Text

Enclosure to NLS2012124, Cooper Nuclear Station Flooding Walkdown Report
	ML12333A320
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Site:	Cooper
Issue date:	11/26/2012
From:	; Nebraska Public Power District (NPPD)
To:	; Office of Nuclear Reactor Regulation
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	NLS2012124
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NLS2012124 Enclosure NLS2012124 ENCLOSURE COOPER NUCLEAR STATION FLOODING WALKDOWN REPORT

H Nebraska Public Power District "Always there when you need us" CNS Memo 12-0002 To: Cooper Nuclear Station Licensing Department From: Cooper Nuclear Station Design Engineering Department CC: N/A Date: 11/26/2012 Re: Response to 10 CFR 50.54(f) Section 2.3 Flooding Validation and Acceptance of Vendor Provided Evaluations In response to the nuclear fuel damage at Fukushima Daiichi due to earthquake and subsequent tsunami, the United States Nuclear Regulatory Commission (NRC) is requesting information pursuant to Title 10 of the Code of Federal Regulations, Section 50.54 (f). As part of this request which is as defined in the Recommendation 2.3, Flooding, Enclosure 4 of the 50.54(f) Letter dated March 12, 2012, CNS was required to perform walkdowns to verify that plant features credited in the current licensing basis (CLB) for protection and mitigation from external flood events is available, functional, and properly maintained. In addition, the purpose of the walkdowns was to identify and address plant-specific degraded, non-conforming, or unanalyzed conditions (through the corrective action program) and associated APM (Available Physical Margin) and verify the adequacy of monitoring and maintenance procedures. This information was obtained in accordance with NEI 12-07, "Guidelines for Verification Walkdowns of Plant Flood Protection Features". This memo is being written for CNS Design Engineering to formally accept the walkdown packages, and final walkdown report as being technically accurate.

The walkdowns were developed with APM determined from 906', which is what CNS is committed to the NRC to protect up to. CNS licensing basis is 903'.

During the walkdowns many features were found to be non-conforming to the design basis. CR's were written for all non-conforming features as is stated in the NEI 12-07 guidance. DED determined whether the feature was deficient or not. If a feature was determined deficient, a recovery plan was created to correct the deficiency. These deficiencies are included in the Final Walkdown Report.

The attached walkdown packages and final walkdown report are found technically accurate with the CNS design and licensing bases and will be appropriate for a response to Recommendation 2.3, Flooding, of the 50.54(q Letter dated March 12, 2012. The information collected in this evaluation will not impact the existing design basis as recommendation 2.3 is a review of current CNS flood mitigation strategies. Any change to the licensing basis will come out of Recommendation 2.1 which will reference the material from Recommendation 2.3.

CNS Memo 12-0002 Revision 0 Page 1 of 2

ATTACHMENTS:

Final walkdown report Walkdown packages Walkdown team credentials CNS Design Engineer Matthew Nienaber

/if26 2ý CNS Design Engineering Brian T. Wolken Supervisor CNS Design Engineering IfZ~

Roman M. Estrada Manager CNS Memo DED 12-0002 Revision 0 Page 2 of 2

Page I of 36 CNS Flooding Walkdown Submittal Report LIST OF ACROMYMS Abbreviation Description AEC Atomic Energy Commission APM Available Physical Margin B&R Burns and Roe CA Corrective Action CAP Corrective Action Program CED Change Evaluation Document CFR Code of Federal Regulation CLB Current Licensing Basis CNS Cooper Nuclear Station COE Corps of Engineers(USACE)

CR Condition Report DB Design Basis ECCS Emergency Core Cooling System EE Engineering Evaluation ERP Elevated Release Point FSAR Final Safety Analysis Report HPCI High Pressure Core Injection IPEEE Individual Plant Examination of External Events IER INPO Industry Event Report MPF Multi-Purpose Facility MSL Mean Sea Level (based on NGVD29)

NGVD29 National Geodetic Vertical Datum of 1929 NEI Nuclear Energy Institute NPPD Nebraska Public Power District NRC Nuclear Regulatory Commission OWC Optimum Water Chemistry PM Preventative Maintenance PMF Probable Maximum Flood PMP Probable Maximum Precipitation PRA Probabilistic Risk Assessment RCA Radiological Controlled Area RCIC Reactor Core Injection Cooling RHR Residual Heat Removal RPS Reactor Protection System SER Safety Evaluation Report TRM Technical Requirements Manual TLCO Technical Requirements Manual Limiting Conditions of Operation URT Unit Reliability Team USACE United States Army Corps of Engineers USAR Updated Safety Analysis Report USNRC United States Nuclear Regulatory Commission Page 2 of 36

CNS Flooding Walkdown Submittal Report TABLE OF CONTENTS SCOPE AND OBJECTIVE ............................................................................................ 5 2 DESIGN BASIS FLOOD HAZARD LEVEL ............................................................... 6 2.1 Probable Maximum Flood (PMF) .......................................................................... 6 2.2 Postulated Dam Failure .......................................................................................... 6 2.3 Probable Maximum Precipitation (PMP) ............................................................... 7 2.4 Other Evaluated Flooding Events .......................................................................... 8 2.5 Original Supporting Evaluations and Methodology ............................................. 8 2.6 Other Analysis and Evaluations ............................................................................ 9 2.7 CLB Flooding Summary Table ............................................................................. 11 3 EXTERNAL FLOOD PROTECTION AND MITIGATION FEATURES ................. 12 3.1 Flood Licensing Basis and Protected SSCs ........................................................ 12 3.2 Plant Operation During Flooding ........................................................................ 13 3.3 Flood D uration .................................................................................................... 14 3.4 Flood Protection Features ..................................................................................... 15 3.5 Procedures ................................................................................................................ 16 3.6 Adverse Weather Conditions .............................................................................. 17 3.7 Groundwater Ingress .......................................................................................... 17 4 INTERNAL WARNING SYSTEMS ..................................... 18 5 EFFECTIVENESS OF FLOOD PROTECTION SYSTEMS ...................................... 22 5.1 A cceptance Criteria .............................................................................................. 22 5.2 Overall Effectiveness of Plant Flood Protection Features .................................. 23 5.3 Other Existing Plant SSCs and Procedures that May Provide Flood Mitigation ..... 23 6 IMPLEMENTATION OF WALKDOWNS ................................................................. 24 6.1 Walkdown Package Development ..................................................................... 24 6.2 Team O rganization .............................................................................................. 24 6.3 Training A pproach ............................................................................................. 25 6.4 Peer Review Process ........................................................................................... 25 7 WALKDOWN RESULTS ........................................................................................... 26 7.1 Incorporated or Exterior Passive Features .......................................................... 26 7.2 Incorporated or Exterior Active Features ............................................................ 27 7.3 Temporary Passive Features ................................................................................ 27 7.4 Temporary Active Features ................................................................................ 27 Page 3 of 36

CNS Flooding Walkdown Submittal Report 7.5 Procedural Review .............................................................................................. 28 7.6 Inaccessible Features ........................................................................................... 29 7.7 Deficient Features ................................................................................................ 29 7.8 D elayed Inspection Features ............................................................................... 32 8 AVAILABLE PHY SICA L M ARG IN .......................................................................... 33 9 NEW FLOOD PROTECTION SY STEM S ................................................................. 34 10 REFEREN CES ................................................................................................................. 35 10.1 Regulatory Docum ents, Codes and Guidance .................................................... 35 10.2 NPPD Docum ents ................................................................................................ 35 Page 4 of 36

CNS Flooding Walkdown Submittal Report 1 SCOPE AND OBJECTIVE This Flooding Walkdown Report is prepared in accordance with the request from the U.S.

Nuclear Regulatory Commission as defined in the Recommendation 2.3, Flooding, Enclosure 4 of the 50.54(f) Letter dated March 12, 2012.

In response to the nuclear fuel damage at Fukushima Daiichi due to earthquake and subsequent tsunami, the United States Nuclear Regulatory Commission (NRC) is requesting information pursuant to Title 10 of the Code of Federal Regulations, Section 50.54 (f). As part of this request, CNS was required to perform walkdowns to verify that plant features credited in the current licensing basis (CLB) for protection and mitigation from external flood events is available, functional, and properly maintained. In addition, the purpose of the walkdowns was to identify and address plant-specific degraded, non-conforming, or unanalyzed conditions (through the corrective action program) and associated APM (Available Physical Margin) and verify the adequacy of monitoring and maintenance procedures.

This information obtained and presented in this report is in accordance with NEI 12-07, "Guidelines for Verification Walkdowns of Plant Flood Protection Features" (Ref. 10.1.2) with no exceptions to the guidance. The scope of the report is further described in the subsequent sections of this document.

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CNS Flooding Walkdown Submittal Report 2 DESIGN BASIS FLOOD HAZARD LEVEL The CNS USAR (Ref. 10.2.2) Vol. II, Station Site and Environs, Hydrology Section 4.2.2.1 states that the maximum river level established by studies by the Corps of Engineers was at 899 ft MSL during the flood of record in 1952 prior to the installation of the upstream river controls. The USAR projected upper limit of elevation for a 1,000-year flood discharge is 900 ft MSL and for a 10,000-year flood discharge is 902 ft MSL.

2.1 Probable Maximum Flood (PMF)

The CNS USAR Section 4.2.2.1 states "....The ProbableMaximum Flood (PMF)is establishedat 903 feet MSL with a projected returnfrequency estimated to be in excess of 1,000,000 years. The PMF is derived by centering a probable maximum rainstorm critically over the drainageareaabove Brownville. The Corps of Engineershas estimated that the peak dischargefor the PMFis 600,000 cubicfeet per second. This estimate is based on a qualitativejudgment that the peak of a PMFevent should be between two to three times the peak of a standardprojectflood.Preliminaryestimates of standardproject conditions on the Missouri and PlatteRivers were used in estimating the probable maximum flood peak of 600,000 cfs at CNS. "

CNS USAR Vol. II - Section 4.2.2.2 states; " the stationsite grade level of903feet MSL has been raised 13feet above the naturalgradelevel of 890feet MSL, in order to bringfinal grade onefoot above the existing 902feet MSL levee constructed by the Corps ofEngineers.

This levee was raisedabove its originaldesign level andpresently has a threefoot minimum free board over the 1952flood of record(899feet MSL). Floodingof the station is considered to be extremely unlikely due to the combination of upstream Missouri River flood control and the high final site grade. With respect to the 1,000 year, 10,000 year and 1,000,000 year (PMF)floods, these water levels will provide 3 /2feet, 11/22feet,and 6 inches offreeboardrespectively below the 903'6" gradefloor elevation of the principle structures....... "

.... The wave

.. action discussed within Subsection 4.2.2.1 (6.7feet on a smooth vertical wall and 4.8feet on a riprappedslope), in conjunction with a PMFwill not affect the plantproper since the nearest building is located about 200feet from the river edge and is surroundedby grade to elevation 903'-0". Wave energy would be dissipatedbefore reachingany of the main buildings. Wave action at the Intake Structure will not affect the safe shutdown ofthe plant since the Service Water pumps and controls areprotected by massive reinforcedconcrete walls andslab up to elevation 919"-0" ...... "

".... The Atomic Energy Commission (AEC) staff independently evaluated theflooding potentialat CNS. They estimated PMFto be 901.2feet MSL, which concurrentwith wind effects would result in a maximum water level on the outside of the Intake Structure at 909.2 feet MSL (PMFplus wave effects) and 905 feet MSL (PMFplus surge effects) on other exposed safety relatedstructures. The AEC staff requiredprotection of safety related structures andsystems against these levels in order to ensure the capabilityto place and maintain the plant in a safe shutdown under theflooding conditions described above....

2.2 Postulated Dam Failure CNS USAR Section 4.2.2.1 states ". The failure ofa large upstream dam is not consideredprobable. These dams are massive earth structures with impervious core walls, Page 6 of 36

CNS Flooding Walkdown Submittal Report largefreeboardfor wave action, andadequatespillways. The dams are located in a zone of low seismic activity. The Gavins Point Dam, closest to the site is over 275 miles upstream. It is approximately 8,100feet long with a height of 74 feet. It is 35feet wide at the top and up to 850feet wide at the base. The top of the dam is at 1,234feet MSL with a water level of 1,205 feet MSL indicatinga freeboardof29 feet. Its storage capacity is approximately 500,000 acrefeet. These dams are under constant inspection by local Corps of Engineers personneland are inspected once a year by a team ofprofessionals.If seismicfailure occurredin spite of these circumstances,the failure would most probably be other than instantaneousfailureof a major portion of the dam. Under these circumstances,overtopping of Gavins PointDam, although conceivable, is not likely to occur.

The 901.2foot

....... MSL water surface elevation and the 905foot MSL (PMFplus surge effects for safety related structuresother than the Intake Structure) estimated by the AEC staff are below the 906foot MSL projectedfor the unlikely combination of an upstream dam failure concurrent with the maximum naturalflood .... "

2.3 Probable Maximum Precipitation (PMP)

CNS USAR Vol. II - Section 3.0 Meteorology, Sub-Section 3.1.3 Precipitation states U.S. Department

....... of Commerce - Weather Bureau and U.S. Department ofArmy Corps of Engineers,HydrometeorologicalReport No. 33 datedApril, 1956,from which it was determined that the "probablemaximum precipitation"for the site area,23.5 inches total rainfallfor a 24-hourperiod. This value has been determinedfrom Figure 17 (August) ofthe aforementionedreport. Converting this value to a rate equivalent to a one-hour rainfall, by using the Civil EngineeringBulletin No. 52-8, revised March, 1965, published by the Departmentof the Army, office of the Chiefof Engineers which determines a rainfallrateper hourfrom a 24-hourperiod,the "probablemaximum precipitation"forthe site area was conservatively determined to be 3.56 inches per hourfor a ten year returnperiod.... "

In addition, CNS USAR Vol. II - Section 3.0 Meteorological Design Bases, sub-section 3.2.3 Precipitation states; "....... Class land Class II buildings areprotectedfrom the effects of precipitationthrough the use ofroofdrains and overflow scuppers. The Reactor Building, Diesel GeneratorBuilding, and Control Building use 4 inch roofdrains and 6 inch scuppers.

Using the dischargerates in drainsprovided in the 1971 issue of the National Standard Plumbing Code, with fullflow from the vented systems, the roofdrainageand overflow capacityfrom these buildings can sustain a rainfallrate ofover 10 inches ofwater per hour.

The roofdrainsare designed to eventually be carriedthrough undergroundpiping into the MissouriRiver. The remaininglocal site drainageis designed such that any excess rainfall not immediately absorbed into the ground will flow awayfrom the buildings to be discharged into drywells or low lying areas adjacentto the plant site. Accordingly, these designs can safely remove the accumulatedwaterfrom the probable maximum precipitationrate described in Section 11-3.1.3, and can also accommodate the AEC 's estimated 9.7 in./hr in one hour rainfallrate without adverse effects on the safety-relatedsystems necessaryfor safe shutdown. "

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CNS Flooding Walkdown Submittal Report 2.4 Other Evaluated Flooding Events The CNS USAR and associated original FSAR question responses evaluated several other flooding events which were concluded as bounded by the establish PMF. These included:

Ice Blockage or Damming - The USAR Section 4.2.2.1 states" ... .Floodingcaused by ice blockage is consideredcredible only at riverlevels significantly lower than the PMF.

Floodingcaused by ice blockage would cause water surface elevations below those of the PMF."

> River Diversion Due to Flooding - USAR Vol. II, Section 4.2.3.2 states; "...afailure of the Oahe or Ft. Randallflood control dams is the most likely initiatorof a river diversion. The closer of the two, FortRandall, is almost 350 miles upstreamfrom the plant site and there would be a three day warning before the river reaches a peakflood stage at CNS. During this peakflood stage, shutdown procedures to the reactorcould begin and continue as the flood waters slowly recede. After the river diversion occurs, the resulting isolatedbody of water in the vicinity ofthe site,fed by ground water inflow, would retain essentially the same stage characteristicsthat apply to the present open river as long as the main channel was retainedin the existing valley. Minor variations resultingfrom elimination ofsome bends would be of no consequence to the safe operation of the plant. Extreme low water stages which might be attained in the natural channelwould not occur under these circumstances because ofthe lag in response of groundwaterto short term changes in the riverchannel. It is concluded, therefore, that there would be an adequatesupply of water to effect a safe shutdown of the plant."

2.5 Original Supporting Evaluations and Methodology Various supporting analysis and evaluations were performed during development of the original FSAR and follow up responses to original AEC review questions through amendment.

Corps of Engineers Study - According to FSAR Question No. 2.1 (Ref. 10.2.3) the USACE estimated a Probable Maximum Flood (PMF) elevation between 902-ft and 903-ft Mean Sea Level (MSL), in practice CNS typically regards 903-ft MSL as its PMF value. The USACE also calculated wave heights occurring coincident with the 903-ft MSL PMF event. It estimated a shallow water "significant wave height" of 4-ft, a "one-percent wave height" of 6.7-ft, and the "wave run-up" against a vertical wall (Intake Structure) of 6.7-ft. The calculation used a wind speed of 45 mph as prescribed by the NRC in FSAR Question No. 2.2 (Ref. 10.2.3). The response to FSAR Question No. 2.2 noted that the relationships used to estimate these wave heights were derived from studies made on lakes and oceans, and that it is not believed that waves of this magnitude could be generated in a river flood setting. The FSAR Question No. 2.2 response noted that waves could only impact the intake structure, with the run-up reaching an elevation of 909.7 ft MSL. The response states that wave energy would be dissipated before reaching the other Class I Buildings (Main Building Complex). The Main Building Complex is approximately 200' away from the river channel edge, with the surrounding grade elevated to 903 +/- ft MSL.

The USACE had reported (stated in CNS USAR Section 4.2.2.2) that a major dam break coincident with a PMF event was not credible; however, a maximum flow rate for a dam Page 8 of 36

CNS Flooding Walkdown Submittal Report break event and resulting surface water elevation was estimated. As described in the USAR, the maximum natural flood combined with a "...failure of a major flood control dam - either Oahe or Fort Randall" could produce river flows of 1,250,000 cfs. A water surface elevation based on this flow rate was predicted to reach elevation 906 ft MSL.

The evaluation did not consider wave action coincident with a 906 ft MSL flood event.

Atomic Energy Commission Study - As previously outlined in the USAR Section above, the Atomic Energy Commission reported in the Safety Evaluation Report (SER)

(Ref. 10.2.7) that its conservative estimation of the PMF Elevation at CNS was 901.2 ft MSL, based on a River flow rate of 1,000,000 cfs. AEC calculated coincident wave crests could reach an elevation of 909.2 ft MSL at the intake structure, and 905 ft MSL at the other structures across the site (located away from the river channel). The AEC also concluded that seismically induced dam failure coincident with a PMF is not credible but did consider a dam break concurrent with a 2 PMF event. Their results indicated that the resulting flood elevation was lower than the PMF event alone.

2.6 Other Analysis and Evaluations IPEEE -Individual Plant Examination of External Events In 1991, in accordance with 10CFR50.54(f), the NRC issued Generic Letter 88-20, Supplement 4 based on staff and industry experience with plant-specific probabilistic risk assessments (PRAs), that systematic examinations are beneficial in identifying plant-specific vulnerabilities to severe accidents which could be fixed with low-cost improvements. The supplement was focused on external events that could be significant contributors to core damage in some instances. Section 5 of the CNS IPEEE report (Ref.

10.2.9) submitted to the NRC addresses the occurrence of high winds, floods, and other weather related events with regard to probability of beyond design basis effects.

Potential Dam Failures - This section of the report states" The location of the upstream dams are listed together with their river mile in Table 5.8. Section 11-4.2.1 of the CNS USAR provides a discussion of dam failure scenarios.An analysis of the FortRandall Dam failure showed that waters releasedwould requireat leastfour days to reach the CNS site. If this event occurs, river elevations of 904 feet MSL would be expected, a maximum of 0.5 ft above the groundfloor elevation of 903.5 feet MSL. An emergency procedure is in place to install sandbagsand wood planks to combat theflood. Such actions are effective to protect the plant to water levels up to 907.6'. The procedure was successfully implemented at CNS during the flood in 1993. As such there is confidence in the ability of the plant staff andpersonnel to mitigate the flood event. The elevation of 906 feet MSL is calculated by postulatinga damfailure concurrent with the maximum naturalflood. The effects of wind generatedwave action in the determination of the water level at the plant site were not considered.

This is acceptablefrom previous discussions on the wave height development which concluded that wave height would substantiallydissipateprior to reachingthe plant structures.

Failureof the Oahe Dam upstreamfrom the Fort Randall Dam is discussed in NUREG/CR-4767. According to a recent study, the US. Army Corps ofEngineers Page 9 of 36

CNS Flooding Walkdown Submittal Report has estimated that a peak-water surface elevation of 922 feet MSL (18.5feet above groundfloor) will be reached if the Oahe Dam fails. It would take approximately 3.5 daysfor thefirstfloodwave resultingfrom the dam failure to reach CNS.

NUREG/CR-4767 based thefailurefrequency estimatefor the Oahe Dam on historicaldatafor internalfailuresof earth dams. Studies suggested that earth dams fail due to internalevents with afrequencyfrom 1.OE-OS/yr to 1.OE-04/yr. The NUREG analyses used 5. OE-05 per year as a best estimate. The District reviewed the supporting COE analyses and noted that a 100 year returnfrequency flood event at the Oahe dam site was assumed coincident with dam failure. Assuming that these independent events would have to occur during the same seven day periodand based on the conclusion that core damage would result from a flood to elevation 922feet MSL, the contribution to core damagefrequency due to the Oahe Damfailure was estimated as 9.OE-09/yr.

In the NUREG estimate it was conservatively assumed that the dam was completely full at the time of the failure (concurrentwith a spillway designflood) and that the dam was assumed to fail catastrophically.These two assumptions are very unlikely.

Additionally, the Oahe Dam and reservoirlevel is closely managed by the COE.

Therefore, it isjudged that this event can be screenedper NUREG-1407 andno further actions to reduce the CNS vulnerabilityto the Oahe Dam failure are warranted.... "

NPPD Calculation NEDC 11-076 In preparation for the NRC 50.54(f) response, CNS has directly developed and/or contracted the services of vendors to perform various evaluations and analysis of current potential flooding impact on the plant. These analyses do not change the plant's CLB but serve to provide significant information in support of the established PMF going forward.

Calculation NEDC 11-076 (Ref. 10.2.11) was developed for informational use only, to evaluate issues regarding CNS external flooding eventsas initiated by and described in condition report CR-CNS-2010- 01630. It was also utilized in the disposition of the CR's associated corrective actions CA-6, CA-8, CA-10, and CA- 11. The calculation evaluated against the hydraulic (i.e. stage discharge) of three scenarios including (1) an estimated 500-year event based on the peak flow reported in the Corps of Engineers 2004 Upper Mississippi Flood Frequency Study, (2) the Probable Maximum Flood event established in the CNS USAR, and (3) a Ft. Randall Dam Break Event at the Maximum High Pool Condition as provided by the Corps of Engineers. The calculation assumes that no levees failed during each flood scenario considered. CNS grade is elevated above the tops of adjacent levees, a conservative assumption in terms of maximum flood height (much larger flood area would be available behind the levees resulting in a lower flood level).

The calculation concluded that the predicted stage of the Missouri River estimated in the calculation compared favorably with the river stages determined during the stations original design. It was concluded that the river stage (water level) discussed in the USAR remains a conservative estimate for the flow scenarios considered with respect to this methodology. However, the flow scenarios themselves, while not discounted, could not be verified. A new PMF hydrologic study using current methodology was recommended Page 10 of 36

CNS Flooding Walkdown Submittal Report and is currently being performed in response to Recommendation 2.1, Flooding enclosure of the 50.54(f) Letter. This effort will also include reevaluation of the current site drainage when subjected to a PMP event. The PMP study is due to be completed before the end-of-year.

2.7 CLB Flooding Summary Table The below table summarizes the CNS CLB based upon the information as presented in this report.

CONDITION CNS CLB COMMENTS.

PMF Peak Flow Rate' 600,000 CFS PMP Event centered above Brownville, NE PMF Still Water Plant site elevated 903 +/- ft MSL. First Floor of all Class Surface Elevation 903 ft MSL' I building at 903.5 ft MSL.

Flood Barriers not needed at intake since critical PMF + Wave Run Up equipment is elevated above 906 ft and protected from at Intake Structure 909.7 ft MSL wave impacts.

Class I buildings grade level openings at 903.5 ft MSL, PMF + Wave Action Protected by Flood Barriers from standing water to Main Plant Complex No Impact elevation 906 ft Notes:

I. The USACE estimated a higher river stage during the PMF than the AEC, despite the fact it used a lower flow rate (600,000 cfs vs. 1,000,000 cfs). Details of the methodology utilized by the AEC to develop its stage-flow relationship were not described, except for a statement in the SER text that the AEC constructed an "Analytical Model". The analysis conducted by CNS in 2011 is consistent with the USACE estimates stage-discharge estimates - see NEDC 11-076 (Ref. 10.2.11).

2. This elevation is based on a steady flow Rate of 600,000 cfs

3. This elevation is based on a peak flow rate of 1,000,000 cfs.

Therefore in summary, the Current Licensing Basis as stated in the CNS USAR provides for a value of 903.0 MSL for the Maximum Probable Flood.

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CNS Flooding Walkdown Submittal Report 3 EXTERNAL FLOOD PROTECTION AND MITIGATION FEATURES 3.1 Flood Licensing Basis and Protected SSCs The general ground elevation surrounding CNS Class I Structures is elevated 13-ft above the natural floodplain to 903 ft MSL. The finished floor elevation of all Class I Structures is placed at elevation 903.5 ft MSL, or 1/2 ft above the PMF event. These structures were designed for a hydraulic load equivalent to a groundwater elevation of 903-ft and reviewed for integrity for a river elevation up to 906 ft MSL. Grade level openings on exterior walls of the buildings (except for the intake structure) are protected from wave effects and water surface elevations up to 906 ft MSL with flood barriers erected per CNS Procedure 7.0.11 (Ref. 10.2.14) and 5.1 Flood (Ref. 10.2.13).

The following CNS safety-related plant structures have been identified as protected from flooding as noted:

Intake Structure - As stated in the USAR; the service water motors and controls in the Intake Structure are located above elevation 908-ft MSL. These motors and controls are protected from the predicted wave effects by 24-in thick concrete walls extending up to elevation 919-ft MSL. The Intake Structure need not be isolated due to the fact that there is no essential equipment located there at or below 906 ft MSL that will be adversely affected in performance of a safe shutdown function in the event of flooding.

Reactor Building - Protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL Emergency Diesel Generator Building - Protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL Radwaste Building - Protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL Control Building - Protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL Controlled Corridor - Protected from flood water by grade level Reactor and Turbine Building walls to elevation 906 ft MSL Turbine Building - Protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL Z-Sump (Below ERP Tower) - As stated in the USAR; the top of floor drain sump Z, at the base of the Elevated Release Point tower, is located at 891 ft MSL and therefore is within postulated flood levels. The Z Sump contains equipment essential to the operation of SGTS (Standby Gas Treatment System), and therefore the sump must remain functional whenever Secondary Containment is required. Although the ground elevation at the sump is only 890 ft MSL, the Z Sump will not be affected by flooding since the sump penetrations are sealed and the proper functioning of the sump is monitored when flood levels reach 890 ft MSL.

Diesel Fuel Storage Tanks - As stated in the USAR; there is sufficient fuel in the Diesel Oil Storage Tanks to assure seven days of operation of a single diesel generator powering a single critical division of safe shutdown loads. This time duration is sufficient to obtain more Page 12 of 36

CNS Flooding Walkdown Submittal Report fuel, if needed. The two storage tanks are buried and their appendages are protected by a substantial cover. The manholes providing access to the Diesel Oil Transfer Pumps, the capped fill connections and the tank vents are all located above 906 ft MSL. The design and installation of the tanks assure flotation does not occur when empty during the PMF.

The following CNS plant structures have been identified as important to the protection of the various safety-related structures and equipment and are also protected from flooding as noted:

Augmented Radwaste Building - Protected from wave effects and flood water by grade level building walls and by temporary flood barriers to elevation 906 ft MSL Boiler Room - Protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to elevation 906 ft MSL Fan Room - Protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to elevation 906 ft MSL Water Treatment Plant - Protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to elevation 906 ft MSL Tool Crib - Protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to elevation 906 ft MSL Machine Shop - Protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to elevation 906 ft MSL MPF Building - Protected from wave effects and flood water by grade level building foundation walls and by temporary flood barriers to elevation 906 ft MSL Other Site Structures - Various site out buildings and structures classified as not important to safe operation and shutdown of the plant are located at base elevations lower than the PMF elevation of 903 ft MSL. CNS Procedure 5.1 FLOOD, evaluation of the protection these assets is determined by NPPD plant management by implementing actions based on various parameters including; plant safety, asset value, importance to overall long term power generation, etc.

3.2 Plant Operation During Flooding The operation of the plant based on a forecasted or eminent flooding event is addressed by CNS TRM (Technical Requirements Manual) Section T 3.7 Plant Systems, sub-section T3.7.1 River Level, limiting condition of operation TLCO 3.7.1. TLCO 3.7.1 states, "The River Level shall be < 895 ft MSL and not forecast to be> 902 ft MSL" at all times.

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CNS Flooding Walkdown Submittal Report The conditions are set as follows:

CONDITION REQUIRED ACTION COMPLETION TIME A. River level is > 895 ft MSL A. 1 Implement CNS Site Flood Immediately Procedure 5.1 FLOOD B. River Level is > 902 ft MSL B. 1 Implement CNS Site Flood Immediately or forecast Ž_902 ft MSL Procedure 5.1 FLOOD.

within the next 36 hours4.166667e-4 days 0.01 hours 5.952381e-5 weeks 1.3698e-5 months .

AND B.2 Be in MODE 3 (Hot 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months Shutdown)

AND B.3 Be in MODE 4 (Cold 36 hours4.166667e-4 days 0.01 hours 5.952381e-5 weeks 1.3698e-5 months Shutdown)

The TRM BASES states:

The river level of the Missouri River is controlled by the U.S. Army Corps of Engineers using dams. The closest upstream major flood control dam is approximately 350 miles upstream. The use of these dams reduces the possibility of a site flood. However, should a dam break or in case of a river level of 895 ft MSL, the CNS Site Flood Procedure will be put into effect.

Should the level reach 902 ft MSL or a forecast issued by the official government agency indicates expected levels of 902 ft MSL or greater within the next 36 hours4.166667e-4 days 0.01 hours 5.952381e-5 weeks 1.3698e-5 months , the reactor will be shutdown and vented to atmosphere.

A plant shutdown is initiated under any of the following conditions:

1. Floodwaters either reach 902 ft MSL, or are forecast to reach 902 ft MSL within the next 36 hours4.166667e-4 days 0.01 hours 5.952381e-5 weeks 1.3698e-5 months (as from the 10,000 year flood or an upstream dam failure).

2. Floodwater accumulates in either Diesel Generator Room, any of the four Reactor Building Quads, or the Control Building Basement.

3. Plant conditions warrant reactor to be shut down.

3.3 Flood Duration There is no specifically stated time(s) associated with the PMF event provided within the CNS CLB. CNS USAR Figure 11-4-7, Platte Plus Missouri River (s) Hydrograph, displays the projected river discharge at Cooper Nuclear Station for the PMF in Time in Days versus CFS. Inspection of the hydrograph indicates an approximate duration of 5 1/22 days of flood conditions may be expected from a river flow of 200,000 CFS peaking to 600,000 CFS and back down to 200,000 CFS. Initial inspection of USAR Figure 11-4-8, Estimated Stage Discharge Relation Missouri River at Brownville Nebraska, would correlate to an Page 14 of 36

CNS Flooding Walkdown Submittal Report approximate minimum flood level of 895 ft MSL to the maximum projected PMF value at CNS.

3.4 Flood Protection Features Various methods of protection are specifically detailed within the CNS USAR Section 4.2.2.2 as to the plant's response to an imminent flooding event. The USAR states that material and equipment necessary to perform these protective measures are available at CNS and inventoried on an annual basis. As an example; special equipment includes; two portable gasoline powered pumps and 100 ft minimum (per pump) of 2 1/2/2-inch non-collapsible hose.

The CNS USAR specifically addresses various actions that will be taken to protect safety related SSCs located below the PMF plus wave effects level of 905 ft MSL. The original response to FSAR Question 2.34, Amendment 17 (Ref. 10.2.5) identified specific equipment and components to be protected including the:

" RHR Service Water Booster pumps located at Elevation 882'-6" MSL in the Control Building basement.

" RHR pumps 1A and IC in the northwest quadrant room of the Reactor Building at Elevation 859-'9" MSL.

" RHR pumps 113 and ID in the southwest quadrant room of the Reactor building at Elevation 859-'9" MSL.

RCIC turbine pump set in the northeast quadrant room of the Reactor building at Elevation 859-'9" MSL.

" Diesel generator water tight junction boxes at Elevation 904' MSL.

D.C. switchgear and battery chargers in Control Building 903'-6" level at less than 905' MSL.

ECCS system logic panels on the Control Building 903'-6" level at less than 905' MSL.

RPS M-G set at the 903'-6" level of the Control Building.

Building Features A comprehensive review of all potential CNS external flood barriers and features as originally defined in Regulatory Guide 1.102 (Ref. 10. 1.3) was performed by reviewing all available plant drawings and documentation and performing initial walk downs of all accessible plant areas. These barriers/features include the permanent flood protection provided by the structural walls, penetrations, doors, hatches, water-stops incorporated in the construction of the penetrations and construction joints, special rubber boots, and other related barriers. Temporary flood protection, such as sand bagging, stop logs for specific areas and openings as needed were also included.

The following is a breakdown by area of the number of flood barriers/features identified during the development of the features database contained in the Flood Walkdown CNS DED Correspondence 12-0002 (Ref. 10.2.19) and confirmed by the formal feature walkdown process:

" Turbine Building - 22 Exterior building walls and 76 piping and conduit penetrations

" Radwaste Building - 11 Exterior building walls and 32 piping and conduit penetrations Page 15 of 36

CNS Flooding Walkdown Submittal Report

Augmented Radwaste Building - 13 Exterior building walls and 27 piping and conduit penetrations

Reactor Building - 12 Exterior building walls and 15 piping and conduit penetrations

" Control Building - 9 Exterior building walls and 65 piping and conduit penetrations

Machine Shop - 2 Exterior building walls and 6 piping and conduit penetrations

" Water Treatment Building - 2 Exterior building walls and 23 piping and conduit penetrations

" Exhaust Fan Room - 2 Exterior building walls and 2 piping penetrations

Heating Boiler Room- 1 Exterior building walls and 8 piping penetrations

" Emergency Diesel Generator Rooms - 8 Exterior building walls and 31 conduit penetrations

" Intake Structure - 4 Building walls

Site:

> Manholes - 9 conduit penetrations

> Z Sump - I conduit penetration

" Temporary Features:

> Exterior barrier walls/stop logs - 44

" Site Drainage System:

> Dry Wells- II

> Catch Basins - 7

> Area Inlets - 20 3.5 Procedures CNS has established two primary procedures for guidance in the station's response to an external flooding event.

5. IFLOOD - This is the primary procedure used for response to river level increase and is entered at a rising river level of greater than or equal to 895 ft MSL, notification of upstream dam failure and/or the river level is forecast to rise above a greater than or equal to value of 902 ft MSL within the next 36 hours4.166667e-4 days 0.01 hours 5.952381e-5 weeks 1.3698e-5 months . The procedure invokes numerous flood response measures and activities in addition to the other main response procedure 7.0.11 Flood Control Barriers (Ref. 10.2.14) which directs the CNS Maintenance department in the installation of temporary flood control barriers and features.

This procedure requires specific review during formal Flooding Walkdown Inspections performed in accordance with NEI 12-07 activities to evaluate the practicality of the associated actions performed by site personnel with regard to response timing and equipment staging and implementation.

7.0.11, FLOOD CONTROL BARRIERS - As mentioned previously this Maintenance Procedure directs the CNS maintenance personnel in the installation of temporary flood control barriers and features. The procedure provides a system of primary barriers at the openings of the outside walls of the main buildings complex to seal the buildings up to elevation 906 ft MSL. Secondary barriers are provided strategically inside the buildings to Page 16 of 36

CNS Flooding Walkdown Submittal Report control any minor leakage past the primary barriers and to break the building complex up into small areas that can be more easily protected.

3.6 Adverse Weather Conditions Emergency Procedure 5.1FLOOD and other supporting procedures and documents do not specifically address the intensity of potential adverse weather conditions on the execution or deployment of external flood mitigation activities. The procedures do however provide for the assessment of the severity of conditions which may lead to immediate actions to bring the plant to cold shutdown in a timely manner.

Adverse weather is not an aspect of CNS site design basis. The worst expected weather would be heavy rainfall which will not be a hindrance to stop log barrier construction.

These activities are well established and practiced using procedures and standard physical measures (addressed further in Section 7.5) that can be implemented based on their simplistic nature and design.

3.7 Groundwater Ingress The CNS CLB does not specifically address or quantify ground water inleakage from the site subsurface water table. Groundwater level is monitored/logged once per shift based on level indication located within site well(s) providing plant water supply. According to CNS OPS personnel, site groundwater level normally fluctuates between 875' MSL to 885' MSL with the highest recorded level of 900.8' during the 2011 May flooding event.

USAR Section XII-2.4.4.2 (Ref. 10.2.20) Design Considerations, Statement 5 second to last paragraph states, ".... Where penetrationsenter buildings through sleeves; details relating to the methods of waterproofingandmaintaining buildingintegrity have been developed.".

The above statement is based on CNS original response to FSAR Question/Answer 12.2 Amendment #9 (Ref. 10.2.2 1) which states, "........Membrane waterproofingmaterialused on the exteriorfoundation walls of the Reactor, Turbine, Control and Radwaste Buildings is the same as describedin the answer to Question 12.1 with the exception that integrally moldedprotrusionswere used to obtain a cast-in-place barrierwith the concretefoundation wall. This barrierwas sealed at the top just below grade into a reglet, and at the bottom was sealed to the mat material by the same adhesives and tape strips outlined in the answer to Question 12.1. With respect to in-service inspection of the vertical waterproofingbarrierthe same controlled applicationas describedin the answer to Question 12.1 is applicable, except that the 2 inch protective cover has been deleted. Therefore, no provisionshave been made to check the integrity of the membrane during the life of the plant. Drainsare provided in the base slab ofall buildings to collect any water which may accumulate on the slabfor any reaso n........................................................................................................................................

Where penetrationsenter buildings through sleeves, details relatingto the methods of waterproofingand maintainingbuilding integrity have been developed and are shown in Figure 12.2-1. "

(Note: Figure 12.2-1 is CNS B & R Drawing 2299 (Ref. 10.2.22).)

Page 17 of 36

CNS Flooding Walkdown Submittal Report 4 INTERNAL WARNING SYSTEMS Currently there are no official plant internal warning systems dedicated specifically to detection of water infiltration related to an External Flooding Event in the current licensing basis. However various level alarms are provided for sumps, low building elevations and yard manholes which provide annunciation in the CNS Control Room (Panel B-3 and S-1 annunciator windows). These include the following: (Note: All reactor building and turbine building sumps are HI-HI alarms which signal the control room at the setpoint when one pump is overloaded and will concurrently call the second pump into service)

Reactor Building Sumps - EL. 859'-9" Sump 1-A: is located in the RHR Pump Room in northwest Quad of the Reactor Building at elevation 859'-9". The sump receives discharge from various plumbing fixtures and floor drains located on multiple elevations of the Reactor Building, noted in CNS Procedure 2.2.27 "Equipment, Floor, and Chemical Drain System", Attachment A. The sump contains dual sump pumps (1-SP- lA1 & 1-SP- 1A2) which controls sump water level with discharge to the radioactive floor drain line (FDR-1). Setpoint is 34" of water in the sumnp.

" Sump I-B: is located in the Core Spray Pump Room in northeast Quad of the Reactor Building at elevation 859'-9". The sump receives discharge from various plumbing fixtures and floor drains located on multiple elevations of the Reactor Building, noted in CNS Procedure 2.2.27 "Equipment, Floor, and Chemical Drain System", Attachment A.

The sump contains dual sump pumps (l-SP- IBI & I-SP- 1B2) which controls sump water level with discharge to the radioactive floor drain line (FDR-1). Setpoint is 34" of water in the sump.

" Sump 1-C: is located in the RHR Pump Room in southeast Quad of the Reactor Building at elevation 859'-9". The sump receives discharge from various plumbing fixtures and floor drains located on multiple elevations of the Reactor Building, noted in CNS Procedure 2.2.27 "Equipment, Floor, and Chemical Drain System", Attachment A. The sump contains dual sump pumps (1-SP- ICI & l-SP- 1C2) which controls sump water level with discharge to the radioactive floor drain line (FDR-1). Setpoint is 34" of water in the sump.

" Sump l-D: is located in the Core Spray Pump Room in southeast Quad of the Reactor Building at elevation 859'-9". The sump receives discharge from various plumbing fixtures and floor drains located on multiple elevations of the Reactor Building, noted in CNS Procedure 2.2.27 "Equipment, Floor, and Chemical Drain System", Attachment A.

The sump contains dual sump pumps (l-SP- IDI & l-SP- 1D2) which controls sump water level with discharge to the radioactive floor drain line (FDR-1). Setpoint is 34" of water in the sump.

Sump 1-E: is located in the Core Spray Pump Room in southeast Quad of the Reactor Building at elevation 859'-9". The sump receives discharge from various plumbing fixtures and floor drains located on multiple elevations of the Reactor Building, noted in CNS Procedure 2.2.27 "Equipment, Floor, and Chemical Drain System", Attachment A.

The sump contains dual sump pumps (l-SP- IEI & 1-SP- 1E2) which controls sump water level with discharge to the radioactive floor drain line (PW-1). Setpoint is 24" of water in the sump.

Page 18 of 36

CNS Flooding Walkdown Submittal Report Turbine Building Sumps - Basement (EL. 882'-6")

Sump I M: is located in the northeast comer of the Turbine Generator Equipment Area at elevation 882'-6" in the bay between column lines 14-E and 14-F. The sump receives discharge from various plumbing fixtures and floor drains located on multiple elevations of the Turbine Building, noted in CNS Procedure 2.2.27 "Equipment, Floor, and Chemical Drain System", Attachment A. The sump contains dual sump pumps which controls sump water level with discharge to the non-radioactive floor drain line (FDN- 1).