ML16351A210

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External Flooding Assessment Focused Evaluation. (Redacted)
ML16351A210
Person / Time
Site: Prairie Island  Xcel Energy icon.png
Issue date: 12/13/2016
From:
Northern States Power Company, Minnesota, Xcel Energy
To:
Office of Nuclear Reactor Regulation
Shared Package
ML16351A227 List:
References
L-PI-095
Download: ML16351A210 (23)
v • d • e


Text

L-Pl-16-095 NSPM ENCLOSURE 2 PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNITS 1 AND 2 Prairie Island External Flooding Assessment Focused Evaluation (REDACTED VERSION)

(22 pages to follow)

Xcel Energy Contract No. 00047588 Prairie Island External Flooding Assessment Focused Evaluation CLIENT APP.: N/A E.

BLACK & VEATCH Overland Park, KS Issued for Client Use DVR-180461-0 11/14/2016 SOT N/A SOT (RAR-180461-0004) 0028 NO. DATE DESCRIPTION ORN DES CHK APP FILE NUMBER 51.1000 REVIEW LEVEL N/A THIS DOCUMENT CONTAINS THIS DOCUMENT CONTAINS SAFETY-RELATED ITEMS SEISMIC CATEGORY I ITEMS (81 YES D NO ~YES D NO CLIENT DOCUMENT REFERENCE NUMBER TOTAL SHEETS PROJECT DOCUMENT NUMBER N/A 22 180461.51.1000-03

Prairie Island External Flooding Assessment Focused Evaluation Rev.a Table of Contents 1.0 EXECUTIVE

SUMMARY

..................................................................................................................... 2

2.0 BACKGROUND

.................................................................................................................................. 3

3.0 REFERENCES

......................................................................................................................................j4 4.0 TERMS AND DEFINITIONS ................................................................................................................ 6 5.0 FLOOD HAZARD PARAMETERS FOR UNBOUNDED MECHANISMS ................................................. 7 6.0 OVERALL SITE FLOODING RESPONSE ............................................................................................... 9

6.1 DESCRIPTION

OF OVERALL SITE FLOODING RESPONSE ............................................................................ 9 6.2

SUMMARY

OF PLANT MODIFICATIONS AND CHANGES .......................................................................... 10 7.0 FLOOD IMPACT ASSESSMENT ........................................................................................................ 11 7.1 LOCAL INTENSE PRECIPITATION ......................................................................................................... 11 7.1.1 Description of Flood lmpact ............................................................................................... 11 7.1.2 *Adequate APM Justification ............................................................................................... 16 7.1.3 Reliability of Flood Protection ........................................................................................... 18 7.1.4 Adequate Overall Site Response ........................................................................................ 19

8.0 CONCLUSION

.................................................................................................................................. 19 APPENDIX 1 ................................................................................................................................................. 20 Page 1of21

Prairie Island External Flooding Assessment Focused Evaluation Rev.a PRAIRIE ISLAND NUCLEAR GENERATING PLANT FLOODING FOCUSED EVALUATION

SUMMARY

1.0 EXECUTIVE

SUMMARY

The Prairie Island Nuclear Generating Plant (PINGP} has reevaluated its flooding hazard in accordance with the NRC's March 12, 2012, 10 CFR 50.54(f} request for information (RFI} (Reference 1}. The RFI was issued as part of implementing lessons learned from the Fukushima Dai-ichi accident; specifically, to address Recommendation 2.1 of the NRC's Near-Term Task Force report .. This information was submitted to NRC in a flood hazard reevaluation report (FHRR} on May 9, 2016, (Reference 2} as supplemented by letter dated September 29, 2016 (Reference 3}, and is provided in the Mitigating Strategies Flood Hazard Information (MSFHI} documented in NRC's "Interim Staff Response to Reevaluated Flood Hazards" letter dated October 17, 2016 (Reference 10}. No changes to the flooding analysis have been performed since the issuance of the MSFHI letter and this flooding analysis will serve as the input to this Focused Evaluation (FE}. There is one mechanism that was found to exceed the design basis flood level at the PINGP. This mechanism is listed below and addressed in this FE:

1. Local Intense Precipitation (LIP}

Associated effects (AE} and flood event duration (FED} parameters were assessed and submitted as a part of the FHRR. The FE affirms that during LIP events the site has effective flood protection through the determination of adequate Available Physical Margin (APM} and the reliability of protection features. The site does not require any human actions to protect Key SSCs so an evaluation of the overall site response was not necessary. This FE follows Path 2 of NEI 16-05, Rev. 1 (Reference 8}, and utilizes Appendix B for guidance for evaluating the site protection features. This submittal completes the actions related to External Flooding required by the March 12, 2012 10 CFR 50.54(f} letter.

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Prairie Island External Flooding Assessment Focused Evaluation Rev.a

2.0 BACKGROUND

On March 12, 2012, the NRC issued Reference 1 to request information associated with Near-Term Task Force (NTIF) Recommendation 2.1 for flooding. The RFI (Reference 1) directed licensees, in part, to submit a Flood Hazard Reevaluation Report {FHRR) to reevaluate the flood hazards for their sites using present-day methods and guidance used for early site permits and combined operating licenses. For the PINGP, Units 1 and 2, the FHRR was submitted on May 9, 2016 (Reference 2) and supplemented by letter dated September 29, 2016 {Reference 3).

Following the Commission's directive to NRC Staff in Reference 7, the NRC issued a letter to industry

{Reference 6) indicating that new guidance is being prepared to replace instructions in Reference 5 and provide for a "graded approach to flooding reevaluations" and "more focused evaluations of local intense precipitation and available physical margin in lieu of proceeding to an integrated assessment."

NEI prepared the new "External Flooding Assessment Guidelines" in NEI 16-05 (Reference 8), which was endorsed by the NRC in Reference 9. NEI 16-05 indicates that each flood-causing mechanism not bounded by the design basis flood (using only stillwater and/or wind-wave runup level) should follow one of the following five assessment paths:

  • Path 1: Demonstrate Flood Mechanism is Bounded Through Improve Realism
  • Path 2: Demonstrate Effective Flood Protection
  • Path 3: Demonstrate a Feasible Response to LIP
  • Path 4: Demonstrate Effective Mitigation
  • Path 5: Scenario Based Approach Non-bounded flood-causing mechanisms in Paths 1, 2, or 3 only require an FE to complete the actions related to external flooding required by the March 12, 2012, 10 CFR 50.54(f) letter. Mechanisms in Paths 4 or 5 require an Integrated Assessment.

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Prairie Island External Flooding Assessment Focused Evaluation Rev.a

3.0 REFERENCES

1. U.S. NuclearRegulatory Commission Letter, Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident; dated March 12, 2012.
2. NSPM Letter L-Pl-16-039, to the U.S. Nuclear Regulatory Commission, "Prairie Island Nuclear Generating Plant, Units 1 and 2, Response to March 12, 2012 Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 2, Flooding Hazard Reevaluation Report,"

dated May 9, 2016, (ADAMS Accession No. ML16133A041).

3. NSPM Letter L-Pl-16-076 to the U.S. Nuclear Regulatory Commission, "Prairie Island Nuclear Generating Plant, Units 1 and 2 - Supplement to the Response to March 12, 2012, Request for Information Enclosure 2, Recommendation 2.1, Flooding, Required Response 2, Flood Hazard Reevaluation Report," dated September 29, 2016, (ADAMS Accession No. ML16273A556).
4. U.S. Nuclear Regulatory Commission Letter, Supplemental Information Related to Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) regarding Flooding Hazard Reevaluations for Recommendation 2.1 of the Near Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated March 1, 2013.
5. U.S. Nuclear Regulatory Commission Letter, "Trigger Conditions For Performing An Integrated Assessment And Due Date For Response," dated December 3, 2012, (ADAMS Accession No. ML12326A912).
6. U.S. Nuclear Regulatory Commission Letter, "Coordination of Requests for Information Regarding Flooding Hazard Reevaluations and Mitigating Strategies for Beyond-Design-Basis External Events," dated September 1, 2015, (ADAMS Accession No. ML15174A257).
7. Commission Staff Requirements Memo (SRM), "SRM-COMSECY-14-0037: Integration of Mitigating Strategies for Beyond-Design-Basis External Events and the Reevaluation of Flooding Hazards," dated March 30, 2015, (ADAMS Accession No. ML15089A236}.
8. Nuclear Energy Institute (NEI), Report NEI 16-05 [Rev 1], External Flooding Assessment Guidelines, dated June 2016.
9. U.S. Nuclear Regulatory Commission, JLD-ISG-2016-01, Revision 1, Guidance for Activities Related to Near-Term Task Force Recommendation 2.1, Flooding Hazard Reevaluation; Focused Evaluation and Integrated Assessment, dated July 11, 2016.

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Prairie Island External Flooding Assessment Focused Evaluation Rev.a

10. U.S. Nuclear Regulatory Commission, Letter to Scott D. Northard, Northern States Power Company- Minnesota, "

Subject:

Prairie Island Nuclear Generator Plant, Units 1 and 2 -

Correction to Interim Staff Response to Reevaluated Flood Hazards Submitted in Response to 10 CFR 50.54(f) Information Request - Flood-Causing Mechanism Reevaluation (CAC Nos. MF7710 and MF7711)," Dated October 17, 2016, (ADAMS Accession No. ML16286A161).

11. Black & Veatch, "Local Intense PMP & Hydrology," Calculation 180461.51.1005, Revision 1.
12. NSPM, "Prairie Island Updated Safety Analysis Report," Revision 34P.
13. NSPM, Procedure AB-4, "Flood," Revision 50.
14. NSPM, Calculation ENG-ME-529, "Flood Barrier Leakage Criteria," Revision 0.
15. Black & Veatch, "D5/D6 Fuel Oil Tank Vault Free Volume," Calculation 180689.51.1016, Revision 0.
16. NSPM, Drawing NF-117027, "Fuel Oil Storage Vault Plans," Revision A.
17. Black & Veatch, "Evaluation of Structural Elements - Flood," Calculation 180461.51.1008, Revision 1.
18. NSPM, Calculation ENG-ME-448, "Auxiliary Building Flooding Analysis," Revision 1.
19. NSPM, Drawing NF-117023, "D5/D6 Bldg. - Architectural Door Schedule & Door Details,"

Revision B.

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Prairie Island External Flooding Assessment Focused Evaluation Rev.a 4.0 TERMS AND DEFINITIONS AE - Associated Effects AFW -Auxiliary ~eedwater APM -Available Physical Margin EOG - Emergency Diesel Generator FE - Focused Evaluation FED - Flood Event Duration FFE - Finished Floor Elevation FHRR - Flood Hazard Reevaluation Report FIAP - Flooding Impact Assessment Process FLEX- Diverse and flexible coping strategies covered by NRC order EA-12-049 Key SSC-A system Structure or Component relied upon to fulfill a Key Safety Function KSF - Key Safety function, i.e. core cooling, spent fuel pool cooling, or containment function.

LIP - Local Intense Precipitation MSA- Mitigating Strategies Assessment MSFHI - Mitigating Strategies Flood Hazard Information NITF - Near Term Task Force commissioned by the NRC to recommend actions following the Fukushima Dai-ichi accidents PINGP- Prairie Island Nuclear Generating Plant PMF- Probable Maximum Flood RFI - Request for Information RHR - Residual Heat Removal WSE-Water Surface Elevation Page 6 of 21

Prairie Island External Flooding Assessment Focused Evaluation Rev.a 5.0 FLOOD HAZARD PARAMETERS FOR UNBOUNDED MECHANISMS The NRC has completed the "Interim Staff Response to Reevaluated Flood Hazards" (Reference 10) which contains the Mitigating Strategies Flood Hazard Information (MSFHI) related to the PINGP's Flood Hazard Reevaluation Report (Reference 2). In Reference 10, the NRC states that:

"The NRC staff has concluded that the licensee's reevaluated flood hazards information, as summarized in the enclosure, is suitable for the assessment of mitigation strategies developed in response to Order EA-12-049 (i.e., defines the mitigating strategies flood hazard information described in guidance documents currently being finalized by the industry and NRC staff) for Prairie Island. Further, the NRC staff has concluded that the licensee's reevaluated flood hazar.d information is a suitable input for the other assessments associated with Near-Term Task Force Recommendation 2.1 'Flooding. 111 The enclosure to Reference 10 includes a summary of the current design basis and reevaluated flood hazard parameters, respectively. In Table 1 of the enclosure to Reference 10, the NRC lists the following flood-causing mechanisms for the design basis flood:

  • Local Intense Precipitation;
  • Streams and Rivers;
  • Failure of Dams and Onsite Water Control/Storage Structures;
  • Storm Surge;
  • Seiche;
  • Tsunami;
  • Ice Induced Flooding; and
  • Channel Migrations/Diversions.

In Table 2 of the enclosure to Reference 10, the NRC lists flood hazard information (specifically stillwater elevation and wind-wave runup elevation) for the following flood-causing mechanism that is not bounded by the design basis hazard flood level. This is provided below in Table 5-1. ,

Table 5-1 Reevaluated Flood Hazards for Flood-Causing Mechanisms for Use in the MSA Reevaluated Flood Mechanism Stillwater Elevation Waves/Run up Hazard Local Intense 695.4 ft NGVD29 Minimal 695.4 ft NGVD29 Precipitation Page 7 of 21

Prairie Island External Flooding Assessment Focused Evaluation Rev.a This is the reevaluated flood-causing mechanism that should be addressed in the external flooding assessment. The one non-bounding flood mechanism for the PINGP is described in detail in References 2 and 3, the FHRR submittals. Table 5-2 summarizes how the unbounded mechanism is addressed in this external flooding assessment:

Table 5-2 Approach for Evaluation of Non-Bounded Flood Mechanism Flood Mechanism Summary of Assessment Path 2 is pursued for the PINGP since permanent passive protection features are solely relied upon to 1 Local Intense Precipitation maintain KSFs (see FIAP Path Determination Table, Section 6.3.3 of NEI 16-05).

Page 8 of 21

Prairie Island External Flooding Assessment Focused Evaluation Rev.a 6.0 OVERALL SITE FLOODING RESPONSE

6.1 DESCRIPTION

OF OVERALL SITE FLOODING RESPONSE The LIP calculation for the PINGP is provided in Reference 11; which describes the inputs, assumptions, methodology, and results. Permanent protection features such as characterized topographic and man-made features that affected runoff from a LIP were modeled. The timelines for the cumulative precipitation and precipitation rates during the LIP are shown in Table 6.1-1. The precipitation rate is determined by dividing the change in cumulative precipitation by the change in time duration.

Table 6.1-1, Precipitation Cumulative Precipitation and Rates Time Cumulative Precipitation Rate Duration Precipitation (inches) (inches/hour) 5 min 4.6 55.2 15 min 7.3 16.2 30min 10.4 12.4 1 hr 13.4 6.0 6 hr 21.0 1.5 The period of inundation during the LIP varies throughout the site; however, at the location with the highest flood depth, it was estimated that water level would remain above finished floor elevation for 66 minutes (Reference 11). Once the flood waters recede below finished floor elevation, it would take approximately 5.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> for flood waters to completely recede from areas near the critical doors, which is approximately within 30 minutes after the end of the 6-hr storm LIP event.

The PINGP is designed for a Probable Maximum Flood (PMF) from the Mississippi River with a flood water elevation up to 703.6 ft (Reference 12). The majority of the plant structures are capable of withstanding the PMF without protection measures being implemented; i.e., permanent passive protection. Selected actions are implemented in anticipation of a PMF to provide full protection. The water surface elevation during a PMF is much greater than during a LIP; thus, the permanent passive protection features are capable of withstanding a LIP. For the LIP, warning time is not credited.

Flood preparation measures for a PMF are implemented per procedure AB-4 (Reference 13). Specific measures are taken as part of Reference 13 for preparation for a flood from the Mississippi River. Due to absence of warning time the following actions would not be implemented for a LIP flood. Thus, the evaluation for the LIP focuses on these protection features credited for the PMF that would not be in place for the LIP.

  • Installation of flood bulkheads and sealing flood doors. As part of preparation for a PMF, flood waters entering the plant through doors are precluded by either sealing plant access doors, or installing bulkheads over the other access doors.
  • Installation of blind flanges on the D5/D6 fuel oil tank overflow lines. The tank overflow line is routed to the associated tank vault. This action precludes water from entering the fuel oil tanks for Emergency Diesel Generators D5 and D6 through the tank overflow line in the event that in leakage to the vault occurred during the PMF.

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Prairie Island External Flooding Assessment Focused Evaluation Rev.a The evaluation of the plant flood protection features for the LIP considers these differences; specifically, the impact of water intrusion at doors that would be protected during a PMF, the structural impacts of the hydraulic loads to doors that would be protected by the bulkheads, and the potential for water intrusion into the DS/06 Fuel Oil Tank Vaults.

6.2

SUMMARY

OF PLANT MODIFICATIONS AND CHANGES The PINGP has completed the flooding evaluations for the LIP. There are no remaining actions (plant modifications, procedural changes, or procurement activities) necessary to implement flood strategies described.

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Prairie Island External Flooding Assessment Focused Evaluation Rev.0 7.0 FLOOD IMPACT ASSESSMENT 7.1 LOCAL INTENSE PRECIPITATION 7.1.1 Description of Flood Impact As described in Section 6.1, the majority of the plant is passively protected for a PMF; which has a much higher flood elevation than the LIP. Therefore, these passive protection features are bounded for the LIP by the PMF. The exceptions are:

  • During a LIP the access doors to the plant structures may either be closed and not sealed or possibly open.
  • During a LIP the blind flanges would not be installed in the D5/D6 Fuel Oil Tank overflow lines.

Table 7.1-1 below summarizes Key SSCs and the minimum critical water elevation in each structure that could impact Key SSCs. There may be other Key SSCs located in the structure at higher elevations. To be conservative only the lowest elevation is considered.

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Prairie Island External Flooding Assessment Focused Evaluation Rev.a Table 7-1.1, Key SSCs and Associated Critical Elevation Critical Structure Key SSC Notes Elevation (ft)

Unit 1 Turbine Building Dl/D2 EDG Room 694.90 (1)

Unit 2 Turbine Building Dl/D2 EDG Room 694.90 (2)

Auxiliary Building RHR Pits 695.75 (3)

D5/D6 Building Fuel Oil Pump Motors 694.90 (4)

Screen house Safety Related Power Cables 694.90 (5)

D5/D6 Fuel Oil Tank Vault Fuel Oil Tanks 686.92 (6)

Notes:

(1) At elevation 694.90 ft, water could enter the Unit 1 Turbine Building. lnleakage would start to fill the condenser pit. The limiting water elevation in the Unit 1 condenser pit is where water could start to back-up into the 01 and 02 Room trenches at 693.83 ft in the Unit 1 condenser pit. The Unit 1 3

condenser pit can accommodate a total of 89,537 ft not including the sump pit (Reference 14) below elevation 693.83 ft.

(2) The Unit 2 condenser pit can accommodate a total of 101,672 ft3 below elevation 695 ft (Reference 14).

It is possible for water to leak from the Unit 2 Turbine Building into the Unit 1 Turbine Building past closed doors at the 480 VAC Bus Rooms, the Battery Rooms, or the AFW Pump Rooms. In this case total leakage that can be accommodated into the Unit 2 Turbine Building is the sum of the Unit 1.and Unit 2 3 3 3 condenser pits; 89,537 ft + 101,672 ft = 191,209 ft .

(3) Above elevation 695.75 ft, water would flow over the barriers surrounding the openings into the Residual Heat Removal (RHR) pits. To fill the Auxiliary Building to 695.75 ft would require approximately 3

23,959 ft of water (Reference 18).

(4) At elevation 694.90 ft, water could enter the 05/06 Diesel Generator Rooms from inleakage past closed doors. In leakage to the 05 and/or 06 Room would accumulate in the lower elevation. The lower elevation can accommodate water level up to the bottom of the motors for the Fuel Oil Transfer Pumps and the Fuel Oil Recirculation Pump (Reference 14). At this elevation there is a total available volume of 3

16,760 gallons (2240 ft3) in the 05 compartment and 17,627 gallons (2356 ft ) in the 06 compartment to accommodate potential inleakage.

(5) At elevation 694.90 ft, water could enter the Screenhouse. In leakage would start to fill the Screen house basement. Water depth in the Screen house basement greater than elevation 687 ft (water depth of 17 ft) will cover cables supplying power to the safety related cooling water pumps (Reference 14). It is considered to be conservative to use this as a minimum water level as the cables contain no splices or terminations at this elevation. In the Screenhouse basement, there are 22,242 gallons/ft of available water volume per foot (Reference 14). The available volume to accommodate inleakage below elevation 687 ft is 17 ft* 22,242 gallons per ft= 378,114 gallons (50,550 ft\

(6) Water depth in the fuel oil vault above 686.92 ft could enter the fuel oil storage tanks through the tank overflow line. The available volume to accommodate inleakage below elevation 686.92 ft in the vault is 3

45,932 gallons (6140.3 ft ) (Reference 15).

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Prairie Island External Flooding Assessment Focused Evaluation Rev.a Table 7.1-2 shows the predicted maximum water surface elevations (WSE) at the plant access doors during the LIP (Reference 11). As shown in Table 7.1-2, the maximum water surface elevations around the plant structures can be up to 0.45 ft above the finished floor elevation (FFE) elevation for some of the plant access doors. The locations of the plant access doors are shown in Figure 7.1-1.

Table 7 .1-2, Maximum Water Surface Elevations (WSE) at Plant Access Doors Maximum Door MaxWSE Survey FFE Description Depth Above Number (ft) (ft)

FFE (ft) 237 Screen house 694.82 694.90 Below FFE 257 Screen house 694.82 694.90 Below FFE 258 Screen house 694.82 694.90 Below FFE 238 Screen house 694.82 694.90 Below FFE 1 Old Admin Building 694.82 694.90 Below FFE 47 Turbine Building 695.17 694.90 0.27 46 Turbine Building 694.74 694.90 Below FFE 45 Turbine Building 694.82 694.90 Below FFE 44 Turbine Building/Service Building 694.77 694.90 Below FFE 73 Turbine Building 694.76 694.90 Below FFE 104 Auxiliary Building/Rad Waste Building 695.35 694.90* 0.45 100 Auxiliary Building/Rad Waste Building 695.35 694.90* 0.45 164 Auxiliary Building/Rad Waste Building 695.24 694.90 0.34 102 Auxiliary Building/Rad Waste Building 695.24 694.90 0.34 420 05/06 Building 695.17 694.90 0.27 423 05/06 Building 695.17 694.90 0.27 437 05/06 Building 695.19 694.90 0.29

  • No survey FFE point available at door, closest FFE survey point was used.

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Prairie Island External Flood ing Assessment Focused Evaluation Rev. a Figure 7.1-1, Plant Access Door Locations C? ~

©----*-*- ~;-----------~

cY--*-*-- ~\ r~

DOOR237 ODOR Z' LJ 'Sx,R 258 DOOR238 C0-*-*----- -==,_----====Xl 0 00 0 0 00 0 00 0 0 0 0 0 0

. . . i i

' . . . . . i j

Tl.R81NE BU1 LOI NC DOOR44 ~

  • .11 J SERV 9lJ1LI NJl l LI Nl'f IUI LO! trei L_ ~

lJr(f T 2 R(AC TOR UNIT I DOOR 73~ ~=-~-**

SUI LOI NG REollC TOA BUI LOI HG 8-*-----*---*---*-*--*-*-*-*-*-*---*-*-*---- *-*---*-*----

0 --*-*-*-*-*---*-*-*-*--*-*--*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*

0 *-*---*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*----- -*-----*-------*---*-*-*-*---- --*-

8 -*-*---*-*-*--*-*-*****-*-- -*-*-*-*-*-*-* *- *- *- *--*-*- *- *- *- -- *----- -- *- *- -DOOR 104 RAO WASTE SUI LDIN'.i Figures 7.1-2 and 7.1-3 show potential leakage pathways for water between the Auxiliary Building, the Unit 1 Turbine Building and the Unit 2 Turbine Building.

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Prairie Island External Flooding Assessment Focused Evaluation Rev. O Figure 7.1-2 Unit 1 and Unit 2 Turbine Building Page 15 of 21

Pra irie Island Externa l Flood ing Assessment Focused Evaluation Rev. O 7.1.2 Adequate APM Justification The APM for each of the Key SSCs is determ ined based on the difference between the crit ica l water e levation in Table 7.1-1 and the maximum water surface e levation in Table 7.1-2. This is shown fo r each of the structures in Tables 7.1-3 through 7.1-7.

Table 7.1-3, APM Determination - Screenhouse Door MaxWSE (ft) Critical Elevation Key SSC Affected Structure APM (ft)

Number (Table 7.1-2) (Table 7.1-1) Affected 237 Screen house 694.82 694.90 0.08 No 238 Screen house 694.82 694.90 0.08 No 257 Screen house 694.82 694.90 0.08 No 258 Screen house 694.82 694.90 0.08 No In addition to the 0.08 ft APM, the Screenhouse can accommodate 370,000 ga llons of inleakage before a Key SSC could be affected. Given the relatively short duration of the LIP, the APM, and the significant ava ilab le volume to accommodate inleakage, there is adequate ma rgin.

Table 7.1-4, APM Determination - DS/D6 Building and Fuel Oil Vault Door Max WSE (ft) Critical Elevation Key SSC Affected Structure APM (ft)

Number (Table 7.1-2) (Table 7.1-1) Affected 420 05/06 Building 695.17 694.90 See Below No 423 05/06 Building 695.17 694.90 See Below No 437 05/06 Building 695.19 694.90 See Below No D5/D6 Fuel Oil Tank

-- Vaults 695.19 686.92 See Below No The predicted maxi mum water surface e levation at Doors 420 and 423 is 0.27 ft above the crit ica l e levation; i.e ., the FFE. Doors 420 and 423 are exterior access doors to the OS and D6 diese l generator rooms from the west side of the bui lding. Doors 420 and 423 are mainta ined closed. Figure 7.1-1 also shows that Door 437 cou ld provide access to the bu ilding. However, flood protection bu lkhead MK-11 is installed at Door 437 as controlled by station configuration documents. Predicted fl ood e levations for a PMF are much greater than for a LIP. Thus, leakage past Door 437 is not considered for a LI P.

The maximum water surface e levation and stage hydrograph at Doors 420 and 423 is the tota l water ingress through each door is 1069 ft [3700 The maxi mum allowable inlea kage during an externa l flood is 16,760 gallons (2240 ft 3 ) into the D5 room and 17,627 ga llons (2356 ft3 ) into the 06 room (Reference 14). This is greater than the maxi mum vo lume of water that cou ld enter e ither room with the door open. Given t hat the doors are maint ained closed, Page 16 of 21

Prairie Island External Flooding Assessment Focused Evaluation Rev. a that there is margin between the maximum in leakage, and the available capacity assuming the doors are open, there is adequate APM.

The tank vaults are accessed through covers located at grade elevation . The tank vault covers are a heavy duty watertight design (Reference 16). The actions in AB-4 (Reference 13) to install the blank flanges on the tank overflow lines are additional protective measures (i.e., defense-in-depth) due to the duration and water surface elevation above the tank covers during the design basis PMF. The vault can accommodate accumulated inleakage of 45,932 gallons (6140.3 ft3) before water could enter the fuel oil tanks (Reference 15). Given the heavy duty watertight design of the vault covers, the relatively short time period of the LIP, the relatively small head of water above the vault covers during the LIP, and the available capacity of the fuel oil vaults to accept in leakage, there is adequate APM.

Table 7.1-5, APM Determination - Unit 1 Turbine Building Door Max WSE (ft) Critical Elevation Key SSC Affected Structure APM (ft)

Number (Table 7.1-2) (Table 7.1-1) Affected 1 Unit 1 Turbine Building 694.82 694.90 0.08 No 44 Unit 1 Turbine Building 694.77 694.90 0.13 No 45 Unit 1 Turbine Building 694.82 694.90 0.08 No 73 Unit 1 Turbine Building 694.76 694.90 0.14 No 3

In addition to the 0.08 ft minimum APM, the Unit 1 Turbine Building can accommodate up to 89,537 ft of inleakage before a Key SSC could be affected . Given the duration of the LIP, the APM and the available volume to accommodate in leakage provide adequate APM.

Table 7.1-6, APM Determination - Unit 2 Turbine Building Door Max WSE (ft) Critical Elevation Key SSC Affected Structure APM (ft)

Number (Table 7 .1-2) (Table 7.1-1) Affected 46 Unit 2 Turbine Building 694.74 694.90 0.16 No 47 Unit 2 Turbine Building 695 .17 694.90 See Below No The predicted maximum water surface elevation at Door 47 is 0.27 ft above the critical elevation; i.e.,

the FFE. Door 47 is . Based on the predicted water elevation vs. time and the duration of the LIP it was determined that 3700 ft 3 of water could enter the Unit 2 Turbine Building (Reference 11). The Unit 2 Turbine Building Condenser Pit can accommodate 101,672 ft 3 up to elevation 695 ft . Thus, the total inleakage during the LIP is only a small fraction of the available volume. The 3700 ft 3 of water inleakage will result in less than six inches of water on the condenser pit floor, which will have no impact to Key SSCs. Therefore, there is adequate APM .

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Prairie Island External Flooding Assessment Focused Evaluation Rev.a Table 7 .1-7, APM Determination -Auxiliary Building Door Max WSE (ft) Critical Elevation Key SSC Affected Structure APM (ft)

Number (Table 7.1-2) (Table 7.1-1) Affected 100 Auxiliary Building 695.35 695.75 0.40 No 102 Auxiliary Building 695.24 695.75 0.51 No 104 Auxiliary Building 695.35 695.75 0.40 No 164 Auxiliary Building 695.24 695.75 0.51 No The APM at Doors 100 and 104 is 0.40 ft. The APM at Doors 102 and 164 is 0.51 ft. Doors 102 and 104 are roll up doors from the exterior to the Fuel Receipt Area of the Auxiliary Building. Doors 100 and 164 provide access between the Fuel Receipt Area of the Auxiliary Building and the Rad Waste Building. Door 164 is surrounded by a block wall on the exterior side that would not allow water into the Auxiliary Building. Doors 100, 102, and 104 are normally maintained closed and will limit the volume of water that is able to enter the Auxiliary Building during a LIP event. If water in leakage occurs past Doors 100, 102, and/or 104 it will first accumulate in the Fuel Receipt area (refer to Figures 7.1-2 and 7.1-3). There are additional interior doors that are normally maintained closed between the Fuel Receipt area and the locations of SSCs important to safety in the Auxiliary Building. lnleakage would need to traverse a relatively long torturous path to reach SSCs important to safety. Furthermore, the water would need to fill the large interior surface area of the Auxiliary Building to a level of 695.75 ft before any SSCs important to safety are affected (Reference 14). To fill this area in the Auxiliary Building to 695.75 ft would require approximately 23,959 ft 3 of water (Reference 18). LIP events are of limited duration that precludes accumulating significant water through the closed doors. Furthermore, even if it is assumed that Doors 100, 102, and 104 were open and the water level in the Auxiliary Building equalized with the maximum water surface elevation outside the doors, the maximum water level in the Auxiliary Building would be 695.35 ft. This is below the water level of 695.75 ft where Key SSCs could be affected.

Therefore, there is adequate APM.

As shown on Figures 7.1-2 and 7.1-3, there are two closed doors between the Auxiliary Building and the Turbine Building. Leakage by either of these door(s) could enter the Turbine Building. Similar to the discussion of the Unit 1 and Unit 2 Turbine Buildings, this leakage will initially accumulate in the Condenser Pits. If it conservatively assumed that only the Auxiliary Building to Unit 1 Turbine Building door leaks, leakage would accumulate in the Unit 1 Condenser Pit; which has an available capacity of 89,537 ft 3

  • Given the duration of the LIP, the available volume to accommodate inleakage provides adequate APM.

Summary As described above the limiting flood elevations are below the critical elevations for Key SSCs.

Therefore, the KSFs are protected by the characteristics of the site itself such as plant grading, by locations of the Key SSCs, and by the capability of the structures to accommodate in leakage. Therefore, the LIP is not a consequential flood for the PINGP. Furthermore, any flood up to the LIP flood described above would also not be considered a consequential flood for the PINGP.

7.1.3 Reliability of Flood Protection As described above, flood protection for the LIP is provided by the permanently installed plant structures that are designed for a PMF. The WSE for the PMF is much higher than a LIP, thus the permanently installed plant structures will provide flood protection for the LIP. Since some plant doors Page 18 of 21

Prairie Island External Flooding Assessment Focused Evaluation Rev.a will not be protected by flood bulkheads that would be installed as part of the PMF flood response, potential loads during the LIP event were evaluated at these doors. These doors and associated supporting structures have been evaluated (Reference 17) and determined to be capable of withstanding the loads from the LIP water level. The LIP event will not include debris impact or appreciable hydrodynamic effects due to the direction of flow being away from the buildings.

7.1.4 Adequate Overall Site Response The site does not require any human actions to protect Key SSCs during the LIP. Thus, an evaluation of the overall site response was not necessary.

8.0 CONCLUSION

Associated effects (AE) and flood event duration (FED) parameters were assessed and submitted as a part of the FHRR. The FE affirms that during LIP events the site has effective flood protection through the determination of Available Physical Margin (APM) and the reliability of protection features. The site does not require any human actions to protect Key SSCs so an evaluation of the overall site response was not necessary. This FE follows Path 2 of NEI 16-05, Rev. 1, and utilizes Appendix B for guidance for evaluating the site protection features. This submittal completes the actions related to External Flooding required by the March 12, 2012, 10 CFR 50.54(f) letter.

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Prairie Island External Flooding Assessment Focused Evaluation Rev.a APPENDIX!

This appendix provides a matrix of the items identified in Section 9.2, "Documentation," of NEI 16-05, for Path 2, with the corresponding section(s) in the PINGP Focused Evaluation where the requested information is provided.

  • Characterization of Flood Parameters Flood hazard parameters are summarized in Table 5-1.
  • Evaluation and Description of Flood Impacts Section 6.1 provides a description of the overall site flooding response during a LIP. Section 7.1 summarizes the impacts to the site during a LIP. Table 7.1-2 identifies the maximum water surface elevations at each of the plant access doors during the LIP.
  • Key SSCs Potentially Impacted by Flood Waters Table 7.1-1, including the notes identifies the Key SSCs that could potentially be impacted by flood waters during a LIP. As described in Section 7.1.1, the Key SSCs identified are those that would be initially impacted by water in each structure; i.e., those at the lowest elevation.
  • Critical Elevations That Could Impact Key SSCs Table 7.1-1 identifies the critical elevations for the Key SSCs for each of the structures. As described in Section 7.1.1, to be conservative, the critical elevation corresponding to the Key SSC at the lowest elevation is identified.
  • Flood Features Relied On To Protect Key SSCs As summarized in Table 5-2, permanent passive protection features are relied on to protect Key SSCs to maintain KSFs. Section 6.1 describes the permanent passive protection as the plant structures. To be conservative, plant access doors were not credited with limiting water in leakage during a LIP. Although not credited, these doors are present and would limit the amount of water in leakage. As summarized in Section 7.1.3, plant access doors were evaluated to ensure that they are capable of withstanding the loads from the LIP.
  • Demonstration of Effective Protection, Including:

o Calculation of APM for Each Flood Protection Feature The determination of APM for the flood protection features for each of the plant structures are provided in Tables 7.1-3 through 7.1-7.

o Justification that Calculated APM is Adequate Appropriate justification that the APM for the flood protection features for each of the plant structures is adequate is provided in the discussion associated with Tables 7.1-3 through 7.1-7.

o Evaluation of Reliability of Each Flood Protection Feature Page 20 of 21

Prairie Island External Flooding Assessment Focused Evaluation Rev.a As. described in Secti.on 7.1.3, flood protection for the LIP is provided by the permanently installed plant structures (passive protection) that are designed for a PMF. The WSE for the PM F is much higher than a LIP, thus the permanently installed plant structures will provide reliable flood protection for the LIP. Doors and the associated supporting structures have been evaluated and determined to be capable of withstanding the loads from the LIP water level.

o Evaluation of Human Actions and an Adequate Site Response As described in Section 7.1.4, the site does not require any human actions to protect Key SSCs during the LIP. Thus, an evaluation of the adequacy of the overall site response was not necessary.

  • Summary of Results and Conclusions of Assessment Demonstrating Effective Protection As summarized in Section 8.0, associated effects and flood event duration parameters were assessed and submitted as a part of the FHRR. The FE affirms that during LIP events the site has effective flood protection through the determination of Available Physical Margin and the reliability of protection features. The site does not require any human actions to protect Key SSCs so an evaluation of the overall site response was not necessary. This FE follows Path 2 of NEI 16-05, Rev.

1, and utilizes Appendix B for guidance for evaluating the site protection features. This submittal completes the actions related to External Flooding required by the March 12, 2012, 10 CFR S0.54(f) letter.

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