ML112840114

10/3/11 Summary of Meeting Via Conference Call with STP Nuclear Operating Company to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas

ML112840114
Person / Time
Site:	South Texas
Issue date:	10/31/2011
From:	Balwant Singal Plant Licensing Branch IV
To:
Singal, B K, NRR/DORL, 301-415-301
References
TAC ME5358, GSI-191, TAC ME5359
Download: ML112840114 (6)

Text

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LICENSEE: STP Nuclear Operating Company FACILITY: South Texas Project, Units 1 and 2

SUMMARY

OF OCTOBER 3,2011, PRE-LICENSING PUBLIC MEETING WITH STP NUCLEAR OPERATING COMPANY HELD VIA CONFERENCE CALL TO DISCUSS THE PROPOSED RISK*INFORMED APPROACH TO THE RESOLUTION OF GSI-191, "ASSESSMENT OF DEBRIS ACCUMULATION ON PWR SUMP PERFORMANCE" (TAC NOS. ME5358 AND ME5359)

On October 3, 2011, a public meeting was held via conference call between the U.S. Nuclear Regulatory Commission (NRC), and representatives of STP Nuclear Operating Company (STPNOC, the licensee), at NRC Headquarters, Rockville, MD. The meeting notice and agenda, dated September 15, 2011, is located in the Agencywide Documents Access and Management System (ADAMS) under Accession No. ML112510148. The purpose of the meeting was to discuss the proposed risk-informed approach to the resolution of Generic Safety Issue (GSI)-191, "Assessment of Debris Accumulation on PWR [Pressurized-Water Reactor]

Sump Performance." South Texas Project (STP) is the lead plant and STPNOC plans to submit a license amendment request (LAR) in mid-2012. The licensee previously provided an overview of its proposed approach during the public meetings held on June 2, July 6, July 26, and August 22, 2011 . The purpose of this conference call was to provide an overview and results of the initial Loss-of-Coolant Accident (LOCA) Initiating Event Frequencies and Uncertainties Analysis.

The licensee's presentation slides and additional materials provided for the meeting are located at ADAMS Accession No. ML112770162. A list of meeting attendees is provided in the Enclosure to this meeting summary.

Meeting Summary The licensee provided copies of the following presentations prior to the meeting:

1. LOCA Initiating Event Frequencies - Final Results for 2011

2. Technical Review of SIP LOCA Frequency Estim;3tion Methodology

3. Development of LOCA Initiating Event Frequencies for South Texas Project GSI-191 - Final Report for 2011 Work Scope ..

4. Questions Associated with LOCA Frequency Analysis 1 Summaries of the meetings held on June 2, July 7, July 26, and August 22, 2011, are available in ADAMS Accession Nos. ML111640160, ML111950094, ML112130165, and ML112411419, respectively.

-2 The presentation slides were made available to the NRC staff just prior to the meeting; therefore, the NRC staff did not have sufficient time to review the materials to be presented during the meeting. Item 3 was provided for NRC staff information as a supplement to item 1 and was not to be discussed during the meeting. The NRC staff agreed to review the information presented in item 4 for discussion in a future public meeting.

The licensee presented an overview of the topics covered by items 1 and 2 and covered the following key areas.

LOCA Initiating Event Frequencies - Final Results for 2011

• Briefing on final results for 2011

• Review of technical approach with focus on recent refinements

• Highlights of results for component level for Containment Accident Sequence Stochastic Analysis Grande (CASAGRANDE), total LOCA frequencies for RISKMAN, and comparison with NUREG-18292

• Issues to be completed in 2012 Technical Review of STP LOCA Frequency Estimation Methodology

• LOCA frequency estimation model

• Interpretation and use of NUREG-1829 information

• Other key assumptions and computational steps used to generate the numerical results

• Discussion on results of reviews performed in August 2011 and September 2011 Results of Discussions

• Based on the previous public meetings, the NRC staff had identified several preliminary issues and concerns associated with the LOCA frequency analysis.

Some of the known preliminary issues and concerns based on limited information provided in the previous meetings were transmitted to STPNOC via e-mail dated September 20, 2011 (ADAMS Accession No. ML112630671). STPNOC's presentation during the meeting was intended to address these concerns.

STPNOC also provided its preliminary responses to the NRC staff's concerns (item 4). The NRC staff stated that it is in the process of understanding the complex analysis being used to develop location-specific LOCA frequencies that will serve as input to the model determining the debris source term and for determining total LOCA frequencies for the probabilistic risk analysis (PRA) 2 U.S. Nuclear Regulatory Commission, "Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process," April 2008 (Volumes 1 and 2 at ADAMS Accession Nos. ML080630013 and ML081060300, respectively).

- 3 analysis. Since the NRC staff did not have sufficient time to review the presentation slides (items 1! 2, and 4) including the supporting materials (item 3),

it was agreed to discuss the topic in a future public meeting to be arranged early in November 2011.

• STPNOC stated that it intends to use the geometric mean methodology to aggregate the different expert elicitation estimates of LOCA frequencies of different sizes into a single frequency for each size. STPNOC provided example curves for several different LOCA sizes which compared the frequency results using the alternative mixed distribution aggregation technique compared with the results using geometric mean aggregation. The results illustrate that using the mixed aggregation instead of geometric aggregation can increase the rupture frequencies by up to two orders of magnitude. The NRC staff noted that NUREG-1829 identified the sensitivity of the results on the aggregation technique and concluded that the context of the application should be considered when determining which method was most applicable. STPNOC did not clarify whether the sensitivity studies would be carried thorough the analysis used to support its planned risk-informed submittal to provide the alternative aggregation technique estimates of the risk of sump blockage. The NRC staff stated that a sensitivity study providing the risk of sump blockage using the mixed distribution aggregation methodology should be provided as part of planned risk-informed submittal.

• STPNOC agreed to provide more information on the nine expert distributions, including which LOCA categories were covered by each expert and how this impacted the method of applying geometric means.

• STPNOC agreed to provide more information on how pipe-induced LOCA frequencies were extracted from NUREG-1829, including references to tables and figures used to generate the NUREG-1829 comparisons.

• STPNOC indicated that it will perform additional sensitivity analysis on LOCA frequencies when more information on break location sensitivity to sump failure from CASAGRANDE becomes available. This will include sensitivity to assumptions regarding possible synergy between two or more degradation mechanisms at applicable locations.

- 4 No Public Meeting Feedback Forms were received for this meeting.

Please direct any inquiries to me at (301) 415-3016, or balwant.singal@nrc.gov.

Sincerely, b~~'~as<-

Balwant K. Singal, Senior Project Manager Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499

Enclosure:

List of Attendees cc w/encl: Distribution via Listserv

LIST OF ATTENDEES FOR MEETING WITH STP NUCLEAR OPERATING COMPANY REGARDING RISK-INFORMED APPROACH TO RESOLUTION OF GSI-191 ISSUE SOUTH TEXAS PROJECT, UNITS 1 AND 2 OCTOBER 3, 2011 NAME TITLE ORGANIZATION I Paul Jamie* Licensing STPNOC Rick Grantom* Manager, Risk Projects STPNOC Sara Wright* Administrative Assistant STPNOC Wes Schulz* Design Engineer STPNOC Tim Sande* Principal Engineer Alion Science and Technology, Represented STPNOC Ali Mosleh* Professor Nuclear Engineering University of Maryland, Represented STPNOC Karl Fleming* Consultant KNF Consulting, Represented STPNOC

• Mike Golay* President MGI, Represented STPNOC Gil Zilger* Senior Engineer Alion Science and Technology, Represented STPNOC Bengt Lydell* -- ScandPower I Diego Soenz* General Engineer NRC I

John Tsao Materials Engineer NRC Michael Snodderly Senior Reliability and Risk Engineer NRC Balwant K. Singal Senior Project Manager NRC Robert Tregoning* NRC I Stephen Dinsmore Senior Reliability and Risk Engineer NRC Stewart Bailey Branch Chief NRC Donnie Harrison Branch Chief NRC

• Participated via phone NRC - U.S. Nuclear Regulatory Commission STPNOC - STP Nuclear Operating Company Enclosure

ML112840114 _._._. *Via E-mail I OFFICE NRR/LPL4/PM I\IRR/LPL4/LA NRR/DSS/SSIB/BC NAME BSingal JBurkhardt SBailey*

DATE 10/14/11 10/14/11 10/14/11 OFFICE NRRIDRNAPLNBC NRR/LPL4/BC NRR/LPL4/PM NAME SDinsmore(A)", MMarkley BSingal DATE 10/14/11 10/31/11 10/31/11