ML15084A003

2/4/15 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, Units 1 and 2 (TAC MF2400-MF24

ML15084A003
Person / Time
Site:	South Texas
Issue date:	04/06/2015
From:	Lisa Regner Plant Licensing Branch IV
To:	Koehl D South Texas
Regner L
References
TAC MF2400, TAC MF2401, TAC MF2402, TAC MF2403, TAC MF2404, TAC MF2405, TAC MF2406, TAC MF2407, TAC MF2408, TAC MF2409
Download: ML15084A003 (6)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 April 6, 2015 LICENSEE: STP Nuclear Operating Company FACILITY: South Texas Project, Units 1 and 2

SUMMARY

OF FEBRUARY 4, 2015, 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 February 4, 2015, 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 January 20, 2015, are located in the Agencywide Documents Access and Management System (ADAMS) at Accession No. ML15034A502. The licensee's handouts from the meeting are available in ADAMS at Accession No. ML15034A114. 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 NRC staff used a webinar format for the meeting and the purpose was to discuss the licensee's proposed change in methodology for resolution of GSl-191. The licensee stated that the proposal is a test-based debris risk assessment referred to as 'Risk over Deterministic' or

'RoverD.'

Meeting Summary The licensee explained that the motivation for the methodology change include 1) to reduce its reliance on correlations and complexities in the analysis, 2) to reduce the scope of the review by screening out scenarios from the risk analysis, and 3) to add confidence to the risk-based conclusions.

As discussed in the December 1-3, 2014, meeting summary (ADAMS Accession No. ML15020A106), the licensee's Rovero provides a "bounding debris 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. The NRC staff observed much of this strainer testing and observed that it was based on staff-approved methods.

Using the deterministic testing results, the licensee would find largest break sizes, which are dependent on the break location, below which strainer and in-vessel failures do not occur.

Under this approach, the debris generated at each break location is compared to the debris limit to prevent core damage as determined using the 2008 strainer test data. Breaks with less debris would be counted as successes (no core damage) and those with more debris are 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 licensee stated that for the deterministic evaluation, it would generally use design basis assumptions, for example, two trains of emergency core coolant system/core spray will be assumed to be operating with the third train out of service. The licensee also plans to use a cold-leg break fiber limit of 15 grams which is supported by testing for WCAP-16793, "Evaluation of Long-Term Cooling Considering Particulate, Fibrous and Chemical Debris in the Recirculating Fluid." For the hot-leg break, RELAP analysis has shown that water will enter the core by alternate flowpaths if the core inlet becomes blocked; however, the boric acid precipitation analysis has not been finalized.

The licensee stated that it would use the CASA Grande debris generation and transport methodology to find the smallest break at each location that could lead to exceeding debris limits. The NRC staff noted that independent calculations, using the CASA Grande methodology, were resulting in larger debris masses than those presented by the STPNOC staff. STPNOC and NRC staffs plan to discuss the discrepancy further at a public meeting scheduled for April 8, 2015.

The licensee will also use CASA Grande to calculate in-vessel debris amounts. The NRC staff stated that it is conservative for the strainer evaluation to have fewer trains in service, but for the in-vessel evaluation, it may be conservative to assume that all three trains are in service.

The licensee presented a table showing each risk-significant break, the amount of debris generated and transported, and the diameter of the break as suggested by NRC staff during the December 2014 public meeting.

The licensee presented a table of RAI questions that the licensee proposed would be eliminated by Rovero. The NRC staff stated that the licensee would need to justify the proposed elimination in its response to the RAI. Further, the staff noted during the meeting that some of the questions that STP concluded would be resolved by using the new methodology may still need to be answered. Specifically, the NRC's Safety Issue and Resolution Branch (SSIB)

RA ls 27, 31, 33, and 51 were identified as potentially still needing a full response. The staff also requested a status of the response to an RAI issued in 2009 related to Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation During Design Basis Accidents at Pressurized-Water Reactors" (ADAMS Accession No. ML09341060). The licensee stated that since it is referencing a test that was the subject of several of those questions, it will include responses in its June 2015 supplement.

There was significant discussion regarding the proposed changes to the licensing basis, the technical specifications, and operability. The NRC and licensee will discuss these topics further at the scheduled April 8, 2015, public meeting.

The licensee stated that the testing planned to address strainer head loss discussed during the December 2014 public meeting has been eliminated due to the new Rovero methodology.

Additionally, the use of the L* chemical effects correlation discussed during the December public meeting will no longer be necessary with the implementation of the proposed Rovero approach.

The NRC staff stressed that it is important for docketed information on Rovero be provided to NRC staff as soon as possible. The STPNOC staff stated that every attempt would be made to provide a response by March 12, 2015.

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.

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 FEBRUARY 4, 2015, MEETING WITH STP NUCLEAR OPERATING COMPANY REGARDING RISK-INFORMED APPROACH TO RESOLUTION OF GSl-191 SOUTH TEXAS PROJECT, UNITS 1AND2 DOCKET NOS. 50-498 AND 50-499 NAME ORGANIZATION Lisa M. Regner U.S. Nuclear Regulatory Commission (NRC)

John Stang NRC Steve Smith NRC Victor Cusumano NRC Paul Klein NRC Matthew Yoder NRC Ashley Guzzetta NRC Rob Elliott NRC Andrea Russell NRC Marioly Diaz-Colon NRC CJ Fong NRC Y.C. (Renee) Li NRC Steve Laur NRC Osvaldo Pensado Southwest Research Institute, NRC Contractor Steven M. Unikewicz Alion Science and Technology Tim Sande Enercon Services Inc. (Enercon)

Phil Grissom Southern Nuclear Company Paul Leonard Enercon Steve Blossom STP Nuclear Operating Company (STPNOC)

Bruce Letellier Alion Science and Technology (Alion)

Ernie Kee STPNOC Janet Leavitt Ali on Wayne Harrison STPNOC Wes Schulz STPNOC Mike Murray STPNOC Drew Richards STPNOC David Johnson ABS Consulting Kip Walker Enercon Mardy Kazarians Kazarians & Associates, Inc.

Craig Sellers Calvert Cliffs Rasool Baradaran Pacific Electric & Gas, Diablo Canyon Roger Andreasen Ameren Missouri - Callaway Ron Holloway Wolf Creek Nuclear Operating Company Rob Engen STP Energy Projects Enclosure

ML15084A003 *via email OFFICE NRR/DORL/LPL4-1 /PM NRR/DORL/LPL4-1 /LA NRR/DSS/SSIB/BC

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• NAME LRegner JBurkhardt VCusumano RDennig HHamzehee DATE 3/24/15 3/26/15 3/31 /15 3/30/15 3/31 /15 OFFICE NRR/DE/ESGB/BC

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