ML113120129

Summary of 11/1/11 Meeting by 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, Un

ML113120129
Person / Time
Site:	South Texas
Issue date:	11/29/2011
From:	Balwant Singal Plant Licensing Branch IV
To:	South Texas
Singal, Balwant, 415-3016, NRR/DORL/LPL4
References
TAC ME5358, TAC ME5359, GSI-191
Download: ML113120129 (6)

Text

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1-'} ****i' ",0 November 29. 2011 LICENSEE: STP Nuclear Operating Company FACILITY: South Texas Project, Units 1 and 2

SUMMARY

OF NOVEMBER 1, 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 November 1, 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, Maryland. The meeting notice and agenda, dated October 11, 2011, is located in the Agencywide Documents Access and Management System (ADAMS) under Accession No. ML112790151. 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, August 22, and October 3, 20111. The purpose of this conference call was to discuss the proposed approach by STPNOC to address topiC of chemical effects testing.

The licensee's presentation slides and additional materials provided for the meeting are located at ADAMS Accession No. ML113050615. A list of meeting attendees is provided in the Enclosure to this meeting summary.

Meeting Summary The licensee provided the following documentation prior to the meeting:

Expected Impact of Chemical Effects on GSI-191 Risk-Informed Evaluation for South Texas Project (ADAMS Accession No. ML113050623)

The licensee did not provide a copy of its presentation slides to the NRC staff in advance of the meeting. Consequently, the NRC staff's advance review was based exclusively on the report noted above.

Summaries of the meetings held on June 2, July 7, July 26, August 22, and October 3, 2011, are available in ADAMS Accession Nos. ML111640160, ML111950094, ML112130165, ML112411419, and ML112840114, respectively.

-2 The licensee provided an overview of the following topics in its chemical effects report:

• Objective of the Meeting

• Purpose of Chemical Effects Program

• Significant/Insignificant Contributors

• STP Parameters

• Previous Tests Relevant to STP

• Preliminary Ideas for Testing

• Preliminary Ideas for Risk Unformed Application

• Conclusions NRC Staff Comments

• The NRC staff agreed with the licensee's assessment that some test results not specific to STP appear to suggest that chemical effects at STP may be over predicted by the base WCAP-16530-Np 2 methodology. The NRC staff also noted that unfiltered dissolved zinc levels in Integrated Chemical Effects Test 2 went from 10 to 0 parts per million in approximately 5 days, indicative of precipitate formation.

• The NRC noted that although the NRC staff has addressed 41 technical issues raised by an outside expert panel, in some cases this disposition relied on conservatism built into previous industry evaluation methods. Some of these issues may be revisited when considering a best-estimate approach that may provide more realistic evaluations.

• The NRC staff expressed the view that the overall approach including thermodynamic modeling, kinetic modeling, and development of a chemical effects head loss algorithm appears to be an ambitious undertaking. The NRC staff noted that some precipitates that may form during an emergency core cooling system mission time are metastable, not equilibrium phases. The NRC staff has also observed testing where the chemical effects head loss appeared to be a function of not only the precipitate but was also strongly dependent on the filtering characteristics of the debris bed.

• The NRC staff expressed concerns regarding the test conditions that would be considered "prototypical" for validation of a chemical effects model.

2 Westinghouse Electric Company, LLC, WCAP-16530-NP, Revision 0, "Evaluation of Post-Accident Chemical Effects in Containment Sump Fluids to Support GSI-191 ," dated February 2006 (ADAMS Accession No. ML060890509).

- 3

• The NRC staff expressed the view that there will likely be significant challenges with developing and validating a "chemical effects" base model given:

>> the emergence of new information in this area (e.g., the potential difference between demineralized water and tap water for strainer head loss testing),

the difficulties in performing tests in a representative post-LOCA [post loss-of-coolant accident1 environment, and the high consequences of forming a small amount of amorphous or highly hydrated precipitate.

• The NRC staff has not accepted the NUREG/CR-6224 3 correlation as a methodology for determining strainer design head loss for reasons provided in the NRC staff safety evaluation dated December 6, 2004, to Nuclear Energy Institute (NEI) 04-07, "Pressurized Water Reactor Sump Performance Evaluation Methodology," December 2004 (ADAMS Accession Nos. ML051460182 and ML050550138), unless the correlation has been validated for the range of parameters expected for the plant strainer. Since the safety evaluation was issued, the NRC staff has identified additional issues with the correlation. The use of a chemical model to adjust questionable calculated head loss values may significantly increase the uncertainty. Additional experimental data may be required to reduce uncertainty.

• The NRC staff expressed the view that the licensee's plans for estimating chemical effects require further development. The NRC requested the licensee to provide its plan for the development and confirmation of a model for the estimates of chemical effects.

3 U.S. Nuclear Regulatory Commission, NUREG/CR-6224, "Parametric Study of the Potential for BWR ECCS Strainer Blockage Due to LOCA Generated Debris," October 1995 (ADAMS Accession No. ML083290498).

- 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, P c&L----t \a~1 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 FOR MEETING WITH STP NUCLEAR OPERATING COMPANY REGARDING RISK-INFORMED APPROACH TO RESOLUTION OF GSI-191 ISSUE SOUTH TEXAS PROJECT, UNITS 1 AND 2 NOVEMBER 1, 2011 NAME TITLE ORGANIZATION Paul Jamie* Licensing STPNOC Wes Schulz* Design Engineer STPNOC Tim Sande* Principal Engineer Alion Science and Technology, Represented STPNOC Steve Blossom* Project Manager, Special Projects STPNOC Ernie Kee* Risk Management STPNOC John Butler* Senior Director, Engineering and Nuclear Energy Institute Operations Support Phillip Grissom* - Southern Nuclear Company David Midlik* - Southern Nuclear Company Tom Moorer* - Southern Nuclear Company Mike MacFarlane* - Southern Nuclear Company Jeff Waites* - Southern Nuclear Company Mike Wright* - Southern Nuclear Company John Swailes* - Calvert Cliffs Nuclear Power Plant Andre Drake* - Calvert Cliffs Nuclear Power Plant Craig Sellers* - Calvert Cliffs Nuclear Power Plant Michael Snodderly Senior Reliability and Risk Engineer NRC Balwant K. Singal Senior Project Manager NRC Steve Smith Reactor Systems Engineer NRC Matthew Yoder Senior Chemical Engineer NRC Stewart Bailey Branch Chief NRC Paul Klein Senior Materials Engineer NRC Victor Cusumano Branch Chief NRC

• PartIcIpated vIa phone NRC - U.S. Nuclear Regulatory Commission STPNOC - STP Nuclear Operating Company Enclosure

-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, IRAJ 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 CSteger, NRR LPLIV rlf MFranke, EDO RIV RidsAcrsAcnw_MailCTR Resource SDinsmore, NRRlDRAJAPLA RidsNrrDeEsgb Resource BPurnell, NRRlDPR/PGCB RidsNrrDorlLpl4 Resource DHarrison, NRR/DRAJAPLA RidsNrrDprPgcb Resource SBailey, NRRlDSS/SSIB RidsNrrDraApla Resource MSnodderly, NRRlDRAJAPLA RidsNrrDssSsib Resource DHarrison, NRRlDRAlAPLA RidsNrrLAJBurkhardt Resource PKlein, NRR/DE/ESGB RidsNrrPMSouthTexas Resource VCusumano, NRRlDE/ESGB RidsOgcRp Resource SSmith, NRRlDSS/SSIB RidsRgn4MailCenter Resource MYoder, NRRlDE/ESGB ML113120129 *Via E-mail

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