ML11270A060

Response to Requests for Additional Information for License Renewal Application

ML11270A060
Person / Time
Site:	South Texas
Issue date:	09/22/2011
From:	Gerry Powell Southern Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NOC-AE-1 1002735
Download: ML11270A060 (4)

Text

ALM/'/AM Nuclear Operating Company South Texas Project Electric GeneratinS Station PO. Bae 289 Wadsworth, Texas 77483 _/_/_

September 22, 2011 NOC-AE-1 1002735 10CFR54 STI: 32945070 File: G25 U. S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2746 South Texas Project Units 1 and 2 Docket Nos. STN 50-498, STN 50-499 Response to Requests for Additional Information for the South Texas Proiect License Renewal Application (TAC Nos. ME4938 and ME5122)

References:

1. STPNOC Letter dated October 25, 2010, from G. T. Powell to NRC Document Control Desk, "License Renewal Application" (NOC-AE-10002607) (ML103010257)

2. NRC letter dated September 1, 2011, "Requests for Additional Information for the Review of the South Texas Project, License Renewal Application" (ML112360114)

By Reference 1, STP Nuclear Operating Company (STPNOC) submitted a License Renewal Application (LRA) for South Texas Project (STP) Units 1 and 2. By Reference 2, the NRC staff requests additional information for review of the STP LRA. STPNOC's response to the request for additional information is provided in the Enclosure to this letter.

There are no regulatory commitments in this letter.

Should you have any questions regarding this letter, please contact either Arden Aldridge, STP License Renewal Project Lead, at (361) 972-8243 or Ken Taplett, STP License Renewal Project regulatory point-of-contact, at (361) 972-8416.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on e 'al Date G. T. Powell Vice President, Technical Support & Oversight KJT

Enclosure:

STPNOC Response to Requests for Additional Information

NOC-AE-1 1002735 Page 2 cc:

(paper copy)

(electronic copy)

Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 612 East Lamar Blvd, Suite 400 Arlington, Texas 76011-4125 Balwant K. Singal Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North (MS 8B1) 11555 Rockville Pike Rockville, MD 20852 Senior Resident Inspector U. S. Nuclear Regulatory Commission P. 0. Box 289, Mail Code: MN1 16 Wadsworth, TX 77483 C. M. Canady City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 John W. Daily License Renewal Project Manager (Safety)

U.S. Nuclear Regulatory Commission One White Flint North (MS 011-Fl)

Washington, DC 20555-0001 Tam Tran License Renewal Project Manager (Environmental)

U. S. Nuclear Regulatory Commission One White Flint North (MS O11F01)

Washington, DC 20555-0001 A. H. Gutterman, Esquire Kathryn M. Sutton, Esquire Morgan, Lewis & Bockius, LLP John Ragan Catherine Callaway Jim von Suskil NRG South Texas LP Ed Alarcon Kevin Polio Richard Pena City Public Service Peter Nemeth Crain Caton & James, P.C.

C. Mele City of Austin Richard A. Ratliff Alice Rogers Texas Department of State Health Services Balwant K. Singal John W. Daily Tam Tran U. S. Nuclear Regulatory Commission

Enclosure NOC-AE-1 1002735 Page 1 of 2 STPNOC Response to Requests for Additional Information SOUTH TEXAS PROJECT LICENSE RENEWAL APPLICATION REQUESTS FOR ADDITIONAL INFORMATION REGARDING THE ANALYSIS OF SEVERE ACCIDENT MITIGATION ALTERNATIVES The requests for information (RAIs) listed below were derived from the discussion during the conference call of July 28, 2011 (ML11216A263). The purpose for the call was to seek additional clarification for the RAI responses of July 5, 2011 (ML11193A016).

NRC RAI 3.b: Fire-analysis Individual plant examination (IPE) - use of technical report NUREGICR-6850

Background:

The response to this RAI simply indicates that a review of the NUREG/CR-6850 will be performed in the future. However, the recent research and guidance reported in NUREG/CR-6850, specifically in the areas of hot short probabilities, fire ignition frequencies, and non-suppression probabilities, indicate that the fire analysis methodologies utilized for the IPE may underestimate fire risk.

Requested information: Provide assurance that consideration of this new information is not expected to impact the selection of cost beneficial severe accident mitigation alternatives (SAMAs) for South Texas Project (STP).

STPNOC Response:

STPNOC will perform an assessment using the new information provided in NUREG/CR-6850, "EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities," for assessing impact on the selection of cost beneficial severe accident mitigation alternatives (SAMAs) for the South Texas Project (STP). The assessment will consider insights provided in NUREG/CR-6850 regarding hot short probabilities, fire ignition frequencies, and non-suppression probabilities.

The STP Fire Probabilistic Risk Analysis (PRA) model will not be revised as a result of this study.

The insights from NUREG/CR-6850 will be applied to the fire analyses from the IPE and as augmented through the STPREV 6 version of the PRA model. The insights from NUREG/CR-6850 will be applied to the fire scenarios currently in the PRA model. The resultant core damage frequency (CDF) from the assessment will be used to screen the list of SAMAs currently considered in the LRA to re-evaluate if any SAMA would be cost-beneficial.

STPNOC expects to complete the assessment and report the results to the NRC by December 15, 2011.

Enclosure NOC-AE-1 1002735 Page 2 of 2 NRC RAI 3.c: Seismic-analysis IPE of external events (IPEEE) - use of Lawrence Livermore National Laboratory (LLNL) or United States Geological Survey (USGS) hazard curves

Background:

The response to this RAI did not provide the requested updated seismic core damage frequency (CDF) results. Instead, the applicant cited Notice IN 2010-18. While this Information Notice concluded that the US plants had adequate safety margin, it did indicate that the seismic CDF for STP could be as high as 3E-06 per year (for spectral accelerations of 5 hz and 10 hz). This is 40 times the total seismic CDF given in the environmental report (ER). Also, note that the STP IPE gives a seismic CDF using the LLNL hazard curve of 1.7E-05 per year which is over 200 times the value used in the probabilistic risk assessment (PRA). Since the seismic CDF was determined using point estimates, the seismic CDF for the analysis STPREV6, based on the LLNL hazard curve, can be obtained from the LLNL seismic frequencies from Table 3.4.4-9 of the IPE or IPEEE or both and the conditional core damage probabilities (CCDPs) from Table F.2-1 of the ER. The result is a seismic core damage frequency (SCDF) of 8.7E-06 per year.

Comparing the USGS hazard curves for the STP site with the Electric Power Research Institute (EPRI) hazard curves indicates that the frequency for the USGS curves is 60 to 150 times those for the EPRI curves over the range of 0.4 to 0.6 g which is the range for the largest contributors to STP seismic CDF. Furthermore, the USGS hazard curve is higher than the LLNL hazard curve by a factor of 1.5 to 2 over the same range.

Using the above method for determining the CDF for SEIS3 and SEIS4 initiators for the seismic event scenarios gives seismic CDFs of 4E-06 and 5E-06 per year, respectively.

This indicates that applying the LLNL hazard curves or the 2008 USGS hazard curves to the SEIS3 and SEIS4 initiators could lead to CDF contributions of about 60 to 150% of the STPREV6 total CDF.

Requested information: Provide an assessment of the seismic CDF contribution due to the updated USGS hazard curves and the potential for cost beneficial SAMAs.

STPNOC Response:

STPNOC will perform an assessment of the seismic CDF contribution due to the updated USGS hazard curves for impact on the selection of cost beneficial SAMAs for STP. The STP PRA model will not be revised as a result of this assessment.

The acceleration values from the USGS hazard curves will be applied to the current STP PRA model and will examine the impact on those key components previously identified in the current STP PRA model. Because the fragilities for many of these key components were conservative, revised fragilities may be assumed, if necessary and where justified, to determine the resultant CDF. The resultant CDF from the assessment will be used to screen the list of SAMAs currently considered in the LRA to re-evaluate if any SAMA would be cost-beneficial.

STPNOC expects to complete the assessment and report the results to the NRC by December 15, 2011.