ML120830086

Summary of Meeting by Conference Call with STP Nuclear Operating Co. to Discuss Risk-Informed GSI-191, Assessment of Debris Accumulation on Pressurized-Water Reactor (PWR) Sump Performance, Resolution Approach for South Texas, Units 1 & 2

ML120830086
Person / Time
Site:	South Texas
Issue date:	03/29/2012
From:	Balwant Singal Plant Licensing Branch IV
To:
Singal, Balwant, 415-3016, NRR/DORL/LPL4
References
TAC ME7735, TAC ME7736
Download: ML120830086 (7)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 March 29, 2012 LICENSEE: STP Nuclear Operating Company FACILITY: South Texas Project, Units 1 and 2 SUB,JECT:

SUMMARY

OF MARCH 8, 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 March 8, 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 February 2, 2012, is located in the Agencywide Documents Access and Management System (ADAMS) under Accession No. ML120300364. 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 and March 1,20121. The purpose of this conference call was to discuss GSI-191 bypass testing and head-loss protocols and plans for the STP pilot program.

A list of meeting attendees is provided in the Enclosure to this meeting summary.

Meeting Summary The licensee provided a copy of the following documents prior to the meeting:

1 Introduction - NRC Public Meeting on Risk-Informed Resolution of GSI-191, Topic:

Head Loss Experiments (ADAMS Accession No. ML120610063)

2. STP Corrosion Head Loss Experiments (CHLE) Test Plan (Working Draft) (ADAMS Accession No. ML120610074)

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 and March 1, 2012, are available in ADAMS Accession Nos. ML111640160, ML111950094, ML112130165, ML112411419, ML112840114, ML113120129, ML113180196, ML113430087, ML120620541, and ML120830103, respectively.

- 2

3. Test Plan for STP High Temperature Vertical Loop Testing, Document No. ALiON-PLN-STPEGS-8511-01 (ADAMS Accession No. ML120610068)

4. Revised STP Strainer Fiber Bypass Test Protocol (ADAMS Accession No. ML120610102)

Results of Discussions Bypass Test Protocol Discussion The NRC staff stated that bypass testing for STP may be somewhat simplified because the strainer is designed to have uniform flow. The NRC staff stated that the following issues should be considered when bypass testing is conducted:

1. Agitation, if used, should keep the debris suspended without affecting the debris bed.

2. The potential for various combinations of trains operating should be considered.

3. Sacrificial area should be considered.

4. The weights of filters, including any labels, should be carefully controlled.

5. The NRC staff noted that head loss may not be a relevant parameter to indicate whether bypass had stopped and the test should be terminated.

Corrosion Head Loss Experiment (CHLE) Test Discussion

• The NRC staff requested the licensee to explain how the information gained from the chemical testing would be incorporated into the Containment Accident Sequence Stochastic Analysis (CASA) model. It appears that CASA would calculate a chemical debris load, and then determine what effect the chemical precipitate would have on a debris bed. Based on the NRC staff's observations of previous strainer and fuel assembly tests, the pressure drop across a debris bed due to chemical precipitates appears to be dependent upon both the type of precipitate and the debris bed characteristics. Therefore, further NRC staff review will be required in this area. The NRC staff stated that many head-loss tests, including various debris beds and chemical loads, would likely be required to ensure that the CASA model accurately reflects the range of head losses that may occur.

• The NRC staff also requested the licensee to explain how it would be assured that any chemical precipitates that may form in the tests would not settle in a non-conservative manner in the CHLE tank before being transported to the debris beds. The NRC staff asked if the licensee had considered adding a small quantity of precipitate generated using the WCAP-16530-NP-A 2 methodology during shakedown testing to evaluate the 2 Westinghouse Electric Company LLC, WCAP-16530-NP-A, Revision 0, "Evaluation of Post-Accident Chemical Effects in Containment Sump Fluids to Support GSI-191," February 2006.

-3 transport of precipitate from the CHLE tank to the three parallel head-loss loops. The NRC staff also asked if the debris beds in the CHLE loop would be correlated to head loss tests conducted in the Alion high-temperature vertical loop. The licensee indicated that similar beds would be used in the two test loops and that the CHLE tests could be performed with different beds in the three parallel pressure-drop loops for each test.

• The NRC staff discussed the importance of ensuring the appropriate contribution of corroded or leached species from the highest post-Ioss-of-coolant accident (LOCA)]

temperatures is included in the CHLE. The maximum CHLE tank operating temperatures is approximately 190 degrees Fahrenheit. Currently, STP is planning to perform bench testing and use those results to add extra quantities of plant materials to the CHLE tank. While the NRC staff acknowledged that this may be a valid approach for accounting for the highest temperature portions of a post-LOCA environment, the NRC staff also stated that there were several potential issues with this approach that would need to be considered. For example, since the corrosion or leaching behavior of some materials could be a function of temperature (e.g., differences in passivation rates), the NRC staff stated that it would be important to predict the high-temperature contribution in the CHLE tests and then understand any differences between the predicted and actual chemical contributions from the extra coupons. The NRC staff expressed its concern that the extra tank materials could create non-representative flow conditions in the CHLE tank due to sample crowding. The licensee indicated that they would be sensitive to that concern but that the CHLE tests would have significantly less materials than the Integrated Chemical Effects Tests (ICET) that were previously performed using the tank.

The licensee and NRC staff discussed the importance of pH in the planned tests since it can affect corrosion rate and solubility. The NRC staff stated that it would be more representative to make any acid additions later in the test to simulate longer term formation of hydrochloric or nitric acid following a LOCA.

• STP described a series of bench testing experiments that will be performed to evaluate leaching of materials, corrosion of aluminum, the effects of different test parameters, and the characteristics of precipitates. The NRC staff indicated that the bench tests should have sample size to preclude non-representative test samples for certain heterogeneous materials such as insulation and concrete. The licensee stated they were considering using 500 mL bottles approximately three-quarters full for the bench tests.

• Since the NRC staff did not have time to fully review the draft CHLE Test Plan document prior to the call, and there were other topics that needed to be discussed during the meeting, the NRC staff and licensee agreed to further discuss the test plan and a call was subsequently planned for March 29, 2012.

High-Temperature Vertical Loop Test Plan

• The major NRC staff concern with the vertical loop testing was the small test matrix identified in the plan. The licensee stated that the test plan was intended to validate the NUREG/CR-6224 3 correlation, but that it was understood that additional testing would 3 Science and Engineering Associates, NUREG/CR-6224, "Parametric Study of the Potential for BWR ECCS Strainer Blockage Due to LOCA Generated Debris," October 1995.

- 4 likely be required. The NRC staff stated that the correlation had been determined to be invalid for the NRC staff for design basis calculations for several reasons. The NRC staff stated that it was unlikely that the tests would correspond to results from the correlation because of changes in testing techniques and the use of different debris types. The NRC staff stated that many more tests may be required to ensure that the potential head losses from the range of conditions and debris loads at STP are adequately defined. The basis for the test matrix was not understood by the NRC staff.

The NRC staff stated that the test matrix should include the various debris bed thicknesses and particulate to fiber ratios that could occur at STP.

• The NRC staff also stated that some of the debris preparation and addition practices described in the procedure may need to be adjusted. SpeCifically, in some cases, it was apparent that the debris would not be adequately diluted prior to addition to the test loop.

The NRC staff was also concerned that mixing fibrous and particulate debris prior to addition to the test loop could result in non-conservative results due to interactions between the debris constituents due to extreme concentrations of debris in the mixing vessel. Although the licensee made provisions to inspect the debris for agglomeration prior to and during addition, the debris interactions may not be visually detectable. The NRC staff stated that the NUREG/CR-6224 head-loss correlation was validated by comparing its predictions to a series of tests. These tests had particulate added and mixed in the test loop prior to the addition of any fiber. The staff stated that it would be more consistent if future testing was conducted Similarly to the testing which was used to validate the correlation. The NRC staff emphasized that the particulate and fibrous debris should be added separately, even if homogeneolJs type additions were used.

That is, separate mixing containers should be used and debris types added sequentially to prevent over concentration and potential interactions.

• The NRC staff emphasized that the formation of uniform debris beds as being critical to attaining acceptable results. Additionally, the NRC staff stated that the debris beds should be formed under flow.

• The velocity through the strainer was discussed. The licensee stated that the velocity through the strainer would decrease if containment spray is secured or does not start following a LOCA. Additionally, if a pump fails, flow through the strainer would be reduced.

• The NRC staff asked how the correlation would be adjusted based on the results of the tests, if required. The licensee stated that the compressibility and the specific surface areas would be adjusted.

No Public Meeting Feedback Forms were received for this meeting.

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

Sincerely,

'6~ t.1::>,~~

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 MARCH 8, 2012, MEETING WITH STP NUCLEAR OPERATING COMPANY REGARDING RISK-INFORMED APPROACH TO RESOLUTION OF GSI-191 ISSUE SOUTH TEXAS PRO..IECT. UNITS 1 AND 2 DOCKET NOS. 50-498 AND 50-499 NAME TITLE ORGANIZATION Rick Grantum** Manager Risk Project STPNOC Ernie Kee** Risk Management STPNOC Wes Schulz** - l.§..TPNOC Jamie Paul** Licensing Engineer STPNOC John Crenshaw** - STPNOC Rodolfo Vagetto** - Texas A&M University Zahra Mohaghegh** - Soteria Consultants ISeyed Reihani** - Soteria Consultants Tim Sande** Principal Engineer Alion Science and Technology David Johnson** - ABS Consulting Bruce Letellier** - Las Alamos National Laboratory Kerry Howe** - University of New Mexico Janet Leavitt** - University of New Mexico Gil Zigler** - Alion Science and Technology i Phillip Grissom* Principal Engineer Southern Nuclear Company Mark Richter* Senior Project Manager Nuclear Energy Institute Michael Snodderly Senior Reliability and Risk Engineer U.S. Nuclear Regulatory Commission (NRC)

Matt Yoder Senior Chemical Engineer 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

• • Participated via phone and represented STPNOC Enclosure

ML120830086 *Via E-mail OFFICE NRR/LPL4/PM NRR/LPL4/LA NRR/DRAIAPLA NRR/DSS/SSIB/BC NAME BSingal JBurkhardt* MSnodderly* SBailey*

DATE 3/23/12 3/29/12 3/26/12 3/23/12 OFFICE NRR/DE/ESGB NRR/LPL4/BC NRR/LPL4/PM -

NAME GKulesa* MMarkley BSingal DATE 3/23/12 3/29/12 3/29/12