Text

Non-concurrence on Oconee Assessment Letter
	ML110260443
Person / Time
Site:	Oconee
Issue date:	01/28/2011
From:	Meena Khanna, George Wilson; Division of Engineering
To:	Jeffrey Mitman; NRC/NRR/DRA
	Khanna M, DCI/CVIB, 415-2150
References
	TAC ME3065, TAC ME3066, TAC ME3067, FOIA/PA-2013-0213, FOIA/PA-2015-0348
	Download: ML110260443 (39)
	v • d • e

NRC FORM 757 NRC M D 10.158 (3-2009) U.S. NUCLEAR REGULATORY COMMISSION NON-CONCURRENCE PROCESS SECTION A *T O BE COMP LETED BY NON-CONCURRING INDIVIDUAL TITLE OF DOCUMENT Confirmatory Action Letter-Oconee Commitm ents to Address External Floodin g Concerns DOCUMENT SPONSOR M e ena Khanna /

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Mitma n, Jeffrey F ri day , Ja nu ary 28 , 2011 3:35 PM Khanna , Meena Rodriguez, Veron i ca; Lee , Samso n; Cunningham , Mark; Wilson , George; Ferrante , Fernando Oconee Non-Concurrence Meena , as we discussed , after reviewing the response to my non-concurrence, I'v e decided to cont i nue to concur. Please mark the letter appropriately.

As far as marking the non-concurrence packages as OUO , I have no problems with it being so marked. A final note, at Jack's request I discussed my non-concurrence with him today. I do not know what his decision will be. Jeff 1 NRC FORM 757 NRC MD 10.158 (3-2009) NON-CONCURRENCE PROCESS U.S. NUCLEAR REGULATORY COMMISSION T ITLE OF DOCUMENT I ADAMS ACCESSION NO. Confirmatorv Action Letter-Oconee CoJD.IItitments to Address External Floodine Concerns I ML103280043 SECTION 0: CONTINUATION PAGE CONTINUATION OF SECTION [ l A [ I B N RC FORM 757 (3-2009) Use ADAMS Template NRC-006 PRINTED ON RECYCLED PAPER OFFICAL USE ONLY-SECURITY RELATED INFORMATION Introduction and Summary The NRC is preparing to issue a letter to Duke Energ y Carolinas, LLC.1 The draft of this letter states "tha t the parameters chosen by the licensee and the analysis performed bound the inundation of the ONS (Oconee Nuclear Station) site resulting from a potentia l failure of the Jocassee Dam." I am non-concurring on the conclus i on that the parameters chosen, specifically the reservoir levels, are bounding.

In a NRC letter to Duke in April 2009, 2 the NRC states that: The NRC staff agrees that a study with more advanced model and sensitivity analyses would be beneficial because of the uncertainty in volved in predicting dam failure and resultant flood levels at Oconee. Dam des i gn operating parameters, including reseNoir level, should be used as input to the inundation study to support the safety of the Oconee facility.

The sensit i vity analysis should include varying key parameters that can affect the on-site flood height (e.g., breach size, reseNoir levels, and time to dam failure) individually and in combination over a sufficient range to prov i de an understanding of how changes impact the flood height estimates.

[emphasis added] In the resultant studies, Duke has not varied the reservoir levels as required by the April 30, 2009, letter. All of the analysis was performed assuming a "sunny day" failure with the Jocassee Reservoir at a level of 1110 ft. mean sea level (msl) and with Keowee Reservoir at a level of 800ft. msl (e.g., Duke's letter dated August 2, 2010 2). Prior to accepting any inundation analysis results , Duke should be required, as the April 2009 letter stated, to conduct and submit additional sensitivity analysis varying Jocassee and Keowee Reservoir levels up to and including a defendable most severe level. Background Lake Jocassee was created in 1973 with the construction of the Jocassee Dam on the Keowee River. The lake provides pump storage capacity to the reversible turbine-generators of the Jocassee Hydroelectric Station, located approximate l y 11 miles north of the plant. At full pond, elevation 1110 ft. msl, Lake Jocassee has a surface area of 7565 acres, a shoreline of approximately 75 m i les a volume of 1.16 million acre-ft., and a total drainage area of about 14 8 square miles. 3 The Jocassee Dam is a rockfill earthen dam 385 ft. in height and a length of 1800 ft. At a reservoir level of 1125 ft. it impounds approximately 1.28 million acre-ft. It has 2 spillway Tainter gates, each 38ft. wide and 33ft. high, and a crest elevation of 1110 ft. msl. It has 4 hydro-electric units with a total capacity of approximately 600 MWs. 1 NRC letter E.J. Leeds to T.P. Gillespie , Confirmatory Ac tion Letter-Oconee Nuclear Station , Units 1, 2, and 3 (ONS) Commitments to Address External Flooding Concerns Closure of Inundation Results (TAG Nos. ME3065, ME3066, and ME3067) (ML103280043), draft December 2010 2 NRC letter to Duke titled " Evaluation of Duke Energy Carol inas, LLC (Du ke), September 26, 2008 Response to Nuclear Regulatory Commission (NRC) L etter Dated August 15, 2008, Related to External Flooding at Oconee Nuclear Station, Units 1, 2 , and 3 (Oconee) (TAC Nos. MD8224, MD8225, and MD8226)" dated April30, 2009 (ML090570779) 3 ONS UFSAR Section 2.4 Hydrologic Engineering OFFICAL US E ONLY -SECURITY RELATED INFORMATION OFFICAL USE ONLY-SECURITY RELATED INFORMATION Lake Keowee was created in 1971 with the construction of the Keowee Dam on the Keowee River and the Little River Dam on the Little River. Its primary purpose is to provide cooling water for the plant and water to turn the turbines of the Keowee Hydroelectric Station. At full pond, elevation 800ft. msl, Lake Keowee has a surface area of 18,372 acres, a shore l ine of approximately 300 miles, a volume of 955,586 acre-ft., and a total drainage area of about 439 square miles. The Jocassee and Keowee Reservoirs and the hydroelectric stations located at these reservoirs are owned and operated by Duke.3 In analysis leading up to the NRC's 50.54(f) letter, 4 the NRC staff identified an adequate protection issue. The NRC's concern involved a Jocassee Dam failure, which inundates the ONS. I n this scenario, flooding of the site leads to a f ailure of all emergency core cooling systems (ECCS), all balance of plant (BOP) equipment and both onsite and offsite electrical power systems. If the inundation overtops the protective wall around the standby shutdown facility (SSF) all means of cooling the three reactor cores and the two spent fuel pools will be lost. In subsequent analysis and correspondence, Duke has confirmed this scenario and its impact. The one-and two-dimensional (1-0 and 2-0) analysis indicates that a Jocassee Dam breach will inundate the ONS. At the SSF yard, water depth will rise to approximately 18.5 ft., overtopping the floodwall protecting the SSF (which is currently 7.5 ft. in he i ght).5 Per Duke's analysis, without mitigation this will lead to core damage in 8 to 9 hours1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months (the conditional core damage probabi lity or CCDP is 1.0) and containment failure in 59 to 68 hours7.87037e-4 days 0.0189 hours 1.124339e-4 weeks 2.5874e-5 months .6 As the introduction states, this flood height is based on a Jocassee Reservoir leve l of 111 0 ft. msl and a Keowee Reservoir level of 800 ft. msl. The reservoir levels are significant for severa l reasons. First, a dam's failure li kelihood is highly sensitive to reservoir level? The higher the reservoir level the more likely the dam is to fail. Second, higher water levels in Jocassee and Keowee at the time of failure will lead to higher inundation levels at ONS. Finally, higher levels can lead to more rapid dam failure and more rapid inund at ion, allowing less time for warning and preparation.

Addressing the first of these reasons, Duke has stated that, in the approximately 38 years of Jocassee Dam operation, the reserv oir has never exceeded the normal operating level of 1110 ft. The reservoir has operated up to a level of 1 110 ft. However, Duke's analysis of a probable maximum participation (PMP) event, assuming operation of both spillways and all four hydro units, water level will reach approximate l y 1122 ft. 8 Studies performed by the NRR Division of Risk Assessment (ORA) indicate that a large storm equ ivalent to 30% of a PMP event with failure of the hydro units will ra ise water level to approximately 1111 ft. msl. Additional ORA results for various storm sizes and combinations of unavailability of spillways and hydro units are given in Table 1 below. T his combin at ion of Duke and NRC staff analysis clearly indicates that water levels higher than 1110 ft. can be anticipated w i th large storms. 4 NRC le tter to Duke dated August 15 , 2008 (ML081640244) 5 Duke letter to NRC dated August 2 , 2010 (ML102170006) 6 Duke letter to NRC dated September 26, 2008 (ML082750106) 7 The Status of Methods for Estimation of the Probability of Failures of Dams for Use in Quantitative Risk Assessment, R. Fell, D.S. Bowles, et. el. International Commission on Large Dams 20th Congress Beijing, China. September 2000 8 Jocassee Dam Hydrologic Analysis, Law Environmental , January 1991 and updated through June 2009 OFFICAL US E ONLY-SECURITY RELAT E D INFORMATION OFFICAL USE ONLY-SECURITY RELATED INFORMATION ORA analysis also indicates that the Jocassee Dam could overtop given a large storm with comb inations of failures of th e Jocassee spil lways and hydro turbines.

A review of the Duke 1-D analysis commissioned by NRR and performed by the US Bureau of Reclamation also recommended that scenarios leading to overtopping b e considered:

" I f the spillway was for some reason, not able to operate, overtopping of the dam could occur. It would be worth performing a level pool flood routing ana lysis to determine the depth and duration of overtopping at Jocassee Dam assuming PMP inflow and i noperable or partially blocked spillway gates." 9 Table 1 Storm Size Assumed Number of Assumed Number of Es timated Jocassee Reservoir Level (PMP fraction)

Operational Spillways Operational Hydro Units (ft. msl) 100% 2 4 1122 100% 2 0, 1125 100% 1 2< 1125 100% 0 01 Dam overtops 90% 0 0 1 Dam overtops 40% 2 4 1111 30% 2 0 1111 Table Notes: 1 -In these sce narios the hydro units are assumed to be available early but not during storm peak conditions possibly due to storm causing a loss of hydro units' switch yard 2-Law Environmental analysis i ndicates hydro unit unavailability was approximately 8% between 1985 and 1989 The NRR Division of Engineering (DE) has suggested that the probability of a large storm concurrent with an independent dam failure would be a highly improbab le event. However, neither Duke nor NRC staff has developed a PMP Jocassee Dam hazard curve to determine the probabilities of various large storms. Addit ion ally, because the Jocassee Reservoir has never exceeded 1110 ft. the dam performance above 1110 ft. is an unknown. The dam was designed for these condit ions, but has never experienced these conditions.

Any existing design or construction flaws may manifest themselves for the first time under these high stress conditions.

It should be unders tood that hydrostatic loads on the dam at 1125 ft. will be approximately 10% greater than the loads at norma l peak level of 1110 ft. The second reason reservoir level is important is that it significantly increases the potential water volume and flow to which the ONS is subjected. At normal full pond elevations, Keowee at 800 ft. and Jocassee at 1110 ft., these two reservoirs ho l d approximately a combined 2.1 million acre-ft. With Keowee at 815 ft. (the crest of Keowee Dam) and Jocassee at 1125 ft. the combined impoundment is approximately 2.5 millio n acre-ft. T his 20% increase will change the flood conditions at ONS. As stated previously, the flood conditions at ONS with a Jocassee Reservoir level of 1110 ft. will lead to a flood height at the SSF of approximately 18.5 ft. above grade. Duke's completed 1-D analys i s determined that peak flow rates across the Keowee Dam are between 2.3 and 2.8 m i llion cubic feet per second (cfs) and peak flow rates across the Oconee Inta ke Canal Dike are 9 Jocassee Dam , South Carolina Inundation Study Review Comments, US Bureau of Reclamation.

July 2009 OFFICAL USE ONLY-SECUR ITY RELATED INFORMATION OF F I C AL U SE O NLY-SE CURITY R E LAT E D INFORMATION between 0.6 5 and 0.84 mi lli on cfs.10 As a point of reference , th e average flow i n the M i ssissipp i River at New Or l eans is approximately 0.6 million cfs.11 The third reason that reservoir l eve l s are signi fi cant i s due to t he i r impact on warning and r esponse times. With a dam fai l ure at higher reservo i r l eve l s , the failure is l ikely to proceed at a faster pace. Also , waters re l eased from the reservoir may trave l faster down river. In both cases , th i s wil l lead to less warning time a n d therefore, l ess time to prepare ONS for inundation. Duke's current 1-D and 2-D ana l ysis (based on 1110 ft. and 800 ft.) ind i cates that the Keowee Dam will overtop between 2.1 and 2.2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months and the i ntake canal in about 2.9 hours1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months after failure of the Jocassee Dam. Peak wa t er level at the SSF will be reached in abou t 3.7 hours8.101852e-5 days 0.00194 hours 1.157407e-5 weeks 2.6635e-6 months .1 0 These times define the l i m i ti n g constrain t s under wh i ch t he l i censee personnel must understand the size, speed and consequence o f the d am breach, m a ke the difficult decisions to sh u tdo w n th e reactors, r ap i dly cooldown a n d depre ss ur i ze the primary and secondary systems so that the H ale pumps a n d the mit ig ati n g s tr ate gi e s c an be used to in jec t la k e w a t er into the steam generators.

H i g h e r initial r ese rv o ir lev e ls w i ll po t entially decrease the time available for these responses.

To date , only a partial consequence analys i s has been performed.

As previous ly d i scussed, a Jocassee Dam fai l ure with a re s ervoir l eve l of 1 110 ft., will lead to a failure of the ECCS, BOP and all e l ectrical power and to an inundation height a t the SSF of approx i mate l y 18.5 ft. Duke has also determ i ned that because a ll three access r o ads cross bridges that wi ll be destroyed by the flooding , access to the site wil l on l y be ava il ab l e vi a he li copter. Duke's in t erim compensatory measures (ICM) d i rect utility personn e l to m iti gate the flood u sing " Ha l e" pumps (Ha l e pumps are sk i d mounted portab l e fire pumps) and hoses by i n j ecting l ake water into the un i ts' steam generators and/or containments.

Howe v er , D u ke has not add r essed the feasib ili ty of these I CMs given the very large flow rates a c ross the si t e. T hese flow ra t es may l ead to significant scouring on the s i te which can lead t o "fl oat i ng" of buried piping t hat are relied upon by the ICMs. A third potential consequence is i llustr a ted by the ONS' UFSAR that states tha t the wall separat i ng the Turbine and Auxiliary Buildin g s (the " N" line) "is capable of withs t anding a flood to a depth of 20ft. abov e elevation 775 + 0." 1 2 A flood of this magnitude will direct approx i mately 40ft. of water again s t this wall. The turb i ne and auxiliary building are a m ixture of re i nforce concrete and bl o ck wall s. It is unclear w h at the consequences of these load s will be to th i s and other structures, s y st e m s and components (SSC). There may be other typ es o f consequences beyond th e three e xa m pl e s presented. A t h orough investiga ti on f or all consequences should be performed giv en t he uncertainty in the Jocassee Dam br e ach an al y s is. Defe ns e-in-D epth Analy s i s Regulatory Guide 1.174 1 3 supplies a conc i se definiti o n of defe n se-in-depth.

Each of th e defense-in-depth attributes is discussed. The Regulatory Gu i de 1.17 4 attribute definitions are underlined be l ow. 10 Duke l ett er to NRC dated August 2, 2010 (ML102170006) 11 h ttp://www.nps.g o v/mi ss/r i verfacts.htm 12 ONS U F SAR Revision 18 Section 3.4.1.1.1 , Interna l Floo d ing 13 An Appro a ch for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis, Rev i sion 1. November 2002 O F FI C A L U SE O NLY-SEC U R ITY RE LA TED INF O RM AT I O N OFFICAL USE ONLY-SECURITY RELATED INFORMATION

Reasonable balance is preserved among preven t ion of core damage. containment failure and consequence mitigation:

A sing l e failure, i.e., a failure of the Jocassee Dam, can lead to core damage and containment failure. Thus the required balance does not exist.

Over-reliance on programmatic activities to compensate for weaknesses in plant design is avoided: The only current means of preventing consequences are Duke's ICMs. These by definition are programmatic activities.

System redundancy. independence. and diversity are preserved commensurate with the expected frequency, consequences of challenges.

and uncertainties:

Because the flooding scenarios outlined above will lead to loss of all ECCS, BOP, electrical systems and the SSF, ONS has little system redundanc y. Duke has su p plied two "Hale" pumps as part of the ICM strategy. Thus there is no independence, or diversity of the systems to deal with the inunda tion. This lim ited capability is n ot commensurate with risk given the current best estimate Jocassee Dam failu re frequency of approximately 2E-4 per year.14 Nor is it commensurate with the consequences of challenges given the Duke estimated CCDP (without mitigating strategies) of 1.0. Fina ll y, it is not commensurate with the high uncertainty. The uncertainty is described in a peer review of the Duke 1-D and 2-D analysis: "I want to emphasize that applications of complex hydraulic models is an art. The objective of ... modeling is to simplify an imposs i bly complex natural system so that it can be simulated

... Not all of the laws of phys i cs are even represen ted in the extreme conditions such as those associated with a dam breach. The models cannot be ca l ib r ated using observed data because the regulated stream system has never exceeded full pond elevation." 15

Defenses against potential common cause failures are preserved, and the potential for the introduct ion of new common cause fa ilur e mechanisms is assessed:

A failure of the Jocassee Dam is a common cause failure of the ECCS, BOP, all electrical power systems and the SSF. T hus this criterion is not met.

Independence of barriers is not degraded:

The reactor coolant system is expected to fail, core damage is expected as is containment failu r e -all caused by the Jocassee Dam failure -unless the ICM mitigating strategies succeed. Thus there is no independence of barriers.

Defenses against human errors are preserved: The only line of completely rests on human actions as directed by ICM mitigating strategies.

The intent of the General Design Criteria (GDC) in Appendix A to 10 CFR 50 is maintained:

ONS was licensed pr ior to the issuanc e of the GDCs. However , the ONS licensing basis includes a design criterion titled "C riter io n 2 -Performance Standards (Category A)," 16 which is similar to GDC 2. It states in part , "Those systems and components of reactor facilities which are essential to the prevention of accidents which could affect the public health and safety or to mitigation their conseque n ces shall be designed, fabricated and erected to performance standards that w ill enable the facility to withstand, without loss of the 1 4 Generic Failure Rate Evaluation for Jocassee Dam (ML100780084)

March 15, 2010 15 1ndependent Technical Review HEC-RAS and SRH-20 Hydraulic Modeling Wilson Engineering Project WE10009. June 14, 2010 16 ONS UFSAR Section 3.1.2 OFFICAL USE ONLY-SECURITY RELATED INFORMATION OFF I CAL USE ONLY-SECUR I TY RELATED I NFOR M AT I ON capab i lity to pro t ect the public, the additiona l forces that might be imposed by natural phenomena such as earthquakes, tornadoes, flooding conditions, winds, ice, and other local effects. The design bases so established shall re fl ect: (a) appropriate consideration of the most severe of these natura l phenomena t ha t have been recorded for the s it e and the surrounding area and (b) an approp r iate margin for withstanding forces greater than those recorded to reflect uncertainties abou t the histor i cal data and their suitability as a basis for design [emphasis added]." This design criterio n clearly requires safety grade SSC capable of deal i ng with flood i ng. ONS lacks those SSCs. I n summary, I conclude that ONS l acks defense-i n-depth against a Jocassee Dam fai l ure. This agrees with the DE memo to The NRR Division of Operating Reactor Licensing (DORL) dated October 26, 2010, 1 7 which states in part: 'Thu s, if a fl ooding event from a Jocassee Dam failure occu r red at the ONS site, all three un i ts have no de f ense-in-depth to prevent core damage. T he remaining intact element of defense-in-depth of con t ainment integ r ity wi ll be severely cha ll enged, if unmitigated, resu l ting in the potential f or radionuclide release to be high l y p r obab l e. These results have led the NRC t o concl u de that the licensee l acks de f ense-in-depth to ensure that there is adequate p r otection at the O N S site against such fl oods." Conclus i ons The Duke suggested l evels o f 111 0 ft. at Jocassee and 800 ft. at Keowee are at t he top of the normal operating limits for the respective reservo i rs. As such they a r e not bounding.

They are neither most severe as required by ONS des i gn "Cr i terion 2" nor worst case. Inundation from a large and rapid Jocassee Dam failure from these s u ggested l eve l l imits will, in approximately 2 to 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months after dam failure, lead to a simu l taneo u s l oss of defense-in

-dep t h. Without mitigation , core damage on t hree uni t s can be expected in 8 to 9 hou r s, containment failu r e in 59 to 68 hours7.87037e-4 days 0.0189 hours 1.124339e-4 weeks 2.5874e-5 months and a simu l taneous l oss cooling on bo t h spent fue l pools. T he m i tigating strategies supply a sing l e line of defense using non-safety related equipment aga i nst a haza r d that currently has a like l ihood of occurrence approximately ten times highe r than a large loss of coolant acciden t. Fai l ure of the Jocassee Dam from a higher starting reservoi r levels will worsen these impacts. Without sensitiv i ty ana l ys i s from higher reservoir levels the inunda ti on depth, tim i ng and consequences of a Jocassee Dam failure are not a d equately unde r stood or addressed.

Duke s h ould be r equ i red to perform the inundatio n sensit i vity analysis as originally required in the NRC's letter of Apr i l 30, 2009, 2 to a technica ll y def e ndable most severe level limit. 1 7 NRC Memo Wi l son to Persinko, NRC Staff Assessme n t of Duke Energy Carol in as, LL C., Oconee External F l ooding Issue (TAC Nos. ME4441, ME4442, and M E 4443), (ML102990064)

Oc t ober 26, 2010 OFF I CAL U SE ONLY-SECUR I T Y RELATED I NFOR M ATIO N OFFICIAL USE ONLY-SECURITY RELATED INFORMATION STAFF RESPONSE TO NON-CONCURRENCE ON THE INITIAL STARTING RESERVOIR LEVEL OF THE JOCASSEE DAM FOR THE FLOODING INUNDATION STUDY OF THE OCONEE NUCLEAR SITE FOR DEMONSTRATING REASONABLE ASSURANCE January 25, 2011 I. INTRODUCTION On January 10 , 2011 , a non-concurrence was submitted by Jeffrey Mitman , associated with the Staff's Assessment Letter of the flooding inundation study for the Oconee Nuclear Site (ONS). In accordance with the non-concurrence process (draft Management Directive 10.158 , "NRC Non-Concurrence Process"), the staff is providing the following:

(1) summary of the dissenting view , (2) a summary of the staff's response to the d i ssenting view, and (3) a detailed response to the specific conclusions and statements provided in the non-concurrence. During the staff's review of the flooding inundation study of the Oconee Nuclear Site, Mr. Mitman was assigned to evaluate the overa ll risk of the random failure of the Jocassee Dam. He also attended some of the meet i ngs and discussions associated with the analysis of the f l ooding scenario.

Veronica Rodriguez is his current supervisor and George Wilson, who is the Nuclear Regulatory Commission (NRC) Dam Safety Officer , is the document sponsor for the memo titled, "STAFF ASSESSMENT OF CONFIRMATORY ACTION LETTER ACTION-ONS UNITS 1, 2, AND 3 COMMITMENTS TO ADDRESS EXTERNAL FLOODING CONCERNS CLOSURE OF INUNDATION RESULTS (TAC NOS. ME3065, ME3066, AND ME3067) (ADAMS Accession No. ML103280043)." II.

SUMMARY

OF NON-CONCURRENCE The non-concurrence states that the 1110 fee t (ft) mean sea level (msl) value for the Jocassee Reservoir level and the 800 ft msl for the Keowee Reservo ir level are not bounding values for the flooding inundation study of the ONS. The non-concurrence notes that the reservoir levels are significant factors, due to the overall impact on the potential failure of the dam, flooding levels, and mitigation of the flooding eve nt. I n addit i on , the non-concurrence states that ONS lacks defense-in-depth against a Jocassee Dam failure. A. SAFETY SIGNIFICANCE OF ISSUES ASSOCIATED WITH THE CONCURRENCE The non-concurrence states the initial reservo i r levels are significant factors because higher initial reservoir levels for the Jocassee Reservoir and Keowee Reservoir could impact several parameters associated with the licensee's flooding inundation study. Higher i nitial water levels could lead to higher inundation levels at the ONS , or could cause a more rapid dam failu re, thereby causing less warning for mitigation of the flooding event , and/or could increa se the likelihood of a dam failure. If a flooding event were t o occur , a ll three uni t s at the ONS have no defense-in-depth to prevent core damage. OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION B. SYNOPSIS/

SUMMARY

OF NON-CONCURRENCE STATEMENTS ADDRESSING NON-BOUNDING RESERVOIR LEVELS, THE EFFECTS OF THE RESERVOIR LEVELS, AND THE LACK OF DEFENSE-IN-DEPTH AT THE ONS The probable maximum precipitation (PMP) analysis for the Jocassee Reservoir, which was performed by the Division of Risk Assessment , ind i cates th at the reservoir level can exceed 1110 ft msl, during a 40 percent PMP storm with maximum outflow from the turbines and spillways.

The same rationale could be applied to the Keowee Reservoir level, but no stud ies have been presently performed.

This analysis demonstrates that the reservoir levels could go above the top of the maximum operating band, during certain events. The initial height of the reservoir levels for the Jocassee and Keowee Dams impact the l ikeliho od of the dams failing, the amount of flooding at the ONS , and diminish the warning and response times to mitigate the flooding event. The overall potential effects , demonstrate the significance of the initial reservoir levels. The licens ee evaluated the results of a Jocassee Dam failure. The evaluation showed that the outcome without mitigation was core damage within 8 to 9 hours1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months , followed by a containment failure in 59 to 68 hours7.87037e-4 days 0.0189 hours 1.124339e-4 weeks 2.5874e-5 months . This evaluation demonstrates the lack of defense-in-depth for the mitigation of the flooding event at the site. Ill. Background The Jocassee and Keowee Dams were licensed and are regulated by the Federal Energy Regulatory Commission (FE RC). FERC performs annual inspections at these facilities to evaluate the operating condition of the dams. Any abnorm a l condition that is identified during these insp ect ions is evaluated and remediated accordingly.

In add ition , an independent evaluation by a consultant is required every five years by Part 12 subpart D of Title 18 of the Code of Federal Regulations, on the overall condition and capability of the dam. The Duke Staff performs weekly dam safety inspections; inspections following any 2-inch or greater rainfall or felt seismic event , annual dam inspections, and five year underwater inspections.

In addition , Duke conducts the following monitoring activities:

remote m on itoring from the Hydro Central Operating Center , which is manned around the clock; monthly monitoring of the observation wells , weekly monitoring of seepage; and annual surveys of displacement monuments.

All of these monitoring and inspection activities help to ensure that any abnorma lity is remediated to maintain the overall health and safety of the dams. In response to the potential external flooding issue at ONS, the NRR Deputy Director directed the staff to develop a closure plan in 2009 to address the external flooding issue at Oconee. The Oconee closure plan is attached.

The purpose of the closure plan was to ensure that reasonabl e assurance of adequate protection for the health and safety of the public is provided by the Oconee licensee in response to the overall external flooding inundation analysis.

The plan was discussed with the NRR Deputy Director , before being approved by the Oversight Group, consisting of the Deputy Director of Engineering in NRR. and first line supervisors from other offices and NRR Divisions.

OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION The proposed assessment l etter on which the staff r eceived the non-concurrence , documents the staffs evaluat i on of the licensee's i n i tial parame t ers for the Jocassee Dam failure that were utilized for the inundation study. It does not address the evaluation of the licensee's planned actions to mitigate the potential effects of a dam failure, because that evaluation will be performed during the staff's review of the final mitigation strategy, and any associated design changes proposed by the licensee. Based on the staffs rev i ew of t he non-co n cu r re n ce , the staff realized that t here is a need to c l ar i fy the mean i ng of t he word " bound i ng ," as used i n the proposed Assessment Lette r, in order to avoid any misunderstand i ng. The use of t he wor d " bounded," as used in the Conf i rmatory Action Letter (CAL), refers to cond i tions t h at bound t he random sunny day failure of the Jocassee Dam. Therefore, the bounding r eservoir levels would be taken at the FERC maximum allowable operating levels, which are 111 0 ft msl for the Jocassee Dam and 800 ft msl for the Keowee Dam. The staff's t echn i cal experts determ i ned that using the max i mum allowable operat i ng leve l s allowed by FERC were appropriate l y conservat i ve to bound t he consequences of a random sun n y day fa il ure of the Jocassee Da m, s i nce dam fa il ure at higher reservoir l evels wou l d not be cons i dered a " random" sunny day fa ilu re event. The above clar ifi cation of the word " bound i ng" will be added to the assessment letter. IV. RESPONSE TO CONCLUSION AND STATEMENTS IN THE NON-CONCURRRENCE The following is a response to the conclusion and statements in the non-concurrence. 1. The reservoir levels of 1110 ft at Jocassee and 800 ft at Keowee are at the top of the normal operating limits for the respective reservoirs.

As such , they are not bounding.

Higher in i tial water levels could lead to higher inundation levels at the ONS, or could cause a more rapid dam failure, thereby causing less warning and preparation for mitigating the flooding event, and/or could increase the likelihood of a dam failure. Response:

The Jocassee Reservoir level of 1110 ft msl level and Keowee Reservoir level of 800 ft msl used in the flooding inundation study of the ONS were evaluated by the staffs technical experts in hydrology and ground water hydrology, as well as the Bureau of Rec l amation acting as a contractor to NRC , and de t ermined to be appropriate for the failure scenario of concern , i.e. a random sunny day f ailure of the Jocassee Da m. T h e random sunny day fail u re scenar i o was se l ected after the NRC tec h nica l experts' eva l uat i o n of the fa il ure modes determ i ned that the potential fa i lure of t he J o cassee Dam from e i ther an overtopp i ng event or a seismic even t was not credible.

The non-concurrence has been reviewed and evaluated by NRC staff hydrologists and geologists , who are subjec t matter experts. The major point in the non-concurrence is that the initial reservoir levels for Jocassee and Keowee are not bounding. This point will be addressed by provid i ng a techn i cal eva l uation for why the initia l reservoir leve l of 1110 ft msl for the Jocassee Reservo i r and 800 ft msl f o r the Keowee Reservo i r are conserva t i ve a n d therefore , p r ovide a reasonable starti n g po i nt f or t he flood i ng i n unda t ion study of the ONS for a random sunny day fai l ure of the Jocassee Dam. OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY -SECURITY RELATED INFORMATION The additional points discussed in the non-concurrence regarding the effects or consequences of reservoir levels being above the top of t he maximum operating level allowed by FERC, will be addressed by providing a technical evaluation on w h y the random sunny day failure provides the credib l e failure scenario for the Jocassee Dam. Early in the evaluation of the flooding scenario, the staff agreed that the flooding inundation study would be based on a random sunny day failure scenario. The reason for basing the potential dam failure only on a random sunny day failure was based on the staff's assessment of the potent i al failure of the Jocassee Dam , specifically due to overtopping and seismic events. T he Probab l e Maximum F lood (PMF) is the extreme flood for the dam design or evaluation.

It is based on the assumption of the most severe hydrologic and meteorological conditions considered to be reasonable at a site. The NRC staff subject matter experts evaluated the Jocassee Dam to ensure that it could safely capture and release a PMF resulting from a probable maximum precipitat i on (PMP). The PMP is theoretically defined as , the greatest depth of prec i p i tation for a given duration that is physically possible over a given size storm area at a particular geographic locat i on at a certain time of the year. There are two engineered features for discharging water from the Jocassee Dam. There is a large deep spillway with two control gates , and there are also two tunnels beneath the dam that convey water to the four hydroelectric turbines. The spillway gates have been evaluated by FERC , to ensure that they are designed to sa f ely pass a PMF discharge.

FERC accepted Duke's 1991 and 1993 PMF analyses , wh i ch demonstrate that the Jocassee Dam can receive and release a PMF without overtopping, inc l uding consideration of an an t ecedent storm and antecedent soil moisture values. Also, FERC put together a Core Team consisting of subject matter experts from FERC, Duke, and ind ependent dam consultants to perform a Potential Fa ilure Mode Analysis (PFMA) in 1984. In the FERC Core Team's evaluation of the potential failures of the dam , they could not envision a likely scenar i o for overtopping , given the current programs of i nspection , test i ng , maintenance and backup power , as well as the pro j ect survei ll ance (the reservo i r level is monitored by Duke's Hydro Central group in Char l otte, North Carolina , around the clock). Therefore, the FERC Core Team ruled out overtopping as a failure mode, since it was considered to be a non-c r edible event. In addition to the analyses performed by the l i censee and FERC in 1984, a consultant to the Atomic Energy Commiss i on (AEC) during the i nitial licens i ng of ONS (LBC&W Associates) issued a November 15 , 1972 , letter stating that an overtopping failure would not occur due to a PMF. The NRC staff, consisting of subject matter experts in hydrology and ground water geology, also performed an independent analysis of the potential for an overtopping event in 2010, based on th e runoff model approved by FERC. This model demonstra t ed that a PMF with an antecedent storm can be safely contained and released in the Jocassee Reservoir without overtopping the dam. In the staffs analys i s , the mo i sture i nfiltration (runoff) rates were increased and different combinations of ava il ab l e dewatering equipment were a l tered to add conservatism to the model. The staff also noted that there are two earthen sadd l e dikes at the Jocassee Dam that could provide additional defense-in-depth against an overtopping failure of the Jocassee Dam. The grass covered earthen saddle dikes only have riprap on the lake side to prevent wave erosion. R i prap i s a permanent , erosion-resistant ground cover of large , loose , angular stone w i th fi l ter fabric or granular under li ning. The saddle d i ke cres t i s at the same level as the Jocassee Dam OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION at 1125 ft msl, and If overtopped for any reason, it is expected that the saddle dikes would fail much more quickly than the main dam, due to their earthen design. Most importantly, if the saddle dikes fail, they would drain the lake down to a stage elevation of -1090 ft, which is still in the operating range of the spillway gates. Thus, a failure of a saddle dike would avert an overtopping failure of the Jocassee Dam. Failure of a single saddle dike would drain the lake down to an elevation of approximately1 090 ft msl, fully averting a catastrophic draining of the entire la k e, thereby protecting the Keowee Dam and the ONS from damage. Based on the discussion above , the NRC staff concluded that overtopping of the Jocassee Dam is not a credible event. FERC stated that based on the evaluation of the design of the Jocassee Dam, it would not fail due to a seismic event. In a 2009 conversation with NRC staff, Dr. Steve Collins, who is the overall lead geotechnical engineer for FERC , stated that the evaluation takes into consideration the low peak ground acceleration, dam design, and rock filled dam performance.

The FERC Core Team , as described above , also ruled out the seismic failure as a credible event during the PFMA evaluations in 1984. This was based on performing a pseudodynamic analysis utilizing a ground response spectrum at the Jocassee Dam lo cation, which was the same as that used for the analysis of the nearby ONS by the NRC (PSAR response spectrum).

The pseudo-dynamic analysis indicated that the body stresses during a seismic event were be low the allowable limits. In addition , the post earthquake analysis was conducted us ing the base cracking predicted by the pseudo-dynamic portion of the analysis. The resultant factors of safety are in excess of those currently required by the FERC Guidelines, where a reasonable cohesion value is assumed. Duke has also performed two different fragility studies on the Jocassee Dam in 1981 and 2007. Both evaluations demonstrated that the amount of sliding displacement that occurs during a seismic event ensures that the ratio of shear stress to effective overburden pressure is sufficiently low. This ratio will limit any potential liq u efaction in the compacted sand regions of the dam; therefore, the Jocassee Dam will not fail due to seismic events. Liquefaction is the transformation of a granular material (soil) from a solid state into a liquefied state as a consequence of increased pore-water pressure induced by earthquakes , thereby allowing the material to flow. The NRC staff, consisting of subject matter experts i n geotechnical engineering and geology , performed a qualitative evaluation of the seismic stability of the Jocassee Dam. The qualitative evaluation was based on the following:

a review of the available information in the technical lit e rature pertaining to the performance of rock filled dams; the revi ew and certification by Duke's Consulting Board of the quality control performed during construction

and finally based on the overall condition of the Jocassee Dam as certified by FERC's annua l inspections.

The NRC staff verified that the original construct ion data , including the compaction data, were reviewed and approved by FERC at the time of construction.

The licensee's ongoing monitoring of monuments and piezometers in the Jocassee Dam core and abutments ind icates no significant movement of the dam, either in the vertical or in the horizontal direction even though the dam has experienced several seismic events during its life time over the last 30 years. The NRC staff a l so visited the ONS on June 15, 2009, a n d rev i ewed the material records provided by Duke. The staff assessment of the dam concluded that the dam appeared to be a constructed , stable, and a well-maintained engineering structure, that it is regularly monitored for any significant change in seepage rates and embankment or foundation stability.

Past work t o minimize and control seepage appears to have been successful. . The liquefaction potential for well compacted saturated sands with i n the dam is low. Rock-fill dams have high resistance to seismic loads. Furthermore, the seismic hazard for western South Carolina, where the Jocassee Dam is located , has been r educ ed since the time the dam was des i gned and OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION constructed. The 2002 mapping data suggested tha t for a probability of recurrence of 2 percent in 50 years, the peak ground acceleration at the dam site would be 0.197 g. The latest update from the Un i ted States Geological Survey (USGS) (Petersen et al., 2008 , Fig. 28) lowers this est i mate to less than 0.1 g, which significantly reduces the risk of dam failu r e due to a postu l ated seismic event. The seismic attributes of the Jocassee Dam were analyzed by the NRC staff experts , and they have determined that a seismic failure of the Jocassee Dam is not a credible event. T he overtopping and seismic failure evaluations discussed above are key points to the Staffs overall assessment of the ONS flooding inundation.

The FERC Core Team in the PFMA concluded that the most likely Jocassee Da m failure would be from a piping failure in one of the abutments. After reviewing the data, the NRC staff experts also concluded that the m ost credible failure scena r io for a random sunny day failure o f t h e Jocassee Dam was due to a piping failure in one of the abutments.

The random sunny day failure of the Jocassee Dam results in the fai l ure of the Keowee Dam and associated structures , t h ereby flooding the ONS. Since the evaluation is based on a random sunny day failure of the Jocassee Dam , it is appropriate and conservat i ve to assume that the Jocassee and Keowee Reservoir levels are at the top of the maximum allowable operating band. To assume the i nit i al reservoir levels to be greater than the top of the operating band , additional equipment failures or natural phenomena have to be combined , as described below , thereby resulting in a "non-random" sunny day failure event. As stated above, this is a key point, since the non-concurre n ce also d escribes the potential effects of a higher in i tial reservoir level. The staff acknowledges the concern that the h i gher reservoir levels for the Jocassee Reservoir and Keowee Reservoir could potentially have an impact on the outcome of var i ous paramete r s such as: higher inundation levels at the ONS; a more rapid dam failure, thereby resulting in less warning and preparat i on fo r the mitigation of the f l ooding event; and/or increase the likelihood of a dam failure. However, as stated above, in order for the initial reservo i r l evels to be above the normal operating pool levels, additional equipment failures or natural phenomena have to occu r, the r eby making the event a "non-random" sunny day fai l u r e , which would be less likely to occur due to the condit i ons necessary for water to be above the maximum operating range. FERC has stipulated the normal operating range of the Jocassee Reservoir as 1080 to 111 0 ft msl. The Keowee Reservoir has a norma l operating range from 794 to 800 ft msl. FERC also approved the random sunny day failure ana l ysis at a starting reservoir of 11 08 ft ms l for the Jocassee Reservoir in the 1992 FERC Study performed by Duke Energy. T he same rationale app l ies for the Keowee Reservo i r level for bei n g below the top of the operating band. Duke Hydro operates the dams in accordance with the "Keowee-Toxaway Project High-Water Operations Process" procedure. T he proce d ure co v ers normal and contingency actions for the operat i on of the dams, specifically the control of the reservo i r levels. The contingency actions include lowering the reservoir levels for abnormal rises in lake level and any anticipated s i gnificant prec i pitation.

The normal operating pool leve l of the Jocassee Dam Reservoir is 1108 ft msl, wh i ch is 2 ft below the top of the two spillway flood gates, which are at an elevation of 1 11 0 ft msl. Any water level above th i s elevation would flow over the top of the two spillway flood gates (see figure below). In addition, the max i mum allowable operating level during the hurricane season is reduced to 1108 feet msl, t o account for any unant i cipated sudden heavy OFF I CIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION rainfall.

This would be the same rationale for the Keowee Dam except i t has four gated spillways at 800 ft ms l. Figure 1: Jocassee Spillway Figure 2: Keowee Spillway The NRC staff contracted with the Bureau of Reclamation to perform an independent evaluat ion of the Jocassee Dam flooding scenario , and their evaluation was submitted to the NRC staff on Ju l y 6, 2009. That study stated that , if the Jocassee Reservoir is operated at 1,110 feet on a regular basis, or if reservoir elevation 1,110 is considered to be a normal maximum operating level , then 1,110 feet should be used as an initial reservoir level for the sunny day breach analysis. There would be a water storage volume difference between 1,108 and 1,110 feet, and this volume difference will likely affect the flooding impacts at the Keowee Dam and the ONS. The Bureau of Reclamation routinely evalua t es the sunny day dam failure flood inundation studies for Rec l amation dams. These studies typically use an initial reservoir level at the normal maximum operat ing levels for Reclamation dams; t h erefore , a sunny day analysis for the Jocassee Dam shou l d be based on a normal maximum operating l evel for the reservoir.

The same rationale would apply to the Keowee Reservo i r , s in ce the normal maximum operating level for the Keowee Reservoir is 800 ft msl. OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION Based on the operating procedures and monitoring of the Jocassee and Keowee Reservoir levels, any increase over 1110 ft msl or 800ft msl excluding an over pumping event (Jocassee Reservoir) would probably involve a flood. Th e standard for evaluating flooding at nuclea r sites is American Nuclear Society (ANS) 2.8 (1992), Determining Design Basis Flooding at Power Reactor Sites. Section 9.2.4 of ANS 2.8 (1992) does not address or requ ire event combinations with non-hydrologic and non-seismic dam failures.

The ANS standards are consistent with the requiremen ts in T itle1 0 of the Code of Federal Regulations (CFR) Part 50, Appendix A, Criterion 2--Design bases for protection against natural phenomena.

Structures, sys tems, and components important to safety shall be designed to withstand the effects of natural phenomena such as earth quakes, tornadoes, hurricanes, floods , tsunami, and seiches without loss of capability to perform their safety functions.

The design bases for these structures , systems, and components shall reflect: (1) Appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area, with suffic i ent margin for the limited accuracy, quantity, and period of time in which the histo rical data have been accumulated, (2) appropriate combinations of the effects of normal and accident conditions with the effects of the natural p h enomena. Therefore, there is no regulatory requirement to combine two different severe events, a flooding scenario followed by the dam fai lure into one initial starting scenario.

One of the reasons that different severe events are not r equ ired to be combined is due to the initiating frequency of those individual events. Fo r example, one set of potential conditions that could result in the Jocass ee reservoir level exceeding 111 0 ft msl could be a storm consisting of at least 40 percent PMP or the combination of a 40 percent PMP storm with additional dam equipment (spillway gates) malfunctioning. Duke's operating procedures require that all the turbines and spillway gates be operated to maintain the reservoir levels. It is more likely that it would take a combination of a storm and an equipment malfunction to result in the water levels going above the maximum operating leve l. The in itiat ing frequency for a storm of 40 percent PMP rainfall storm based on Point Precipitation frequency estimates for South Carolina (NOAA Atlas 14) would have an exceedance probability of less than 10*3 per year. This frequency was approximated from the rainfall frequency analysis described as follows: The PMF for the Jocassee reservoir basin was determined from the 72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months (hr) PMP in Hydro meteorological Report No. 51. The 10 square mile 72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months (hr) PMP from Hydro meteorological Report 51 is about 46.5 inches; therefore the 40 percent value is about 18.6 inches of rain. The 1000 year recurrence interval po int values for 48 hr and 96 hr rainfalls are 14.47 and 15.00 inches, respectively.

Therefore, 18.6 inches is greater than the amount of rainfall that could be expected from a 1000 year storm. The failure rate for the spillway flood ga tes is derived from actual historical data of the gates. Each of the Jocassee spillway flood gates have been tested twice a year for about 30 years with no fai lures. Consequently, each gate has a probability of failure on demand of 4 x 1 o*3 per gate. Therefore, to have a combination of a 40 percent PMP storm with a fa ilure of a spillway flood gate, the event would be less than 4 x 1 o.e per year, which is a very low occurrence event. The same ra t ionale applies to the Keowee Reservoir level. The goal of the staff's overall assessment is to ensure that reasonable assurance of adequate protection fo r the health and safety of the public is provided by the overall flooding inundation analysis.

The initial reservoir level is just one of the input para mete rs for the flooding inundation study. The other input parameters chosen for the inundation study, such as breach time, breach height, breach width, etc., also included conservatism.

With the conservatisms included in each parameter used i n the inundation study, the staff believes there is sufficient margin in the study to provide reasonable assurance that pub l ic health and safety will be adequately OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION protected , if the ONS can take measures to mitigate the estimated flood that results from the postulated random sunny day failure of the Jocassee Dam. 2. ONS Lacks Defense-In-Depth Against a Jocassee Dam Failure Response:

The non-concurrence comments on defense-in-depth are outside of the scope of the Assessment Letter. The scope of the Assessment Letter only addresses the evaluation and assessment of the licensee's initial conditions or parameters to be used in the flooding inundation study of the ONS. The licensee's interim mitigation strategy was evaluated by NRC regional and headquarters staff during an i nspectio n of the interim compensatory measures performed June 7 -10, 2010, and the results a r e co n tained in Inspection Report 05000269/2010-002, 05000270/2010006 , 05000287/2010006 (ADAMS ML1018807680).

However, the defense-in-depth comments from the non-concurre n ce may be relevant to the staff's evaluation of the licensee's final mitigation strategy, and will be considered during the staffs review of the licensee's final m i tigation and any associa t ed plant design changes. V. CONCLUSIONS AND RECOMMENDATIONS The staffs review and documented conclusions were evaluated to ensure that the review was of sufficient scope and provided reasonable assurance of adequate protection of the health and safety of the public. Based on the staff's rev i ew of the non-concurrence, t he staff realized that there is a need to clarify the meaning of the word "bounding," as used in the proposed Assessment Lette r , in order to avoid any m i sunderstanding.

The use of the word "bounded ," as used in the CAL , refers to conditions that bound the random sunny day fa i lure of the Jocassee Dam. Therefore , the bounding reservoir levels would be taken at the FERC maximum allowable operating l eve ls , which is 1110 ft msl for the Jocassee Dam and 800ft msl for the Keowee Dam. The bounding conditions would not be the absolute worst case for the dams. The above clarification of the word " bounding" will be added to the assessment letter. The concerns in the non-concurrence invo l ved the Jocassee Dam Reservoir level of 111 0 ft msl and Keowee Reservoir level of 800 ft msl, not being bounding.

As discussed above, the licensee demonstrated that the initial starting reservoir levels for Jocassee and Keowee reservo i rs are conservative and provide reasonable assurance for the flooding inundation study for ONS during a random sunny day failure of the Jocassee Dam. T herefore , the staffs conclusion that the selected reservo i r leve l s provide reasonable assurance is still valid. Defense-in-depth is not addressed in the Assessment Letter. The assessment letter documents the staff's eva lua tion of the licensee's initial parameters utilized for the inundation study. It does not address the evaluation of the mitigation of the event itself. That evaluation will be performed during the sta ff's review of the licensee's final mitigation and any associated designs. The interim mitigation strategy was evaluated by NRC staff personnel during an inspection of the compensatory measures performed June 7-10 , 2010 , and the results are contained in Inspection Report 05000269/2010-002, 05000270/2010006 , 05000287/2010006 (ADAMS ML1018807680). OFFICIAL USE ONLY-SECURITY RELATED INFORMATION Purpose: OFFICIAL USE ONLY-SECURITY RELATED INFORMATION NRR ACTION PLAN Closure Plan for Dam/Hydrology Issues 711512009 (Updated:

January 19, 2011) The purpose of this action plan is to address: (1) the question of reasonable assurance of adequate protection for the Oconee site based on the external flooding issues, (2) impact of TVA hydrology modeling errors on operating plants, and (3) potential generic issues which arise from the Oconee and TVA issues. Process: The process that will be used in addressing the dam and hydrology issues is LIC-502, "Procedur e for Development , Implementation, and Management of Action Plans." Other guidance documents will be used as necessary.

Scope of Project Plan:

Assess Duke's dam breach report and supplemental information to determine if reasonable assurance is provided for Oconee for adequate protection against external flooding, taking into consideration various staff insights and independent reviews (USSR, FERC, and staff independent reviews). (See Enclosure

1)

Address TVA hydro l ogy issues that resulted f rom the recent findings associated with the discrepancies of the Bellefonte SOCH Code t hat could impact Browns Ferry , Sequoyah , and Watts Bar. (See Enclosure

2)

Pursue any generic issues, as app licable, that result from the reviews of the Oconee external flooding issues and the TVA hydrology issues. (See Enclosure

3) ATIACHMENT OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION ENCLOSURE 1 Closure Plan for Duke's Oconee External Flooding Issues TAC Nos.: MD8224 , MD8225 , and MD8226 Las t Update: January 19, 2011 Historical

Background:

Lead Division:

DE Supporting Divisions: ORA, DORL , DPR Supporting Offices: OGC, OE, NMSS, and Rll The Oconee Nuclear Station (ONS) i s locate d in eastern Oconee County, South Carolina, approximately 8 miles northeast of Seneca, South Carolina.

The ONS licensee, Duke Power Company (Duke), owns Lake Keowee, which occupies the area immediately north and west of the site. Duke also owns Lake Jocassee , which lies approximately 11 miles to the north of the site. The Jocassee Dam was completed in 1967. I t is 385ft high above the deepest po i nt of its foundation (no t counting the excavation of about 40ft of weathered rock and backfilling beneath th e core of the dam). The dam is 1825 ft long at the crest and has a volume of 11 million cu yd of rock and earth fill. The dam includes a central earth core and transition filters supported by zoned rock fill shells. As part of its national program of Emergency Action Plans (EAPs), in 1992 , FERC required Duke to perform the Jocassee Dal)1 inu ndation study which indicated tha t the flooding caused by a " sunny day" failure of th e dam could cause the flood water l evel at the Oconee site to rise 12.5 ft above the plant grade level , and that a comb i nation of a sunny day failure and the probable maximum flood (PMF) at the Jocassee Dam would increase the water level to 16.8 ft above grade. In add ition, while reviewing an in spection finding du r ing 2007 , the staff i dent ified an error in the random dam failure analys is for s i te flooding which in creased the failure frequency by approximately an order of magn i tude. S in ce a flood of such magnitude could jeopardize the safety of the Standby Shutdown Facility (SSF) at the Oconee site if it were not adequately protected, the NRC requested that Duke provide an explanation for concluding that the site was still protected against external flooding , given the results of the 1992 study performed for FERC. In response to the NRC's request, the licensee is performing a new inundation study, using a more advanced computer model (HEC-RAS) for the specific purpose of determining the effect of flood waters on the SSF. Duke provided t he preliminary resu lts of i ts analys is for. the staffs review on April 27, 2009. A meeting was held on May 11, 2009 , whereby Duke discussed its analysis with the NRC and FERC. In June 2009, Duke will provide the schedule for completing the study and will i dentify any modifications by November 2009. Regulatory Bas i s: The requirements

that app ly to the Oconee external flooding is sues include the following:

Oconee's Pre-GDC 2 criterion requires that: Those systems and components of reactor facilit i es which are essential to the prevention of accidents which could affect the public health and safety or to mitigation of their OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION consequences shall be designed , fabricated and erected to performance standards that will enable the facility to withstand, without loss of the capability to protect the public, the additional forces that might be imposed by natural phenomena such as earthquakes, tornadoes , flooding conditions, winds, ice , and other local site effects. The design bases so established shall reflect: (a) appropriate consideration of the most severe of these natural phenomena that have been recorded for the site and the surrounding area and (b) an appropriate margin for withstanding forces greater than those recorded to reflect uncertainties about the historical data and their suitability as a basis for design. Other NRC Guidance Associated with Dams: Regulatory Guide 1.59, "Design Basis Floods for Nuclear Power Plants," Rev. 2, 1977: This Regulatory Guide describes acceptable methods of determining design basis floods, referencing the American National Standards I nstitute (ANSI) Standard N170-1976 (ANS 2.8), "Standards for Determining Design Basis Flooding at Power Reactor Sites" almost in its entirety as the source for estimating Probable Maximum Floods (PMF), with the exception of specif i c port i ons related to the evaluation of erosion failure. GDC 2 is explicit l y mentioned in RG 1.59. Nuclear power plants should be designed to p revent the loss of capability for cold shutdown and maintenance thereof result i ng from the most severe flood conditions that can reasonably be predicted to occur at a site as a result of severe hydrometeorological condit i ons, seismic activity , or both. The conditions resulting from the worst site-rela t ed flood probable at the nuclear power plant (e.g., PMF, seismically induced flood, seiche , surge, severe l oca l precipitation) with attendant wind-generated wave activity cons t itute the design basis flood conditions that safety-related structures, systems, and components identified in Regu l atory Guide 1.291

should be designed to withstand and retain capability for cold shutdown and maintenance thereof. For sites along streams , the PMF gene r ally provides the design basis flood. For s i tes along lakes or seashores, a flood condit i on of comparable severity could be produced by the mos t severe combination of hydrometeorological parameters reasonably possible ... or a reasonab l e combination of less severe phenomenologically caused flooding events should be considered in arr i v i ng at design basis flood conditions comparable in frequency of occurrence with a PMF on streams. The material previously contained in Append ix A has been replaced by American Nat i onal Standards Institute (ANSI) Standard N170-1976, "Standards for Determining Design Basis Flooding at Power Reactor Sites ," with the following exception: Sections 5.5.4.2.3 and 5.5.5 of ANSI N170-1976 contain references to methods for evaluating the erosion failure of earth fill or rock fill dams and determining the resulting outflow hydrographs.

The staff has found that some of these methods may not be conservative because they predict slower rates of erosion than have historically occurred. Modifications to the mode l s may be made to increase their conservatism.

Such modifications will be reviewed by the NRC staff on a case-by-case basis. OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY -SECURITY RELATED INFORMATION Regulatory Guide 1.1 02, " Flood Protection for Nuclear Power Plants", Rev. 1 , 1976, describes the acceptable types of flood protection for the structures, systems and components (see also SRP 2.4.10). For purposes of this guide, the Design Basis Flooding Level (DBFL) is defined as the maximum water elevation attained by the controlling flood , including coincident generated wave effects. The wind-generated wave component of elevation is generally controlled by fetch and water depth and may differ at locations around the plant. Further distinction must be made between estimates of "structural" effects (i.e., static and dynamic forces) and flood i ng or inundation effects. Additionally, the controlling flood event may be different for evaluating structu r al effects than for evaluating inundation effects. For example, the Probable Maximum Flood (PMF) may produce the highest water level and static forces on a given structure, but the total static and dynamic forces on the structure may be greater during a smaller (in elevation) flood wave from the seismically induced failure of an ups t rea m dam. Originating Document/Regulatory Assessment:

Duke Energy Carolinas , LLC (the licensee) performed an inundation study 1 in 1992 to meet a Federal Energy Regulatory Commission (FERC) requirement for formulating an emergency action p l an in the event that the Jocassee Dam failed. Th is study showed that approximately 16.5 ft. of water would inundate the site. In April 2006 , while performing a Reactor Oversight Process (ROP) evaluation, the NRC staff questioned the licensee's maintenance of the SSF f l ood protection barrier. During the subsequent ROP Significance Determinat i on Process (SOP), the NRC identified that the licensee had incorrectly calculated the Jocassee Dam failure frequency and had not adequate ly addressed the potential consequences of flood heights predicted at the Oconee Nuclear Stat i on (ONS) site, based on the 1992 inundation study. The NRC staff also recognized that the licensee's 1992 inundation study did not follow the guidelines for the probable maximum flood (PMF) evaluat ion, as described in Regulatory Guides 1.59 2 and 1.102 3.

The NRC sent a 10 CFR 50.54 (f) request for information on August 15, 2008 4*5. In response to this letter, in 2009 , the licensee conducted additional inundation analyses 6 consisting of and two-dimensional studies. These stud ies ind i cated that the resultant flood, which results in approximately 18.5 feet of water on the site , would cause the site to be inundated with flood waters. The licensee, in its response to the 10 CFR 50.54 (f) letter, stated that the inundation will lead to core damage , containment failure , and the loss of spent fuel pool cooling at all three units. Thus, if a flooding event from a Jocassee Dam failure occurred at the ONS site , all three units have no defense-in-depth to prevent core damage. The remaining intact element of 1 "Jocassee Hydro Project, Dam Failure In undation Study," Federal Energy Regulatory Commission (FERC) Projects No. 2503, December 1992. 2 Regulatory Guide 1.59, "Design Basis Floods for Nuclear Power Plants." U.S. Nuclear Regulatory Commission,

2) August 1977. Regulatory Guide 1.102, "Flo od Protection for Nuclear Power P lants." U.S. Nuclear Regulatory Commission, (Rev. 1) September 1976. 4 Letter to D. Baxter of Duke Energy Carolinas, LLC, dated Aug u st 15, 2008, Information Request Pursuant to 10 CFR 50.54(f) related to External Flooding, Including F ailure of the Jocassee Dam at ONS , (ML0816402440).

5 Letter from D. Baxter of Duke Energy Carolinas, L L C, to US NRC, dated September 26, 2008. 6 See Duke's presentation to NRC dated October 28 , 2009. OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED IN F ORMATION defense-in

-depth of containment integrity wi ll be severely challenged , if unmitigated , result i ng i n the potential for radionuclide release to be highly probable.

These results have led the NRC to conclude that the licensee l acks defense-in-depth to ensure that the r e is adequate protection at the ONS site against such floods. As a result , the NRC expressed , via the aforementioned 10 CFR 50.54(f) lette r, a concern that the licensee has not demonstrated " ... ove r all adequacy of the flood protec ti on of Oconee g i ven the Jocassee Hydro Project. .. Specifically, the NRC is seeking information

... whether Oconee lacks approp r iate and adequate compensating engineering safeguards for such an event." Subsequent to the licensee's response to t he 10 CFR 50.54(f) letter , the NRC, in its April 20, 2009, letter 7 stated, in part, "the NRC staff remains concerned that the licensee has not demonstrated that Oconee will be adequa t e l y protected in the l ong term from external flooding events." By letter dated Ja n uary 15, 2010 8 , the licensee subm i tted a letter to the NRC which prov i ded its compensa t ory measures (CMs) to ensure that ONS will be adequately protected from externa l flood i ng events until the final mitigating strategies have been implemented and all site modifications have been completed.

The NRC staff plans to perform a furthe r review of the CMs and will perform a future inspection.

Then, by letter dated January 29, 2010 9 , the staff issued its response to the licensee regarding its November 30, 2009, response to the NRC letter dated April 30 , 2009, r elated to external fl ooding at ONS. The staff indicated that although the licensee prov i ded a more accurate estimate of t he flooding caused by a failure of the Jocassee Dam , the staff found that additional information was needed. The information was needed for the staff to determine if the ana l yses performed to date w ill demonstrate, for the entire Jocassee earthen works , that the ONS site will be adequately protected from externa l flooding eve n ts. The licensee submitted a preliminary set of responses to the staff's questions by letter da t ed March 5, 2010 10* On June 22, 2010 11 , the staff issued a Confirmatory Action Letter (CAL) to the l icensee, requesting the following: (1) that the compensatory measures remain in place until final resolu ti on has been agreed upon between the licensee and the NRC staff, (2) the licensee to submit to the NRC all documentation necessary to d emonstrate that the inundation of the Oconee site from the failure of the Jocassee Dam has been bounded , (3) licensee to submit a l ist of all necessary modifications t o mitigate the inundat i on by November 30, 20 1 0, and (4) l i censee to make all necessary modifications by No v ember 30, 2011. To date, the licensee has committed to keep the CMs in p l ace until final resolution has been agreed upon between the licensee and the NRC staff and the licensee has adequately 7 Letter to D. Baxter , Evaluation of Duke Energy Carol i nas, LLC , September 26, 2008 Response to NRC Letter Dated August 15, 2008 Re l ated to External Flooding at ONS (ML0905707791

). 8 L etter from D. Baxter of Duke Energy Carolinas , L L C,. to US NRC , dated January 15, 2010 tha t addresses the Interim Compensatory Measures at ONS. 9 Letter to D. Baxter of Duke Energy Carolinas, L L C , dated January 29, 2010 , Evaluation of D u ke's Response to NRC L etter Dated April30 , 2009 Related to External Flooding at ONS (ML100271591). 10 Letter f r om D. Baxter of Duke Energy Carolinas , LLC, t o US NRC , dated March 5 , 20 1 0, Partial Response to NRC RAI dated February 3 , 2010, Re l ated to External Flooding at O N S. 11 Confirmatory Action Letter f r om L. Reyes (NRC) to D. Baxter (Duke), dated June 22, 20 1 0 (Ml 101730329)

OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION submitted to the NRC all documentation necessary to demonstrate that the inundation of the Oconee site from the failure of the Jocassee Dam has been bounded. Goals and Objectives:

Assess and evaluate all input (from FERC, USSR, and NRC Safety Review Group) associated with the r eview of Duke's site inundation study and any supplemental information that may be submitted by Duke a t a later date.

Develop the agency's position rega rding reasonable assurance of adequate protection, considering all input s , and finalize a summary report describing the path forward with concurrence from OGC.

Ensure the licensing basis is updated to clearly address the externa l flooding hazard, and associated protective features.

Consider any generic implications identified through this site-speci fic Oconee work or other ongoing related activities within the framework described in Enclosure

3. Outcomes:

Resolve Oconee-specific issues ident if i ed in NRC's letters dated August 15, 2008, and April 30, 2009, and take appropriate regulatory action, as necessary.

Ensure that the licensing basis of the Oconee Nuclear Station with respect to external flooding hazards is clearly documented in accordance with applicable regulatory processes (e.g., adequate protection backfit, if appropriate).

Current Status: The project plan was shared with all parties involved at a meeting that was he ld on June 10, 2009, to discuss rol es and re sponsibi lities and pro jec ted milestones.

Process: 1. An Oversight Group (OG) was created to provide guida nce and oversight to the Safety Review Group regarding assessments and final recommendation.

The OG also provided all briefings to upper level management.

The (OG), which was led by Deputy Division Director of DE , and will consist of the following folks: Dam Safe ty Officer, DE/EMCB BC, DE/SLA, DRNAPOS SC, DORLILPL 2-1 SC, NRO/RHEB SC , and RGN II/DR P/RPS1 SC; the Safety Review Group (SRG), which will be led by the Dam Safety Officer and will consist of the following folks: DE/SLA, DE/EMCB Geotechnical E n ginee r, NMSS and ACRS Hydrologists, FERC reps, USSR contractor, Region I I reps, and NRR/DRA and NRO representatives, as determined by the Oversight G r oup. OGC and OE will be involved , as necessary. (Completed)

2. A Safety Review Group (SRG) was created to assess Duke's dam breach report and any supplemental information on sensitivity ana lys es , etc, to address the question of reasonable assurance of adequate protection from external flooding for the Oconee site. NRC Dam Safety Officer to lead the SRG and will conduct routine status meetings with the team. The OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY -SECURITY RELATED INFORMATION SRG will be comprised of DE/SLA, DE/EMCB Geotechnical Engineer, NMSS and ACRS Hydro l ogists, other hydrologists, if needed, with additional support from FERC representatives, USSR contractor, Region II representatives as assigned by Division D i rector, and NRR/DRA and NRO representatives, as determined by t he Oversight Group. OGC and OE will be involved , as necessary.

SRG will address any previously identified issues. SRG status meetings will be conducted bi-weekly and the SRG will be responsible for providing monthly status reports. (Completed)

3. NRC Dam Safety Officer or EMCB Branch Chief to serve as Liaison between the OG and the SRG. (Completed)

4. Conduct a review of Duke's site inundation study and supplemental information. (Completed)

5. Develop and issue questions regarding Duke's s i te inundation study and supplementa l information. (Completed)

6. Conduct monthly management status conference calls with Duke. (Completed)

7. Conduct monthly "working level" scheduled mee t ings with the licensee to facilitate resolut i on of the technical issues. (Completed)

8. Conduct site visit. (Completed)

9. Develop the agency's position regarding reasonable assurance of adequate protection of the Oconee site from external flooding, tak i ng into consideration all parties' inputs. (Ongoing-Document is currently in concurrence.)

Roles and Responsibilit i es (Enclosure 1): Division of Engineering:

Has overall responsibility for coordination , implementation and execut i on of Closure Plan. Responsible for perform i ng or reviewing all technical evaluations within the scope of this work , including evaluating input from other Divisions and Offices regarding Duke's inundation analyses. Responsible for overseeing all ac t iv i ties associated w i th this project , including overseeing the USSR contractor and the OG and SRG. Will lead the SRG meet i ngs and facilitate resolution of issues and will serve as liaison between all stakeholders and communicate overall recommendation to management.

Will ensure proper commun i cations occur within and between all stakeholders to ensure a comprehensive and all i nclusive evalua t ion is performed.

DE, with input from the associated working groups, will write the overall summary report for the evaluation and assessment on Duke's inundat i on study to ens u re reasonable assurance of adequate protection is provided at the Oconee site. The Dam Safety Officer will concur on all dam safety related work. (See attached Charter) Division of Risk Assessment:

Responsible for providing support in the area of risk assessme n t associated w i th dam failure frequency.

Office of New Reactors:

Participates for technical consistency by providing insights on h ow the issue would be evaluated for new reactor licensing to DE regarding review of dam breach report and other information submitted by Duke regarding inundation and sensit i vity analyses.

O FF ICIAL USE ONLY-SECURITY RELATED INFORMAT I ON OFFICIAL USE ONLY-SECUR I TY RELATED INFORMATION Region II: Responsible for providing operating plant input and assessment to DE regarding review of dam breach report and other information submitted by Duke regarding inundation and sensitivity analyses. Division of Operating Reactor Licensing: Provide project management support to overall plan. Provide technical analysis and support on issues related to regulatory framework and the plant's l i censing bas i s. DORL will serve as a point of contact with the licensee, including the coordina tion of meetings and calls and request for in formation/c lar ificat ion. Maintain and update the sharepoint website related to this issue. Office of General Counsel: Responsible for advising staff on legal acceptability of potential staff actions. OGC will also provide support on backfit dec i sions , as needed. Office of Research:

Provide support to DE w i th rega r ds to the Generic I ssues Process to determine potential generic implications.

Actions/Milestones Proposed: Issue Interagency Agreement and Task Order to USSR for contract Complete support of External Flooding Issues and conduct conference call with USSR to provide guidelines on rev i ews Sr. Management Alignment regarding scope of May 11 t n meet ing with Complete Duke Staff Alignment regarding scope of May 11 m meeting with Duke Complete Develop ques tions from NRO's Assessment to address at May 11m Complete meeting with Duke for i nput to USSR Obta i n preliminary Jocassee Dam inundation ana l ysis results and Complete calculations from Duke and NRO evaluation and send them to USSR and FERC ADES/AD Prep. Meeting/Develop talking points for ADES Complete Conduct pre-meeting with FERC Complete Conduct meeting with Duke and FERC at Headquarters Complete Coordinate with FERC (Dan Mahoney) to obtain FERC review results of Complete Duke's analysis and NRO inp ut Create an Oversight Group (OG) to p r ovide guidance and oversight t o Complete the Safety Review Group regarding assessments and final recommendat i on. Create the Safety Review Group (SRG) to assess Duke's dam breach Complete report and any supplemental information on sensitivity analyses , etc , to address t h e question of reasonable assurance o f adeq u ate protection from external flooding for the Oconee site, i n concert with ensuring technical consistency between N RR and NRO. Conduct conference ca ll s wi th USSR on review status and additional Complete review items, such as NRO's Assessment USSR complete review/SRG complete review Complete SRG review FERC's and USSR's analyses Complete Duke to provide letter to address interim compensatory measures (ICMs) Comp l ete Region 2 to conduct audit of ICMs and document resul t s in an inspection Co mplete r eport. OFFIC I AL USE ON L Y-SECUR I TY RELATED IN F ORMAT I ON OFFICIAL USE ONLY-SECURITY RELATED INFORMATION Obtain final results from Duke regarding Jocassee Dam Inundat ion Complete Study DE, with input from the SRG and OG, to develop final position and wr i te Ongoing/document is in closeout safety assessment/package regarding reasonable assurance of concurrence adequate protection.

DORL and DE to determine appropriate path forward regarding TBD justification for continued operation Duke to submit permanent mitigation resolution April2011 Staff to rev iew Duke's permanent mitigation resolution and to address TBD defense-in depth issue raised by ORA. OFFICIAL USE ONLY-SECURITY RELAT E D INFORMATION OF F ICIAL USE ONLY-SECURITY RELATED INFORMATION Actions/Milestones Proposed: Safety Review Group Milestones Deve l op prelim i nary set of questions regarding Oconee Jocassee Dam Complete Breach Report Conduct Oconee/Jocassee Dam Site Visit Complete Conduct meet i ng with OG and SRG to d i scuss definition of reasonable Complete assurance of adequa t e protection, key paramete r s to be included in sensitivity ana l ysis , and " what does success look like." Provide high level assessment of Oconee Jocassee Dam Breach Report Complete Part i cipate in meeting to discuss all assessments (developed by FERC , Complete USBR, and Dam Safety Team) and develop recommendat i on for overall assessment considering all views. Review additional i nformation submitted from D u ke (responses to Complete quest i ons from meeting , April 30th letter (modeling/sensitivity stud i es) Develop 2nd set of quest i ons, as appropriate Complete Mee t ing w i th all parties to d i scuss assess m ents and develop justification Complete fo r varying positions Submit recom m endat i on to managemen t i n cluding reasonable Ongoing/In concurrence assu r ance of adequate protection dete r mination Schedule Changes Since Last Update: N/A Resource Expendi tu re: FTE: 5 F T E Contract Do ll ars: USBR $43,100 (FY 2009) Plan C l osure: A determ i nation of reasonable assurance of adequate protect i on related to external flooding issues at the Oconee si t e will represent successful completion of this plan. Contacts:

N ame Position P h one N o. Dav i d Skeen OG Lead 415-3298 Geo r qe Wilson Dam Safety Officer 415-1711 Kama l Manoly DEPOC 415-2765 Meena Khanna DEPOC 415-2150 Melanie Wonq/Gioria Kulesa DORLPOC 415-2911 N a m e Position Phone No. Mike FranovichNeronica DRAPOC 415-1067 Rodriguez Richard Ra i one NRO POC 415-7190 Jonathon Bartley Region II POC 404-562-6334 Raman Pichumani/Juan Uribe EMCB POC 415-3621 Neil Coleman SRG POC 415-7656 OFFICIAL USE ONLY-SECURITY RELATED I NFORMA T ION OFFICIAL USE ONLY -SECURITY RELATED INFORMATION Rex Wescott SRG POC 492-3107 B ill Ott ' RES POC 251-7407 John Wray OE POC (as 415-1288 necessary)

Kimberly Sexton/Marcia S i mon OGC POC 415-1151 OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION References

1. NRC letter to Duke dated August 15 , 2008 , "I nformation Request Pursuant to 10 CFR 50.54 (f) Related to External Flooding , Including Failure of the Jocassee Dam , a t Oconee Nuclear Station , Units 1/2/3. 2. NRC Communication Plan for Information Request Pursuant to 10 CFR 50.54(f) Related to External Flooding , Including Failure of the Jocassee Dam , at Oconee Nuclear Station. 3. NRC letter to Duke dated Apr il 30, 2009, "Evaluation of Duke Energy Carolinas, LLC, September 26, 2008, Response to NRC Letter Dated August 15, 2008, Related to External Flooding at Oconee Nuclear Station. 4. Oconee Nuclear Station Jocassee-Keowee Dam Breach Model Report from Duke Energy Carolinas, dated March 2009. 5. Jocassee Main Dam Design, Constr uc tion and Performance Report , dated Apri l , 1987 , G.F. Sowers , Hon. Member , ASCE. 6. F i gures of Jocassee Dam (including the cross section of the dam showing the weak base F i lled with concrete) provided by FERC. 7. 2004 Part 12 Inspection Report-Jocassee Pumped Storage Development dated December , 2004 , provided by FERC. 8. NRC Regulatory Guide 1.59, "Design Basis F loods for Nuclear Power Plants," dated August , 1977. 9. ANSI/ANS 2.8, "Determine Design Basis Flood i ng at Power Reactor Sites ," dated July 28, 1992. 10. SRP Sections 2.4.1, "Hydrology Descript ion," 2.4.2 , "Floods," 2.4.3, "Probable Maximum Flood on Streams and Rivers," and 2.4.4, "Potential Dam Failures," dated March 2007. OFFICIAL USE ONLY-SECURITY RELATED INFORMATION ENCLOSURE 2 TAC Nos.: OFFICIAL USE ONLY-SECURITY RELATED INFORMATION Path Forward in Addressing TVA's Hydrology Issues Last Update: January 19, 2011 Lead Division:

DE Supporting Div isions: DORL Supporting Offices: NRO , Rll Historical

Background:

On February 19-22, 2008, the NRC staff conducted an inspection at BLN. The purpose of the inspection was to verify that quality assurance processes and procedures were effectively implemented with regards to the Simulated Open Channel Hydraulics (SOCH) model for the BLN combined license application (COLA). The SOCH model was used to calculate the design basis flood presented in the BLN Safety Analysis Re p ort Sections 2.4.3 , Probable Maximum F l ood on Streams and Rivers , and 2.4.4 , Potential Dam Failures.

The NRC insp ectors reviewed the relevant quality assurance (QA) procedures for design control , software verification and validation, and QA records related to the SOCH model , and reviewed the 1998 F l ood Reassessment for the Effects of Dam Safety Modifications calculation package. The verification and validation of the SOCH model, and all the design data inputs to the SOCH model, including the supporting FORTRAN programs, used as a basis for the BLN COLA were not available fo r review. Based on the results of this inspection, the NRC issued three violations of NRC requirements. Starting in June 2008 , the NRC staff conducted several calls with TVA to discuss the i dentified BLN non-compliances and the applicability of these concerns to operat ing units. The NRC staff expressed a concern that the significance of the BLN issues on the design basis had not been analyzed for the operat in g units , and requested a copy of their ope r ability/functionality evaluation.

On June 17, 2008, the licensee forwarded the original corrective action document [prob l em evaluation report (PER)] and a functionality assessment.

The NRC staff identified that the licensee relied on the same QA controls that were not followed at BLN in support of establishing the acceptability of this condition on the operating units. As a result , the NRC staff rema i ned concerned that the sign i ficance of this i ssue remained indeterminate.

TVA notified the NRC staff that the V&V efforts on the SOCH code would not be complete until -April 2009. Subsequent opportunities have been provided to TVA to appropriately address the safety significance of the input and SOCH code e rro rs identified by the NRC in February 2008. TVA has continually represented to the NRC, that the V&V efforts of both the SOCH code and the data for the Tennessee River's 46 watersheds were being conducted and completed as part of the Bellefon te Units 3 and 4 COLA review. Since then, TVA has submitted requests to reschedule the hydrology COLA review to as late as Fiscal Year 2010. The letter indicated that TVA has not been able to meet many of the milestones established in its plan to correct the problems identified in the ins pection. As a resu lt of TVA's request, the NRC suspended the hydrology COLA review for Section 2.4 , Hydrologic Description.

However , TVA has yet to provide an analys is which provides reasonable assurance that the operating units are with i n OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION their current design bases. The NRC staff is assessing whether the changes to the Tennessee Valley watersheds and operation of the associated dams and spillways has affected the original site flood protection measures for the operating units. The Updated Final Safety Analysis Report (UFSAR) for each site states that the principal design criteria for each site was developed in consideration of the seventy General Design Criteria (GDC) for Nuclear Power Plant Construction Permits proposed by the Atomic Energy Commission (AEC) in a proposed rule-making published in 10 CFR 50 in the Federal Register of July 11, 1967. For SON and WBN, the current GDC contained in Appendix A to 10 CFR 50 addresses the design bases, while BFN used the earlier AEC version. Regardless, the design criterion is essentially the same. The criterion requires sys t ems and components of reac tor facilities which are essential to the prevention of accidents which could affect public health and safety or to mi tigation of their consequences to be designed, fabricated and erected to performance standards that will enable the facility to withstand, without loss of the capability to protect the public, the additional forces that might be imposed by natural phenomena such as earthquakes, tornadoes, flooding conditions, winds, ice, and other local site effects. The NRC staff has identified that the data inpiUt and hydrology code (SOCH) does not accurately reflect the existing configuration and operat i on of the Tennessee River, and TVA has not provided sufficient information to demonstrate that the design basis for these facilities has been properly maintained. Therefore, the NRC staff seeks additional information from TVA to identify all errors in the code, the sites that are affected by those errors , and confirmation that existing flood mit igating measures are adequate to bound any errors identified to date with the current design basis data i nputs and the SOCH code for all three operating facilities.

The NRC staff is assessing whether the changes to the Tennessee River watershed and operation of associated dams has adversely affected the original site f l oo d protection measures for safety-r elated SSC , and important-to-safety components, on the operating units. In addition, the staff is concerned that: (1) the loss of design bases infor ma tion prevents the licensee from accurate l y addressing the safety significance of errors in the SOCH Code; (2) the licensee is not within current design bases; and (3) the licensee has not maintained design bases [50.59(d)(1)]. Regulatory Basis: The regulations tha t apply to the TVA hydrology issues include the following:

Pursuant to 10 CFR Part 50, Appendix A, General Design Criter i on (GDC) 2 (or the Atomic Energy Commission (AEC) equiva l ent), nuclear power plant structures, systems and components (SSCs) important to safety be des i gned to withstand the effects of natural phenomena such as earthquake, tornado, hurricane, flood, tsunami, and seiche without loss of capability to perform their safety functions.

The crite r io n further specifies that the design bases for these SSCs shall reflect the following:

A Appropriate consideration of the most severe natural phenomena historically reported for the site and sur rounding area, with sufficient margin for the limited accuracy, quantity, and time period in which the historica l data have been accumulated; OFFICIAL USE ONLY-SECURITY RELATED INFORMAT ION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION B. Appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena; and C. The importance of the safety functions to be performed.

Section 50.71 (e) requires that the licensee shall update periodically, the final safety analysis report (FSAR) originally submitted as part of the application for the license, to assure that the information included in the report contains the latest i nformation developed. Originating Document:

The staff originally identified the TVA hydro l ogy issues based on the Bellefonte Combined License Application

-Nuclear Regulatory Commission Inspection of the Implementat i on of the Quality Assurance Program Governing the Simulated Open Channel Hydraulics Model, as documented in the Inspection Report Numbers 05200014/2008-001 and 05200015/2008-001 and Notice of Violation. Scope of Project:

To address the operability and safety concerns related t o the hydrology issues at the TVA sites (Watts Bar, Sequoya, and Browns Ferry). Outcome:

The overall goal is for the staff to determine if there are any safety concerns related to the TVA hydrology issues and determine the correct vehicle to convey our concerns and obtain information from TV A regard i ng status of the i r corrective action programs at each of the sites. Goals and Objectives

1. Based on status of corrective actions taken by TVA fo r each of the i r sites, determine whether adequate and timely actions have been taken to address the hydrology issues and to ensure that there are no safety implications.

2. If it is determined that a need for additional information is needed, determine proper vehicle to use i n obtaining the information (e.g., letter, audit, etc.) 3. Assess the proposed initiative and rev i se as necessary.

Roles and Responsibilities (Enclosure 2): NRC Dam Safety Officer (George Wilson): Responsible for overseeing all activities associated with this project. Will ensure proper commun i cations occurs within and between the groups to ensure an overall encompassing and all inclusive evaluation and assessment occurs. All related work will be channeled through and concurred by the Dam Safety Officer. O F FICIAL USE ONLY-SECURITY RELATED INFORMATION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION Division of Engineering:

Responsible for performing or reviewing all technical evaluations associated within the scope of this work. DE, with input and concurrence from the associated working groups , will also write the overall summary and conclusion report for the evaluation and assessment associated with TVA's hydro l ogy issues. Office of New Reactors: Responsible for providing insights on how the issue would be evaluated present day for new reactor licensing to DE regarding review of information submitted by TVA. Region II: Responsible for providing operating plant i nput and assessment to DE regarding review of to DE regard ing review of information submitted by TV A. Division of Operating Reactor Licensing:

Provide technical analys i s and support re lated to regulatory framework and the plant's licens ing basis. Serves as the point of contact with the licensee, including the following:

coo rdinating meetings and calls and req ue st for informat ion/cla r ification.

Proposed Actions/Milestones:

Obtain inspection reports from the Resident Inspectors that address the Complete PERs; request information regarding corrective action program and copies of all the PERs issued to date. DE and DORL to review information to determine whether TVA's timeline Complete for corrective actions for each plant is reasonable Conduct meeting with RES , NRO, Reg i on II, to determine TVA's Complete actions/initiatives that are ongoing with regards to hydrology issues. Share NRR's assessment for the purpose of technical consistency and to ensure that duplicative efforts are not being done. Conduct Conference Call with Regional BCs , TVA Plants , Gene Guthrie Complete (Region II) . Identify any additional issues to be included in a l etter to TVA. As Complete needed, Region to submit TIA for HQ assistance for up to 6 months. Conduct meeting with DORL and DE management to discuss the Complete Region's concerns, and to agree on the text for a proposed letter to TVA identi fying staff's concerns and requesting responses to questions as well as completion schedule for each p l ant. Current Status: The closure plan regarding the TVA hydrology i ssues was shared with all parties involved at a meeting that was conducted on July 16, 2009. Schedule Changes Since Last Update: Milestone dates were updated on January 19, 2011. OFFICIAL USE ONLY-SECURITY RELATED INFORMATION OFF I CIAL USE ONLY -SECURITY RELATED I NFORMATION Resource Expend i ture: FTE: 1.0 F T E Contacts:

N ame Position P h o n e N o. Pat Hiland/ SES Contacts 4 1 5-3298 Anne Boland/ Dave Skee n Joe G ii tter/AIIen 4 1 5-1453 Howe George Wilson Dam Safe t y Off i cer 415-1711 Kamal Manolv DE Contact 41_5-2765 Gene Guthr i e R l l POC 404-562-4662 NRO Richard Raione 415-7190 Meena Khanna EMCB POC 4 1 5-2150 Raman P i chumani EMCB POC 415-3621 Ev a Brown DORLPOC 415-2315 T om Bovee DOR L POC 4 1 5-0184 References

1. Bellefonte Comb i ned License App l i cation -Nuc l ear Regu l atory Comm i ssion Inspect i on of t he I mplementat i on of the Quality Assu r ance P r og r am Govern i ng the S i mu l ated Open Channe l Hydrau li cs Model-Inspection Report Numbe r s 05200014/2008-001 and 05200015/2008

-001 and Not i ce of Violation

2. Meet i ng Summary fro m Septembe r 12 , 2008 Meeting w i th TVA regarding TVA Hydrology Code. 3. Problem Evaluation Reports for Watts Bar, Sequoya , and Browns Ferry OFFICIAL USE O N LY-SECURITY RELATED I NFOR M A T ION OFFICIAL USE ONLY-SECURITY RELATED INFORMATION E NCLO S URE 3 IN CONJUNCTION WITH THE INDEPENDENT ASSESSMENTS, THE STAFF WILL DETERMINE THE NEED AND PROCESSES TO RESOLVE GENERIC ISSUES Process: Eva lu ate issuance of Information Notice for dam failure frequency error. Identify potential generic issues and needed external coordination for input to Generic Issues Process as an outcome of the Oconee and TVA reviews. Roles and Responsibilities:

ORA will lead the effort associated with the Infor mation Notice for dam failure frequency error. DE will le ad the effort in filling out the form and contacting RES to determine entry to the GIP. (Complete)

Proposed Actions/M ilestones:

Inc orporate potential externa l flood sources in existing USI/GSI TBD programs.

Develop Generic Communication TBD Current Known Generic Issues: 1. RESOLVE DAM FAILURE FREQUENCY

Background:

In its review of the Oconee issue , NRC staff identified an error i n dam failure frequency estimates used by Duke. It is likely that this error has been propagated into subsequent technical studies performed by other operating reactors and by the NRC staff. The implica tions of this error are not yet clear. Duke disagrees that their dam failure frequ ency estimates are in error. Purpose: Assess impact of dam failure frequency estimate error on other NRC studies and actions. Communicate dam failure frequency estimate error to other licensees via Information Notice. Responsibility

ORA responsible for all activit i es associated with dam failure frequency estimate error. OFFICIAL USE ONLY-SECURITY RELATED INFORMAT ION OFFICIAL USE ONLY-SECURITY RELATED INFORMAT I ON Proposed Actions/Milestones:

[ORA TO PROVIDE ADDITIONAL DETAILS] Define relative risk reduction of various modifications compared to TBD address ing external flooding Assess stud i es using I PEEE information Address what the implications TBD t o other plan t s that are down-stream of dams , ge n er i cally. As a gener i c issue , RES w ill have a ro l e in it s reso l u t ion. O th er generic issues w ill be added , as necess a ry. OFF I CIAL USE ONLY-SECURITY RELATED I NFORMATION

v t e Letter Sequence Other
TAC:ME3065, (Open) TAC:ME3066, (Open) TAC:ME3067, (Open)
Initiation Request Acceptance... Administration Meeting Questions 11 January 2010 Answers 8 February 2010 Results Approval... Other: ML100271591, ML110260443, ML110280153, ML12363A085, ML12363A086
MONTHYEAR2010-06-22 [Table View]

ML110260443

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