ML14133A059

Summary of Closed Meeting Between Representatives of the Army Corps of Engineers, Nuclear Regulatory Commission, Federal Energy Regulatory Commission, Exelon Generation Co, LLC, and PPL Susquehanna, LLC, to Discuss Dam Failure Analysis..

ML14133A059
Person / Time
Site:	Peach Bottom, Three Mile Island, Susquehanna
Issue date:	07/01/2014
From:	Stephen Monarque Containment and Balance of Plant Branch
To:	Matthew Mitchell Containment and Balance of Plant Branch
Monarque S, NRR/JLD, 415-1544
References
Download: ML14133A059 (8)

Text

July 1, 2014 MEMORANDUM TO: Matthew A. Mitchell, Chief Hazards Management Branch Japan Lessons-Learned Division Office of Nuclear Reactor Regulation FROM: Stephen R. Monarque, Project Manager /RA/

Orders Management Branch Japan Lessons-Learned Division Office of Nuclear Reactor Regulation

SUMMARY

OF THE APRIL 24, 2014, CLOSED MEETING BETWEEN REPRESENTATIVES OF THE U.S. ARMY CORPS OF ENGINEERS, THE U.S. NUCLEAR REGULATORY COMMISSION, FEDERAL ENERGY REGULATORY COMMISSION, EXELON GENERATION CO, LLC, AND PPL SUSQUEHANNA, LLC TO DISCUSS DAM FAILURE ANALYSIS FOR PEACH BOTTOM ATOMIC POWER STATION, SUSQUEHANNA STEAM ELECTRIC STATION, AND THREE MILE ISLAND NUCLEAR STATION On April 24, 2014, the U.S. Nuclear Regulatory Commission (NRC) staff held a closed meeting with the U.S. Army Corps of Engineers (USACE), Federal Energy Regulatory Commission (FERC), Exelon Generation Co, LLC (Exelon) and PPL Susquehanna LLC (PPL) to discuss the dam failure analysis for Peach Bottom Atomic Power Station, Units 2 and 3 (Peach Bottom),

Susquehanna Steam Electric Station, Units 1 and 2 (Susquehanna) and Three Mile Island Nuclear Station, Unit 1 (TMI). The list of meeting participants is included as Enclosure 1.

The USACE opened this meeting by discussing the Susquehanna River Basin Water Management Program. The purpose of this program is to maintain flood control, water quality control, water supply for municipal and industrial uses, and hydropower. USACE also presented the basin storage capacities and dam heights along the Susquehanna River. Exelon requested to receive the operating curves for the dam spillways, to which, the staff replied that the USACE will not distribute that information to NRC licensees.

The USACE then discussed the screening methodology used for the Susquehanna River Basin.

The USACE plans to follow the guidance in Interim Staff Guidance (ISG) JLD-ISG-2013-01, Guidance for Assessment of Flooding Hazards Due to Dam Failure, Revision 0, dated July 29, 2013 (Agencywide Documents Access and Management System (ADAMS) Accession CONTACT: Stephen R. Monarque, NRR/JLD 301-415-1544

M. Mitchell No. ML13151A153) when developing their numerical models of the watershed upstream of the nuclear power plants (NPPs).

The staff is working with the USACE to screen non-critical dams from a detailed failure evaluation. Those dams determined to be potentially critical, meaning their potential failure could inundate the NPPs, will be further analyzed by the USACE for several postulated failures; sunny day, hydrologic, and seismic.

FERC discussed the Conowingo Dam, which is regulated by FERC, and is located downstream of the Peach Bottom NPP site. FERC is currently conducting a study of this dam to determine whether the design flood could exceed the discharge capacity of this dam. In the event, that this study confirms this scenario, then flood mitigative measures would have to be added and this dam would have to be stabilized. FERC considers Conowingo Dam to be a high hazard structure, meaning its failure has the potential to cause loss of life. FERC presented the following project milestones for this study. The initial hydrologic model is scheduled to be completed by May 2014, the final report for the probable maximum precipitation is scheduled to be completed by October 2014, and the final report for the probable maximum flood is scheduled to be completed by April 2015.

It was requested that FERC provide the HMS model to the USACE. This would allow the USACE to use the model in order to develop the analysis for the three NPPs.

Prior to this meeting, Exelon provided the staff with a list of questions regarding the Hydrology Analysis of the Susquehanna River Watershed. USACE, FERC, and the staff discussed Exelons questions and provided responses to these questions. These questions, along with their respective answers, are shown in Enclosure 2.

At the end of the meeting, there was a discussion on how the USACE and FERC were going to provide the flood-hazard reevaluation (FHR) to the licensees and the NRC staff. There was general agreement that the USACE will complete the evaluation of the flood hazards, based on the ISG criteria, and the basin wide probable maximum precipitation. Additionally, the USACE will provide the results of the FHR to the NRC and the NRC will provide the hydrographs to the licensees. However, the NRC staff and FERC could not come to an agreement on how FERC would forward its FHR information to their respective licensees as the USACE considers this information to be sensitive and security related. FERC and the NRC plan to have further discussions on this matter.

Docket Nos. 50-277, 50-278, 50-387, 50-388 and 50-289

Enclosures:

1. List of Meeting Attendees

2. Questions from Exelon Regarding Hydrologic Analysis of the Susquehanna River Watershed

ML14133A059 *via email OFFICE NRR/JLD/PMB/ PM NRR/JLD/LA

• NRO/DSEA/RHMB/BC NRR/JLD/PMB/BC NRR/JLD/FTL/ BC NAME SMonarque SLent CCook (KErwin for) MMitchell GWilson DATE 05/29/14 05/13/14 06/26/14 07/01/14 06/26/14 List of Meeting Attendees April 24, 2014 NAME ORGANIZATION Stephen Monarque U.S. Nuclear Regulatory Commission (NRC) NRR/JLD Roger Kay U. S. Army Corps of Engineers (USACE) - Omaha Nicholas Agnoli Federal Energy Regulatory Commission (FERC)

Ken See NRC Ken Fearon FERC - Headquarters Dave Capka FERC - Headquarters Tom Rossbach USACE- North Atlantic Baltimore District (NAB)

Jim Snyder USACE- NAB Christopher Cook NRC Teresa Reinig USACE - Omaha George Wilson NRC David Distel Exelon Julie Fritz USACE- NAB John Emmett PPL Susquehanna Joe Bellini Aterra / Exelon Kevin Craft Exelon Generation (Conowingo)

Jay Campbell Exelon Generation Matthew Lehrer AMEL Barbara Hayes NRC Brad Harvey NRC Yohannes Assefa USACE- NAB Hosung Ahn NRC Dan Risley USACE- NAB Jerry Gomez Gomez and Sullivan Engineers Bill McSorley Exelon Three Mile Island Design Engineering Chuck Behrend Exelon Director Severe Accident Management Jesse Lucas Exelon PBAPS Engineering Harvey Johnson USACE-NAB Enclosure 1

QUESTIONS FROM EXELON REGARDING THE HYDROLOGIC ANALYSIS OF THE SUSQUEHANNA RIVER WATERSHED Question /Answer

1. Exelon understands the NRC is planning to use the USACEs hydrologic analysis of the Susquehanna River watershed (to a point just downstream of Conowingo Dam) as a confirmatory analysis to facilitate the review of the Peach Bottom and TMI flood hazard reevaluations, with the focus being on the effects of potential failure of USACE dams in the watershed. The NRC is not expecting Exelon to use the results of the USACE analysis (i.e. flood hydrographs) as inputs into the flood hazard reevaluations. Please confirm that these are correct understandings.

Correct, the NRC staff is using the USACE results to assist the staff in reviewing the Near-Term Task Force (NTTF) Recommendations 2.1, Flooding, flood hazard reevaluations submitted by the three nuclear power plant licensees. To date, only the TMI flood hazard reevaluation has been submitted to the NRC.

2. Please describe the guidance that will serve as the basis of the USACEs evaluation, such as NRCs Dam Failure Interim Staff Guidance (ISG) (JLD-ISG-2013-01),

NUREG/CR-7046, Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, or other guidance.

The USACE plans to use the Interim Staff Guidance, cited above, NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Plants, NUREG/CR-7046, and other guidance cited in the letter titled Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3 of the Near-Term Task Force Review of Insights From the Fukushima Dai-Ichi Accident, dated March 12, 2012.

3. Please describe how the NRC intends to incorporate the results of the USACE analysis into their review of the NTTF 2.1 flood hazard reevaluations.

The staff will obtain the results from the USACE and compare the results to those generated by the three nuclear power plant licensees. See response to Question Number 1 above.

4. Please confirm that the USACEs scope does not include hydraulic analyses to compute stillwater elevations at the sites, along with a computation of wind-wave run-up heights.

The USACE will not compute the wind wave run-up heights at the sites. The USACE will perform the dam failure analysis, then provide the NRC with its analysis and hydrographs.

5. The NRCs Dam Failure Interim Staff Guidance (JLD-ISG-2013-01) provides technical criteria and justification needed to show that failure of a potentially-critical dam is not Enclosure 2

credible. Will the USACE develop the required technical justification for any of its upstream dams to show that hydrologic, seismic, and/or sunny-day failure is not credible? In particular, for the hydrologic dam failure scenario, where the peak flood stage (for the sites PMF) is well within the design stage of the dam, will hydrologic failure be considered not credible? Exelon has a particular interest in Raystown Dam.

The USACE will perform its analysis by following the guidance described in Question No. 2 above. USACE will first perform a screening analysis following Chapter 3 of the ISG. A detailed analysis of the remaining potentially critical dams in the watershed will then be performed. At the time of this meeting, the remaining potentially critical dams had not yet been identified.

6. For dams assumed to fail or where failure is considered to be credible, the Dam Failure ISG discusses how the dam failure mechanisms (seismic and sunny-day) should be analyzed. Please address the following questions regarding the USACEs approach to the evaluation of each mechanism:

The staff stated that Exelon should follow the interim staff guidance and all other guidance in accordance with the staffs letter titled Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3 of the Near-Term Task Force Review of Insights From the Fukushima Dai-Ichi Accident, dated March 12, 2012, when evaluating the dams for all failure mechanisms.

a. Seismic Dam Failure

i. USACE upstream dams are located in the headwaters of the Susquehanna River watershed. Please clarify whether the seismic dam failure evaluation will assume failure (regardless of the dams ability to withstand a 10-4 annual exceedance seismic hazard) occurs during the 500-year flood at the site or at each dam.

ii. Please describe the USACEs approach to how failure will be triggered in the hydrologic model for the seismic dam failure mechanism. Exelons approach has been to trigger failure at the same time (when the seismic event occurs) for each potentially-critical dam during the 500-year flood at the site (based on the 500-year rainfall applied to the entire watershed to the site). The pool elevation in each dam at the time of failure is determined by the model, which then works out the combination of hydrographs downstream. The approach does not force peak flows from upstream dam failures to reach the plants simultaneously. Rather, numerous trials are run to determine the worse timing of the

seismic event, in terms of highest flows at the site, during a 500-year flood.

iii. Please provide the USACEs assumptions and approach to establishing the initial (starting) pool elevations at the beginning of the 500-year flood. The Dam Failure ISG states the default starting water surface elevation for evaluation should be the maximum normal pool elevation (i.e., the top of the active storage pool) but that other starting water surface elevations may be used, with appropriate justification (e.g. operating rules and history).

The USACE analysis will follow the ISG guidance. For any potentially critical dams, seismic failure will be considered in accordance with Chapter 5 of the ISG.

b. Sunny-Day Failure

i. Sunny-day failure is not being considered by Exelon since failure is conservatively assumed for the seismic failure mechanism.

Sunny-day failure is considered completely bounded (in terms of flood magnitude and warning time) by the seismic failure mechanism. Given this, please address the USACEs approach to sunny-day failure.

ii. If the USACE still plans to run the sunny-day scenario, it is Exelons understanding that simultaneous sunny-day failures (cascading failures notwithstanding) would not be considered.

Similar to the seismic failure mechanism discussed above, please describe the USACEs assumptions related to pool elevation at the time of failure and criteria for cascading failures.

The USACE will be developing sunny-day failure results for any potentially critical dams in the watershed. The USACE will follow the staff position in Section 6.2.2 of the ISG regarding initial pool elevations.

7. Please describe the USACEs approach to modeling attenuation (routing) of the flood hydrographs.

The modeling will be performed using the guidance described in Chapter 9 of the ISG.

8. Please describe the USACEs method for differentiating inconsequential, non-critical, and potentially critical dams, per Section 3 of the Dam Failure ISG, and if volume from non-critical dams will be incorporated.

The USACE will follow the definitions provided in ISG, Section 10, Terms and Definitions when differentiating between inconsequential, non-critical, and potentially critical dams.

9. Could the USACE provide operational rules and procedures for the gated spillways at Raystown Dam to Exelon?

The USACE will not provide this security related information to the public.

10. Questions regarding dam breach parameters:

a. Please describe the USACEs method(s) for computing dam breach parameters.

ISG Section 7.2.2 discusses the use of regression equations for breach parameters.

Subsection 7.2.2.1 contains a staff position that Because of the large uncertainties, inconsistencies, and potential biases associated with breach modeling, licensees should not rely on a single modeling method. Instead, licensees should compare the results of several models judged appropriate. This includes explicitly addressing parameter uncertainty and sensitivity. USACE will follow this ISG.

b. The Dam Failure ISG raises concerns about the use of the Xu/Zhang method.

However, since the ISG was written and released in July 2013, Duke Energy (for the Oconee flood hazard reevaluation) has facilitated further review of the Xu/Zhang method that may have addressed some of the NRCs concerns, particularly the use of the erodibility index and definition of breach formation time.

Exelon understands that the NRC is performing a more thorough review of the Xu/Zhang method. Note that sensitivity calculations for the TMI reevaluation, using the Froehlich method (2008), show good comparison in key parameters with the Xu/Zhang method, with the Xu/Zhang method actually producing shorter (more conservative) breach formation times. Please provide an update on the on-going review of the Xu/Zhang method.

The staff is reviewing the Duke Energy Report. The staff continues to not recommend use of the Xu/Zhang breach parameter model for the purposes of conducting the Recommendation 2.1 hazard review (See staffs Position on Page 7-6 of the ISG).