ML15020A106

12/1-3/2014 Summary of Meeting with STP Nuclear Operating Company to Discuss Revised Pilot Submittal and Request for Exemptions for a Risk-Informed Approach to Resolve Generic Safety Issue (GSI)-191 at South Texas, Unit 1 and 2 (TAC MF2400-

ML15020A106
Person / Time
Site:	South Texas
Issue date:	02/19/2015
From:	Lisa Regner Plant Licensing Branch IV
To:
Singal B
References
TAC MF2400, TAC MF2401, TAC MF2402, TAC MF2403, TAC MF2404, TAC MF2405, TAC MF2406, TAC MF2407, TAC MF2408, TAC MF2409
Download: ML15020A106 (7)

Text

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

SUMMARY

OF DECEMBER 1, 2, AND 3, 2014, PUBLIC MEETING WITH STP NUCLEAR OPERATING COMPANY TO DISCUSS THE LICENSE AMENDMENT AND EXEMPTION REQUESTS TO USE A RISK-INFORMED APPROACH TO THE RESOLUTION OF GENERIC SAFETY ISSUE 191, "ASSESSMENT OF DEBRIS ACCUMULATION ON PWR SUMP PERFORMANCE" (TAC NOS. MF2400, MF2401, MF2402, MF2403, MF2404, MF2405, MF2406, MF2407, MF2408, AND MF2409)

On December 1, 2, and 3, 2014, a public meeting was held 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 November 5, 2014, are located in the Agencywide Documents Access and Management System (ADAMS) at Accession No. ML14317A142. The licensee's handouts from the meeting are available in ADAMS at Accession Nos. ML14315A087, ML14349A788, ML14349A789, and ML14349A790. A list of meeting attendees is provided in the Enclosure to this meeting summary.

By letter dated June 19, 2013 (ADAMS Accession No. ML131750250), as supplemented by letters dated October 3, October 31, November 13, November 21, and December 23, 2013 (two letters); and January 9, February 13, February 27, March 17, March 18, May 15 (two letters),

May 22, June 25, and July 15, 2014 (ADAMS Accession Nos. ML13295A222, ML13323A673, ML13323A128, ML13338A165, ML14015A312, ML14015A311, ML14029A533, ML14052A053, ML14072A076, ML14086A383, ML14087A126, ML14149A353, ML14149A354, ML14149A434, ML14178A481, and ML14202A045, respectively), STPNOC submitted exemption requests accompanied by a license amendment request (LAR) for a risk-informed approach to resolve the issue of potential impact of debris blockage on emergency recirculation during design-basis accidents Generic Safety Issue (GSl)-191, "Assessment of Debris Accumulation on PWR

[Pressurized-Water Reactor] Sump Performance," at South Texas Project, Units 1 and 2 (STP).

The NRC staff issued a Request for Additional Information (RAI) by letter dated April 15, 2014 (ADAMS Accession No. ML14087A075). The licensee provided its response to the RAI request by letters dated May 22, June 25, and July 15, 2014.

The purpose of the meeting was to discuss the following:

• Proposed head loss test and thermal hydraulics model;

• Proposed chemical effects test plan;

• Treatment of coating; and

• Draft RAI clarifications Meeting Summary The following key topics, summarized in the licensee's presentation slides, were discussed by STPNOC during the meeting:

• STP Strainer Testing to Address GSl-191

• L* Test Approach and Application

• Bounding Debris Approach

• Risk-Informed GSl-191 Second Round RAls STP Talking Points Results of Discussions

• The licensee presented slides describing a "bounding debris approach." Under this approach, the licensee would use the results of previous strainer testing (performed in July 2008) to find the largest break size below which strainer and in-vessel failures do not occur. Under this approach, each break's zone of influence (ZOI) would be compared to the assumed ZOI from the 2008 test. Breaks with a smaller ZOI would be counted as successes (no core damage) and those with larger ZOls would be counted as failures (core damage). The frequency of the breaks assumed to lead to core damage would be compared to the risk acceptance guidelines in Regulatory Guide (RG) 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis," Revision 2, dated May 2011 (ADAMS Accession No. ML100910006).

The NRG staff acknowledged the merits of the method in that it allows comparison with the risk acceptance guidelines without a reliance on the modified NUREG/CR-6224, "Parametric Study of the Potential for BWR [Boiling Water Reactor] ECCS [Emergency Core Cooling System] Strainer Blockage Due to LOCA [Loss-of-Coolant Accident] Generated Debris,"

October 1997 (ADAMS Accession No. ML083290498), head loss correlation currently described in the LAR. The NRC staff and the Advisory Committee on Reactor Safety (ACRS) have concerns about the accuracy of this correlation. The staff also noted that the licensee's proposed approach was - in effect - using ZOI as a surrogate for head loss in that the size of the ZOI was assumed to correspond to the mass of debris that is generated and transported.

The NRG staff is concerned about the validity of this assumption given that a) the amount of debris generated is a function of the ZOl location, not just the size b) the amount of debris that reaches the sump is a function not only of the total debris generated but also the assumed transport fractions c) the assumed head loss associated with debris is a function not just of the overall amount that is generated and transported but also on its physical properties (e.g., fiber to particulate ratio) and these are a function of the ZOl's location, not just volume.

The NRC staff stated that the debris size distributions used in the 2008 testing and the number of strainers assumed to be in service for the evaluation may need to be considered

in the evaluation process. The staff further stated that the deterministic evaluation has different assumptions than a probabilistic evaluation. For example, the number of strainers in service may be different. Hence, such issues would need to be adequately addressed, if a bounding debris approach is used.

The licensee acknowledged the NRC staff's concerns and suggested that the bounding approach could be modified to compare the specific debris source term from each break (rather than simply the ZOI) to the 2008 test data. The licensee stated that this information could be readily extracted from CASA Grande. The staff suggested that a table showing each break, the amount of debris generated and transported, and a comparison to the 2008 test data might be a useful format for this information. The staff and licensee agreed to discuss the specifics in greater detail in a future meeting.

• The licensee presented information regarding testing that is planned to address strainer head loss for the STP evaluation. The NRC staff emphasized that the testing should cover the range of plant conditions to which any correlation is applies and should be conducted under plant specific conditions. The licensee clarified that they will be using a new correlation (VISTA) in the LAR instead of the NUREG/CR-6224 correlation. The staff expressed concern that the testing and validation of the correlation for STP could delay the final approval of the licensing action. The staff noted that the ability to accurately determine the head loss of a debris bed consisting of various debris types and sizes via a correlation has yet to be demonstrated and may not be a feasible solution.

The licensee clarified some of the aspects of the planned testing. All chemical surrogates will be prepared external to the test loop in accordance with the preparation method contained in Westinghouse Electric Company LLC's topical report, WCAP-16530-NP-A, "Evaluation of Post-Accident Chemical Effects in Containment Sump Fluids to Support GSl-191," March 2008 (ADAMS Accession No. ML081150379). The NRC staff suggested that temperature sweeps be performed prior to chemical precipitate addition since increasing test temperatures after precipitate addition may complicate data interpretation due to the possibility of precipitate dissolution. Also, if flow sweeps disturb the bed 1 -i<

additional debris may be added to bring the head loss to its nominal value before the flow sweep. The licensee also clarified that the test would attempt to ensure that all debris reaches the strainer.

• The licensee and NRC staff discussed the L* chemical approach and how the additional tests would inform the L* correlation. The NRC staff stated that it would be important to show how the L* approach accounts for the uncertainty associated with plant-specific chemical effects.

In addition, the NRC staff provided clarifications to the proposed second round RAI.

Action Items No action items were identified.

No Public Meeting Feedback Forms were received for this meeting.

Please direct any inquiries to me at 301-415-1906, or lisa.regner@nrc.gov.

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1 Lisa M. Regner, Senior Project Manager Plant Licensing Branch IV-1 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 DECEMBER 1, 2, AND 3, 2014. MEETING WITH STP NUCLEAR OPERATING COMPANY REGARDING RISK-INFORMED APPROACH TO RESOLUTION OF GSl-191 SOUTH TEXAS PROJECT, UNITS 1 AND 2 DOCKET NOS. 50-498 AND 50-499 NAME TITLE ORGANIZATION Balwant K. Singal Senior Project Manager U.S. Nuclear Regulatory Commission (NRC)

John Stang Senior Project Manager NRC Steve Smith Reactor Systems Engineer NRC Victor Cusumano Branch Chief NRC Paul Klein Senior Materials Engineer NRC Matthew Yoder Sr. Chemical Engineer NRC John Tsao Materials Engineer NRC Ashley Guzzetta Engineer NRC Rob Elliott Branch Chief NRC Ahsan Sallman Senior Reactor Systems NRC Engineer Khadijah West Reactor Systems Engineer NRC David Boirel -- NRC CJ Fong Reliability and Risk Analyst NRC Mark Banks Senior Staff Engineer NRC Steve Laur Senior Risk Analyst NRC Leonard Ward -- NRC Pensado Osvaldo Group Manager Southwest Research Institute, NRC Contractor Steven M. Unikewicz** Senior Principal Engineer Alion Science and Technology Tim Sande* - Enercon Services Inc. (Enercon)

Phil Grissom - Southern Nuclear Company Paul Leonard* - Enercon Steve Blossom STPNOC Project Manager STP Nuclear Operating Company (STPNOC)

Bruce Letellier** -- Alion Science and Technology (Alion)

Edward Blandford** Assistant Professor University of New Mexico (UNM)

Ernie Kee Technical Team Lead STPNOC Janet Leavitt** Director Lab Operations Al ion

• Attended via phone

• • Attended via phone in support of STPNOC Enclosure

NAME TITLE ORGANIZATION Wayne Harrison Licensing Lead STPNOC Wes Schulz Design Engineering STPNOC Mike Murray Regulatory Affairs Manager STPNOC Seyed Reihani** -- University of Illinois Blake Stair Chemical Engineer Enercon Drew Richards Licensing Engineer STPNOC David Recurrel Senior Vice President STPNOC Operations Dominic Munoz** Mechanical Engineer Ali on David Johnson** -- ABS Consulting Dan Labnier** -- UNM Rodolfo Vagheto+ -- TAMU Ed Blandford** Assistant Professor UNM John Hasenbeh** Associate Professor University of Texas Austin Kip Walker* Lead Mechanical Engineer Enercon

• Participated via Phone

• • Represented STPNOC

+ Represented STPNOC and participated via phone

ML15020A106 OFFICE NRR/DORULPL4-1 /PM NRR/DORULPL4-1 /PM NRR/DORULPL4-1/LA NRR/DSS/SSIB/BC NRR/DSS/SCVB/BC NAME BSingal LRegner JBurkhardt VCusumano ~

DATE 1/27/15 2/13/15 1/23/15 2/2/15 I~

OFFICE NRR/DRA/APLA/BC NRR/DE/ESGB/BC NRR/DSS/SNPB/BC NRR/DORULPL4-1 /BC(A) NRR/DORULPL4-1 /PM NAME HHamzehee GKulesa ~ EOesterle LRegner DATE 2/11/15 2/2/15 _,,,.,,,,,,,,-- 2/18/15 2/19/15