ML17097A196

Audit Report Relating to the Flood Hazard Reevaluation Report

ML17097A196
Person / Time
Site:	Prairie Island
Issue date:	04/18/2017
From:	Lauren Gibson Japan Lessons-Learned Division
To:	Northard S Northern States Power Company, Minnesota
Gibson L, NRR/JLD, 415-1056
References
CAC MF7710, CAC MF7711
Download: ML17097A196 (11)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 April 18, 2017 Mr. Scott D. Northard Vice President Northern States Power Company - Minnesota Prairie Island Nuclear Generating Plant 1717 Wakonade Drive East Welch, MN 55089-9642

SUBJECT:

NUCLEAR REGULATORY COMMISSION REPORT FOR THE AUDIT OF NORTHERN STATES POWER COMPANY'S FLOOD HAZARD REEVALUATION REPORT SUBMITTAL RELATING TO THE NEAR-TERM TASK FORCE RECOMMENDATION 2.1 -FLOODING FOR PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNITS 1 AND 2 (CAC NOS. MF7710 AND MF7711 ))

Dear Mr. Northard:

The purpose of this letter is to provide you with the final audit report which summarizes and documents the U.S. Nuclear Regulatory Commission's (NRC's) regulatory audit of the Flood Hazard Reevaluation Report (FHRR) submitted by Northern States Power Company, a Minnesota corporation (NSPM, the licensee), doing business as Xcel Energy, related to Prairie Island Nuclear Generating Plant (Prairie Island). The FHRR was submitted as part of implementing lessons learned from the 2011 accident at the Fukushima Dai-ichi nuclear plant.

Specifically, the FHRR documents the results of the flood hazard reevaluation being completed as part of NRC Near-Term Task Force Recommendation 2.1.

By letter dated June 7, 2015 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML16152A126), the NRC informed you of the staff's plan to conduct a regulatory audit of NSPM's FHRR submittal for Prairie Island. The audit was intended to support the NRC staff's review of the licensee's FHRR and the subsequent issuance of a staff assessment documenting the staff's review. The audit was conducted remotely during the months of June 2016 - March 2017, with a teleconference on August 18, 2016. The audit was performed consistent with NRC Office of Nuclear Reactor Regulation Office Instruction LIC-111 ,

"Regulatory Audits," dated December 29, 2008 (ADAMS Accession No. ML082900195). The details of the audit were discussed with Ms. Lynne Gunderson of your staff.

S. Northard If you have any questions, please contact me at (301) 415-1056 or by e-mail at Lauren.Gibson@nrc.gov.

Sincerely, Lautd:./;!Manager Hazards Management Branch Japan Lessons-Learned Division Office of Nuclear Reactor Regulation Docket Nos. 50-282 and 50-306

Enclosure:

Audit Report cc w/encl: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 AUDIT REPORT BY THE OFFICE OF NUCLEAR REACTOR REGULATION FOR THE AUDIT OF NORTHERN STATES POWER COMPANY'S FLOOD HAZARD REEVALUATION REPORT SUBMITTAL RELATING TO THE NEAR-TERM TASK FORCE RECOMMENDATION 2.1-FLOODING FOR PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNITS 1 AND 2 DOCKET NO. 50-282 AND 50-306 BACKGROUND AND AUDIT BASIS By letter dated March 12, 2012, the U.S. Nuclear Regulatory Commission (NRC) issued a request for information to all power reactor licensees and holders of construction permits in active or deferred status, pursuant to Title 10 of the Code of Federal Regulations ( 10 CFR),

Section 50.54(f), "Conditions of Licenses" (hereafter referred to as the "50.54(f) letter). The request was issued in connection with implementing lessons learned from the 2011 accident at the Fukushima Dai-ichi nuclear power plant, as documented in the NRC's Near-Term Task Force report. Recommendation 2.1 in that document recommended that the NRC staff issue orders to all licensees to reevaluate seismic and flooding hazards for their sites using current NRC requirements and guidance. Subsequent staff requirements memoranda associated with SECY-11-0124 and SECY-11 -0137 instructed the NRC staff address this recommendation through the issuance of requests for information to licensees pursuant to 10 CFR 50.54(f).

By letter dated May 9, 2016 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML16133A041 ), Northern States Power Company, a Minnesota corporation (NSPM, the licensee), doing business as Xcel Energy, submitted its Flood Hazard Reevaluation Report (FHRR) for Prairie Island Nuclear Generating Plant, Units 1 and 2 (Prairie Island). The NRC is in the process of reviewing the aforementioned submittals and has completed a regulatory audit of NSPM to inform the licensee of its review of the submittals, identify any similarities/differences with past work completed, and ultimately aid in its review of licensees' FHRR. This audit summary is being completed in accordance with the guidance set forth in NRC Office of Nuclear Reactor Regulation Office Instruction LIC-111 , "Regulatory Audits," dated December 29, 2008 (ADAMS Accession No. ML082900195}.

AUDIT LOCATION AND DATES The audit was completed by document review via electronic reading room (ERR) and a teleconference held on August 18, 2016. A closeout phone call was held on April 5, 201 7.

Enclosure

AUDIT TEAM Title Team Member Organization Team Leader, NRR/JLD Anthony Minarik NRG Project Manager, NRR/JLD Lauren Gibson NRG Branch Chief, NRO/DSEA Aida Rivera NRG Branch Chief, NRO/DSEA Christopher Cook NRG Technical Manager Richard Rivera-Lugo NRG Lead Hydrologist Mike Lee NRG Contractor Vinod Mahat ANL Contractor Nicholoas Haas ANL Contractor John Quinn ANL Contractor Eugene Yan ANL DOCUMENTS AUDITED of this report contains a list that details all the documents reviewed by the NRG staff, in part or in whole, as part of this audit. The documents were located in an ERR during the NRG staff review.

AUDIT ACTIVITIES In general, the audit activities consisted of the following actions:

• Review background information on site topography and geographical characteristics of the watershed.

• Review site physical features and plant layout.

• Understand the selection of important assumptions and parameters that would be the basis for evaluating the individual flood-causing mechanisms described in the 50.54(f) letter.

• Review model input/output computer files, such as Hydrologic Engineering Center (HEC)-River Analysis System (RAS), FL0-2D, and HEC- Hydrologic Modeling System (HMS), to gain an understanding of how modeling assumptions were programmed and executed. of this report provides more detail and summarizes specific technical topics (and resolution) of important items that were discussed and clarified during the audit. The items discussed in Attachment 2 may be referenced/mentioned in the staff assessment in more detail.

CLOSEOUT TELECONFERENCE MEETING Following the August 18, 2016, teleconference, the NRC staff identified certain information that needed to be provided on the docket in order to resolve some of the items discussed during the audit. The information updated or supplemented the FHRR based on the audit discussions.

This information included the following :

1) Certain plant diagrams showing the locations of key doors The requested information was received by e-mail dated September 29, 2016 (ADAMS Accession No. ML16279A479, non-public) , with three attachments (ADAMS Accession Nos.

ML16280A035, ML16280A037, and ML16280A042, all non-public).

On April 5, 2017, the NRC informed the licensee that no further information was needed for the audit and that the virtual audit was henceforth considered closed .

Attachments:

1. Audit Documents

2. Prairie Island Information Needs - Audit/Post-Audit Summary

ATTACHMENT 1 Prairie Island Nuclear Generating Plant, Units 1 and 2 Audit Document List

1. Black & Veatch, 2014, "Local Intense PMP Hydrology and Hydraulics," Calculation No.

180461 .51 .1005, Revision 0. September 2014.

2. Black & Veatch , 2016, "Local Intense PMP Hydrology and Hydraulics," Calculation No.

180461.51.1005, Revision 1. September 2016.

3. NSPM (Northern States Power - Minnesota), 2016a, "FHRR (Flood Hazard Reevaluation Report) Audit Presentation 8-18-16-Webinar Slides", in response to Prairie Island Nuclear Generating Plant (PINGP) Information Needs - Local Intense Precipitation, August 18, 2016.

4. NSPM, 2016b, "

Subject:

Prairie Island Nuclear Generating Plant Flood Hazard Reevaluation Report - Responses to Requested Information (CAC Nos. MF7710 and MF7711 )," email from Lynne Gunderson, Prairie Island Projects Licensing to Lauren Gibson, Project Manager, U.S. Nuclear Regulatory Commission , September 29, 2016, 4:05 PM, ADAMS Accession No. ML16279A476.

5. USDA (U.S. Department of Agriculture) , 1986, "Urban Hydrology for Small Watersheds",

Technical Release 55, Natural Resources Conservation Service, USDA, June 1986.

6. Xcel Energy, 2016a, "Calculation 180461 .51 .1005 Rev O - Local Intense Precipitation, HEC-HMS and HEC-RAS Input & Output files", in a CD of "Prairie Island Nuclear Generating Plant" prepared on June 15, 2016 and sent to Victor Hall, Project Manager, U.S. Nuclear Regulatory Commission , June 2016.

7. Xcel Energy, 2017, "Calculation 180461.51 .1005 Rev 1 - Local Intense Precipitation ,

HEC-HMS and HEC-RAS Input & Output files", in a CD prepared for U.S. Nuclear Regulatory Commission, received in February 2017.

ATTACHMENT 2 Prairie Island Nuclear Generating Plant Information Needs - Audit/Post-Audit Summary Information Information Need Description Response Need No.

1 Local Intense PreciQitation - Drainage basin #205 The licensee provided figures that showed topographic outflow routing in HEC-RAS Model contours of the ground surface within the reactor site; those contours illustrated a relatively steep slope for subbasin #205

Background:

In the LIP flood hazard calculation in comparison to the balance of the site's topography.

package (Black & Veatch, 2014), Figure 5.3.2-2 is Moreover, the orientation of the topographic contours within entitled "HEC-RAS Model Schematic in the Vicinity subbasin #205 indicates that the ground surface slopes away of Structures of Concern." Each subbasin depicted from areas and structures of concern within the powerblock.

within the figure has associated with it an inflow and The licensee also performed a simple hydraulic analysis to outflow. However, the outflow from subbasin #205 is estimate the Froude number for the three reaches that pass not routed to any of the potential reaches identified through subbasin 205 based on the estimated flow rate, within the LIP model (i.e., river reach #203, river slope, and flow depth for each of the reaches within subbasin reach #204, or river reach #234 marked by the black #205. The resultant Froude numbers were all found to be arrows), nor is the outflow routed over any potential greater than 1. The licensee stated that the upstream water lateral structures (none of which are shown as being depth is not impacted by downstream flow depths based on available to subbasin #205). the hydraulic condition of a Froude number greater than 1 (NSPM, 2016a).

Request: It is requested that the licensee describe how the HEC-RAS modeling structures cited above The NRG staff checked the assumptions described by the were developed, and clarify how flow routing from licensee during the audit, as outlined in the response to this subbasin #205 to the appropriate river reach was information need request, and concluded that the information treated. provided by the licensee was sufficient to address the information need request.

2 Local Intense PreciQitation - Source of inflow to In response to the information need request, the licensee river reach #210 in HEC-RAS Model indicated that the inflow hydrograph used for stream reach

1. 210 in the HEC-RAS model was incorrectly taken from the

Background:

In the LIP flood hazard calculation outflow hydrograph of subbasin #210 based on a previous package (Black & Veatch , 2014), Figure 5.3.2-2 is run of the HEC-HMS model with a higher lag time which entitled "HEC-RAS Model Schematic in the Vicinity resulted in lower flow. The licensee noted that it

Information Information Need Description Response Need No.

of Structures of Concern." Each subbasin depicted subsequently updated the inflow hydrograph for reach #210 within the figure has associated with it an inflow and with the correct HEC-HMS outflow hydrograph for that outflow. Upon review, it was found that the inflow to particular subbasin. A preliminary run of the HEC-RAS model river reach #21 O could not be matched to output from with updated inflow hydrograph was performed, and the any of the HEC-HMS subbasins to which it might be model results indicated that changes in the estimated physically correlated in the licensee's LIP model - maximum water surface elevations (WSEs) at all the critical specifically subbasins #210, #214, #217, #294, or door locations were insignificant (<0.01 ft). The licensee also

1. 299 . stated that it intended to initiate a corrective action process with its technical assistance contractor to verify and update Request: It is requested that the licensee describe the LIP calculation packages and models. Nevertheless, the the source of the inflow hydrograph for river reach licensee stated that it anticipates no changes to the WSEs

1. 210, and describe how it was treated for the reported in the FHRR based on the preliminary results from purpose of maintaining mass balance within the LIP its corrected HEC-RAS model.

model.

The NRC staff performed a sensitivity of the computer model and with its results and the licensee's responses concluded that the information presented by the licensee was sufficient to address the information need request.

3 Local Intense Preci~itation - General reguest In response to the information need request, the licensee related to HEC-RAS modeling provided two tables that illustrated: (a) the linkage/correlation among the respective HEC-HMS subbasins, the

Background:

Figure 5.3.2-2 in the LIP calculation corresponding river reaches in the HEC-RAS model, and the package is a schematic diagram that shows a cross sections that receive flows from the various subbasins; general overview of the HEC-RAS modeling and (b) the correspondence between the subbasins in the structure. However, detailed information about HEC-HMS model and the respective storage areas in the which river reaches in the HEC-RAS model receive HEC-RAS model (NSPM 2016a) .

their water (hydrograph) from the corresponding drainage basin(s) in the HEC-HMS model is not The licensee also presented additional new information on explicitly specified. Review of the LIP model shows three critical door opening locations (Doors 420, 423, and that there is a total of 32 subbasins, 1O river reaches, 437) at the building designated "05/06". In response to this and 18 storage areas. Upon review of the new information, the staff requested that the licensee provide calculation package, the staff determined that figure(s) to illustrate all critical door opening locations information about river reach boundary conditions (includinq the three additional doors) at this new buildinq

Information Information Need Description Response Need No.

(including the missing data for subbasin #205), location as well as HEC-RAS river reaches and cross storage area boundary conditions, and connections sections associated with each of the critical door locations between these respective features was not specified using appropriate annotations and legends. In response to or discussed in any of the documents available to the this request, the figures were submitted to the NRC staff. electronically on September 29, 2016 (NSPM 2016b).

Request: It is requested that the licensee describe The licensee also updated calculation package "Local Intense for each river reach, where the water comes from PMP Hydrology and Hydraulics" (180461.51.1005 Rev. 1), to and is added at which cross section in the HEC-RAS include an evaluation of LIP at the three new door locations model. A table might be useful to convey this (Black & Veatch, 2016).

information . Also, it is requested that the licensee briefly describe the correspondence between the The NRC staff reviewed information provided during the reach in the HEC-RAS model and the respective audit, as well as the revised figures and revised calculation drainage basins in the HEC-HMS model. Again, a package (180461.51.1005 Rev. 1) subsequently provided by table might be useful to convey this information. the licensee, and concluded that the information provided was sufficient to address the information need request.

4 Local Intense PreciQitation - Unit h~drograQh In response to the information need request, the licensee explained that the lag time for the respective subbasins was

Background:

The licensee used the Soil chosen based on the minimum time of concentration used in Conservation Service (SCS) Unit Hydrograph the Technical Release 55 (TR-55) software (USDA 1986) due method to transform precipitation into runoff. A to the small size of the subbasins, and further reduction of lag derived unit hydrograph (including the SCS unit time is not necessary. The licensee also indicated that the hydrograph) may not always represent conservatively-chosen lag time would automatically result in hydrometeorological conditions that would prevail an increase in the unit hydrograph peak discharge, and thus during the probable maximum flood (PMF), and thus further adjustment in the peak discharge was not warranted.

non-linearity adjustments to the unit hydrograph should be made by increasing the peak of the unit The staff subsequently conducted an independent sensitivity hydrograph by 20% and reducing the time to peak by analysis and based on the results concluded that the 33% as per recommendations presented in information provided by the licensee is sufficient to address NUREG/CR-7046 (NRC, 2011 ). In connection with the information need request.

its review, the staff determined that this adjustment was not applied in estimation of the unit hydrograph.

Information Information Need Description Response Need No.

Request: It is requested that the licensee explain why the unit hydrograph was not adjusted to account for the effects of a non-linear basin response to the peak flow.

Sources:

Black & Veatch, 2014, "Local Intense PMP Hydrology and Hydraulics," Calculation No. 180461.51 .1005, Revision 0. September 2014.

Black & Veatch, 2016, "Local Intense PMP Hydrology and Hydraulics," Calculation No. 180461 .51.1005, Revision 1. September 2016.

NSPM, 2016a, "FHRR (Flood Hazard Reevaluation Report) Audit Presentation 8-18 Webinar Slides", in response to Prairie Island Nuclear Generating Plant (PINGP) Information Needs - Local Intense Precipitation, August 18, 2016.

NSPM, 2016b, "

Subject:

Prairie Island Nuclear Generating Plant Flood Hazard Reevaluation Report - Responses to Requested Information (CAC nos. MF7710 and MF7711 ), email from Lynne Gunderson , Prairie Island Projects Licensing to Lauren Gibson, Project Manager, U.S. Nuclear Regulatory Commission, September 29, 2016, 4:05 PM, ADAMS Accession No. ML16279A476.

Xcel Energy, 2016a, "Calculation 180461.51.1005 Rev O - Local Intense Precipitation, HEC-HMS and HEC-RAS Input & Output files", in a CD of "Prairie Island Nuclear Generating Plant" prepared on June 15, 2016 and sent to Victor Hall, Project Manager, U.S.

Nuclear Regulatory Commission , June 2016.

Xcel Energy, 2017, "Calculation 180461.51.1005 Rev 1 - Local Intense Precipitation , HEC-HMS and HEC-RAS Input & Output files",

in a CD prepared for U.S. Nuclear Regulatory Commission, received in February 2017.

S. Northard NUCLEAR REGULATORY COMMISSION REPORT FOR THE AUDIT NORTHERN STATES POWER COMPANY'S FLOOD HAZARD REEVALUATION REPORT SUBMITTAL RELATING TO THE NEAR-TERM TASK FORCE RECOMMENDATION 2.1-FLOODING FOR PRAIRIE ISLAND-NUCLEAR GENERATING PLANT, UNITS 1 AND 2 DATED APRIL 18, 2017 DISTRIBUTION:

PUBLIC JLD R/ F RidsNRRJLD Resource RidsNrrPMPrairielsland Resource MShams, NRR BHayes, NRO CWolf, OCA RRivera-Lugo, NRO CCook, NRO KQuinlan, NRO Mlee, NRO LGibson , NRR LQuinn-Willingham, NRO MWillingham, NRO RidsNrrDorlLPL3 Resource ADAMS Accession No.: ML17097A196

• via email OFFICE NRR/JLD/JHMB/PM NRR/JLD/JHMB/LA NRO/DSEA/RHM1/BC NRR/JLD/JHMB/BC NAME LKGibson Slent CCook NSanfiliooo DATE 4/13/17 4/10/17 4/13/17 4/14/17 OFFICE NRR/JLD/JHMB/PM NAME LKGibson (FVega for)

DATE 4/18/17