ML14329B209

Summary of Regulatory Conference to Discuss Safety Significance of Arkansas Nuclear One Flood Protection Deficiencies

ML14329B209
Person / Time
Site:	Arkansas Nuclear
Issue date:	11/25/2014
From:	Ryan Lantz NRC/RGN-IV/DRP/RPB-E
To:	Jeremy G. Browning Entergy Operations
C. Young
References
EA-14-088
Download: ML14329B209 (40)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION REGION IV 1600 E LAMAR BLVD ARLINGTON, TX 76011-4511 November 25, 2014 EA 14-088 Jeremy Browning, Site Vice President Arkansas Nuclear One Entergy Operations, Inc.

1448 SR 333 Russellville, AR 72802-0967

SUMMARY

OF REGULATORY CONFERENCE TO DISCUSS SAFETY SIGNIFICANCE OF ARKANSAS NUCLEAR ONE FLOOD PROTECTION DEFICIENCIES

Dear Mr. Browning:

On October 28, 2014, members of the U.S. Nuclear Regulatory Commission staff met with representatives of the Arkansas Nuclear One facility to discuss apparent violations affecting Units 1 and 2 related to flood protection deficiencies as documented in Nuclear Regulatory Commission Inspection Report 05000313; 368/2014009, issued on September 9, 2014 (ML14253A122). The focus of the regulatory conference was a discussion of information important to characterize the safety significance of the flood protection deficiencies. The discussion included methodologies used by Entergy to develop the probable maximum precipitation and probable maximum flood for the Arkansas Nuclear One site, including development of an annual exceedance probability for the probable maximum precipitation. The discussion also included actions that may have been taken in the event of flooding at the site to mitigate the consequences of the flooding performance deficiencies.

The Nuclear Regulatory Commission staff asked questions during this regulatory conference, with some questions requiring additional information that you indicated you would supply to us.

The Nuclear Regulatory Commission will continue to review the information that you provided during the Regulatory Conference and the subsequent information that was requested in order to reach a final significance determination. We will issue a final significance determination letter to you when that review has been completed.

This Category 1 public meeting was attended by two members of the public at the Region IV office, as well as several members of the public on the teleconference bridge that was provided.

A copy of your presentation slides is included as (Enclosure 1). Copies of the Nuclear Regulatory Commission slides (Enclosure 2) and meeting attendance lists (Enclosure 3) are also included.

J. Browning In accordance with 10 CFR 2.390 of the NRCs Rules of Practice, a copy of this letter and its enclosures will be available electronically for public inspection in the NRCs Public Document Room or from the Publicly Available Records (PARS) component of the NRCs ADAMS. ADAMS is accessible from the NRC web site at http://www.nrc.gov/reading-rm/adams.html (The Public Electronic Reading Room).

Sincerely,

/RA/

Ryan E. Lantz, Chief Project Branch E Division of Reactor Projects Docket Nos.: 50-313, 50-368 License Nos.: DPR-51, NPF-6

Enclosures:

1. ANO Presentation Slides

2. NRC Slides

3. Meeting Attendance Forms

ARKANSAS NUCLEAR ONE REGULATORY CONFERENCE October 28, 2014 OPENING COMMENTS Jeremy Browning ANO Site Vice-President Agenda Opening Comments

• ANO and Entergy recognize the significance of the performance

• Opening Comments deficiency

• Performance Deficiency

• Entergy concurs with the performance deficiency

• Root cause evaluations performed

• Risk Significance Assessment

• Effective immediate and long-term corrective actions have been taken

• Overview of Risk Assessment

• Fleet actions

• Station Response

• Focus of this meeting is to discuss risk significance of the violation

• Provide best estimate of initiating event frequency

• PMP and PMF Analysis

• Site specific flood hazard analysis

• Industry experts

• PMF Hydrology and Hydraulics External Peer Review

• Up to date techniques

• PMP Probability Evaluation

• Credit given to reasonable actions that would be pursued by the station to mitigate effects of flooding

• Significance Determinations

• We appreciate the opportunity to share additional information that

• Closing Comments improves the accuracy of the estimated risk following the event and supports a qualitative risk assessment 3 4

Performance Deficiency

• ANO agrees that there were deficiencies in the flood boundary

• Deficiencies can be placed in three categories

1. Original construction

2. Preventative Maintenance associated with hatches

3. Equipment removed from service PERFORMANCE DEFICIENCY

• Deficiencies are legacy issues

• Deficiencies have been corrected or compensated for Bryan Daiber

• Inspection conducted using industry approved guidelines ANO Design Engineering Manager in Nuclear Energy Institute (NEI) 12-07

• Incorporated lessons learned 6

Performance Deficiency

• Plant grade elevation 354

• No mitigating actions required

• The design flood elevation is 361

• Risk significance varies with elevation OVERVIEW OF RISK ASSESSMENT

• Below 356 - Mitigating actions available

• Unit 1 - 28 deficiencies (~1.0 ft2)

Dale James

• Unit 2 - 35 deficiencies (~0.72 ft2) Regulatory and Performance Improvement Director

• Emergency Diesel Generator (EDG) Fuel Oil Vault - No deficiencies 7

Overview of Risk Assessment Overview of Risk Assessment

• Vulnerability of performance deficiencies

• The World Meteorological Organization defines the PMP as The greatest depth of precipitation for a given duration meteorologically

• Site mitigating actions possible over a given size storm area at a particular location and at a

• Flood protection particular time of the year, with no allowance made for [future] long

• Operator response term climatic trends.

• ANO flooding reevaluation performed

• The PMF is defined by ANSI/ANS-2.8-1992 (ANS 1992) as the

• Probable Maximum Precipitation (PMP) Study hypothetical flood (peak discharge, volume, and hydrograph shape)

• Probable Maximum Flooding (PMF) Evaluation that is considered to be the most severe reasonably possible, based on comprehensive hydrometeorological application of PMP and other hydrologic factors favorable for maximum flood runoff such as sequential storms and snowmelt.

9 10 Overview of Risk Assessment Overview of Risk Assessment

• PMP/PMF evaluation

• Probability of PMP/PMF

• Site-specific study performed for 50.54(f)

• Probability is not zero response to Fukushima flooding reassessment

• Site-specific study performed to derive probabilistic estimate of PMP

• Consistent with NRC and other federal

• Multiple methods applied agencies guidelines

• Consistent with methodology used by other federal agencies to

• Where information was not available make risk-based decisions conservative assumptions were made

• Annual Exceedance Probability (AEP) based on PMP studied conservative with respect to PMF

• Results in site PMF level of 353.8 ft.

11 12

Overview of Risk Assessment Overview of Risk Assessment

• Risk Assessment performed utilizing PMP probability

• Manual Chapter 0609 - Appendix M Assessment combined with site mitigating actions

• 1.4 E-5 bounding risk - Based on site specific upper

• Risk from internal flooding in turbine building combined 95% for PMP resulting in 354 site flood elevation with external risk to determine overall risk

• Bounding value should be approximately an order of

• PRA Results magnitude lower when considering PMF

• Unit 1

• Mitigating actions would reduce risk further

• CDF = 7.99E-07/year

• Unit 2

• CDF = 2.16E-06/year 13 14 Objective

• Describe plant response to a flooding event

• Actions to prepare the plant

• Equipment effects

• Mitigating actions for flooding of Auxiliary Buildings

• Focus on water level between 354 and 356

• Developed in accordance with procedures in effect at STATION RESPONSE the time Gary Sullins

• No knowledge of deficiencies Unit 1 Operations Manager, Shift John Hathcote Unit 2 Operations Manager, Shift 16

Plant 404 TURB.

Initiating Event AUXILIARY BLDG BLDG Layout Offsite Control Power Room SFP

• Unprecedented rainfall upstream of ANO 386 FUEL OIL INTAKE AC/DC Switchgear, VAULT 378 378

• Flood is forecasted days in advance Batteries, etc.

SW Pumps 372 EDGs Fire M 368

• 5-day (120-hour) advance forecast per ANO SARs Water 366 Pumps 362

• PMP/PMF analysis supports > 5 day advance warning Ground Level 354 355

• Abnormal Operating Procedure (AOP) entry occurs at 354 335 General Area forecast of > 350

• Corporate Severe Weather procedure Normal U1 EFW SFP Clg U2 Charging U1 HPI Lake U2 Level AFW 338 335 317 329 U2 EFW General LPI/CS/DHR Note: 317 and 335 general areas are Area U2 HPSI isolated between units. AB Sump 317 18 17 Warning Time Site Preparation Warning Time for PMF

• Corporate Severe Weather Procedure 356 355 7.00

• Establishes severe weather duty roster 354

• Staffs Corporate Emergency Response Center 353 135 hr 6.00 352 120

• Prompts installation of temporary flood barriers 351 hr PMF Peak Stage 353.8 ft 350 5.00

• Natural Emergencies AOP Antecedent Storm (40% PMP)

End of PMP Onset of PMP 349

• Establishes contact with Corps of Engineers Stage (feet, NGVD29) Precipitation (inch) 348

• Shuts down both units 347 4.00 346 345

• Aligns SU2 Transformer for high water conditions 344 3.00 343

• Protects equipment (i.e., portable pump for steam generator (SG) feed) 342 341 340 2.00

• Response for Forecasted Flood > 350 339

• Well-staffed severe weather response teams (on and off site) 338 1.00 337

• Timely plant shutdown 336

• Intensive effort to protect the site 335 0.00 0 5 10 15 20 25 30 Time (days)

Precipitation PMF Stage 19 20

Timeline Temporary Flood Barriers Time (hrs)

• Prompted by Corporate Severe Weather Procedure Pre-Flood Actions 120 Enter severe weather procedures (forecast > 350)

• Two Options/Examples 108 Implement severe weather duty roster

• Water Tube System Initiate flood protection actions

• Use of local materials 96 Commence shut down of both units 84 Both units in Mode 3 Hot Standby (Reactor Subcritical) 72 Both units in Mode 5 Cold Shutdown (CSD) (RCS < 200F) 30 Notification of Unusual Event (NUE) Declared at > 345 21 22 Water Tube System Flood Protection - Use of Local Materials Entergy Sub-station - New Orleans Unit 1 South Entrance - Elevation 354 23 24

Unit 1 - Challenges to Plant Equipment Equipment Effects - Unit 1 Time

• Initial Conditions Estimates Event (hours)

• Mode 5 CSD (RCS <200F) with Decay Heat Removal (DHR) in service 0 Water begins entering the Auxiliary Building

• Reactor Coolant System (RCS) intact 4.5 Level at 335. Rising at 1.7 ft/hr

• Emergency Feedwater (EFW) available 4.5 A DH Vault HI LEVEL alarm 5 B DH Vault HI LEVEL alarm

• Potential Impact to Plant Equipment 5 B Motor Driven EFW pump not available

• Water accumulates in general areas of Auxiliary Building 6.5 Level at 338.8, lowest elevation of MOV for EFW

• As water rises in Auxiliary Building, water eventually enters DHR suction alignment vaults and DHR System becomes unavailable 9 A DHR Pump unavailable

• As water level rises above 335, EFW and High Pressure Injection 12 B DHR Pump unavailable (HPI) pumps become unavailable Based on in-flow analysis of identified barrier deficiencies 25 26 Procedure Options to Mitigate Unit 1 Service Water to EFW Flooding of Unit 1 Auxiliary Building

• Operating Crew and Support Staff recognize loss or

• Service Water (SW) to EFW impending loss of DHR and EFW

• Aligned at suction to EFW pumps

• Field monitoring of water level in Auxiliary Building

• DH Vault flood alarms (2 in room)

• Portable Pump for SG Feed

• Connected via Main Feedwater header

• Service Water aligned to suction of EFW Pump(s) per Overheating Emergency Operating Procedure (EOP)

(Control Room action)

• Two handswitches per train from the Control Room

• Injection control remains available from the Control Room 27 28

Unit 1 Portable Pump for SG Feed Unit 2 - Challenges to Plant Equipment

• Three portable pumps for SG feed available

• Similar initial conditions at time of postulated flood Unit 2

• Method of core cooling independent of EFW and DHR

• Mode 5 CSD (RCS < 200F) with Shutdown Cooling (SDC) in

• 1203.048 Security Event - Feedwater Actions service

• Operators trained on procedure

• RCS intact

• Feed source connected to Main Feedwater piping >372

• EFW available

• Provides 200 gpm flow to Steam Generator

• Potential Impact to Plant Equipment

• Available response time > 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> from loss of DHR

• Water accumulation in general areas of Auxiliary Building, based on Time to Core Uncovery (TTCU) calculations Emergency Safeguard Features (ESF) Vaults and EFW Rooms

• Demonstrated implementation time ~ 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />

• As water rises in the ESF Vaults, the SDC system becomes

• Practical to 356 unavailable

• As water level continues to rise, the EFW pumps become unavailable 29 30 Equipment Effects - Unit 2 Unit 2 SW to EFW Success Path Time Estimates

• Operating crew and plant support staff recognize the (hours) Event impending loss of EFW and SDC 0 External flood level at 354.2

• Room alarms and field reports

<0.5 Water begins to enter Aux Building General Area, B ESF

• 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> before option is unavailable Vault, 2P-7B EFW Room

<0.5 B ESF Vault and 2P-7B Room HI LVL Alarms

• Procedural Guidance to seek alternate sources of water 3 2P-7B unavailable for SGs 15 SW MOV to 2P-7A Unavailable

• Lower Mode Functional Recovery (LMFR) EOP 16 A SDC Pump unavailable Continuing Actions 29 B SDC pump unavailable (Loss of forced DHR)

• Heightened site focus on heat removal safety function

• Common approach to Unit 1

• Simple Control Room action to line up SW MOVs 31

• Two handswitches in Control Room 32

Unit 2 Portable Pump for SG Feed Station Response - Conclusion

• Consistent with Unit 1

• RCS Heat Removal independent of SDC

• Flooding conditions forecasted days in advance

• 1203.048 Security Event Attachment J Feedwater Actions

• Actions to prepare

• Guidance to feed Unit 2 SGs using portable pump

• Augment staffing

• Operations training provided on specific approach

• Shut down both units

• Procedural Actions

• Install temporary flood barriers

• Stage portable pump for SG feed near hydrant

• Advance plant shutdown provides time and resources to

• Connect hose from hydrant to flange on Startup and Blowdown support mitigating actions (SU/BD) system

• Mitigating actions

• Requires cutting 4 pipe to allow access to flange

• Service Water to EFW Pump Suction

• Procedure successfully mocked-up in less than one hour

• Portable Pump for SG feed connected via Main Feedwater Piping

• Response time estimate >24 hours from loss of SDC 33 34 Overview

• Calculations initiated to respond to NRC 50.54(f) request

• Conforms to NRC guidance and other federal guidelines (NUREG/CR-7046, FERC, USACE & NWS HMRs)

• Addressed large watershed (153,000+ sq.mi.) and data availability through

• Site specific PMP using methods endorsed by FERC, NRCS & USACE, and various state dam safety PMP AND PMF ANALYSIS agencies

• Extensive calibration and verification in lieu of complete David M. Leone, P.E.

USACE dam information Associate Principal / Hydraulic Engineer, GZA

• Incorporation of conservatisms (non-linearity, etc.)

• Unsteady USACE HEC-RAS model used to calculate PMF elevation at ANO of 353.8 ft (NGVD29) 36

Background:

Original Design Basis Flood

Background

• Straight line interpolation used to estimate water surface profile

• Original Design Basis Flood (from tailwater of Ozark L&D to Dardanelle L&D headwater)

• Maximum Probable Flood analysis by USACE in 1956 Ozark tailwater ANO

• Design Discharges for Dardanelle Dam, USACE, June 1956

• Watershed PMP developed based on 1943 historic storms Dardanelle

• Moved to critical locations and maximized headwater

• Occurred in series (back-to-back)

• Storms covered an area of 49,612 square miles

• Infiltration losses for Maximum Probable Flood (MPF) computed

• PMF maximum stillwater elevation = 358 ft based on 1943 stream gage data

• Wind-generated waves add 2.5 ft = 360.5 ft

• Peak discharge = 1.5 million cfs

• Alternative combined effect flood used was PMF (358 ft) plus

• Effects of flood regulation from dams and reservoirs were minimal failure of Ozark Dam (3 ft) = 361 ft (at that time)

• No waves added to this alternative 37 38 Overview David Leone, GZA, PMF Calculation Preparer Overview

• B.S/M.S. in Civil Engineering, Licensed P.E. in three states

• Over 16 years of hydrologic and hydraulic engineering experience focusing on rainfall-runoff

• Background Information and Consistency with Standards and hydraulic computer modeling and assessment and design of hydraulic structures such as dams. and Guidance for Flood Evaluation

• Team member for Post-Fukushima 50.54(f) Flood calculations on 18 NPP sites Peter Baril, GZA, PMF Calculation Reviewer

• Hydrologic Setting

• B.S. Biology /M.S. Hydrology, Licensed P.E. in 4 states, Professional Hydrologist (AIH) since 1988

• Probable Maximum Precipitation (PMP)

• Over 26 years of hydrologic and hydraulic experience focusing on flood control analysis and

• Probable Maximum Flood (PMF) - Hydrology design.

• Reviewer for Post-Fukushima 50.54(f) calculations on more than 10 Nuclear Power Plant

• Probable Maximum Flood (PMF) - Hydraulics (NPP) sites Bill Kappel, Applied Weather Associates, PMP Calculation Meteorologist Preparer

• B.S. Physical Science / M.S. Broadcast Meteorology

• Over 17 years of meteorology experience. Probable Maximum Precipitation and extreme storm analysis specialist since 2003.

• Applied Weather has completed over 60 site-specific PMP studies, including numerous 50.54(f) nuclear power plants.

Dr. Ed Tomlinson, Applied Weather Associates, PMP Calculation Meteorologist Reviewer

• B.A. Mathematics / M.S. and Ph.D. in Meteorology

• Over 40 years of meteorology experience. Peer reviewer for HMR-57.

39 40 PMP and extreme storm analysis specialist.

Consistency with Standards and Hydrologic Setting Guidance for Flood Evaluation

• Watershed is large: 153,000+ square miles

• Work performed to support NRC request (50.54(f) letter):

• Uses current state of knowledge and analytical methods

• Methods used in present-day standard engineering practice to develop the flood hazard

• NRC guidance: NUREG/CR-7046

• Federal guidance for standard hydrologic investigations:

• PMF:

• FERC (Engineering Guidelines for the Evaluation of Hydro power ANO Projects Chapter 8 Determination of the Probable Maximum Flood)

• USACE Engineering Manuals (EM1110-2-1417 Flood Runoff Analysis, etc.)

• PMP:

• NWS/USACE HMR Publications (HMRs) 41 42 Hydrologic Setting

• Watershed has changed over the years: Dams and reservoirs constructed PMF Hydrology - Flood Control Dams between c.1940 and c.1970 for flood control, most after 1956 Date Completed Number of Dams Percent 1800 - 1939 9 1%

1940 - 1949 25 1%

1950 - 1959 (Design Basis 1956) 102 6%

1960 - 1969 688 39%

1970 - 1979 487 27%

1980 - 1989 213 12%

1990 - 1999 138 8%

2000 - 2011 55 3%

Unknown 55 3%

Total 1,772 100%

43 44

Hydrologic Setting Hydrologic Setting

• Arkansas River highly regulated since completion of MKARNS Dardanelle Lock and Dam:

• ANO located 5 miles upstream of Dardanelle Lock & Dam Regulates water level 336 to 338 ft for flows up to 600,000 cfs ANO:

Site Finished Elevation 354 ft ANO 45 46 PMP Calculation Process Site Specific PMP - Consistency with Standards and Guidance Evaluate Applicability of HMR51/52

• Site specific PMP studies are standard hydrologic practice Watershed Area > 20,000 sq.mi.? NO Derive PMP Depth using Hydrometeorological Reports and World Meteorological OR Area Duration with HMR51/52, etc.

Organization procedures Is Watershed in Stippled Area?

• Site specific PMP Perform Site-Specific PMP case studies have YES Meteorology Study been generally Derive PMP Depth Area accepted on an Duration Using Study Results individual basis by FERC, NRCS &

Apply Depth Area Duration to USACE, various Watershed (Calculate state dam safety Hyetographs) agencies

Computing PMP Values Conservatisms - PMP

• Storm Maximization, transposition and elevation-adjusted

• Technical conservatisms used from study:

to watershed

• Increase observed extreme rainfall by increasing available moisture

• Storm rainfall patterns positioned within HMR-52

• Dates: 1895 to 2013 guidelines to preserve full rainfall value of the PMP

• Dew points increased to a

• PMP conservatively simulates the movement of a storm, climatological maximum covering as much of the watershed as practicable (Not

• Vary time of occurrence +/-2 included in HMR-51/52) weeks toward warm/wet season

• PMP speed and storm track for moving storms selected

• Depth-Area-Duration to maximize precipitation in the watershed up to 72-hours for area sizes of up to 100,000-square miles (meteorological limits) 49 50 Results: PMP Values PMP Application

• Analyzed three stationary and two moving PMP candidates

• Storm orientation optimized for maximum rainfall per NUREG/CR-7046, consistent with FERC guidelines

• PMP moving at 80 miles per day results in the most

• PMP temporal distribution per NUREG/CR-7046 and HMR-52 precipitation within the watershed.

recommendations Example of moving PMP

• 40% of the PMP used as an antecedent storm per NUREG/CR- with different storm center at each 24-hr increment.

7046 Heaviest rainfall is closest Antecedent Storm Probable Maximum Precipitation to the storm center with Storm Area Estimated Estimated Storm Area Estimated Estimated Ellipses of equal rainfall Source (square Volume Average Depth (square Volume Average Depth offset from center.

miles) (acre-feet) (inches) miles) (acre-feet) (inches)

FSAR / Original 7.5 49,612 19 million 49,612 27 million 10.0 PMP (5 day break)

(about (about N/A 2.5 N/A 10.7 Reevaluation 50,000) 50,000)

PMP (moving at 80 miles per day) 2.3 ANO 116,747 12 million 119,103 41 million 8.7 (3 day break) 51 52

PMF Hydrology - Consistency with ANO PMF Calculation Process Standards and Guidance

• PMF development performed per NRC, USACE, and FERC guidance Delineate Watershed and Subwatersheds

• Use of USACE HEC-HMS software as per NUREG/CR-7046 and USACE standard procedure Apply Site Specific PMP Results to Calculate PMP Input

• Use of Unit Hydrograph method as per NUREG/CR-7046, USACE, and FERC guidance

• HEC-HMS model was calibrated/verified to observed floods per NRC, Calibrate and Verify HEC-HMS Rainfall-Runoff Model (20 stream gages, 6 floods used for each) USACE and FERC guidance

• Initial losses are zero for the PMF (conservative) per NUREG/CR-7046 Develop PMF Flows with HEC-HMS using PMP Inputs

• Non-linearity adjustment per NUREG/CR-7046 and USACE guidance Develop PMF Elevations with HEC-RAS using HEC-HMS Inputs 53 54 PMF Hydrology - Dams PMF Hydrology - Dams

• 5,200+ dams located in watershed

• Six flood control dams explicitly modeled (of 1,772)

• 1,772 dams list flood control as a purpose

• Conservative assumptions based on publically available information about watershed dams were used

• No operator actions to create or preserve flood storage:

• The starting pool elevation was conservatively modeled at the upper limit of normal pool elevation during the PMF

• Low level outlet works were not modeled in HEC-HMS

• Gate operations were not modeled in HEC-HMS

• Six large dams were modeled based on publically available info

• Other flood control dams were represented by river routing parameters and rainfall-runoff transformation parameters, as calculated through calibration / verification 55 56

PMF Hydrology - Calibrate and Verify PMF Hydrology - Calibrate & Verify

• This process addresses uncertainty due to lack of dam information

• Demonstrates conservatism

• Conservatism added to account for the PMF significantly

• 20 USGS/USACE stream gages used exceeding the magnitude of the calibration and

• Three calibration and three verification floods used for each gage verification floods:

• Verified parameters bounded by calibrated parameters

• Non-linearity: NUREG/CR-7046 recommends increasing the peak discharge of the unit hydrograph by one-fifth and decreasing the time-to-peak by one third.

• HEC-HMS model was designed to over-predict peak flow vs observed flood data and minimize flood volume differences

• Initial losses of rainfall set to zero for PMF simulations 57 58 Summary of Hydrology Conservatisms PMF Hydrology - Nonlinearity

• Initial losses during the PMF were zero 120,000 Non-linearity Response Adjustment to Unit Hydrograph

• Constant losses initially estimated from the minimum published This adjustment was done AFTER the typical infiltration rate for each hydrologic soil group calibration and verification process was

• Soil group with the higher runoff potential was used in constant 100,000 completed Unit Hydrograph Discharge (CFS) 80,000 loss calculation for dual class soils

• Model typically slightly over-predicted peak flows and flood 60,000 volumes for calibration / verification floods

• The starting pool elevation was conservatively modeled at the 40,000 upper limit of normal pool elevation during the PMF 20,000

• Spillway weir coefficient for ogee-shaped crests were conservatively assumed to be 3.2 0

0 20 40 60 80 100 120 140 160

• Low level outlets and gates were not modeled in HEC-HMS

• Non-linearity adjustments were made Time (hours)

Original Nonlinear 59 60

PMF Hydraulics - Consistency with PMF Hydrology Maximum PMF Peak Flow Standards and Guidance PMF Hydrograph - at Dardanelle Rate (Re-evaluated) =

1,250,000 1,226,000 cfs

• PMF Hydraulics used standard-of-practice USACE FSAR PMF Flow Rate = computer models and conformed to NRC and USACE 1,500,000 cfs 1,000,000 (18% change likely guidance attributable to the effects

• Use of USACE HEC-RAS per NUREG/CR-7046, Pre-MKARNS Flood of watershed 750,000 Appendix C Flow (cfs) of Record: 683,000 cfs regulation/dams and use (1943) of more accurate modern

• Unsteady flow routines (more accurate than steady flow) day methods) 500,000 used to fully account for dynamic and momentum effects Post-MKARNS Flood of Record: 433,000 cfs

• Roughness for Arkansas River and floodplain were 250,000 (1990) selected based on published FEMA values 0

0 5 10 15 20 25 30 Time (days) 61 62 PMF - Hydraulics Conservatisms - PMF Hydraulics

• No floods after MKARNS exceed the 600,000 cfs Conservative assumptions for bathymetry (underwater threshold (about 338 ft) areas)

• HEC-RAS: Over 500 cross-sections over 117 miles, Bathymetry and channel geometry was based on data from including four Locks & Dams and two bridges USGS topographic maps in certain areas Channel invert elevations and dimensions based on USACE information

• Nine-foot by 250-foot rectangular channel

• Channel is a small part of overall conveyance and below water area in lake areas

• Channel shape does not artificially lower entire lake bed

• Conservative because sections of the channel may be wider and deeper, yielding increased channel capacity 64

PMF - Hydraulics 430 Typical Cross Section Info Sources PMF - Hydraulics 410 DEM Data Stage Hydrograph at ANO 353.8 ft Elevation (feet, NGVD29)

DEM Data 354 390 370 352 350 350 330 348 Stage (feet, NGVD29) 310 USGS Bathymetric Data 346 290 USACE Channel Data 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 344 Distance (feet) 342 340 338 336 334 0 5 10 15 20 25 30 Time (days) 66 Candidate PMPs / PMFs Warning Time Warning Time for PMF PMF Peak Discharge Peak Elevation at 356 7.00 Candidate Total Outflow Volume 205 hr Adjusted for Nonlinearity ANO 355 PMP Storm (acre-feet) 354 (cfs) (feet, NGVD29) 353 135 hr 6.00 Moving PMP 352 1,226,000 20,970,202 353.8 120 351 hr PMF Peak Stage 353.8 ft (80 miles per day) 350 5.00 Antecedent Storm (40% PMP)

End of PMP Onset of PMP 349 Watershed Centroid 1,222,000 16,195,091 353.3 Stage (feet, NGVD29) Precipitation (inch) 348 347 4.00 John Martin Subwatershed 346 90,000 4,487,452 <338.0 Centroid 345 344 3.00 Robert Kerr Subwatershed 343 1,260,000 18,273,796 351.7 Centroid 342 341 2.00 Moving PMP 340 1,015,000 16,559,493 351.6 (160 miles per day) 339 338 1.00 337 336 335 0.00 0 5 10 15 20 25 30 Time (days)

Precipitation PMF Stage 67 68

Waves Flood Re-evaluation Comparison Current Flood Notable Calculation Licensing Basis Re-evaluation improvements

• Wave action minimal PMP Used May 6-12, 1943 Comprehensive site- Incorporates several

• shallow flood depths generally storm followed by specific PMP study decades of additional less than one foot transposed May 6-12, using the 1943 storms data collection and

• Maximum possible wave is 0.78 x 1943 storm, increased and dozens of others numerous analyses depth from crest to trough by 34% per HMR and WMO improvements. Use of a

• Wave crest heights are thus even procedures. moving PMP, which lower Study performed in would not have been

• Waves would be broken by the 1950s by the U.S. easily done in the 1950s barriers prior to reaching important Weather Bureau and was not included in buildings HMR-51/52.

• Waves at peak flood are independent from PMP storm due to 5+ day lag time 69 70 Flood Re-evaluation Comparison Flood Re-evaluation Comparison Calculation Current Licensing Flood Re-evaluation Notable Basis improvements Calculation Current Flood Notable Licensing Basis Re-evaluation improvements 358.0 ft (stillwater) 353.8 ft (stillwater)

PMF- Study performed in HEC-HMS computer Comprehensive HEC-Hydrology 1956. model using unit HMS computer model Flows from manual hydrograph method used. Calibration and PMF- Study performed HEC-RAS computer Unsteady (flow varying) hydrograph and Muskingum verification per NRC, Hydraulics in 1950s. model using dynamic analysis based manipulation based on channel routing. USACE, and FERC Estimated flood unsteady (dynamic) on actual floodplain 1943 flood, adjusting Modeled 22 guidance. elevation at ANO flow module. geometry and lock & dam for increased rain subwatersheds. Six Demonstrably / using a straight- Hydraulic routing of configuration.

(PMP) & estimated reservoirs explicitly conservatively line interpolation hydrograph through HEC-RAS model captures rainfall modeled with captures response of from USACE Ozark Lock and complexities of water losses. Manual calibration/verification the post-MKARNS information at the Dam and surface profile variation channel routing with used to provide reality watershed. tailwater of Ozark Dardanelle Lock through Lake Dardanelle minimal reservoir check. Applied non- Lock and Dam and and Dam. instead of simplified effects. Essentially linearity response crest of Dardanelle straight-line method.

unregulated adjustments to PMF. Dam watershed.

71 72

Jeff Harris, P.H.

• 36-year career in Hydrology and Hydraulics at USACE

• Retired May, 2013

• Last 12 Years at Hydrologic Engineering Center

• HEC is USACE CX

• Eight years Chief of Hydrology and Hydraulics PMF HYDROLOGY AND HYDRAULICS Technology Division EXTERNAL PEER REVIEW

• Chair of USACE Committee on Hydrology Jeff Harris

• USACE Surface Water Hydrology Subject Matter Expert Senior Engineer, WEST Consultants, Inc

• H&H Lead for USACE Katrina IPET 74 HEC-HMS Model Parameters Selected Hydrology and Hydraulics Analysis Comparison to USACE PMF Practices

• Challenge

• Maximum Runoff

• Develop Hydrologic Modeling System (HMS) and River Analysis

• Initial Loss System (RAS) models of Arkansas River Basin for Probable

• Set to zero.

Maximum Flood computation

• Typical USACE assumption. (In accordance with NUREG/CR-7046)

• Obstacle

• Constant Loss

• Lack of available data for modeling multiple reservoirs and routing

• STATSGO flows. Only public data available

• Loss rates used conform to USACE Guidance EM 1110-2-1417

• Used soil type with highest runoff potential

• Solution

• Hydrologic Routing

• Since PMF elevation in Lake Dardanelle is the goal, model

• Muskingum method parameters were used in the hydrologic models to generate the

• Storage coefficient set low as possible and still maintain stability maximum PMF flow and stage in the lake and stay consistent with

• Decrease channel storage, more water moves downstream.

USACE methods.

• Described in HEC-HMS User Manual and textbooks (i.e. Chow) 75 76

HEC-HMS Dam Modeling Decisions Comparison to USACE PMF Practices Upstream Dam Modeling

• No Failures Assumed

• Maximize PMF Runoff

• PMP generated for specific location

• Used HMS Reservoir Element

• Arkansas a very large basin

• Six Large Dams Modeled

• PMP does not occur at all locations

• Storage at normal pool which is above spillway crest

• Three large Dams not included

• In general, spillways designed for PMF

• 4.1M ac-ft. storage

• Including failures would make PMF a more rare event

• Small dams not included

• Increased runoff

• Dardanelle

• Low weir coefficient (USACE HEC-RAS Hydraulic Reference Manual)

• Model Calibration 77 78 HEC-RAS Model Parameters USACE Guidance ER 1110-8-2 (FR)

• USACE PMF Computation

• Antecedent Conditions

• Spillway Adequacy

• Reservoir at full flood control pool elevation

• Dardanelle Weir Coefficient

• Elevation five days after an event equal to 1/2 PMF

• Low weir coefficients. (USACE HEC-RAS Hydraulic Reference

• Gate Operation Manual)

• Reservoir regulating outlets should not be assumed operable

• Topographical Data during PMF unless designed for PMF

• Dardanelle manned 24/7/365

• Assumptions made to minimize storage

• Long warning time

• USACE model may differ

• Unit Hydrograph

• Peaked 25-50%

• NRC guidance NUREG/CR-7046 79 80

Summary

• Modeling methods maximized PMF runoff

• Losses

• Routing

• Dam Modeling

• USACE Software Methods and Parameters (HMS, RAS)

• Applied correctly

• Applied in accordance with USACE guidance PMP PROBABILITY EVALUATION

• USACE PMF modeling will follow similar steps

• Methodology GZA applied is conservative but consistent Jason Caldwell, Ph.D.

with USACE guidance Sr. Project Engineer/Modeler Leonard Rice Engineers, Inc.

81 Overview Organization

• Jason Caldwell, Ph.D., P.H., LRE, Lead - Probability of PMP

• Review of the multiple methods approach to hydrologic

• B.S./M.S. Meteorology; Ph.D. Civil Engineering (Stochastic methods/uncertainty)

• Over ten years of atmospheric, hydrologic, and climate modeling experience hazards focusing on extreme precipitation events

• Calculations to evaluate probability of PMP consistent

• General and site-specific PMP and regional frequency for hydrologic hazards analysis with procedures at federal level (NOAA, Reclamation,

• Research projects for NRC on evaluation of existing PMP estimates in the Carolinas NRC) and Tennessee River Valley

• Address limitations of large watershed and AEP

• LRE Team:

• Monica Bortolini: Group Manager - Civil Engineering information in national products through regional analysis

• Todd Street: Project Engineer - Civil Engineering

• Review of conservatisms associated with the PMP and

• Others: Katy Kaproth-Gerecht, James Tobler, Jessica DiToro relationship to the PMF

• Peer Reviewer and Technical Support:

• Mel Schaefer, MGS: Stochastic hydrologic modeling, precipitation frequency, Watts Bar/Sequoyah probability study

• Tye Parzybok and Debbie Martin, MetStat: Co-authors on NOAA Atlas 14, WMO extreme precipitation evaluation committee member 83 84

Background:

Inspection Report Notes

Background:

AEP of PMP

• Extreme events vary between 1 x 10-3 and 1 x 10-6 AEP

• Schaefer (1994) based on Harris and Brunner conference paper

• Similar estimates available from literature review

• Probability of PMP 0

• Typically based on generalized PMP at 20,000 mi2 or smaller

• Difference between theoretical and operational

• Flood frequency extrapolations limited to approximately twice upper limits the length of record (Interagency Advisory Committee on Water Data 1982)

• AEP of PMP ranges from 10-5 to 10-9 AEP

• Regional methods allow statistical extension beyond individual site period of record

• Varies by location, duration, and storm area

• USNRC NUREG/CP-0302: PFHA Workshop Proceeding

• Based on generalized PMP at small area sizes identifies Bulletin 17B as not intended for extending estimates to 1-in-10,000 year events or for identifying outliers

• Multiple methods and approaches utilized at federal level to statistically extend beyond 10,000 years 85 86

Background:

AEP of PMP

Background:

Site-Specific Studies

• Why AEP estimates of PMP and PMF are conservative

• PMP Estimates: (Applied Weather Associates)

(i.e., too frequent)

• 80-mile per day storm hyetographs

• Generalized PMP values only valid to 20,000 mi2 - large rainfall amounts over larger area sizes less likely to occur due to physical

• Basin Average Precipitation:

limitations of meteorology

• 3-Day Antecedent Storm (40% PMP) = 1.72

• Generalized PMP studies do not typically include antecedent

• 3-Day Full PMP Storm (100%PMP) = 6.76 rainfall prior to the PMP event to prime the hydrologic response -

• 9-Day Storm Total = 8.48 joint probabilities lower the likelihood of the event

• Generalized PMP used in PMF studies use stationary events -

• PMF Estimates: (GZA) stationary events for ANO watershed reduced PMF

• Peak Flow ~ 1,226,000 cfs (9-Day PMP of 8.48)

• PMF studies include additional conservatisms independent of the precipitation falling on the watershed 87 88

Background:

Hydrologic Hazards Analysis

Background:

Federal Products/Methods

• Key Concepts of HHA: (Merz and Bloschl, WRR 2008)

• Precipitation Frequency:

• Integrated Teams

• NOAA Atlas 14

• Geologists, hydrologists, meteorologists, engineers

• Regional frequency analysis using L-Moments

• Multiple Methods Approach

• Regional Analyses National Research Council(1988) Estimating

• State-level studies

• Hydrologic Modeling Probabilities of Extreme

• WA, OR, TX, IL/MO, etc.

Floods

• Expansion of Data (temporal, spatial, causal)

• Reclamation Dam Safety Studies

• Quantification of Uncertainty

• Friant, Altus, El Vado, others

• NRC PFHA Workshop (Jan 2013)

• NRC Pilot Project

• Focus on state-of-the-science on probabilistic methods

• Carolinas NOAA14 Extension

• Reclamation Dam Safety Program

• Evaluation of Recent PMP Events

• Issue Evaluations and Corrective Action Studies

• TVA Watts Bar and Sequoyah (Schaefer)

• Best Practices Course in HHA

• NOAA14 Extension 89 90

Background:

NOAA Atlas 14

Background:

L-Moments

• Available in most US

• Homogeneous region of similar locations climatological characteristics

• Point-specific

• Numerous stations large #

• 5-min to 60-day durations station-years of record (EIRL)

• Up to AEP of 10-3

• Reduces sampling variability and

• Median and 90% enhances reliability of regional confidence bounds probability distribution and

• Underlying annual estimation of magnitude-maximum precipitation data frequency relationship

• Regions not specific to

• Allows uncertainty analysis watersheds (Monte Carlo and Latin Hypercube) based on variability of parameters from the underlying distribution (typically GEV - use Kappa for GLO to 91 GPA) Hosking and Wallis (1997) 92

Multiple Methods Employed: NOAA14 Statistical Extension

• Steps in statistical NOAA Atlas 14 Statistical Extension extension:

Identifies a key gauge representative of the watershed mean

• Identify a site representative of the region (Coldwater, KS)

• Reduction of Point to Area L-Moments Regional Frequency Analysis (precipitation)

• Fit polynomial regression Uses NOAA14 annual maximum time series using EV1 as explanatory variable

• Simulate from EV1 to Stochastic Storm Transposition generate annual maximum Uses DAD information from the AWA PMP study and HMRs time series

• Use Kappa distribution parameters to statistically extend 93 94 NOAA14 Statistical Extension L-moments

• ANO Watershed L-moments

• 454 Stations amounting to 20,000+ years of station record

• Equivalent independent record length = 3,433 years

• 3-day analysis for comparison to Coldwater and Stochastic Storm Transposition

• 10-day analysis for comparison to 9-day PMP Factors Affecting AEP: AEP of 72-hour PMP:

• 72-hour precipitation (not 9-day) Ranges from 10-5 to < 10-7 95 96

L-moments (3-Day) Stochastic Storm Transposition

• Stochastic Storm Transposition

• 92 storms available from the AWA PMP study

• Compute ratios of storm magnitude to PMP at the location of occurrence

• Transpose storms into the basin through moisture adjustment

• Calculate the probability using Cunnane

• Conservative estimate compared to 9-Day

• AEP of PMP from <10-5 to < 10-7 97 98 Stochastic Storm Transposition Stochastic Storm Transposition

• Historical storms indicate

• Stochastic Storm Transposition the 72-hour, 20,000 mi2

• Product of : precipitation has AEP of 4.3 x 10-5 (1) probability of precipitation occurrence

• Conservative by at least (2) probability of storm size within watershed one order of magnitude due to short duration (3) probability of watershed size storm from (only 3 days) and small area size transposition region (Collier et al., 2011) where:

• For 153,366 mi2 basin,

• P(1) = Cunnane with Gringorten = (r-0.44)/N or estimated AEP of

= Estimate from # storms vs % PMP 5.6 x 10-6

• P(2) = 20,000/153,366 = 0.13

• P(3) = 153,366/1,744,188 = 8.8 x 10-2 99 100 Foufoula-Georgiou 1989; Franchini et al. 1996; Schaefer 2013)

Stochastic Storm Transposition Summary of 3-Day Precip Frequency

• Reference to 3-day L-Moments curves (aid in selection)

• Multiple methods:

• Historical storms indicate the 72-hour, 153,366 mi2 precipitation value of

- PMP and estimate of 4.05 has return period of ~2500 years (AEP = 4 x 10-4) from SST adjusted for

• Provides cross-check to regional frequency analysis and estimates of AEP of PMP (multiple methods) 153,366 mi2 101 102 Summary of 3-Day Precip Frequency Summary of 3-Day Precip Frequency

• Multiple methods:

• Multiple methods:

- PMP and estimate of - PMP and estimate of from SST adjusted for from SST adjusted for 153,366 mi2 153,366 mi2

- Statistical extension - Statistical extension using NOAA14 (site at using NOAA14 (site at Coldwater, KS) Coldwater, KS)

- L-moments watershed analysis shows similar results 103 104

Summary of 3-Day Precip Frequency Summary of 3-Day Precip Frequency

• Multiple methods:

• Multiple methods:

- PMP and estimate of - PMP and estimate of from SST adjusted for from SST adjusted for 153,366 mi2 153,366 mi2

- Statistical extension

- Statistical extension using NOAA14 (site at using NOAA14 (site at Coldwater, KS)

Coldwater, KS) - L-moments watershed

- L-moments watershed analysis shows similar analysis shows similar results results - SST Results fall within

- SST Results fall within uncertainty bounds uncertainty bounds - Used most frequent AEP from each for best estimate 9-Day more conservative due to additional antecedent rainfall 105 106 L-moments (10-Day) Probability of PMP (and PMF) 10-Day Results:

• Large Precipitation is a requirement for a PMF

• Upper estimate for AEP of

• PMP probabilities affected by PMP is < 10-5

• Large domain of the watershed

• No 9-Day available from

• Spatial variability of rainfall (location and orientation)

NOAA, used 10-Day =

• Joint probability of sequenced events Conservative Estimate

• Sustained, conducive atmospheric conditions

• In addition, other factors must be present

SUMMARY

• Critical soil moisture conditions Day results support the

• Limited storage capacity AEP of PMP for the

• Season of occurrence watershed is

• Reservoir operations conservatively around 10-6

• Hydrologic parameters 107 108

Summary and Conclusions

• Existing estimates of the AEP of PMP and PMF are based on generalized PMP estimates for watershed sizes much smaller than Arkansas River Basin

• Joint/conditional probabilities for PMP storm and conducive hydrologic conditions result in reduced AEP of the PMF

• Multiple methods approach provides justification for selection of a best estimate and upper/lower confidence bounds

• In comparison to the PMF, the estimates are likely conservative due to the addition of factors from the hydrologic/hydraulic modeling by an order of magnitude Best SIGNIFICANCE DETERMINATION (as AEP) Lower Upper Estimate Richard Harris 3-day PMP 8.26E-10 1.39E-06 1.69E-05 associated with 353.1' (3-day only) 9-day PMP 1.71E-10 2.04E-08 2.63E-06 associated with 353.8' (Antecedent + PMP) Emergency Planning Manager 1.025*3dayPMP 5.78E-10 1.15E-06 1.44E-05 associated with 354' (3-day only) 1.075*3dayPMP 2.99E-10 7.94E-07 1.05E-05 associated with 356' (3-day only)

Focus on precipitation magnitude associated with:

109 354 (1.025*72hPMP = 6.93 inches) and 356 (1.075*72hPMP = 7.27 inches)

Key Objectives Methodology

• Realistic estimate of risk utilizing best available

• The risk analysis is fairly straightforward information

• Event Tree is used to understand the sequences and

• Quantitatively characterize the risk significance determine the probabilities

• Present ANO risk results to include

• Initiating Event Frequencies as discussed in previous

• External Flood presentation were used

• Internal Flood 111 112

Methodology External Flood Analysis

• Recovery Factors

• Operator actions to mitigate impact of flooding were credited

• Assumptions

• SHARP Decision Tree used in conjunction with HRA Calculator

• Plant is in CSD (RCS < 200F)

• Analysis performed by partitioning the flood level

• External Flooding 354-356 Elevation

• SDC or DH, HPI, RBS, and EFW potentially failed from deficiencies

• Recovery Credited

• Portable Pump for Steam Generator Feed

• Service Water

• Flood Protection

• AC power available

• External Flooding > 356 Elevation

• SDC or DH, HPI, RBS, and EFW potentially failed from deficiencies

• Potential Recovery actions available (None Credited) 113 114 External Flooding Analysis External Flooding Analysis

• Recovery Actions

• Three diverse actions are available

• EVENT TREE

• Portable Pump for Steam Generator Feed

• Actions directed by OP-1203.048

• Previously trained operator actions

• Mockup performed to install from staging area (approximately one hour to implement)

• Service Water Pump

• Used for feeding the inventory in the Steam Generators

• OP-1202.004 (Unit 1) or OP-2202.011 (Unit 2)

• Control Room action to perform < five minutes

• Flood Protection

• EN-FAP-EP-010 - Fleet Severe Weather Response

• Barrier assumed not effective over 356 elevation

• Available time at least five days 115 116

External Flooding Analysis External Events

• Inputs

• Results

• Flood Frequency

• Unit 1

• 354 to 356 - 1.15E-06/yr

• 354 to 356 External Flood = 5.34E-09/year

• >356 External Flood = 7.94E-07/year

• >356 - 7.94E-07/yr

• Total CDF External Flood from deficiencies = 7.99E-07/year

• Recovery Actions (354-356)

• Unit 2

• Steam Generator Makeup - Failure Probability = 0.05

• 354 to 356 External Flood = 5.34E-09/year

• Portable Pump for SG feed

• > 356 External Flood = 7.94E-07/year

• Service Water

• Total CDF External Flood from deficiencies = 7.99E-07/year

• Flood Protection - Failure Probability = 0.3 117 118 Internal Flooding Analysis Internal Flood Analysis

• Assumptions

• Event Tree

• Plants is operating at 100% power

• Circulating Water Piping failure is the most severe flood mechanism

• Full Range of break sizes considered (Unit 2)

• Large Break >19 diameter (~2 ft2 area) - No Operator action credited to stop the pump in first 30 minutes after break

• Mid Range 8 - 19 diameter - Operator failure to stop pump = 0.1

• Low range <8 diameter (~0.35 ft2 area) - 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> isolation time (improbable that Operator action to stop the pump would not occur)

• Differences between Unit 1 and Unit 2, resulting in different risk results

• Differences in flood deficiencies

• Differences in plant design and equipment vulnerabilities 119 120

Internal Flood Analysis Internal Flood Analysis

• Unit 1

• Unit 2

• Based upon the following

• Flood Frequency (aggregate frequency for the range of break sizes)

• The volume of water required

• 9.03E-05/yr

• Location of deficiencies

• Recovery Actions

• Due to plant design the break will flow back to the lake

• Isolation of CW rupture

• The time available for operations to stop the Circulating

• Large breaks - no credit Water Pumps

• Medium breaks - 0.1 failure probability

• It is improbable that Operator actions would not be taken to

• Small breaks - negligible risk stop the leak (>2 hours)

• Alternate portable pump for SG feed - Failure Probability = 0.05

• Service Water feed to SG - Failure Probability = 0.3

• Risk increase is negligible

• Results

• 1.36E-06/yr 121 122 Overall Results

• Unit 1

• External Flooding + Internal Flooding

• CDF = 7.99E-07/year

• Unit 2

• External Flooding + Internal Flooding

• CDF = 2.16E-06/year RISK ASSESSMENT

SUMMARY

• These results reflect a risk as defined in the Dale James Significance Determination Process (SDP) as very low Regulatory and Performance Improvement Director safety significance for Unit 1 and low to moderate safety significance for Unit 2 123

Manual Chapter 0609 - Appendix M Assessment Risk Assessment Summary NRC Entergy

• Flooding evaluation performed based on current state-of- Bounding 1E-4 1.44 E-5 Based on site specific upper 95% AEP for PMP knowledge techniques endorsed by NRC and other Risk resulting in 354 federal agencies responsible for dam safety Defense-In- No credit

• PMF below site grade Depth

• Operator action available to 356 and beyond

• Conservative assumptions used when information was

• Flood protection adds additional protection not publically available Safety No credit

• Current PMF below site grade - required level of

• Probability of PMP calculated using statically robust Margin protection maintained techniques consistent with methods used by other federal

• From 354 to 356 margin is threatened

• Above 356 margin further eroded agencies to make risk base decisions Extent of PD

• Degraded condition existed on both units

• Mitigating actions available

• Extent of PD is known and corrected

• Utilizing these inputs provide the best available Degree of Equipment

• Degradation not a factor for current PMF information for a accurate assessment of risk Degradation unavailable

• Service water feed to SGs and portable pump for SG feed available to maintain core cooling

• Unit 1 CDF = 7.99E-07/year Green

• Unit 2 CDF = 2.16E-6/year White 125 126 Manual Chapter 0609 - Appendix M Assessment Continued NRC Entergy Exposure Time 1 year

• 1 year Mitigating

• Operator recovery actions feasible recovery actions

• Flood protection measures provide additional defense Additional

• Current PMF below elevation were degraded conditions qualitative are a factor circumstances

• ANO specific PMP/PMF calculations has considerable CLOSING COMMENTS conservatism factored into them and would reduce the bounding risk approximately a order of magnitude Results Yellow White Jeremy Browning ANO Site Vice-President 127

Agenda

• Introduction of Participants

• NRC Opening Remarks Arkansas Nuclear One

• Licensee Presentation Regulatory Conference

• NRC Caucus

• Final Questions

• Closing Remarks Nuclear Regulatory Commission - Region IV

• Conference Adjournment Arlington, TX

• Questions and Comments from Members of October 28, 2014 the Public 1 2

J. Browning In accordance with 10 CFR 2.390 of the NRCs Rules of Practice, a copy of this letter and its enclosures will be available electronically for public inspection in the NRCs Public Document Room or from the Publicly Available Records (PARS) component of the NRCs ADAMS. ADAMS is accessible from the NRC web site at http://www.nrc.gov/reading-rm/adams.html (The Public Electronic Reading Room).

Sincerely,

/RA/

Ryan E. Lantz, Chief Project Branch E Division of Reactor Projects Docket Nos.: 50-313, 50-368 License Nos.: DPR-51, NPF-6

Enclosures:

1. ANO Presentation Slides

2. NRC Slides

3. Meeting Attendance Forms Electronic Distribution to Arkansas Nuclear One ML14329B209 SUNSI Rev Compl. Yes No ADAMS Yes No Reviewer Initials CHY Publicly Avail. Yes No Sensitive Yes No Sens. Type Initials CHY SPE:DRP/E BC:DRP/E CYoung RLantz

/RA/ /RA/

11/24/14 11/25/14 OFFICIAL RECORD COPY

Letter to Jeremy Browning from Ryan Lantz dated November 25, 2014

SUMMARY

OF REGULATORY CONFERENCE TO DISCUSS SAFETY SIGNIFICANCE OF ARKANSAS NUCLEAR ONE FLOOD PROTECTION DEFICIENCIES Electronic distribution by RIV:

Regional Administrator (Marc.Dapas@nrc.gov)

Deputy Regional Administrator (Kriss.Kennedy@nrc.gov)

DRP Acting Director (Troy.Pruett@nrc.gov)

DRP Acting Deputy Director (Jason.Kozal@nrc.gov)

DRS Director (Anton.Vegel@nrc.gov)

DRS Deputy Director (Jeff.Clark@nrc.gov)

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Resident Inspector (Matt.Young@nrc.gov)

Resident Inspector (Abin.Fairbanks@nrc.gov)

Branch Chief, DRP/E (Ryan.Lantz@nrc.gov)

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Project Engineer, DRP/E (Jim.Melfi@nrc.gov)

ANO Administrative Assistant (Gloria.Hatfield@nrc.gov)

Public Affairs Officer (Victor.Dricks@nrc.gov)

Public Affairs Officer (Lara.Uselding@nrc.gov)

Project Manager (Andrea.George@nrc.gov)

Branch Chief, DRS/TSB (Geoff.Miller@nrc.gov)

ACES (R4Enforcement.Resource@nrc.gov)

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RIV/ETA: OEDO (Cayetano.Santos@nrc.gov)

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