ML12187A081

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Summary of 6/11/12 Meeting by Conference Call with STP Nuclear Operating Company; Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Uni
ML12187A081
Person / Time
Site: South Texas  STP Nuclear Operating Company icon.png
Issue date: 07/11/2012
From: Balwant Singal
Plant Licensing Branch IV
To:
South Texas
Singal B
References
TAC ME7735, TAC ME7736, GSI-191
Download: ML12187A081 (5)
v • d • e


Text

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

SUBJECT:

SUMMARY

OF JUNE 11, 2012, 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. ME7735 AND ME7736)

On June 11,2012, 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, Maryland. The meeting notice and agenda, dated May 31, 2012, is located in the Agencywide Documents Access and Management System (ADAMS) under Accession No. ML12146A020. 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 before the end of the year. The licensee previously provided an overview of its proposed approach during the public meetings held on June 2, July 7, July 26, August 22, October 3, November 1, November 2, and December 1,2011, and February 9, March 1, March 8, and March 29, 2012 1 , The purpose of this conference call was to discuss uncertainty modeling of loss-of-coolant accident (LOCA) frequencies and break size distributions for STP GSI-191 resolution and calibration and benchmarking of single- and two-phase jet computational fluid dynamics models.

A list of meeting attendees is provided in the Enclosure to this meeting summary, Meeting Summary The discussion was based on the following previously provided meeting materials/handouts and no additional meeting materials were provided for the purposes of this meeting.

1. Uncertainty Modeling of LOCA Frequencies and Break Size Distributions for the STP GSI-191, May 2012 (ADAMS Accession No. ML12145A466)
2. Calibration and Benchmarking of Single and Two-Phase Jet CFD {Computational Fluid Dynamics] Models, dated May 18, 2012 (ADAMS Accession No. ML12145A438)

Summaries of the meetings held on June 2, July 7, July 26, August 22, October 3, November 1, November 2, and December 1, 2011, and February 9. March 1, March 8, and March 29, 2012, are available in ADAMS Accession Nos. ML111640160, ML111950094, ML112130165, ML112411419, ML112840114, ML113120129, ML113180196, ML113430087, ML120620541. ML120830103, ML120830086, and ML121380522, respectively.

- 2 No separate meeting handout materials were provided by the licensee in addition to the above reports.

Results of Discussions Uncertainty Modeling of LOCA Frequencies and Break Size Distributions

  • The licensee discussed the process used to develop a generic, bottom-up approach to weighting the LOCA Frequencies from NUREG-1829, Vol. 1 "Estimating Loss-of-Coolant Accident (LOCA) Frequencies through the Elicitation Process," April 2008 (ADAMS Accession No. ML080630013), to distribute them over all contributing weld joints. The detailed approach is described in study entitled, "Uncertainty Modeling of LOCA Frequencies and Break Size Distributions for the STP GSI-191 Resolution by Elmira Popova and David Morton," May 2012 (ADAMS Accession No. ML12145A466). The purpose is to determine the relative likelihood of failure of each weld joint for each LOCA size using frequencies from an earlier generic study entitled, "Development of LOCA Initiating Event Frequencies for South Texas Project GSI-191 by Karl N. Fleming and Bengt O. Y. Lydell," October 2011 (ADAMS Accession No. ML113060615).

This earlier study based the failure likelihood of a particular weld joint on the number of indications/failures associated with that weld joint for all specific degradation mechanisms. These weighted likelihoods are summed over all contributing welds and the final frequency is normalized to achieve the NUREG-1829 estimate of the mean. The NRC staff suggested that the uncertainty in both the weighting estimates and the generic LOCA estimates be considered appropriately to support the failure likelihoods in support of the final submittal. Additionally, the NRC staff suggested that the licensee ensure that the absolute frequencies associated with failures of small-bore piping (i.e., 2-inch nominal diameter and less) be consistent with operating experience, especially for socket welded joints that have experienced failures in service. The NRC staff also suggested that the plant-specific issues with the potential for resulting in LOCA frequency estimates higher than the generic estimates determined by either NUREG-1829 or the earlier Lydell and Fleming work, should also be addressed by the final submittal.

  • The NRC staff requested the licensee to verify if STP, Units 1 and 2, have any Alloy/82/182 dissimilar metal welds (DMWs) and, if so, whether these welds have been mitigated for stress-corrosion cracking or if the NUREG-1829 results should be adjusted to account for primary water stress-corrosion cracking of DMWs.

The licensee stated that both units have DMWs and took an action to address the NRC staff's concern.

-3 Calibration and Benchmarking of Single- and Two-Phase Jet CFD Models

  • The licensee indicated that the CFD modeling effort is still ongoing. The NRC staff requested that the licensee clarify the intended use of the models with respect to zone-of-influence (lOI) determination. In particular, the NRC staff asked the licensee to clarify whether it planned to continue to use spherical and hemispherical-shaped lOis or if it intends to use more realistic jet-shaped lOis.

The licensee stated that the current model would maintain the spherical and hemispherical shapes, but future model iterations could attempt to refine the shape, including reflections off structures and components within the containment. The licensee also stated that the degree of refinement will depend upon the success of the modeling effort. The NRC staff stated that it was not aware of any viable CFD models of sub-cooled two-phase jets. The licensee stated that it had some areas of the model that required additional work, but expressed confidence that model development process would ultimately be successful.

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,

~T~~

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 JUNE 11. 2012, MEETING WITH STP NUCLEAR OPERATING COMPANY REGARDING RISK-INFORMED APPROACH TO RESOLUTION OF GSI-191 ISSUE SOUTH TEXAS PROJECT, UNITS 1 AND 2 DOCKET NOS. 50-498 AND 50-499 NAME TITLE ORGANIZATION Rick Grantum** Manager Risk Project STPNOC (STP Nuclear Operating Company)

Ernie Kee** Risk Management, Technical STPNOC Jamie Paul** Licensing Engineer STPNOC Rodolfo Vagetto** Graduate Research Student Texas A&M University Zahra Mohaghegh** Principal Research Scientist Soteria Consultants Elmira Popova** Professor Mechanical Engineering University of Texas Tim Sande** Principal Engineer Alion Science and Technology David Johnson** Vice President, Quantitative Risk ABS Consulting Analysis/PRA Lead David Morton Professor Mechanical Engineering University of Texas Bruce Letellier PRA Los Alamos National Laboratory Mark A. Richter*** Senior Project Manager Nuclear Energy Institute Justin Hiller*** Consulting Engineer Ameren (Callaway)

Delonta Wilson*** Engineer Southern Nuclear Company Owen Scott*** Risk Informed Engineering Southern Nuclear Company Supervisor Phillip Grissom*** Principal Engineer Southern Nuclear Company Michael Snodderly Senior Reliability and Risk Engineer U.S. Nuclear Regulatory Commission (NRC)

John Tsao Materials Engineer NRC Rob Tregoning - NRC Balwant K. Singal Senior Project Manager NRC Paul Klein*** Senior Materials Engineer NRC Stewart Bailey Branch Chief NRC Steve Smith Reactor Systems Engineer NRC Ervin Geiger Senior Engineer NRC

    • Participated via phone and represented STPNOC
      • Participated via phone Enclosure

- 3 Calibration and Benchmarking of Single- and Two-Phase Jet CFD Models

  • The licensee indicated that the CFD modeling effort is still ongoing. The NRC staff requested that the licensee clarify the intended use of the models with respect to zone-of-influence (lOI) determination. In particular, the NRC staff asked the licensee to clarify whether it planned to continue to use spherical and hemispherical-shaped lOis or if it intends to use more realistic jet-shaped lOis.

The licensee stated that the current model would maintain the spherical and hemispherical shapes, but future model iterations could attempt to refine the shape, including reflections off structures and components within the containment. The licensee also stated that the degree of refinement will depend upon the success of the modeling effort. The NRC staff stated that it was not aware of any viable CFD models of sub-cooled two-phase jets. The licensee stated that it had some areas of the model that required additional work, but expressed confidence that model development process would ultimately be successful.

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, IRA!

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 DISTRIBUTION:

PUBLIC RidsNrrLAJBurkhardt Resource SBailey, NRR/DSS/SSIB LPLIV rtf RidsNrrPMSouth Texas Resource MSnodderly, NRRlDRNAPLA RidsAcrsAcnw_MailCTR Resource RidsOgcRp Resource SSmith. NRR/DSS/SSIB RidsNrrDeEsgb Resource RidsRgn4MailCenter Resource EGeiger. NRR/DSS/SSIB RidsNrrDorlLpl4 Resource TWertz, NRR TSao, NRR/DE/EPNB RidsNrrDprPgcb Resource SKennedy, EDO RIV RTregoning, RES RidsNrrDraApla Resource SDinsmore, NRR/DRNAPLA PKlein. NRR/DE/ESGB RidsNrrDssSsib Resource BPurnell, NRR/DPR/PGCB ADAMS Accession No. ML12187A081 *Via e-mail OFFICE NRR/LPL4/PM NRR/LPL4/LA NRR/DRNAPLNBC NAME BSingal JBurkhardt MSnodderly(A)*

DATE 7/61/12 7/6112 7/6112 OFFICE NRR/DSS/SSIB/BC NRR/LPL4/BC NRRlLPL4/PM NAME SSmith(A)* MMarkley BSingal DATE 7/5/12 7/11/12 7/11/12 OFFICIAL RECORD COpy

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