NG-16-0153, Response to Request for Information Supporting Flooding Hazards Reevaluation Report Audit

Response to Request for Information Supporting Flooding Hazards Reevaluation Report Audit

ML16229A159
Person / Time
Site:	Duane Arnold
Issue date:	08/12/2016
From:	Vehec T NextEra Energy Duane Arnold
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NG-16-0153
Download: ML16229A159 (6)

Text

August 12, 2016 NG-16-0153 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Duane Arnold Energy Center Docket No. 50-331 Facility Operating License No DPR-49 Response to Request for Information Supporting Flooding Hazards Reevaluation Report Audit

References:

(1) Response to NRC Request for Information Pursuant to 10 CFR 50.54(f)

Regarding Recommendation 2.1, Flooding, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident: Flood Hazard Reevaluation Report, dated March 10, 2014(ML14072A020)

(2) Nuclear Regulatory Commission Plan for the Audit of NextEra Energy Duane Arnold, LLC's Flood Hazard Reevaluation Report Submittal Relating to the Near-Term Task Force Recommendation 2.1 - Flooding for Duane Arnold Energy Center, dated June 17, 2015(ML15160A715)

By letter dated March 10, 2014, NextEra Energy Duane Arnold, LLC (Duane Arnold) submitted a Flooding Hazards Reevaluation Report (FHRR) (Reference 1) in response to Title 10 of the Code of Federal Regulations 50.54(f) Request for Information, relating to Recommendation 2.1.

By letter dated June 17, 2015 (Reference 2), the NRC notified Duane Arnold of upcoming audit activities related to review of the FHRR submittal. During teleGonferences conducted during the audit, the NRC Staff requested clarifications related the Duane Arnold FHRR submittal.

Enclosure 1 provides the requested information.

This letter contains no new regulatory commitments. If you have any questions or require d~on, please contact Mike Davis at 319-851-7032.

T. A. Vehec Vice President, Duane Arnold Energy Center NextEra Energy Duane Arnold, LLC

. Enclosures cc: Regional Administrator, USNRC, Region Ill Resident Inspector, USNRC, Duane Arnold Energy Center Project Manager, USNRC, Duane Arnold Energy Center NextEra Energy Duane Arnold, LLC, 3277 DAEC Road, Palo, IA 52324

Enclosure 1 to NG-16-0153 NEXTERA ENERGY DUANE ARNOLD, LLC DUANE ARNOLD ENERGY CENTER RESPONSE TO REQUEST FOR INFORMATION SUPPORTING FLOODING HAZARDS REEVALUATION REPORT AUDIT 4 Pages Follow

Clarification Request Provide Local Intense Precipitation (LIP) maximum water surface elevations.

Response

During the audit discussions, NextEra provided flooding elevations associated with a LIP event.

• In the FHRR, only the flooding depths at the four critical door locations for the Turbine Building were given: The flood elevations (the ground elevation plus the depths) as a result of LIP-cau"sed flooding at the four critical doors are provided in Table 1.

Clarification Request In developing the probable maximum precipitation (PMP) used to estimate the probable maximum flood (PMF) at the Duane Arnold site, the analysis selected the complete drainage area of the Cedar River watershed at the point where the Cedar River joins the Iowa River. The*

- FHRR reported thatthe area of the watershed upstream of the Duane Arnold site is 6,250 mi 2 ,

and the total drainage area at the mouth of the Cedar River is 7,824 mi 2 . Because the area upstream of the Duane Arnold site is about 20 percent smaller than the total watershed area, there could be a significant increase in the PMP if the smaller area is used with depth-area-duration curves to estimate basin average precipitation.

Further, the requisite wind-wave calculations associated with the revised PMF elevation resulting from the use of the 6,250 mi 2 drainage basin area must be provided.

R~sponse

- The PMP is developed from envelopment curves (i.e., depth-area-duration relationships) specific to the DAEC location. Updates were made to the depth-area envelopment curves to be closer to actual data through further analytical refinements. These refined PMP envelopment values are provided in Table 2. The smaller drainage area (-6,250 mi 2 ) was evaluated with a refined PMP with calibrated/defined channel roughness and infiltration losses as presented in the DAEC FHRR.

In the FHRR analysis for a total drainage area of 7,824 mi 2 , the peak water surface elevation (WSEL) at DAEC was +763.5 ft-NAVD88. For the smaller drainage area evaluation described above, the peak WSEL increased by 1.3 ft to +764.8 ft-NAVD88.

Due to the increase-in peak PMF WSEL ~t DAEC, wind-wave activity was recomputed using the same methodology as detailed in the DAEC FHRR.

Wave runup was evaluated for the spectrum of waves that can potentially impact DAEC coincident with the PMF event. Wave action and calculations were performed based on methodologies and equations from the United States Army Corps of Engineers (USAGE)

. (USAGE, 1984; USAGE, 2008). The wind-generating wave mechanism considered the 2-year period wind speed along the critical fetch length, wind setup, wave setup and the potential for

- wave breaking, wave refraction, and wave shoaling were examined from topography and bathymetry near DAEG. Cross sections were cut using ArcGIS to show detailed topographic layouts of the ground surface across the fetch length to the DAEC power block. Other cases of

• wind and wave activity and associated wave runup were not examined, as they are less critical cases. Wave runup was calculated using parametric equations.

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The critical scenario for wave run up may occur from waves propagating from the east, west, south, southwest, southeast or northeast over the critical systems, structures, and components (SSCs) at the DAEC power block. These directions would have the most unobstructed route approaching the critical SSCs at DAEC during the PMF event and therefore were analyzed to determine the critical scenario for wave runup.

Fetch is defined as a distance over which the wind speed and direction are reasonably constant.

Fetches fall into two categories, open-water fetches, where wave growth is limited only by the *.

• incident meteorological conditions, and restricted fetches, where wave growth is)imited by .a confined geometry such as that of a lake, river, bay, or reservoir. DAEC is subject to a restricted

• fetch. The restricted fetch methodology applies the concept of wave development in off-wind directions and considers the shape of the basin.

The.results of the wind-wave activity recomputation are summarized in Table 3 for each cardinal and intercardinal side of the site. The bounding total wave activity (i.e., combined wind setup, wave setup and wave runup), which occurs on the south side of DAEC, was 2.6 ft in the DAEC FHRR. For* the revised PMF peak WSEL, the bounding total wave activity remains 2.6 ft above the peak PMF still water elevation. Figure 1 shows the controlling southerly fetch of 11 ,200 feet crosses groups of mature standing trees multiple times before it terminates at a stand of mature trees adjacent to an elevated highway. At this location, the peak PMF water surface is approximately 20 feet*above the ground surface elevation. Hence, the tops of larger vegetation would be expected to be at or above the peak PMF water level. However, it was conservatively assumed that a sustained wind would persist along that entire fetch uninhibited; in actuality, the clusters of mature trees and other vegetation within the fetch length would be expected to shorten the effective fetch length and attenuate wave growth/propagation. Smaller, attenuated waves would be expected to generate lower vertical wave runup heights at the site. Accordingly, the bounding total vertical water elevation is +767.4 ft-NAVD88 (767.8 ft-MSL) on the south side of DAEC. Other sides of the plant experience slightly lower total water elevations primarily because of shorter fetch lengths (Table 3). As noted in the current UFSAR Section 3.4, openings in safety-related buildings are protected from wave runup to an elevation of 770.5 ft-MSL on the northerly side, 773.7 ft-MSL on the southerly side and 769 ft-MSL on all other sides of safety-related buildings. There is available physical margin between the bounding total vertical elevations and the COB protection elevations.

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Table 1 - FHRR LIP Maximum Water Depths and Maximum Water Surface Elevations FL0-2D Cell Maximum Water Maximum Water Surface Door ID Elevation (ft-MSL) Depth (ft) Elevation (ft-MSL) 124 757 .5 0.5 758 .0 136 757.4 0.8 758 .2 137 757.4 0 .8 758 .2 154 757.4 0.6 758 .0 Table 2 - FHRR Site-Specific PMP Envelopment Values Licensee's D-A- D Values (from Excel files)

Duration (hours) 6 12 24 48 n 10 7.1 9.6 13.6 15.5 15.6 100 6.9 9.3 13.4 14.8 14.9 200 6.7 9.0 13.1 14.4 14.5 500 6.4 8.5 12.4 13.8 13.9 1000 6.1 8.1 11.7 13.2 13.3 2000 5.7 7.6 11.0 12.5 12.6 5000 5.2 6.9 9.9 11.5 11 .6 10000 4.5 6.1 8.7 10.5 10.6 20000 3.6 5.3 7.4 9.3 9.4 Table 3 - Wind Wave Results for Smaller Drainage Basin Area PMF Sibul Total Total Affected Wave Wave Wind Stillwater Fetch Wind Vertical Vertical Side of Setup Runup Direction Elevation (ft) Setup Height Height DAEC Site (ft) (ft)

(ft-NAVD88) (ft) (ft-NAVD88) (ft-MSL)

Northerly South +764.8 11,200 0.135 0.289 2.17 +767.4 +767.8 Northeasterly Southwest +764.8 10,000 0.122 0.276 2.06 +767.3 +767.7 Easterly West +764.8 1,600 0.031 0.117 0.85 +765.8 +766.2 Southwesterly Northeast +764.8 6,400 0.083 0.228 1.69 +766.8 +767.2 Westerly East +764.8 3,600 0.053 0.174 1.28 +766.3 +766.7 Northwesterly Southeast +764.8 3,600 0.053 0.174 1.28 +766.3 +766.7 1 1 1 1 1 Southeasterly Northwest +764.8 N/A N/A N/A N/A N/A N/A 1 Southerly North +764.8 N/A 2 N/A 2 N/A 2 N/A 2 N/A2 N/A 2 Note: Wind speed for all directions =40 mph.

1 The elevation increases above the PMF northwest of the site, therefore , it is unlikely that a critical wave run-up scenario would occur with the wind directed southeast.

2 There are no open ings to safety-related structures directly north of the power block, therefore ,

it is unlikely that a critical wave run-up scenario would occur when the wind is directed south.

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Legend PMF Inundated Area

• OTE: Manning's n polygon shapefile from the FHRR calculations containing mature tree gro vth.

Figure 1 - Dense Vegetation and Other Obstacle Locations Page 4 of 4