Text

Focused Evaluation Regarding Near-Term Task Force Recommendation 2.1 for Flooding
	ML17192A069
Person / Time
Site:	Davis Besse
Issue date:	07/11/2017
From:	Boles B; FirstEnergy Nuclear Operating Co
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	CAC MF3721, L-17-176
	Download: ML17192A069 (22)
	v • d • e

FENOC- 550t North Srata Rwte 2 Fi r stE ne g y NucI ear OW rati ng fun pany OaR Harbq Ohio 43449

ian D. Eotsg 419-321-7676 Wce President, Fax:41*321-7582 Nucleu July 11,2017 L-17-176 10 cFR 50.54(0 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852

SUBJECT:

Davis-Besse Nuclear Power Station Docket No. 50-346, License No. NPF-3 Focused Evaluation Reoarding Near-Term Task Force Recommendation 2.1 for Floodinq,(GAC No. MF3721)

On March 12,2012, the Nuclear Regulatory Commission (NRC) issued a letter titled, "Request for lnformation Pursuant to Title 10 of the Code of Fedeml Regulaffons 50.54(0 Regarding Recommendations 2.1,2.3, and 9.3, of the Near-Term Task Force Review of lnsights from the Fukushima Dai-ichi Accident," to all power reactor licensees and holders of construction permits in active or deferred status. EnclosureZ of the 10 CFR 50.54(f) letter addresses Near-Term Task Force (NITF) Recommendation?.l for flooding and requires two responses. The first response is for licensees to submit a hazard reevaluation report (HRR) in accordance with the NRC's prioritization plan. As indicated in NRC Ietterdated March 1,2013, the NRC staff considersthe reevaluated flood hazard to be "beyond the current design/licensing basis of operating plants." By letter dated March 11,2014, FirstEnergy Nuclear Operating Company (FENOC) submifted the flood HRR for Davis-Besse Nuclear Power Station (DBNPS). Additional inforrnation was provided by FENOC letters dated August 25, ?014, December 10, 2014, February 25, 2015, and August 1 1 , 2015.

The second required response from the 10 CFR 50.54(f) letter regarding NTTF Recommendation 2.1 is for licensees to submit an integrated assessment report. By letterdated September 1,2015, the NRC staff described changes in the NRC's approach to flood hazard reevaluations, including its use in evaluating mitigating strategies for beyonddesign-basis external events, and the expected interac"tions and additional information needed to complete these activities. The NRC staff developed a graded approach for determining the need for, and scope of, plant-specific integrated assessments. One step is to perform a mitigating strategies assessment (MSA).

Davis-Besse Nuclear Power $tation L-17-176 Page 2 Guidance for performing MSAs for reevaluated flooding hazards is contained in Appendix G of Nuclear Energy lnstitute (NEl) 12-06, Revision 2, which was endorsed by the NRC in JLD-lSG-2O12-01, Revision 1. FENOC submitted the MSAforflooding for DBNPS by letter dated December 12, 2016.

Another step in the graded approach is to screen the reevaluated flooding hazards results to determine the need for, and $cope of, the integrated assessment. Guidance for performing this screening is contained in NEI 16-05, Revision 1, which was endorsed by the NRC in JLD-ISG-2O16-01 , Revision 1. The screening results for DBNPS are provided in the enclosed focused evaluation. The unbounded reevaluated flood mechanisms previously submitted in the flood HRR, local intense precipitation flood and probable maximum storm surge flooding, do not impact key structures, systems, or components or challenge key safety functions at DBNPS. Based on this focused evaluation, an integrated assessment is not needed. The actions related to the 10 CFR 50.54(f) requestfor information regarding NTTF Recommendation 2.1 for flooding are now complete for DBNPS.

There are no regulatory commitments contained in this letter. lf there are any questions or if additional information is required, please contact Mr. Thoma$ A. Lentz, Manager Fleet Licensing, at 330-315-6810, I declare under penalty of perjury that the foregoing is true and correct. Executed on July lf /_, ?017 .

Sincerely, Brian D. Boles

Enclosure:

Davis-Besse Nuclear Power Station Flooding Focused Evaluation Summary cc Director, Office of Nuclear Reactor Regulation (NRR)

NRC Region lll Administrator NRC Resident lnspector NRR Project Manager Utility Radiological Safety Board

FE:fitOG-FirslEneEy lvr.rclear freratffE Con4pany DAVIS-BESSE NUCLEAR POWER STATION FLOODING FOCUSED EVALUATION

SUMMARY

MAY 5,20L7 LETTER L-L7-L76 Enclosure Fi rstEnergy N uclea r Operating Company 5501 North State Route 2 Oak Harbor, OH 43449-9760 FEru.o.C

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Letter L-L7 -t7 6 Enclosure May 2OL7 TABLE OF CONTENTS 1 EXECUTIVE

SUMMARY

2 2 BACKG RO U N D . r.. r.. r r. . . .. r... . . ...... r...r r. ... r. . ... rrrrr!rrrrrrrr. r. r. r ,..... rrrrr r. r.. .... 3 3 REFERENCES ................r.......r.......r............rrrrrr.rrrr!.rr.r..r.r...rrrrr..!.......4 4 TERMS AND DEFINlTlONS.......rr................rrrrrrrrrrrrrrrrrr.rrr.r...rrrrrrr......6 5 FLOOD HAZARD PARAMETERS FOR UNBOUNDED MECHANISMS .....7

5. 1 Revrseo PnognBLE MAXTMUM Sronru Sungr ( PMSS) ...............r....... 8 5.2 Revlsro Locm lrurrrusE PREcrprrATroN (L!P} ...r.r............r..,r...r.......11 6 oVERALL SITE FLOODING RESPONSE .r...!..rrrr,rrrrrr.rr......rrr,.....rtr..... 15 6.1 DgscmprtoN oF OVERALL Srr FlooorNc REspoNsE ...........,....r.......15 6.1.L Response to PMSS 15 6.L.2 Response to LlP.. ... L5 6.2 Su ut ueRy oF Pumr MoorHcATroNs AND CnnuaES ........ r... r...... r.... 16 7 FLOOD lMPA(gr ASSESSMENT r...r.....r........r..rrrttrrr..r.r.rr...i..r.....rrr ....L7 7 .L Flooo MrcnnNEM PMSS ( Pnru 1 AssrssMENT) .....r.....r.... r,....rr ...L1 7.t.1 Comparison of New Flood Levels to the Design Basis..... ....L7 7.2 Fr-ooo MrcHnNrsM LIP (PnrH 2 AssEssMENrl L7 7.2.1 Dgscription of LIP Flood lmpact .......,..,,..........., ..,,,.L7 7.2.2 Adequate APM Justification and Reliability Flood Protection ........ 18 7.2.3 Adequate Overall Site Response 18 I CO N CLU SIO N .. .... . . r. . r r r r. . r r. . r r . . r r r r ! r r . r. r. r r . r . r . . r. .. . . .. .. . r r. , r. .. r . r. .. r. . r.. .rr.. . 19 FE,tdolc 1

Letter L-L7 -L7 6 Enclosu re May 2OL7 DAVIS.BESSE FLOODING F SED EVALUATION

SUMMARY

1 EXECUTIVE

SUMMARY

The Davis-Besse Nuclear Power Station (DBNPS) has reevaluated its flooding hazard in accordance with the NRC's March L2,201210CFR50.54(f) Request for lnformation (RFl) (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 (NTTF) report.

This information was submitted to NRC in a Flood Hazard Reevaluation Report (FHRR) on 212512A15 and is provided in the Mitigating Strategies Flood Hazard lnformation (MSFHI) documented in NRC's "lnterim Staff Response to Reevaluated Flood Hazards" Ietter dated 913/2OL5 (Reference 12). Additionally, DBNPS has received the "staffAssessment of Response to Request for lnformation Pursuant to 10CFR50.54(f) - Flood-Causing Mechanisms Reevaluation" letter dated LZ.lL4l2OL6 (Reference 13). Additional flooding analyses have been performed since the FHRR submittal and were not evaluated in the MSFHI and Staff Assessment Ietters. These additional flooding analyses will serve as the input to this Focused Evaluation (FE). Open items identified in the StaffAssessment will also be addressed. Two mechanisms, described below, were found to exceed the design basis at DBNPS.

Probahle Maximum Storm Surge Associated Effects (AE) and Flood Event Duration (FED) parameters were assessed and submitted as a part of the Mitigating Strategies Assessment (MSA) (Reference 15). The FE concludes that the Probable Maximum Storm Surge (PMSS) does not affect any Key Safety Function (KSF) as the refined analysis removed all flooding in the power block area. No safety-related structures are subject to flooding from a PMSS event. The PMSS FE followed Path 1of NEI 16-05, Rev. L and utilized revised analysis to improve the realism of the evaluated storm. This FE provides basis for the new flood parameters as well as documenting the resolution of open Staff Assessment items associated with the PMSS.

Local Intense Precipitation AE and FED parameters were assessed and submitted as a part of the MSA (Reference 15). The FE concludes that the Local lntense Precipitation (LlP) does not affect any KSF as the site-specific analysis removed all flooding at critical doors in the power block area. No safety-related structures are subject to flooding from a LIP event. The LIP FE followed Path 2 of NEI L6-05, Rev. 1 and utilized a site-specific analysis to improve the realism of the evaluated storm. This FE provides basis for the new flood parameters as well as documenting the resolution of open Staff Assessment items associated with the LlP.

This submittal completes the actions related to External Flooding required by the March 12, 2OL2, 10CFR50.54(f) Ietter.

FENo,G 7

Letter L-L7 -L7 6 Enclosu re May 2OL7 2 BACKGROUND On March 12, 20L2, the NRC issued Reference L to request information associated with Near-Term Task Force (NTTF) Recommendation 2.1for flooding. The NRC RFI directed licensees, in part, to submit a FHRR to reevaluate the flood hazards for their sites using present-day methods and guidance used for early site permits and combined operating licenses. The DBNPS FHRR, Revision 2 was submitted on 2125120L5 (Reference 3) with supplemental information provided in Reference 4.

Following the Commission's directive to the NRC Staff (Reference 6), the NRC issued a letter to the industry (Reference 9) 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." The Nuclear Energy lnstitute (NEl) prepared the new External Flooding Assessment Guidelines in NEI 16-05, Rev L (Reference 7), which was endorsed by the NRC (Reference 8). NEI 16-05 indicates that each flood-causing mechanism not bounded by the design basis (using stillwater and/or wind-wave runup level) should follow one of the following five assessment paths:

Path 1: Demonstrate FIood Mechanism is Bounded Through lmproved 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 t,2, or 3 would only require a FE to complete the actions related to external flooding required by the March L2,2OL210CFR50.54(f) Ietter.

Mechanisms in Paths 4 or 5 require an lntegrated Assessment.

FENo,C 3

Lette r L-L7 -L7 6 E nclosu re May 2OL7 3 REFERENCES

1. NRC Letter, Request for lnformation Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.L,2.3, and 9.3, of the Near-Term Task Force Review of lnsights from the Fukushima Dai-ichi Accident; dated March L2,2OL2.

2. FENOC Letter to USNRC, Davis-Besse Nuclear Power Station, FHRR Rev L, Response to NRC Request for lnformation Pursuant to 10CFR50.54(f), Regarding the Flooding Aspects of Recommendation 2.L of the Near Term Task Force (NTTF) Review of lnsights from the Fukushima Dai-ichi Accident, dated 3lLLl2A14 (M11.4070A108).

3. FENOC Letterto USNRC, Davis-Besse Nuclear Power Station, FHRR Rev 2, Revision to Flood Hazard Reevaluation Report in Response to Near Term Task Force Recommendation 2.1 (TAC No. MF372Ll, dated 212512015 (M115750A023).

4. FENOC Letter to USNRC, Davis-Besse Nuclear Power Station, Supplement to Flood Hazard Reevaluations Report in Response to Near Term Task Force Recommendation 2.L, dated 7 I L7 /2014 (M114198A400).

5. NRC 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 lnsights from the Fukushima Dai-ichi Accident, dated March 1, 2013.

6. NRC Staff Requirements Memoranda to COMSECY-14-0037, "lntegration of Mitigating Strategies for Beyond-Design-Basis External Events and the Reevaluation of Flooding Hazards",

dated March 30, 2015.

7. Nuclear Energy lnstitute, Report NEI L6-05, Rev 1, External Flooding Assessment Guidelines, dated June 2016.

8. U.S. Nuclear Regulatory Commission, JLD-lSG-2016-01, Guidance for Activities Related to Near-Term Task Force Recommendation 2.L, Flood Hazard Reevaluation; Focused Evaluation and

!ntegrated Assessment, Revision 0, dated July 11, 2016.

9. NRC Letter, Coordination of Requests for lnformation Regarding Flooding Hazard Reevaluations and Mitigating Strategies for Beyond-Design-Basis External Events, dated September 1, 2015.

10. Nuclear Energy lnstitute, Report NEI 12-06 [Rev 2], Diverse and Flexible Coping Strategies (FLEX) lmplementation Guide, dated December 2015.

11-. U.S. Nuclear Regulatory Commission, JLD-lSG-20L2-0L, Revision L, Compliance with Order EA-L2-O49, Order Modifying Licenses with Regard to Requirements for Mitigating Strategies for Beyond-Design-Basis External Events, dated January 22, 2OL6.

12. NRC Letter, Davis-Besse Nuclear Power Station, - lnterim Staff Response to Reevaluated Flood Hazards Submitted in Response to 10CFR50.54(f) lnformation Request - Flood-Causing Mechanism Reevaluation (TAC NO. MF372L), dated 9fi/2AL5 (ML152398212).

L3. NRC Letter, Davis-Besse Nuclear Power Station, - Staff Assessment of Response to Request for lnformation Pursuant to 10CFR50.54(f) - Flood-Causing Mechanisms Reevaluation (CAC NO.

M F372U, dated LU L4/ LG (M 116323A236).

L4. FENOC Letter to USNRC, Davis-Besse Nuclear Power Station, Completion of Required Action by NRC Order EA-12-049, Order Modifying Licenses with Regard to Requirements for Mitigation FE'VOC 4

Letter L-L7 -17 6 Enclosu re May 2OL7 Strategies for Beyond-Design-Basis External Events (TAC No. MF0961), dated 9l23lL6 (M 116267 A47Ll.

15. FENOC Letter to USNRC, Davis-Besse Nuclear Power Station, Mitigating Strategies Assessment (MSA) for Flooding (cAC NO. MF372L), dated L1lLzlL6 (M116348A010).

16, NRC Letter, Davis-Besse Nuclear Power Station, Unit L - StaffAssessment of the Flooding Walkdown Report Supporting lmplementation of Near-Term Task Force Recommendation 2.3 Related to the Fukushima Dai-lchi Nuclear Power Plant Accident (TAC NO.MF022O\, dated 5l30l2}r.4 (M L 14141As2s).

1-7. FENOC Letter to USNRC, FENOC Response to NRC Request for lnformation Pursuant to 10CFR50.54(f) Regarding the Flooding Aspects of Recommendation 2.3 of the Near-Term Task Force Review of lnsights from the Fukushima Dai-ichi Accident, dated LLl27lZ012 (ML 1233sA341).

18. NORM-LP-7221, Davis-Besse Flooding Mitigating Strategy Assessment Support Document.

19. Calculation C-CSS-020.13-017 Rev L, Surge and Seiche Analysis for Davis-Besse Nuclear Power Station.

20. Calculation C-CSS-020.13-021 Rev 1., Surge and Seiche Calibration for Davis-Besse Nuclear Power Station.

21. Calculation C-CSS-020.13-015 Rev 1, Site-specific Wind and Pressure Field Analysis for Davis-Besse Nuclear Power Station.

22. Calculation C-CSS-020.13-022 Rev 1, Combined Event including Wind Wave Analysis for Davis-Besse Nuclear Power Station.

23. Calculation C-CSS-020.13-024 Rev 0, Site-Specific LIP Analysis for Davis-Besse Nuclear Power Station.

24. Calculation C-CSS-020.13-014 Rev 2, Effects of Local Probable Maximum Precipitation Analysis for Davis-Besse Nuclear Power Station.

FE'VOC 5

Letter L-L7 -L7 6 Enclosu re May 2OL7 4 TERMS AND DEFINITIONS AE - Associated Effects APM - Available Physical Margin AlMs - Assumptions, Inputs, and Methods BWST - Borated Water Storage Tank CLB - Current Licensing Basis DBNPS - Davis-Besse Nuclear Power Station FE - Focused Evaluation FED - Flood Event Duration FHRR - Flood Hazard Reevaluation Report FLEX - Diverse and flexible coping strategies covered by NRC order EA-L2-049 FIAP - FIood Impact Assessment Process 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 !ntense Precipitation MSA - Mitigating Strategies Assessment as described in NEI 12-06 Rev 2, App G MSFHI - Mitigating Strategies Flood Hazard !nformation NEI - Nuclear Energy lnstitute NTTF - Near Term Task Force commissioned by the NRC to recommend actions following the Fukushima Dai-ichi accidents PMSS - Probable Maximum Storm Surge PMWS - Probable Maximum Windstorm RFI - Request for lnformation SWT - Service Water Tunnel VBS - Vehicle Barrier System WSE - Water Surface Elevation All elevation values in this report will be in the Site Datum, IGLD55 (lnternational Great Lakes Datum 1955).

FENo.c 6

Letter L-17 -L7 6 Enclosure May 2AL7 5 FLOOD HAZARD PARAMETERS FOR UNBOUNDED MECHANISMS The NRC has completed the "lnterim Staff Response to Reevaluated Flood Hazards" (Reference L2) which contains the MSFHI related to the DBNPS FHRR (Reference 3). Additionally, DBNPS has received the "Staff Assessment of Response to Request for lnformation Pursuant to 10CFR50.54(f)

- Flood-Causing Mechanisms Reevaluation" letter dated tZlL4l2O16 (Reference 13).

ln Reference L2, the NRC states that the "staff has concluded that the licensee's reevaluated flood hazards information 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 NEI guidance document NEI 12-06, 'Diverse and Flexible Coping Strategies (FLEX) lmplementation Guide' for DBNPS. Further, the NRC staff concluded that the licensee's reevaluated flood hazard information is suitable input for the focused evaluation associated with NTTF Recommendation 2.1, Flooding. The enclosure to Reference 12 includes a summary of the current design basis and reevaluated flood hazard parameters, respectively. ln Table L of the enclosure to Reference L2, the NRC lists the following flood-causing mechanisms for the design basis flood:

e Local lntense Precipitation r Streams and Rivers r Failure of Dams and Onsite Water Control/Storage Structures

. Storm Surge

. Seiche

. Tsunami

. lce lnduced Flooding

. Channel Migrations/Diversions ln Table 2 of the enclosure to Reference 12, the NRC lists flood hazard information (specifically stillwater elevation and wind-wave runup elevation) for the following flood-causing mechanisms that are not bounded by the design basis:

. Storm Surge o Local Intense Precipitation These are the reevaluated flood-causing mechanisms that are addressed in the external flooding assessment. The two non-bounded flood mechanisms for DBNPS are described in detai! in References 2 and 3 (the FHRR submittals). The following table summarizes how each of these unbounded mechanisms was addressed in this external flooding assessment.

FE'VOG 7

Letter L-t7 -L7 6 Enclosu re May ?.OL7 Flood Mechanism Summary of Assessment The Storm Surge is evaluated using Path L of the Flood lmpact Assessment Process (FIAP)

Path Determination Table, Section 6.3.3 of 1 Probable Maximum Storm Surge NEI 16-05, The FHRR Storm Surge calculation was refined in 20L5 but not included in the FHRR submittal (Reference 3).

The LIP is evaluated using Path 2 of FIAP Path Determination Table, Section 5.3.3 of NEI 16-

05. The FHRR Effects of Local Intense 2 Local lntense Precipitation Precipitation calculation was refined in 20L5 but not included in the FHRR submitta!

(Reference 3).

ln Reference L3, the NRC states that the "staff confirms that the reevaluated flood hazards information defined in Section 4.1 of Reference 13 is appropriate input to the additional assessments of plant response as described in the 50.54(f) letter and COMSECY-L5-0019, Mitigating Strategies and Flooding Hazard Reevaluation Action Plan." The staff also noted some AEs and FEDs were not reported in Reference 3 and were expected to be provided in subsequent flooding evaluations. The missing AE and FED items were provided in the MSA for Flooding, dated Lzl L2/2016 (Reference 15).

The refined analyses are used as the basis for this FE and were also referenced in the MSA, but were not used as the basis of the MSA evaluation.

5.1 RrvrsED PnoeaelE MAxTMUM Sronru Sunce (PMSSI The PMSS calculation, C-CSS-020.13-017, Surge and Seiche Analysis for Davis-Besse Nuclear Power Station, was revised in January 2015. Calculations C-CSS-020.13-021, Surge and Sieche Calibration for Davis-Besse Nuclear Power Station, and C-CSS-020.13-015, Site-specific Wind and Pressure Field Analysis for Davis-Besse Nuclear Power Station, were also revised as they are inputs to the Surge and Seiche Analysis. Calculation C-CSS-020.13-022, Combined Event including Wind Wave Analysis for Davis-Besse Nuclear Power Station, was also revised as it receives input from the Surge and Seiche analysis.

To develop more realistic conditions, the refined analysis includes: (1) revision of the calibration model parameters based on the statistical evaluations for determining parameter selection, and (2) refinement of the wind events containing the candidate PMWS to exclude certain wind events based on transpositionability.

FE'VOG 8

Letter L-L7 -L7 6 Enclosure May 2OL7 The Assumptions, lnputs, and Methods (AlMs) discussed below will be addressed for each calculation with justification for each change. The changes to the input calculations for the PMSS analysis will be discussed first. The Combined Event calculation will be discussed last as it receives input from the PMSS Analysis.

Discussion of Revised AlMs Item Description of Revised AIM Justification of Reduced Conservatism Revision 1 of the calculation selected the best Model Parameters in Calculation C-CSS-020.13-021 Rev 0 were revised based on fit parameters such as wind drag coefficient, statistical evaluations for determining Manning's roughness and JONSWAP bottom parameter selection. friction coefficient (for WAVE model) by performing a statistica! analysis in terms of Only the wind drag coefficient changed in the revised calculation. Root Mean Square Error (RMSE), Nash Sutcliffe 1 Efficiency (NSE) and coefficient of Wind Drag Coefficient determination (R2). These changes allowed for better model to data verification and resulted Breakpoint B in only one change to the wind drag coefficient at 30 m/s to be used subsequent calculations.

Original 0.0030 Revised 0.0028 Wind events containing the candidate The refined domain of applicable storms Probable Maximum Windstorm (PMWS) includes only those storms that are physically used in C-CSS-020.13-01"5 Rev 0 were capable of occurring over DBNPS. Original refined to exclude certain wind events storm parameters were unrealistic as they did based on transpositionability. Revision 1 not account for the Appalachian Mountains or of the calculation removed data from other geographical considerations. The revised storms occurring east of the transposition limitations follow 2 Appalachians due to affects the Hydrometeorological Report HMR 51 and HMR mountains have on the storm 57 guidelines and provide a realistic storm characteristics. Storm Iocations greater selection for transposition to the DBNPS site.

than 60 latitude distance north or south of the site were also eliminated. This was to account for the change in Coriolis parameters and hence the effect on the vorticity of a given storm.

TEn4oC I

Letter L-Ll -L7 6 Enclosure May 2OL7 Discussion of Revised AlMs Item Description of Revised AIM Justification of Reduced Conservatism PMSS analysis C-CSS-020.13-017 original The major input for a PMSS analysis is the calculation used transpositioned storms PMWS. The removal of the conservatisms, including those described in ltem 2. discussed in ltem 2, is applicable here.

Revision 1 of this calculation is based on 3 inputs from revisions of the calculations discussed in ltems 1 and 2, which removed storms that were unrealistic for DBNPS and improved model inputs.

C-CSS-020.13-022, Combined Event The changes to the input values for the including Wind Wave Analysis, was Combined Event are a direct result of the 4 revised to incorporate the PMSS values changes discussed in Item 3. Therefore, the discussed in ltem 2. justifications for Item 3 apply here.

The following table documents the revised parameters for the PMSS based on calculations C-CSS-020. L3-0L7, Surge and Seiche Analysis for Davis-Besse Nuclear Power Station and C-CS5-020.13-A22, Combined Event including Wind Wave Analysis for Davis-Besse Nuclear Power Station.

PMSS Flood Mechanism Parameters Item l_l I

l---'!-l parameter Description I Values/Discussion L Max Stillwater Elevation s83.8 ft Max Wave Run-up Elevation 2 s87.2 ft (at wave protection dike)

FENo,G L0

Letter L-L7 -L7 6 Enclosu re May 2OL7 5.2 RevrsED Locel lnrrruse PRespmRTloN (LlP)

The LIP calculation, C-CSS-020.13-014, Effects of Local lntense Probable Maximum Precipitation Analysis for Davis-Besse Nuclear Power Station, provided in Reference 3 was revised in January 20L5. Calculation C-CSS-020. L3-024, Site-Specific LIP Analysis for Davis-Besse Nuclear Power Station, was created in December 20LG to provide site specific inputs to the revised LIP analysis.

The revised LIP calculation also included some additional doors but none of these doors lead directly to Key System, Structure or Components (SSCs).

Discussion of Revised AlMs Item rl Description of Revised AIM Justification of Reduced Conservatism I I The original LIP calculation used Use of a site-specific LIP analysis is an accepted general HMR guidelines. The revised industry practice and yields a more realistic LIP 1 calculation uses a site-specific LIP analysis. This conservatism is identified in Table analysis developed in Calculation C- A-1 of NEI L6-05 as a potential conservative css-020.13-024. assumption.

The original calculation considered Considering only a front temporal distribution is various temporal distributions. The consistent with the case study example provided 2

revised calculation only considers a in Appendix B of NUREG/CR-7046.

frontal temporal distribution.

The original calculation used depth- This change is incorporated because the flooding variable roughness parameters. The depths are very shallow for most of the flooding 3 revised calculation uses constant event and a full flow condition (i.e. 3 ft water roughness surface parameters based depth) is not reached.

on land surface cover.

The original calculation surface The use of 0.05 ft was overly conservative detention parameter was reduced because it is the maximum value of the suggested from 0.05 ft to 0.03 ft in the revised range of values for rain runoff model. 0.03 ft is a 4 calculation. more realistic value and is within the provided acceptable range for the model. This conservatism is identified in Table A-1 of NEI 16-05 as a potential conservative assumption.

The revised calculations set the Subcritical flow regime is a typical condition for Floodplain Limiting Froude number to overland flow. Limiting Froude number helps 5 0.99 to assure subcritical flow regime. with model stability for very shallow water The original calculation did not depths.

contain this limitation.

FENo,C 11

Lette r L-Ll -L7 6 Enclosu re May 2OL7 The following table documents the revised parameters for the LIP based on calculation C-CSS-020.13-014, Effects of Local Intense Probable Maximum Precipitation Analysis for Davis-Besse Nuclear Power Station.

LIP Flood Mechanism Parameters Item Parameter Description Values/Discussion I Max Stillwater Elevation s8s.1ft N/A. Due to the short duration, shallow depths 2 Max Wave Run-up Elevation and inadequate fetch lengths there is no wave run due to a LlP.

Debris loading was accounted for in the Vehicle Barrier System (VBS) opening by reducing the space between the barriers due to debris thereby increasing water retention on the site. No debris loading was considered on the plant structures 3 Max Hydrodynamic/Debris Loading due to the area being mostly paved. As a conservatism, all storm drains and culverts are considered non-functional for the LIP analysis.

Hydrodynamic and hydrostatic loading was calculated for each structure and determined to be well below building design loads.

N/A. The LIP is a short duration low velocity event.

Areas surrounding the power block are concrete Effects of Sediment 4 and macadam and not subject to scour. Sediment Deposition/Erosion deposition is not considered credible due to the low velocities and short duration of the event.

5 Other Associated Effects N/A. No other associated effects were identified.

N/A. No concurrent site conditions were 6 Concu rrent Site Conditions identified.

Groundwater effects were not deemed credible due to the impermeable materials surrounding the power block and the short duration of the event.

7 Effects on Ground Water Additionally, critical structures are designed for a 250 psf surcharge load which would bound any potentia! groundwater surcharge if it were to occur.

No specific warning time is identified. Existing site 8 Warning Time procedures rely on weather reports as well as notification from external agencies of impending

=--,-

FENo,C 12

Letter L-L7 -L7 6 Enclosu re May 2OL7 LIP Flood Mechanism Parameters Item t_t Parameter Description I I Values/Discussion severe weather. Once notified the Shift Manager directs action based on the environmental threat.

No doors leading to Key SSC's are flooded in the revised calculation. Site actions in the event of severe weather include closing exterior doors and hatches. Sufficient time exists to execute these actions. Additionally, the MSA has identified a trigger point based on storm predictions which provides adequate warning time.

Adequate preparation time exists as discussed above in ltem 8. The revised calculation has removed flooding from the power block area except for one Turbine Building door (Door 334)

I Period of Site Preparation and three Water Treatment Building doors. None of these doors lead directly to Key SSC's and all would be closed prior to the onset of flooding.

Sufficient time exists for these actions to be com pleted.

The revised calculation has removed flooding in the power block area except for the doors mentioned in ltem 9. Door 334 is flooded for L2 10 Period of lnundation minutes. The Water Treatment Building doors are flooded Iess than 30 minutes. The inundation period above the power block finish floor elevation of 585 ft is Iess than 30 minutes.

Based on the hydrographs (in the new calculation) for the doors mentioned above, water levels peaks at approximately I hour after the onset of the 11 Period of Recession storm. Water level recedes to below site grade approximately 30 minutes Iater. Low Iying areas will remain flooded for a longer period but pose no threat to Key SSC's.

N/A. Plant response to a LIP event is not Mode L2 Plant Mode of Operation dependent.

13 Other Factors N/A. No other factors were identified.

FENo.C r.3

Letter L-L7 -L7 6 Enclosu re May 2AL7 It was noted that the conclusion of the Staff Assessment for the FHRR agreed with the sites determination that the associated effects are minimal. As the revised LIP has reduced the previously reported flooding in the power block area, and removed flooding for all but one power block door (which is subject to flooding for 12 minutes), the associated effects are reduced below those values previously evaluated by the Staff.

The above parameters are discussed in detai! in "Mitigating Strategies Assessment (MSA) for Flooding", dated LZlL2l2016 (Reference 15).

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Letter L-L7 -t7 6 Enclosu re May 2AL7 6 OVERATL SITE FTOODING RESPONSE 6.1 DeScRIPTION OF OVERALL SITE FI.OOOITUG RESPONSE 6.1.1 Response to PMSS The PMSS is evaluated using Path 1 and is bounded by the Current Licensing Basis (CLB) flooding protection. lt is recognized that the maximum stillwater elevation in the revised calculation is slightly greater than the existing CLB value of 583.7 ft. However, the revised elevation, 583.8 ft, is below the power block finish floor elevation of 585 ft and causes no power block area flooding. The maximum wave run-up elevation (at the wave protection dike) is 587.2 ft which is below the CLB of 590.3 ft. Site flooding occurs in the outlying areas, but no structures containing Key SSC's are impacted by the PMSS. The lntake Structure, which contains Key SSC's, is designed for a wave run-up elevation of 590.3 ft, which is above the revised wave run-up elevation of 587.2 ft.

The existing site Emergency Plan Off Normal Occurrence Procedure RA-EP-02830 - Flooding contains actions required to respond to rising lake levels. The procedure recognizes that outlying areas and site access roads can be affected at lake level greater than or equal to 578 ft.

The procedure also directs entry into Emergency Plan Off Normal Occurrence Procedure RA-EP-02870 - Station Isolation. This procedure ensures adequate personnel and resources are available for continued safe operation in the event flooding could impair site access.

6.1.2 Response to LIP The LIP is evaluated using Path 2. The revised calculation reduced the LIP water level to 585.1 ft. The LIP level is above the CLB value of 584.5 ft but is at, or below, all critical doors previously evaluated in the FHRR, except Turbine Building Door 334. Three additional doors included in the revised calculation were identified to have flood levels above 585 ft. These doors are all associated with the Water Treatment Facility and do not lead directly to Key SSC's. These doors would all be closed in the event of a LlP.

Door 334 is flooded for approximately LZ minutes. Leakage through this door would not impact Key SSC's. The door would be closed during a LIP event, but the door is not designed with flood prevention features. Any leakage through the door would remain in the Turbine Building. No accumulation is expected due to the short duration of time the door is flooded. ln the unlikely event that water accumulates in the Turbine Building, safety-related SSC's are not affected due to the low flood water level and the passive barriers in place, such as concrete curbing.

Flooding into the Service Water Tunnel is discussed below. Based on this there is no impact to Key SSCs.

The Water Treatment Building doors would all be closed during a LIP event. The doors are not designed with flood protection features and are flooded for less than 30 minutes. Water leakage past these doors would migrate from the floor elevation at grade (585') to the lower 15

=-

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Letter L-L7 -17 6 Enclosure May 2OL7 elevations of the Water Treatment Building. As the water accumulates in the lower elevations of the Water Treatment Building, the lntake Structure Valve Room would be exposed to this flood water through a non-water tight door. A louver, located 2' 6" above the floor, provides a direct communication path into the lntake Structure Valve Room from the Water Treatment Building. However, it is not anticipated that water would accumulate to the louver height due to the short duration (30 minutes) of the flood and the limited leakage past the doors.

The lntake Structure Valve Room is open to the Service Water Tunnel (SWT) which extends to the Turbine Building. Calculations 054.022, C-ME-021.02-003 and C-CCS-099.16-134 evaluate various flooding scenarios in the SWT. Of these, the most severe evaluates a Circulating System Water line break in the Turbine Building causing flooding of the SWT through an open pipe chase between the SWT and the Turbine Building. The valves of concern are located 52 inches above the SWT floor. The input flooding flows to the SWT in this calculation are in excess 20,000 gpm. Based on engineering judgment (including a review of Beaver Valley Calculation DSC-0368, which estimated water leakage past closed doors during a flood event) the incoming flows from the Water Treatment Building due to the LlP, for a flood duration of 30 minutes, will not approach the flooding values previously evaluated. Based on this, there is no impact to Key SSC's from flooding through the Water Treatment Building doors.

Only permanent passive features are relied upon during the revised site specific LIP event. No Key SSC's are impacted by the revised LlP, thus no additional actions or strategies are required.

The existing site Emergency Plan Off Norma! Occurrence Procedure RA-EP-02810 - Tornado or High Winds contains actions required to respond to severe weather notifications. This procedure uses various external agency inputs for determining the potential for severe weather. The "Hazardous Weather Outlook" is produced daily and identifies any potential significant weather in the next seven days. The procedure contains actions based on the nature of the weather threat. Additionally, a trigger point has been developed which provides sufficient warning time for the site to prepare in the event of excessive rainfall prediction.

6.2 SuruMARy oF Pt.aNT MoDrFrcATroNs AND Cnaucrs Based on the results of the revised PMSS and LIP evaluations, no site actions are required, procedure upgrades are not necessary and no modifications are needed.

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Letter L-L7 -L7 6 Enclosu re May 2OL7 7 FTOOD IMPACT ASSESSMENT 7.1 Flooo MrcHANrsM PMSS (Pnrn l Assrssurrur) 7.1.1Comparison of New Flood Levels to the Design Basis PMSS Flood Mechanism Parameters Plant Design or Bounded (B) or Parameter Description licensing Basis Revised Levels Not Bounded Flood Levels (NBI t Max Stillwater Elevation s83.7 ft s83.8 ft NB Max Wave Run-up 2

Elevation s90.3 ft s87.2 ft B (at wave protection dike)

Although the Max Stillwater Elevation is not bounded, the area of inundation in the revised calculation shows there is no flooding in the power block area. Based on this, no safety-related structures containing Key SSC's are impacted by flooding during a PMSS event. The reduction in the Max Wave Run-up Elevation results in a bounded condition and precludes power block area flooding. Outlying area flooding (non-power block area) has no impact on KSFs or Key SSC's.

7.2 FlooD MEcHANTSM LIP (Pnrn 2 AssrssMENrl 7.2.1Description of LIP Flood lmpact Available Physical Margin (APM) calculations were performed to the new LIP calculation flood height (585.1ft) to support the MSA. The calculations are included in the MSA support document NORM-LP-722L All features were identified as part of the 50.54(f) 2.3 Flooding Walkdown and subsequent RAI response. The results of the APM Calculation identified 10 seals with a small margin and one seal with negative margin. Small margin at DBNPS has been defined as less than 7.2 inches per CR 2014-00373.

The 10 seals with small margin have a positive margin at the new LIP value. The seals are below grade and are for prevention of groundwater ingress. lt has been determined that the LIP event does not cause a groundwater surcharge due to its short duration and the impermeable materials surrounding the power block. The seals are not subject to any other associated effects from the LlP. The seals were walked down and determined to be adequate in accordance with NEI L2-07 guidance used to perform the 2.3 Flooding walkdowns (Reference L7l.

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Letter L-L7 -L7 6 Enclosu re May 2OL7 The seal with negative margin is subject to groundwater only and will not experience any additional pressure during a LIP event. This seal was evaluated in the MSA as not posing a flooding risk during a LIP as the existing groundwater pressure on the seal does not change.

Based on the flooding walkdown, the seal is not showing indications of any leakage and therefore determined to be sound. The seal, located in the Borated Water Storage Tank (BWST) pipe tunnel, is not subject to any other associated effects from the LlP, was walked down and determined to be adequate in accordance with NEI 12-07 guidance used to perform the 2.3 Flooding walkdowns (Reference 17).

Other flood protection features have APM exceeding 10 inches. No above grade flood protection features are subject to the LIP (i.e., lntake Structure water tight doors).

Since the LIP WSE is at the site design elevation for flood protections features, and no grade level protection features are subject to any associated effects there are no additiona! APM calculations to perform.

All Key SSC's have been determined to be adequately protected by the existing flood protection features.

7.2.2 Adequate APM Justification and Reliahility Flood Protection The adequacy of the flood protection features was discussed in the previous section. Reference 17 identified the sites flood protection features and determined all were subject to periodic maintenance to insure there is continued functionality. The revised LIP analysis does not affect the previously submitted information. This was reviewed by the Staff in Reference 16, and found to be acceptable.

7.2.3 Adequate Overall Site Response This section is not applicable to DBNPS as no manual actions are required to implement the flood protection strategy. No flood mitigation equipment is required. Site flooding response discussed in Reference 17 remains unchanged. This was reviewed by the Staff in Reference 16, and found to be acceptable.

The MSA for Flooding (Reference L5) addressed actions related to FLEX implementation. No actions were related to protecting Key SSC's from flooding. No actions were considered Time Sensitive Actions relating to flooding.

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Lette r L-L7 -L7 6 Enclosu re May 2OL7 I CONCTUSTON This evaluation has determined that the unbounded flood mechanisms, PMSS and LlP, previously submitted in the FHRR, do not impact any Key SSC's or challenge any KSFs at DBNPS.

The revised PMSS calculation has removed all flooding in the power block area. Outlying areas still susceptible to flooding pose no threat to continued safe operation of DBNPS. No modifications to plant structures or flood protection features are required. Also, no changes to existing site flooding response procedures are required. Existing site procedures adequately address potential flooding of outlying areas.

The revised LIP calculation has removed flooding from critical doors that lead directly to Key SSC's. Non-critical doors that see minimal flooding are not designated as flood protection features. Leakage through these doors does not impact Key SSC's or present any potential impact to KSFs. No modifications to plant structures or flood protection barriers and no changes to existing site flooding response procedures are required.

This submittal completes the actions related to external flooding required by the March L2, 2OLZ 10C F R50.54(f) letter.

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FENOC- 550t North Srata Rwte 2 Fi r stE ne g y NucI ear OW rati ng fun pany OaR Harbq Ohio 43449

ian D. Eotsg 419-321-7676 Wce President, Fax:41*321-7582 Nucleu July 11,2017 L-17-176 10 cFR 50.54(0 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852