12 AFW pump. Dominant core damage sequences 480V Safeguards U1FDS-22 4.93% involve failure of either the operators to manually start the 11 1.99E-03 1.28E-03 2.55E-06 Switchgear (Bus 121)

AFW pump, or failure of the pump to start or run, together with failure of the operator action to either to initiate bleed and feed RCS cooling or to perform transfer to high head recirculation.

Full compartment burn of FC 20; initiator results in loss of 4kV AC Bus 16. Dominant core damage sequences involve failure Unit 1 4.16 KV Safeguards of either the operators to manually start the 11 AFW pump, or U1FDS-20 3.81% 2.20E-03 8.94E-04 1.97E-06 Swgr (Bus 16) failure of the pump to start or run, together with failure of the operator action to either to initiate bleed and feed RCS cooling or to perform transfer to high head recirculation.

Transient fire leading to hot gas layer in FC 32 (or other fires with failure of automatic suppression) leading to full room B Train Hot Shutdown burn; initiator results in loss of power to 4kV Bus 15, the CT Panel & Air and D2 sources to Bus 16, and OCT failures on Bus 25; U1FDS-32 2.49% 2.87E-04 4.50E-03 1.29E-06 Compressor/Aux dominant sequences include random failure of the Bus 16 load Feedwater Room sequencer or Bus 16 circuit breaker failures to open resulting in failure of bus voltage restoration (SBO with inability to restore power from offsite).

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Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-1 Fire Initiating Events for Unit 1 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF Full compartment burn of FC 81; initiator results in loss of 4kV AC Bus 15 and loss of both offsite sources to Unit 1.

Dominant core damage sequences involve failure of D2 EDG 4.16 KV Safeguard to start or run and failure of the operators to perform Bus 16 U1FDS-81 1.78% 1.02E-03 9.07E-04 9.22E-07 Switchgear Room (Bus 15) manual voltage restoration from Bus 26 (SBO), together with failure of the local manual operator action to control SG level or failure of the RCP shutdown seal to successfully actuate, resulting in an unrecoverable RCP seal LOCA.

Full compartment burn of FC 28; initiator results in a loss of the 1RY and 2RY transformers supply to safeguards 4kV buses on both units, as well as the loss of non-safeguards 4kV buses 13, 14, 23, and 24. Dominant sequences include failure U1FDS-28 Yardgroup 1.78% 3.52E-05 2.61E-02 9.19E-07 of the operators to manually start AFW and to cross-tie to the Unit 2 (21) motor-driven AFW pump (or random failures of 12 MDAFWP occur), and the operators fail to successfully initiate bleed and feed RCS cooling.

Computer room cabinet fire with successful suppression; initiator results in loss of 11 and 12 CC pump trains, 11 and 12 RHR pump trains, and 4kV non-safeguards buses 13 and 23, Relay and Cable and spurious opening of CV-31121 and CV-31124 (Unit 1 and U1FDS-18-1002-00 1.66% 6.56E-04 1.31E-03 8.60E-07 Spreading Room - 1002 Unit 2 condenser makeup from the CSTs). Dominant sequences include failure of the operator response action to isolate CV-31121 and CV-31124, and failure to align Cooling Water to the AFW pumps when the CST supply is lost.

MCR transient fire impacting all offsite power sources to 4kV buses 15 and 16, bus sequencers and D1 and D2 EDGs; U1-MCR-FS-TRAN Main Control Room - overcurrent trips fail bus cross-tie from Unit 2 4kV buses 1.59% 1.14E-03 7.25E-04 8.24E-07 CDF Transient - 20 (SBO). Dominant core damage sequences involve MCR abandonment and failure for the operators to successfully perform alternate shutdown from outside the MCR.

Fire initiated in Relay Room 120V AC Panel 112 that is successfully suppressed (incipient detection and manual suppression success) but that fails all panel equipment; Relay and Cable U1FDS-18-1077-00 1.58% initiator fails SG pressure instrumentation supporting AFW 2.49E-02 3.28E-05 8.18E-07 Spreading Room - 1077 manual start and control; dominant core damage sequences involve operator failure to initiate bleed and feed RCS cooling or transfer to high head recirculation.

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Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-1 Fire Initiating Events for Unit 1 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF Fire initiated in Relay Room Panel 1AP1 that is successfully suppressed (incipient detection and manual suppression success) but that fails all panel equipment; initiator fails SG Relay and Cable U1FDS-18-1003-00 1.56% pressure instrumentation supporting AFW manual start and 2.45E-02 3.28E-05 8.05E-07 Spreading Room - 1003 control; dominant core damage sequences involve operator failure to initiate bleed and feed RCS cooling or transfer to high head recirculation.

Fire initiated in Relay Room Panel 1AP2 that is successfully suppressed (incipient detection and manual suppression success) but that fails all panel equipment; initiator fails SG Relay and Cable U1FDS-18-1004-00 1.56% pressure instrumentation supporting AFW manual start and 2.45E-02 3.28E-05 8.05E-07 Spreading Room - 1004 control; dominant core damage sequences involve operator failure to initiate bleed and feed RCS cooling or transfer to high head recirculation.

Fire initiated in Relay Room Panel 2AP2 that is successfully suppressed (incipient detection and manual suppression success) but that fails all panel equipment; initiator fails SG Relay and Cable U1FDS-18-1032-00 1.56% pressure instrumentation supporting AFW manual start and 2.45E-02 3.28E-05 8.05E-07 Spreading Room - 1032 control; dominant core damage sequences involve operator failure to initiate bleed and feed RCS cooling or transfer to high head recirculation.

MCR transient fire impacting 11, 12, 22 Cooling Water (CL)

U1-MCR-FS-TRAN Main Control Room - pumps. Dominant core damage sequences involve MCR 1.52% 1.09E-03 7.25E-04 7.89E-07 CDF Transient - 22 abandonment and failure fo the operators to successfully perform alternate shutdown from outside the MCR.

Full compartment burn of 69GRP; initiator results in damage to cables supporting D2 EDG and both offsite supplies to both Bus 15 and 16; dominant sequences include failure of D1 U1FDS-8GRP-69GRP Turbine Building - 69GRP 1.44% EDG and failure of operator action to cross-tie Unit 2 4kV 5.75E-05 1.30E-02 7.47E-07 buses to Unit 1 (SBO), followed by failure of operator action to trip the RCPs and failure of the RCP shutdown seal to successfully actuate.

PINGP Page W-7 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-1 Fire Initiating Events for Unit 1 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF T/G oil or H2 fire with failure of fire detection or suppression resulting in catastrophic failure of the turbine and loss of all credited equipment in the Turbine Building (8GRP); initiator causes loss of cables and other support equipment leading to Unit 1 and Unit 2 Turbine loss of all sources to all 4kV AC buses (EDG D5 remains U1FDS-8GRP-ALL Buildings El. 679', 695', 1.30% 4.73E-05 1.42E-02 6.71E-07 available to repower Bus 25 via manual operator action).

715' Dominant sequences include successful action to re-power Bus 25 followed by failure to repower Bus 15 from Bus 25 (SBO) and operator failure to control level in Unit 1 SGs prior to offsite power restoration.

Full compartment burn of FC 34; initiator results in loss of 125V DC Bus 12. Dominant core damage sequences involve failure of either the operators to manually start the 11 AFW U1FDS-34 Battery Room 12 1.28% 9.34E-04 7.07E-04 6.60E-07 pump, or failure of the pump to start or run, together with failure of the operator action to either to initiate bleed and feed RCS cooling or to perform transfer to high head recirculation.

MCR transient fire impacting U1 charging, letdown, and safety injection (SI). Dominant core damage sequences involve U1-MCR-FS-TRAN Main Control Room -

1.27% MCR abandonment and failure for the operators to 9.06E-04 7.25E-04 6.57E-07 CDF Transient - 15 successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting Unit 1 AFW system and pressurizer PORVs. Dominant core damage sequences U1-MCR-FS-TRAN Main Control Room -

1.27% involve MCR abandonment and failure for the operators to 9.05E-04 7.25E-04 6.56E-07 CDF Transient - 14 successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting panels 1RCS1, 1CVCS2, and U1-MCR-FS-TRAN Main Control Room - 1PLP. Dominant core damage sequences involve MCR 1.24% 8.88E-04 7.25E-04 6.44E-07 CDF Transient - 9 abandonment and failure for the operators to successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting panels 1CVCS2, 1PLP and 1SD.

U1-MCR-FS-TRAN Main Control Room - Dominant core damage sequences involve MCR 1.24% 8.87E-04 7.25E-04 6.43E-07 CDF Transient - 13 abandonment and failure for the operators to successfully perform alternate shutdown from outside the MCR.

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Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-1 Fire Initiating Events for Unit 1 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF Full compartment burn of 41GRP (either detection or suppression failure); results in loss of all Cooling Water (CL),

Circulating Water (CW), 4kV Bus 23, and spurious closure of RHR discharge control valves to low head injection.

Screenhouse (General U1FDS-41GRP 1.21% Dominant sequences include consequential loss of offsite 8.45E-05 7.40E-03 6.25E-07 Area) power followed by failure of operator action to cross-tie Unit 1 4kV buses to Unit 2 (SBO), AFW success but offsite power is not recovered in time to prevent core uncovery and core damage.

MCR transient fire impacting Unit 2 Charging, Letdown, and Safety Injection (SI). Dominant core damage sequences U1-MCR-FS-TRAN Main Control Room -

1.18% involve MCR abandonment and failure for the operators to 8.44E-04 7.25E-04 6.12E-07 CDF Transient - 18 successfully perform alternate shutdown from outside the MCR.

Full compartment burn of FA 8; initiator results in a loss of non-safeguards 480V Bus 260, and control power to non-safeguards 4kV Bus 11 (11 RCP and 11 FW pump).

Turbine Deck (Units 1 & 2) Dominant sequences include failure of the operators to U1FDS-8GRP-FA8 1.18% 1.85E-05 3.30E-02 6.09E-07 735 manually start AFW and to cross-tie to the Unit 2 (21) motor-driven AFW pump (or the 21 MDAFWP is unavailable due to preventive maintenance), and the operators fail to successfully initiate bleed and feed RCS cooling.

MCR transient fire impacting Unit 2 AFW system and pressurizer PORVs. Dominant core damage sequences U1-MCR-FS-TRAN Main Control Room -

1.17% involve MCR abandonment and failure for the operators to 8.35E-04 7.25E-04 6.05E-07 CDF Transient - 19 successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting all offsite power sources to 4kV buses 25 and 26, bus sequencers and D5 and D6 EDGs; U1-MCR-FS-TRAN Main Control Room - overcurrent trips fail bus cross-tie from Unit 1 4kV buses 1.17% 8.34E-04 7.25E-04 6.05E-07 CDF Transient - 21 (SBO). Dominant core damage sequences involve MCR abandonment and failure for the operators to successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting Nuclear Instrumentation Protection Channel III, 24MR and panels 2G, 2M, 1R, 1M and U1-MCR-FS-TRAN Main Control Room -

1.17% 1G. Dominant core damage sequences involve MCR 8.34E-04 7.25E-04 6.05E-07 CDF Transient - 6 abandonment and failure for the operators to successfully perform alternate shutdown from outside the MCR.

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Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-1 Fire Initiating Events for Unit 1 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF MCR transient fire impacting Nuclear Instrumentation Protection Channels I, II, III, and IV, and panels 2G, 2M, 1R, U1-MCR-FS-TRAN Main Control Room -

1.17% 1M and 1G. Dominant core damage sequences involve MCR 8.34E-04 7.25E-04 6.05E-07 CDF Transient - 7 abandonment and failure for the operators to successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting Rack #21, panel 1RCS1, and the Incore Detector Panel. Dominant core damage sequences U1-MCR-FS-TRAN Main Control Room -

1.17% involve MCR abandonment and failure for the operators to 8.34E-04 7.25E-04 6.05E-07 CDF Transient - 8 successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting panels 2RCS1, 2CVCS2, and U1-MCR-FS-TRAN Main Control Room - 2PLP. Dominant core damage sequences involve MCR 1.17% 8.34E-04 7.25E-04 6.05E-07 CDF Transient - 2 abandonment and failure for the operators to successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting RMS cabinets I and II, panel 1RCS1, and the Incore Detector Panel. Dominant core U1-MCR-FS-TRAN Main Control Room -

1.17% damage sequences involve MCR abandonment and failure for 8.34E-04 7.25E-04 6.05E-07 CDF Transient - 1 the operators to successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting panels 2CVCS2, 2PLP and 2SD.

U1-MCR-FS-TRAN Main Control Room - Dominant core damage sequences involve MCR 1.17% 8.34E-04 7.25E-04 6.05E-07 CDF Transient - 3 abandonment and failure for the operators to successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting panels 2PLP and 2SD and 2B1 Protection Set II and III. Dominant core damage sequences U1-MCR-FS-TRAN Main Control Room -

1.17% involve MCR abandonment and failure for the operators to 8.34E-04 7.25E-04 6.05E-07 CDF Transient - 4 successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting panels 2SD, 2B1 Protection Set II and III and 2R1 Protection Set I and IV. Dominant core U1-MCR-FS-TRAN Main Control Room -

1.17% damage sequences involve MCR abandonment and failure for 8.34E-04 7.25E-04 6.05E-07 CDF Transient - 5 the operators to successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting panels Protection Set I and IV and Panel 1SD. Dominant core damage sequences involve U1-MCR-FS-TRAN Main Control Room -

1.17% MCR abandonment and failure for the operators to 8.34E-04 7.25E-04 6.05E-07 CDF Transient - 10 successfully perform alternate shutdown from outside the MCR.

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Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-1 Fire Initiating Events for Unit 1 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF MCR transient fire impacting the Incore Detector Panel and Nuclear Instrumentation Protection Channel III. Dominant U1-MCR-FS-TRAN Main Control Room -

1.17% core damage sequences involve MCR abandonment and 3.31E-05 1.83E-02 6.05E-07 CDF Transient - 11 failure for the operators to successfully perform alternate shutdown from outside the MCR.

MCR transient fire impacting the Incore Detector Panel and Nuclear Instrumentation Protection Channels I, II, III, and IV.

U1-MCR-FS-TRAN Main Control Room -

1.17% Dominant core damage sequences involve MCR 8.34E-04 7.25E-04 6.05E-07 CDF Transient - 12 abandonment and failure for the operators to successfully perform alternate shutdown from outside the MCR.

Full compartment burn of FA 31; initiator results in loss of 2RY transformer, damage to cables supporting all power sources to Unit 1 4kV Bus 16 and the CT-11 offsite supply to Bus 15; loss A Train Hot Shutdown of Cooling Water (CL) header B and Train B AFW; dominant Panel & Air U1FDS-31 1.11% sequences include failure of the AFW supply to Unit 1 SGs 2.19E-04 2.62E-03 5.75E-07 Compressor/Aux.

(due to spurious closure of 11 AFW pump discharge MOVs Feedwater Pump Room and operator failure to re-open them, or failure of the operator to manually start AFW), and failure of operator action to initiate RCS bleed and feed cooling.

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Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-2 Fire Initiating Events for Unit 1 LERF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution CLERP IF LERF U1-MCR-FS-TRAN-15-LERF Main Control Room - Transient - 15 19.65% 8.38E-04 7.25E-04 6.07E-07 U1-MCR-FS-TRAN-21-LERF Main Control Room - Transient - 21 19.57% 8.34E-04 7.25E-04 6.05E-07 U1FDS-8GRP-FA69-L Turbine Building Ground Floor & Mezzanine Floors Unit 1 695, 715 5.53% 6.43E-06 2.66E-02 1.71E-07 U1-MCR-FS-EC-14-LERF Main Control Room - Electrical Cabinet 1PLP 4.75% 1.19E-03 1.23E-04 1.47E-07 U1FDS-22-L 480V Safeguards Switchgear (Bus 121) 715 3.53% 8.52E-05 1.28E-03 1.09E-07 U1FDS-20-L Unit 1 4.16 KV Safeguards Swgr, (Bus 16) 715 2.40% 8.31E-05 8.94E-04 7.43E-08 B Train Hot Shutdown Panel & Air Compressor/Aux Feedwater U1FDS-32-L 1.91% 1.36E-05 4.35E-03 5.90E-08 Room 695 U1FDS-18-1077-00-L Relay and Cable Spreading Room - 1077 1.24% 1.17E-03 3.28E-05 3.82E-08 U1FDS-18-1003-00-L Relay and Cable Spreading Room - 1003 1.22% 1.15E-03 3.28E-05 3.76E-08 U1FDS-18-1004-00-L Relay and Cable Spreading Room - 1004 1.22% 1.15E-03 3.28E-05 3.76E-08 U1FDS-18-1032-00-L Relay and Cable Spreading Room - 1032 1.22% 1.15E-03 3.28E-05 3.76E-08 U1FDS-18-1002-00-L Relay and Cable Spreading Room - 1002 1.18% 2.79E-05 1.31E-03 3.66E-08 PINGP Page W-12 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-3 Fire Initiating Events for Unit 2 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF Full compartment burn of FA 70; initiator results in damage to cables supporting normal offsite supply to Unit 2 4kV Bus 25 (2RY transformer), loss of both Bus 25 and 26 load sequencers and loss of the 22 AFW pump; dominant Turbine Building Ground sequences include random failure of 21 AFW pump (or U2FDS-8GRP-FA70 Floor & Mezzanine Floors 5.18% 1.19E-04 2.85E-02 3.38E-06 operator failure to restore offsite power to Bus 25 via the CT12 Unit 2 695, 715 source) with failure of operator action to cross-tie 12 AFW pump to Unit 2 (or random failure of 12 AFW pump), followed by failure of operator action to initiate RCS bleed and feed cooling.

Fire initiated in MCR Panel 2PLP that is successfully suppressed but that fails all panel equipment; includes failure U2-MCR-FS-EC Main Control Room - of SG pressure instrumentation supporting AFW manual start 4.82% 2.56E-02 1.23E-04 3.14E-06 CDF Electrical Cabinet - 10 and control; core damage occurs with operator failure to initiate bleed and feed RCS cooling or to perform transfer to high head recirculation.

Full compartment burn of 58GRP-004; initiator results in damage to cables supporting all AC sources to Unit 2 4kV Bus Aux Building Ground U2FDS-58GRP-004 3.68% 25, all offsite AC sources to 4kV Bus 26, and 22 RHR pump; 3.63E-03 6.61E-04 2.40E-06 Floor - 004 dominant sequences include random failure of 22 AFW pump (or operator failure to manually initiate AFW).

Full compartment burn of FC 118; initiator results in loss of Unit 2 4kV Bus 26, all offsite AC sources to 4kV Bus 25, and loss of 21 RHR train; dominant sequences include random failure of 21 AFW pump (or operator failure to manually initiate AFW) together with operator failure to initiate RCS bleed and 4KV Bus 26; MCC 2TA2 U2FDS-118 3.53% feed cooling, or D5 EDG failure with failure of the operators to 1.93E-03 1.19E-03 2.30E-06 Room provide power to Bus 25 through the bus-tie to Unit 1 Bus 15 (SBO) and failure of either operator action to locally control level in the SGs prior offsite power recovery, or failure of the RCP shutdown seal followed by failure to trip the RCPs leading to a large, unrecoverable RCP seal LOCA.

PINGP Page W-13 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-3 Fire Initiating Events for Unit 2 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF T/G oil or H2 fire with failure of fire detection or suppression resulting in catastrophic failure of the turbine and loss of all credited equipment in the Turbine Building (8GRP); initiator causes loss of cables and other support equipment leading to Unit 1 and Unit 2 Turbine loss of all sources to all 4kV AC buses (EDG D5 remains U2FDS-8GRP-ALL Buildings El. 679', 695', 3.19% 1.46E-04 1.42E-02 2.08E-06 available to repower Bus 25 via manual operator action), and 715' loss of the 22 turbine-driven AFW pump. Dominant sequences include failure of operator action to re-power Bus 25 from D5 (SBO) leading to an unrecoverable RCP seal LOCA.

Full compartment burn of 59GRP-053; initiator results in loss of 2RY transformer, OCT failures of Bus 26 breakers for 22 RHR, SI and CC pumps, D6 EDG and bus-tie breaker to Bus 16; failure of both pressurizer PORVs open function, and loss Aux Building Mezzanine U2FDS-59GRP-053 2.76% of 22 AFW pump; dominant sequences include random failure 6.87E-03 2.62E-04 1.80E-06 Level - 053 of 21 AFW pump (or operator failure to manually initiate AFW) and failure of operator action to locally cross-tie the 12 AFW pump to Unit 2 (or random failures of the 12 AFW pump) or common-cause failure of the 12 and 21 AFW pumps.

Full compartment burn of FC 22; initiator results in loss of 4kV AC Buses 25 and 26 load sequencers, loss of control power to Bus 26, loss of non-safeguards 4kV buses 21, 22, 23, and 24, as well as loss of 22 AFW pump and loss of control power for 480V Safeguards starting the D6 EDG and 22 CL pump. Dominant core U2FDS-22 2.68% 1.37E-03 1.28E-03 1.75E-06 Switchgear (Bus 121) damage sequences involve failure of either the operators to manually start the 21 AFW pump, or failure of the pump to start or run, together with failure of the operator action to either to initiate bleed and feed RCS cooling or to perform transfer to high head recirculation.

MCR transient fire impacting Unit 2 AFW system and pressurizer PORVs. Dominant core damage sequences involve MCR abandonment and failure for the operators to U2-MCR-FS-TRAN Main Control Room - successfully perform alternate shutdown from outside the 2.36% 2.12E-03 7.25E-04 1.54E-06 CDF Transient - 19 MCR, or successful suppression of the fire (precluding MCR abandonment) but failure of operator action to cross-tie the 12 motor-driven AFW pump to Unit 2 (or random failures of the 12 AFW pump).

PINGP Page W-14 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-3 Fire Initiating Events for Unit 2 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF Full compartment burn of FC 80; initiator results in loss of safeguards 480V AC Buses 111 and 112, loss of the 4kV AC Bus 25 and 26 load sequencers, unavailability of the Bus 25 to Bus 15 bus-tie due to OCT trips, and loss of non-safeguards 480V Safeguards U2FDS-80 1.93% 4kV buses 21, 22, 23, and 24, as well as loss of the 12 CL 9.55E-04 1.32E-03 1.26E-06 Switchgear (Bus 111) pump. Dominant sequences include consequential loss of offsite power (SBO), where AFW is successful but offsite power is not recovered in time to prevent core uncovery and core damage.

Full compartment burn of FC 101GRP; initiator results in loss of all sources of power to safeguards 4kV AC Bus 25 except the preferred source (2RY), loss of the Bus 25 load sequencer, loss of most safeguards loads on Bus 25 and the bus-tie to Bus 15 due to OCT trips, and loss of safeguards 480V buses 211 and 212. Dominant sequences include failure of either the operators to manually start the 22 AFW D5 Diesel Generator pump, or failure of the pump to start or run, together with U2FDS-101GRP 1.67% 4.24E-04 2.57E-03 1.09E-06 Rooms failure of the operator action to either to initiate bleed and feed RCS cooling or to perform transfer to high head recirculation.

Other risk significant sequences include failure of the operators to manually start the 22 CC pump (auto-start not credited in the Fire PRA), with pressurizer PORV lift following the initial plant transient and failure to reseat resulting in an unrecoverable small LOCA; and random failures of 480V Bus 221.

Full compartment burn of FC 59GRP-014; initiator results in loss of 2RY transformer, D6 source to safeguards 4kV AC Bus 26, loss of most safeguards loads on Bus 26 and the bus-tie to Bus 16 due to OCT trips, loss of safeguards 480V MCCs 2A2, Aux Building Mezzanine 2KA2 and 2LA2, failure of the open function for both U2FDS-59GRP-014 1.66% 3.29E-02 3.28E-05 1.08E-06 Level - 014 pressurizer PORVs, and loss of the AFW pump supply to the Unit 2 SGs due to instrumentation failures. Dominant sequences include failure of either the operators to manually cross-tie the 12 AFW pump to the Unit 2 SGs, or random failures of the pump to start or run.

PINGP Page W-15 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-3 Fire Initiating Events for Unit 2 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF Full compartment burn of FC 59GRP-051; initiator results in loss of 2RY transformer, D6 source to safeguards 4kV AC Bus 26, loss of most safeguards loads on Bus 26 and the bus-tie to Bus 16 due to OCT trips, loss of safeguards 480V MCCs 2A2, 2KA2 and 2LA2, failure of the open function for pressurizer Aux Building Mezzanine U2FDS-59GRP-051 1.62% PORV CV-31233, loss of 21 RWST instrumentation, and loss 3.23E-02 3.28E-05 1.06E-06 Level - 051 of the AFW pump supply to the Unit 2 SGs due to instrumentation failures. Dominant sequences include failure of either the operators to manually cross-tie the 12 AFW pump to the Unit 2 SGs, or random failures of the pump to start or run.

Full compartment burn of FDS-58GRP-002; initiator results in loss of all sources of power to safeguards 4kV AC Bus 25 and the 2RY transformer, loss of the Bus 25 load sequencer, loss of most safeguards loads on Bus 25 and the bus-tie to Bus 15 due to OCT trips, loss of safeguards 480V buses 211 and 212, Aux Building Ground U2FDS-58GRP-002 1.58% and loss of both pressurizer PORVs. Dominant sequences 1.11E-03 9.24E-04 1.03E-06 Floor - 002 include failure of either the operators to manually start the 22 AFW pump, or failure of the pump to start or run, together with failure of the operator action to manually cross-tie the 12 AFW pump to the Unit 2 SGs (or random failures of the 12 AFW pump).

Full compartment burn of FC 102GRP; initiator results in loss of all sources of power to safeguards 4kV AC Bus 26 , loss of the Bus 26 load sequencer, loss of most safeguards loads on Bus 26 and the bus-tie to Bus 16 due to OCT trips, and loss of safeguards 480V buses 221 and 222. Dominant sequences include failure of either the operators to manually initiate AFW, D6 Diesel Generator together with failure of the operator action to either to initiate U2FDS-102GRP 1.52% 3.63E-04 2.73E-03 9.91E-07 Rooms bleed and feed RCS cooling or to perform transfer to high head recirculation. Other risk significant sequences include failure of the operators to manually start the 21 CC pump (auto-start not credited in the Fire PRA), with pressurizer PORV lift following the initial plant transient and failure to reseat resulting in an unrecoverable small LOCA; and random failures of 480V Bus 211.

PINGP Page W-16 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-3 Fire Initiating Events for Unit 2 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF Full compartment burn of FC 59GRP-073; initiator results in loss of 2RY transformer, loss of D6 source to safeguards 4kV AC Bus 26 and most safeguards loads on Bus 26 and the bus-tie to Bus 16 due to OCT trips, loss of safeguards 480V MCCs Aux Building Mezzanine 2A2, 2KA2 and 2LA2, failure of the open function for one U2FDS-59GRP-073 1.50% 4.55E-03 2.15E-04 9.79E-07 Level - 073 pressurizer PORV (CV-31233), and loss of the 22 AFW pump supply to the Unit 2 SGs due to instrumentation failures.

Dominant sequences include failure of either the operators to manually cross-tie the 12 AFW pump to the Unit 2 SGs, or random failures of the pump to start or run.

Full compartment burn of FC 28; initiator results in a loss of the 1RY and 2RY transformers supply to safeguards 4kV buses on both units, as well as the loss of non-safeguards 4kV buses 13, 14, 23, and 24. Dominant sequences include failure U2FDS-28 Yardgroup 1.48% 3.71E-05 2.61E-02 9.68E-07 of the operators to manually start AFW and to cross-tie to the Unit 1 (12) motor-driven AFW pump (or random failures of 12 MDAFWP occur), and the operators fail to successfully initiate bleed and feed RCS cooling.

Full compartment burn of 70GRP-1; initiator results in loss of 2RY transformer, loss of both Bus 25 and 26 load sequencers, loss of control power to 4kV safeguards Bus 26 and D6 diesel generator, and loss of 22 AFW pump; dominant sequences Turbine Building - include random failure of 21 AFW pump (or operator failure to U2FDS-8GRP-70GRP-1 1.39% 9.88E-05 9.16E-03 9.05E-07 70GRP-1 restore offsite power to Bus 25 via the CT12 source) with failure of operator action to cross-tie 12 AFW pump to Unit 2 (or random failure of 12 AFW pump), followed by failure of operator action to initiate RCS bleed and feed cooling, or random failures of the SI system or RCS PORVs.

Full compartment burn of FC 110; initiator results in loss of Unit 2 4kV Bus 26, all offsite AC sources to 4kV Bus 25, and loss of 21 RHR train; dominant sequences include random failure of 21 AFW pump (or operator failure to manually initiate D6 Normal MCC & Cable AFW) together with operator failure to initiate RCS bleed and U2FDS-110 Tray Area (Grounding 1.38% feed cooling, or D5 EDG failure with failure of the operators to 1.80E-03 4.98E-04 8.97E-07 Cabinet) provide power to Bus 25 through the bus-tie to Unit 1 Bus 15 (SBO) and failure of either operator action to locally control level in the SGs prior offsite power recovery, or failure of the RCP shutdown seal followed by failure to trip the RCPs leading to a large, unrecoverable RCP seal LOCA.

PINGP Page W-17 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-3 Fire Initiating Events for Unit 2 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF Full compartment burn of FC 59GRP-008; initiator results in loss of 2RY transformer, D6 source to safeguards 4kV AC Bus 26, loss of most safeguards loads on Bus 26 and the bus-tie to Bus 16 due to OCT trips, loss of safeguards 480V MCCs 2A2, Aux Building Mezzanine U2FDS-59GRP-008 1.33% 2KA2 and 2LA2, failure of the open function for one 2.64E-02 3.28E-05 8.66E-07 Level - 008 pressurizer PORV (CV-31233), and loss of the 22 AFW pump.

Dominant sequences include failure of either the operators to manually cross-tie the 12 AFW pump to the Unit 2 SGs, or random failures of the pump to start or run.

Fire initiated in Relay Room 120V AC Panel 212 that is successfully suppressed (incipient detection and manual suppression success) but that fails all panel equipment; Relay and Cable initiator fails SG pressure instrumentation supporting AFW U2FDS-18-1088-00 1.25% 2.50E-02 3.28E-05 8.19E-07 Spreading Room - 1088 manual start and control (but only one channel each, AFW remains available); dominant core damage sequences involve operator failure to initiate bleed and feed RCS cooling or transfer to high head recirculation.

MCR transient fire impacting all offsite power sources to 4kV buses 25 and 26, bus sequencers and D5 and D6 EDGs; U2-MCR-FS-TRAN Main Control Room - overcurrent trips fail bus cross-tie from Unit 1 4kV buses 1.25% 1.13E-03 7.25E-04 8.17E-07 CDF Transient - 21 (SBO). Dominant core damage sequences involve MCR abandonment and failure for the operators to successfully perform alternate shutdown from outside the MCR.

Fire initiated in Relay Room Panel 2AP1 that is successfully suppressed (incipient detection and manual suppression success) but that fails all panel equipment; initiator fails SG Relay and Cable U2FDS-18-1031-00 1.23% pressure instrumentation supporting AFW manual start and 2.46E-02 3.28E-05 8.05E-07 Spreading Room - 1031 control; dominant core damage sequences involve operator failure to initiate bleed and feed RCS cooling or transfer to high head recirculation.

Fire initiated in Relay Room Panel AC24 that is successfully suppressed (incipient detection and manual suppression success) but that fails all panel equipment; initiator fails SG Relay and Cable U2FDS-18-1068-00 1.23% pressure instrumentation supporting AFW manual start and 2.46E-02 3.28E-05 8.05E-07 Spreading Room - 1068 control; dominant core damage sequences involve operator failure to initiate bleed and feed RCS cooling or transfer to high head recirculation.

PINGP Page W-18 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-3 Fire Initiating Events for Unit 2 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF Full compartment burn of FC 122; initiator results in loss of Unit 2 480V Buses 221 and 222, 125V DC Panel 22, D6 EDG source to 4kV Bus 26, and 22 AFW pump. Dominant sequences include failure of either the operators to manually start 21 AFW pump, together with failure of the operator action to either to initiate bleed and feed RCS cooling or to perform U2FDS-122 480V Bus 221/222 Room 1.22% 3.44E-04 2.32E-03 7.97E-07 transfer to high head recirculation. Other risk significant sequences include failure of the operators to manually start CC flow (auto-start not credited in the Fire PRA), with pressurizer PORV lift following the initial plant transient and failure to reseat resulting in an unrecoverable small LOCA; and random failures of 480V Bus 211.

Full compartment burn of FC 59GRP-013; initiator results in loss of 2RY transformer, D6 source to safeguards 4kV AC Bus 26, loss of most safeguards loads on Bus 26 and the bus-tie to Bus 16 due to OCT trips, loss of safeguards 480V MCCs 2A2, Aux Building Mezzanine U2FDS-59GRP-013 1.17% 2KA2 and 2LA2, failure of the open function for both 1.16E-02 6.56E-05 7.64E-07 Level - 013 pressurizer PORVs, and loss of the 22 AFW pump. Dominant sequences include failure of either the operators to manually cross-tie the 12 AFW pump to the Unit 2 SGs, or random failures of the pump to start or run.

Full compartment burn of FC 59GRP-019; initiator results in loss of 2RY transformer, D6 source to safeguards 4kV AC Bus 26, loss of most safeguards loads on Bus 26 and the bus-tie to Bus 16 due to OCT trips, loss of safeguards 480V MCCs 2A2, Aux Building Mezzanine U2FDS-59GRP-019 1.11% 2KA2 and 2LA2, failure of the open function for one 2.20E-02 3.28E-05 7.22E-07 Level - 019 pressurizer PORV (CV-31233), and loss of the 22 AFW pump.

Dominant sequences include failure of either the operators to manually cross-tie the 12 AFW pump to the Unit 2 SGs, or random failures of the pump to start or run.

Full compartment burn of FC 59GRP-048; initiator results in loss of 2RY transformer, D6 source to safeguards 4kV AC Bus 26, loss of most safeguards loads on Bus 26 and the bus-tie to Bus 16 due to OCT trips, loss of safeguards 480V MCCs 2A2, Aux Building Mezzanine U2FDS-59GRP-048 1.08% 2KA2 and 2LA2, failure of the open function for one 3.27E-03 2.15E-04 7.02E-07 Level - 048 pressurizer PORV (CV-31233), and loss of the 22 AFW pump.

Dominant sequences include failure of either the operators to manually cross-tie the 12 AFW pump to the Unit 2 SGs, or random failures of the pump to start or run.

PINGP Page W-19 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-3 Fire Initiating Events for Unit 2 CDF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution Risk insights CCDP IF CDF MCR transient fire impacting Unit 2 Charging pumps and spurious operation of SI MOVs, failing high head recirculation.

U2-MCR-FS-TRAN Main Control Room -

1.02% Dominant core damage sequences involve MCR 9.13E-04 7.25E-04 6.62E-07 CDF Transient - 18 abandonment and failure for the operators to successfully perform alternate shutdown from outside the MCR.

PINGP Page W-20 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-4 Fire Initiating Events for Unit 2 LERF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution CLERP IF LERF U2-MCR-FS-TRAN-21-LERF Main Control Room - Transient - 21 10.30% 8.59E-04 7.25E-04 6.23E-07 U2-MCR-FS-TRAN-15-LERF Main Control Room - Transient - 15 10.10% 8.43E-04 7.25E-04 6.11E-07 U2FDS-59GRP-053-L Aux Building Mezzanine Level - 053 4.56% 1.05E-03 2.62E-04 2.76E-07 U2-MCR-FS-EC-10-LERF Main Control Room - Electrical Cabinet 2PLP 4.07% 2.00E-03 1.23E-04 2.46E-07 U2FDS-8GRP-FA70-L Turbine Building Ground Floor & Mezzanine Floors Unit 2 695, 715 3.47% 7.47E-06 2.81E-02 2.10E-07 U2FDS-58GRP-004-L Aux Building Ground Floor - 004 3.06% 2.80E-04 6.61E-04 1.85E-07 U2FDS-59GRP-014-L Aux Building Mezzanine Level - 014 2.76% 5.09E-03 3.28E-05 1.67E-07 U2FDS-59GRP-051-L Aux Building Mezzanine Level - 051 2.73% 5.03E-03 3.28E-05 1.65E-07 U2FDS-8GRP-ALL-L Turbine Deck (Units 1 & 2) 2.68% 1.14E-05 1.42E-02 1.62E-07 U2FDS-59GRP-008-L Aux Building Mezzanine Level - 008 2.22% 4.09E-03 3.28E-05 1.34E-07 U2FDS-118-L 4KV Bus 26; MCC 2TA2 Room 718 2.02% 1.03E-04 1.19E-03 1.22E-07 U2FDS-22-L 480V Safeguards Switchgear (Bus 121) 715 1.98% 9.38E-05 1.28E-03 1.20E-07 U2FDS-80-L 480V Safeguard Switchgear Room (Bus 111) 715 1.97% 9.02E-05 1.32E-03 1.19E-07 U2FDS-59GRP-013-L Aux Building Mezzanine Level - 013 1.93% 1.78E-03 6.56E-05 1.17E-07 U2-MCR-FS-TRAN-19-LERF Main Control Room - Transient - 19 1.88% 1.57E-04 7.25E-04 1.14E-07 U2FDS-59GRP-019-L Aux Building Mezzanine Level - 019 1.85% 3.41E-03 3.28E-05 1.12E-07 U2FDS-59GRP-048-L Aux Building Mezzanine Level - 048 1.79% 5.02E-04 2.15E-04 1.08E-07 U2FDS-59GRP-060-L Aux Building Mezzanine Level - 060 1.57% 1.15E-04 8.23E-04 9.49E-08 U2FDS-59GRP-047-L Aux Building Mezzanine Level - 047 1.29% 3.64E-04 2.15E-04 7.82E-08 PINGP Page W-21 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-4 Fire Initiating Events for Unit 2 LERF Representing > 1% Contribution to the Calculated Fire Risk Scenario Description Contribution CLERP IF LERF U2FDS-58GRP-002-L Aux Building Ground Floor - 002 1.24% 8.13E-05 9.24E-04 7.51E-08 U2FDS-59GRP-073-L Aux Building Mezzanine Level - 073 1.24% 3.49E-04 2.15E-04 7.51E-08 U2FDS-101GRP-L D5 Diesel Generator Rooms 1.16% 2.72E-05 2.57E-03 7.00E-08 U2FDS-8GRP-70GRP-1-L Turbine Building - 70GRP-1 1.14% 1.95E-05 3.53E-03 6.90E-08 U2FDS-102GRP-L D6 Diesel Generator Rooms 1.14% 2.52E-05 2.73E-03 6.87E-08 U2FDS-18-1088-00-L Relay and Cable Spreading Room - 1088 1.06% 1.95E-03 3.28E-05 6.39E-08 U2FDS-18-1031-00-L Relay and Cable Spreading Room - 1031 1.04% 1.92E-03 3.28E-05 6.29E-08 U2FDS-18-1068-00-L Relay and Cable Spreading Room - 1068 1.04% 1.92E-03 3.28E-05 6.29E-08 U2FDS-59GRP-062-L Aux Building Mezzanine Level - 062 1.02% 1.63E-04 3.79E-04 6.16E-08 PINGP Page W-22 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-5 PINGP Unit 1 Fire Area Risk Summary Fire NFPA 805 VFDR Fire Risk Eval Area Description Fire Area CDF/LERF RAs Additional Risk of RAs Area Basis (Yes/No) CDF/LERF 01 Containment Unit 1 4.2.4.2 1.32E-07 / 4.24E-09 Yes No N/A N/A Ventilation Fan Room, Units 1 &

02 4.2.4.2 1.71E-07 / 3.80E-09 Yes Yes 1.71E-07 / 3.80E-09 1.71E-07 / 3.80E-09 2

03 Water Chiller Room 4.2.3.2 2.78E-08 / 6.51E-10 No No N/A N/A 04 Fuel Handling Area 4.2.3.2 2.48E-07 / 6.86E-09 No No N/A N/A 05 Old Administration Building 4.2.3.2 screened No No N/A N/A Old Administration Building, 06 4.2.3.2 / No No N/A N/A HVAC Equipment Area Old Administration Building, 07 4.2.3.2 screened No No N/A N/A Office Area 08 Turbine Building 4.2.3.2 7.82E-06 / 2.68E-07 No No N/A N/A Train A Event Monitoring 10 4.2.4.2 1.24E-07 / 4.34E-09 Yes Yes 1.24E-07 / 4.34E-09 1.24E-07 / 4.34E-09 Equipment Room Unit 1 Normal Switchgear &

11 4.2.3.2 2.21E-07 / 6.33E-09 No No N/A N/A Control Rod Drive Room 12 OSC Room 4.2.3.2 1.25E-08 / 3.34E-10 No No N/A N/A 13 Control Room 4.2.4.2 2.00E-05 / 1.87E-06 Yes Yes 8.03E-06 / 8.36E-07 8.03E-06 / 8.36E-07 14 Working Material, Lunch Room 4.2.3.2 / No No N/A N/A 15 Access Control 4.2.3.2 9.30E-08 / 3.46E-09 No No N/A N/A Train B Event Monitoring 16 4.2.3.2 2.06E-08 / 1.89E-10 No No N/A N/A Equipment Room Unit 2 Normal Switchgear Room 17 4.2.3.2 1.12E-07 / 2.75E-09 No No N/A N/A

& Control Rod Drive Room PINGP Page W-23 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-5 PINGP Unit 1 Fire Area Risk Summary Fire NFPA 805 VFDR Fire Risk Eval Area Description Fire Area CDF/LERF RAs Additional Risk of RAs Area Basis (Yes/No) CDF/LERF 18 Relay & Cable Spreading Room 4.2.4.2 4.69E-06 / 2.09E-07 Yes Yes 2.78E-08 / 2.04E-09 2.78E-08 / 2.04E-09 Unit 1 4.16kV Safeguards 20 4.2.4.2 1.97E-06 / 7.43E-08 Yes Yes / /

Switchgear (Bus 16) 480V Safeguards Switchgear 22 4.2.4.2 2.55E-06 / 1.09E-07 Yes Yes / /

(Bus 121) 24 Oil Storage Area 4.2.3.2 screened No No N/A N/A 25 Diesel Generator 1 Room 4.2.3.3 1.37E-07 / 4.76E-09 Yes No N/A N/A 26 Diesel Generator 2 Room 4.2.3.2 1.12E-07 / 3.84E-09 No No N/A N/A Water Conditioning Equipment 27 4.2.3.2 9.91E-08 / 2.29E-09 No No N/A N/A Area 28 Transformers 4.2.3.2 9.19E-07 / 3.20E-08 No No N/A N/A Administration Building Elect &

29 4.2.4.2 5.58E-10 / 0 Yes Yes 5.58E-10 / 0 5.58E-10 / 0 Piping Room #1 Administration Building Elect &

30 4.2.4.2 7.15E-08 / 2.36E-09 Yes Yes 7.15E-08 / 2.36E-09 7.15E-08 / 2.36E-09 Piping Room #2 A Train Hot Shutdown Panel &

31 Air Compressor/Auxiliary 4.2.4.2 5.94E-07 / 2.54E-08 Yes Yes / /

Feedwater Room B Train Hot Shutdown Panel &

32 Air Compressor/Auxiliary 4.2.4.2 1.30E-06 / 5.93E-08 Yes Yes / /

Feedwater Room 33 Battery Room 11 4.2.3.2 3.11E-07 / 1.21E-08 No No N/A N/A 34 Battery Room 12 4.2.3.2 1.04E-06 / 4.49E-08 No No N/A N/A 35 Battery Room 21 4.2.3.2 3.36E-08 / 6.71E-10 No No N/A N/A 36 Battery Room 22 4.2.3.2 2.59E-07 / 1.06E-08 No No N/A N/A PINGP Page W-24 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-5 PINGP Unit 1 Fire Area Risk Summary Fire NFPA 805 VFDR Fire Risk Eval Area Description Fire Area CDF/LERF RAs Additional Risk of RAs Area Basis (Yes/No) CDF/LERF Unit 1 480V Normal Switchgear 37 4.2.4.2 1.44E-07 / 4.04E-09 Yes Yes 1.44E-07 / 4.04E-09 1.44E-07 / 4.04E-09 Room Unit 2 480V Normal Switchgear 38 4.2.4.2 9.93E-08 / 2.75E-09 Yes Yes 9.93E-08 / 2.75E-09 9.93E-08 / 2.75E-09 Room 41 Screenhouse (General Area) 4.2.3.2 / No No N/A N/A 41A Screenhouse (DDCLP Rooms) 4.2.4.2 3.33E-07 / 1.41E-08 Yes Yes 3.33E-07 / 1.41E-08 3.33E-07 / 1.41E-08 Screenhouse Basement Below 41B 4.2.4.2 6.47E-07 / 2.54E-08 Yes Yes / /

Grade Cooling Tower Equipment 46 4.2.3.2 2.70E-07 / 8.60E-09 No No N/A N/A House and Transformers 57 Gas House 4.2.3.2 screened No No N/A N/A Auxiliary Building Ground Floor 58 4.2.4.2 1.57E-07 / 6.75E-09 Yes Yes / /

Units 1 and 2 Auxiliary Building Mezzanine 59 4.2.4.2 3.50E-07 / 2.18E-08 No No N/A N/A Level Units 1 and 2 Aux Building Operating Level 60 4.2.3.2 1.65E-07 / 5.58E-09 No No N/A N/A Unit 1 Aux Building Anti C Clothing 61 4.2.3.2 Included in FA 4 - - - -

Area 63 Filter Room 4.2.3.2 1.39E-08 / 3.51E-10 No No N/A N/A Aux Building Low Level Decay 64 4.2.3.2 1.11E-08 / 2.86E-10 No No N/A N/A Area Unit 1 Spent Fuel Pool Heat 65 4.2.3.2 included in FA 60 - - - -

Exchanger & Pumps 66 D3 Lunch Room 4.2.4.2 2.12E-08 / 5.73E-10 Yes Yes / /

Containment and Containment 71 4.2.3.2 N/A N/A N/A N/A N/A Annulus Unit 2 PINGP Page W-25 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-5 PINGP Unit 1 Fire Area Risk Summary Fire NFPA 805 VFDR Fire Risk Eval Area Description Fire Area CDF/LERF RAs Additional Risk of RAs Area Basis (Yes/No) CDF/LERF Auxiliary Building Operating 75 4.2.3.2 1.56E-08 / 2.62E-10 No No N/A N/A Level Unit 2 Auxiliary Building Low Level 77 4.2.3.2 3.49E-09 / 5.36E-11 No No N/A N/A Decay Area Unit 2 78 Waste Gas Compressor Area 4.2.3.2 2.55E-08 / 5.33E-10 No No N/A N/A 480V Safeguard Switchgear 79 4.2.3.2 5.07E-08 / 1.56E-09 No No N/A N/A Room (Bus 112) 480V Safeguard Switchgear /

80 4.2.4.2 2.54E-07 / 8.48E-09 Yes Yes /

Room (Bus 111) 4.16KV Safeguard Switchgear /

81 4.2.4.2 9.22E-07 / 2.74E-08 Yes Yes /

Room (Bus 15) 480V Safeguard Switchgear 82 4.2.3.2 5.06E-08 / 1.55E-09 No No N/A N/A Room (Bus 122) 83 Operators Lounge 4.2.3.2 1.82E-08 / 5.50E-10 No No N/A N/A 84 Counting Room and Labs 4.2.3.2 1.94E-08 / 4.73E-10 No No N/A N/A Hold-up Tank 85 4.2.3.2 1.73E-08 / 1.86E-09 No No N/A N/A Area/Demineralizer Area 86 Intake Screenhouse 4.2.3.2 1.93E-07 / 5.45E-09 No No N/A N/A 89 Guard House 4.2.3.2 included in FA 28 - - - -

90 Emergency Generator Building 4.2.3.2 screened No No N/A N/A 92 Water Chiller Room Unit 2 4.2.3.2 2.93E-08 / 6.83E-10 No No N/A N/A Service Building/Computer 94 4.2.3.2 3.84E-07 / 1.04E-08 No No N/A N/A Room 97 D5 Diesel Generator Building 4.2.4.2 3.91E-07 / 1.14E-08 Yes Yes / /

98 D6 Diesel Generator Building 4.2.3.2 3.77E-07 / 1.09E-08 No No N/A N/A PINGP Page W-26 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-5 PINGP Unit 1 Fire Area Risk Summary Fire NFPA 805 VFDR Fire Risk Eval Area Description Fire Area CDF/LERF RAs Additional Risk of RAs Area Basis (Yes/No) CDF/LERF

1. 21 D5/D6 Fuel Oil Receiving 100 4.2.3.2 included in FA 28 - - - -

Tank (South of D6 Room)

Emergency Diesel Generator 3 121 4.2.3.2 included in FA 28 - - - -

& 4 Building 131 New Administration Building 4.2.3.2 screened No No N/A N/A Total 5.17E-05 / 3.09E-06 9.00E-06 / 8.69E-07 PINGP Page W-27 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-6 PINGP Unit 2 Fire Area Risk Summary Fire NFPA 805 VFDR Fire Risk Eval Area Description Fire Area CDF/LERF RAs Additional Risk of RAs Area Basis (Yes/No) CDF/LERF 01 Containment Unit 1 4.2.4.2 N/A N/A N/A N/A N/A Ventilation Fan Room, Units 1 &

02 4.2.4.2 1.31E-07 / 5.11E-09 Yes Yes 1.31E-07 / 5.11E-09 1.31E-07 / 5.11E-09 2

03 Water Chiller Room 4.2.3.2 2.80E-08 / 1.17E-09 No No N/A N/A 04 Fuel Handling Area 4.2.3.2 2.46E-07 / 1.14E-08 No No N/A N/A 05 Old Administration Building 4.2.3.2 screened - - - -

Old Administration Building, 06 4.2.3.2 / No No N/A N/A HVAC Equipment Area Old Administration Building, 07 4.2.3.2 screened - - - -

Office Area 08 Turbine Building 4.2.3.2 7.69E-06 / 5.19E-07 No No N/A N/A Train A Event Monitoring 10 4.2.4.2 2.35E-08 / 4.63E-10 Yes Yes 2.35E-08 / 4.63E-10 2.35E-08 / 4.63E-10 Equipment Room Unit 1 Normal Switchgear &

11 4.2.3.2 1.27E-07 / 5.08E-09 No No N/A N/A Control Rod Drive Room 12 OSC Room 4.2.3.2 1.26E-08 / 5.55E-10 No No N/A N/A 13 Control Room 4.2.4.2 2.09E-05 / 2.17E-06 Yes Yes 8.10E-06 / 9.00E-07 8.10E-06 / 9.00E-07 14 Working Material, Lunch Room 4.2.3.2 / No No N/A N/A 15 Access Control 4.2.3.2 2.95E-08 / 1.63E-09 No No N/A N/A Train B Event Monitoring 16 4.2.3.2 2.22E-08 / 4.47E-10 No No N/A N/A Equipment Room Unit 2 Normal Switchgear Room 17 4.2.3.2 3.22E-07 / 1.48E-08 No No N/A N/A

& Control Rod Drive Room PINGP Page W-28 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-6 PINGP Unit 2 Fire Area Risk Summary Fire NFPA 805 VFDR Fire Risk Eval Area Description Fire Area CDF/LERF RAs Additional Risk of RAs Area Basis (Yes/No) CDF/LERF 18 Relay & Cable Spreading Room 4.2.4.2 3.00E-06 / 2.18E-07 Yes Yes 2.81E-08 / 3.46E-09 2.81E-08 / 3.46E-09 Unit 1 4.16 KV Safeguards 20 4.2.4.2 4.29E-08 / 1.46E-09 Yes Yes / /

Switchgear, (Bus 16) 480V Safeguards Switchgear 22 4.2.4.2 1.75E-06 / 1.20E-07 Yes Yes / /

(Bus 121) 24 Oil Storage Area 4.2.3.2 screened - - - -

25 Diesel Generator 1 Room 4.2.3.3 7.61E-08 / 4.09E-09 Yes No N/A N/A 26 Diesel Generator 2 Room 4.2.3.2 7.51E-08 / 4.06E-09 No No N/A N/A Water Conditioning Equipment 27 4.2.3.2 8.47E-08 / 3.31E-09 No No N/A N/A Area 28 Transformers 4.2.3.2 9.68E-07 / 5.33E-08 No No N/A N/A Administration Building Elect &

29 4.2.4.2 5.13E-10 / 0 Yes Yes 5.13E-10 / 0 5.13E-10 / 0 Piping Room #1 Administration Building Elect &

30 4.2.4.2 5.36E-08 / 3.01E-09 Yes Yes 5.36E-08 / 3.01E-09 5.36E-08 / 3.01E-09 Piping Room #2 A Train Hot Shutdown Panel &

31 Air Compressor/Auxiliary 4.2.4.2 7.51E-07 / 5.00E-08 Yes Yes 9.95E-08 / 7.29E-09 9.95E-08 / 7.29E-09 Feedwater Room B Train Hot Shutdown Panel &

32 Air Compressor/Auxiliary 4.2.4.2 1.58E-07 / 1.08E-08 Yes Yes / /

Feedwater Room 33 Battery Room 11 4.2.3.2 2.76E-07 / 1.66E-08 No No N/A N/A 34 Battery Room 12 4.2.3.2 1.94E-08 / 5.49E-10 No No N/A N/A 35 Battery Room 21 4.2.3.2 2.83E-07 / 1.67E-08 No No N/A N/A 36 Battery Room 22 4.2.3.2 2.59E-07 / 1.85E-08 No No N/A N/A PINGP Page W-29 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-6 PINGP Unit 2 Fire Area Risk Summary Fire NFPA 805 VFDR Fire Risk Eval Area Description Fire Area CDF/LERF RAs Additional Risk of RAs Area Basis (Yes/No) CDF/LERF Unit 1 480V Normal Switchgear 37 4.2.4.2 1.26E-07 / 6.20E-09 Yes Yes 1.26E-07 / 6.20E-09 1.26E-07 / 6.20E-09 Room Unit 2 480V Normal Switchgear 38 4.2.4.2 8.33E-08 / 4.11E-09 Yes Yes 8.33E-08 / 4.11E-09 8.33E-08 / 4.11E-09 Room 41 Screenhouse (General Ara) 4.2.3.2 / No No N/A N/A 41A Screenhouse (DDCLP Rooms) 4.2.4.2 7.05E-08 / 2.66E-09 Yes Yes 7.05E-08 / 2.66E-09 7.05E-08 / 2.66E-09 Screenhouse Basement Below 41B 4.2.4.2 5.73E-08 / 1.68E-09 Yes Yes / /

Grade Cooling Tower Equipment 46 4.2.3.2 2.69E-07 / 1.42E-08 No No N/A N/A House and Transformers 57 Gas House 4.2.3.2 screened - - - -

Aux Building Ground Floor Units 58 4.2.4.2 3.54E-06 / 2.67E-07 Yes Yes / /

1 and 2 Auxiliary Building Mezzanine 59 4.2.4.2 1.29E-05 / 1.86E-06 Yes Yes / /

Level Units 1 and 2 Aux Building Operating Level 60 4.2.3.2 1.67E-08 / 4.50E-10 No No N/A N/A Unit 1 Aux Building Anti C Clothing 61 4.2.3.2 Included in FA 4 - - - -

Area 63 Filter Room 4.2.3.2 1.40E-08 / 5.93E-10 No No N/A N/A Aux Building Low Level Decay 64 4.2.3.2 1.10E-08 / 4.72E-10 No No N/A N/A Area Unit 1 693 Spent Fuel Pool Heat 65 4.2.3.2 included in FA 60 - - N/A N/A Exchanger & Pumps 66 D3 Lunch Room 4.2.4.2 1.57E-07 / 9.19E-09 Yes Yes / /

Containment and Containment 71 4.2.4.2 3.55E-08 / 2.06E-09 Yes No N/A N/A Annulus Unit 2 PINGP Page W-30 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-6 PINGP Unit 2 Fire Area Risk Summary Fire NFPA 805 VFDR Fire Risk Eval Area Description Fire Area CDF/LERF RAs Additional Risk of RAs Area Basis (Yes/No) CDF/LERF Auxiliary Building Operating 75 4.2.3.2 1.70E-07 / 1.01E-08 No No N/A N/A Level Unit 2 Auxiliary Building Low Level 77 4.2.3.2 3.53E-09 / 7.29E-11 No No N/A N/A Decay Area Unit 2 78 Waste Gas Compressor Area 4.2.3.2 2.60E-08 / 9.85E-10 No No N/A N/A 480V Safeguard Switchgear 79 4.2.3.2 3.08E-08 / 1.34E-09 No No N/A N/A Room (Bus 112) 480V Safeguard Switchgear 80 4.2.4.2 1.26E-06 / 1.19E-07 Yes Yes / /

Room (Bus 111) 4.16KV Safeguard Switchgear 81 4.2.4.2 3.93E-08 / 1.59E-09 Yes Yes / /

Room (Bus 15) 480V Safeguard Switchgear 82 4.2.3.2 3.08E-08 / 1.34E-09 No No N/A N/A Room (Bus 122) 83 Operators Lounge 4.2.3.2 1.83E-08 / 9.41E-10 No No N/A N/A 84 Counting Room and Labs 4.2.3.2 1.96E-08 / 7.94E-10 No No N/A N/A Hold-up Tank 85 4.2.3.2 1.13E-08 / 1.53E-09 No No N/A N/A Area/Demineralizer Area 86 Intake Screenhouse 4.2.3.2 1.94E-07 / 9.29E-09 No No N/A N/A 89 Guard House 4.2.3.2 included in FA 28 - - - -

90 Emergency Generator Building 4.2.3.2 screened - - - -

92 Water Chiller Room Unit 2 4.2.3.2 2.96E-08 / 1.23E-09 No No N/A N/A Service Building/Computer 94 4.2.3.2 3.86E-07 / 1.71E-08 No No N/A N/A Room 97 D5 Diesel Generator Building 4.2.4.2 2.35E-06 / 1.38E-07 Yes Yes / /

98 D6 Diesel Generator Building 4.2.3.2 5.19E-06 / 2.96E-07 No No N/A N/A PINGP Page W-31 (Revised)

Northern States Power - Minnesota Attachment W - Fire PRA Insights Table W-6 PINGP Unit 2 Fire Area Risk Summary Fire NFPA 805 VFDR Fire Risk Eval Area Description Fire Area CDF/LERF RAs Additional Risk of RAs Area Basis (Yes/No) CDF/LERF

1. 21 D5/D6 Fuel Oil Receiving 100 4.2.3.2 included in FA 28 - - - -

Tank (South of D6 Room)

Emergency Diesel Generator 3 121 4.2.3.2 included in FA 28 - - - -

& 4 Building 131 New Administration Building 4.2.3.2 screened - - - -

Total 6.51E-05 / 6.05E-06 8.72E-06 / 9.32E-07 Notes for Tables W-5 and W-6

1. Where screened appears in the Fire Area CDF/LERF column, it indicates that all fire compartments in the fire area were qualitatively screened per the methodology in Task 4 of NUREG/CR-6850.

2. The symbol designates CDF and LERF values that are insignificant because of their low numerical value. In most cases, the CDF and LERF values were not determined because the cutsets were below the truncation limit for quantification.

3. The CDF and LERF values for all recovery actions are included as part of the FRE CDF and LERF values. Thus, the column Additional risk of RAs shows the contribution of recovery actions to the FRE CDF and LERF values and is not a separate, extra risk. It can be seen that for some fire areas, the FRE CDF and LERF value is dominated by the additional risk of recovery actions, or can be attributed in its entirety to such recovery actions.

4. In a few cases, VFDRs were identified in a fire area that were resolved by proposed modifications. For these areas, an FRE was not quantified.

PINGP Page W-32 (Revised)