ML063170076
| ML063170076 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 05/29/2007 |
| From: | Catherine Haney Plant Licensing Branch III-2 |
| To: | Sheppard J South Texas |
| Thadani, M C, NRR/DORL/LP4, 415-1476 | |
| References | |
| TAC MD0331, TAC MD0332 | |
| Download: ML063170076 (9) | |
Text
May 29, 2007 Mr. James J. Sheppard President and Chief Executive Officer STP Nuclear Operating Company South Texas Project Electric Generating Station P.O. Box 330 Wadsworth, TX 77483
SUBJECT:
SOUTH TEXAS PROJECT, UNITS 1 AND 2 - RE: REQUEST FOR A ONE-TIME EXTENSION OF INTEGRATED LEAKAGE RATE TEST INTERVAL FROM 15 YEARS TO 20 YEARS (TAC NOS. MD0331 AND MD0332)
Dear Mr. Sheppard:
By letter dated February 28, 2006, STP Nuclear Operating Company (STPNOC), the licensee for South Texas Project (STP), Units 1 and 2, submitted to the U.S. Nuclear Regulatory Commission (NRC) an application for amendments to the Technical Specifications (TSs),
pursuant to Title 10 of the Code of Federal Regulations, Section 50.90. The licensee requested changes to STP, Units 1 and 2, TSs to allow extension of the performance-based integrated leakage rate (Type A) test (ILRT) interval from 15 years to 20 years.
The NRC staff evaluated the licensees request to determine the acceptability of extending the Type A test interval from 15 years to 20 years.
Based on its evaluation, the NRC staff has determined that the industry-wide experience at a number of plants suggests that the materials of construction of containment systems are subject to various types of degradations, which undermine the essentially leak-tight condition of containments. The STP, Units 1 and 2, containments are not immune to the potential of those degradations. The proximity to the marine environment is expected to accelerate the degradation mechanisms at STP, Units 1 and 2. Consequently, the NRC staff finds that the current level of experience does not provide a basis for ensuring adequate protection of public health and safety when ILRT intervals are extended to 20 years.
Additionally, the licensees use of the risk-informed criterion of increase in the large early release frequency supporting the licensees rationale is based on Nuclear Energy Institutes (NEIs) guidance. The NRC staff has reviewed that guidance, and has concluded that the NEI guidance cannot justify approval to perform ILRTs at intervals greater than 15 years. This conclusion is based on the current knowledge of modeling corrosion mechanism and understanding that the risk-informed criterion of increase in the large early release frequency supporting analysis is insensitive to the ILRT testing interval. Therefore, the NRC staff cannot justify approval of an ILRT interval greater than 15 years.
Accordingly, your request to extend the STP, Units 1 and 2, containments ILRT intervals to 20 years is denied.
J. Sheppard The NRC staffs safety evaluation is enclosed. In addition, a copy of the Notice of Denial of Amendments is enclosed and will be forwarded to the Office of the Federal Register for publication.
Sincerely,
/RA Timothy J. McGinty for Catherine Haney/
Catherine Haney, Director Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499
Enclosures:
- 1. Safety Evaluation
- 2. Notice of Denial of Amendments cc w/encls: See next page
Package ML063400276 Letter/SE: ML063170076; Notice: ML063400283
- Revised SE input dated 4/17/07.
OFFICE NRR/LPL4/PM NRR/LPL4/LA OGC.
NRR/LPL4/BC DE/D*
NRR/DORL/D NAME MThadani LFeizollahi JBonanno THiltz PHiland CHaney DATE 5/8/07 5/8/07 5/14/07 5/16/07 4/17/07 5/29/07
March 2007 South Texas Project, Units 1 & 2 cc:
Senior Resident Inspector U.S. Nuclear Regulatory Commission P.O. Box 289 Wadsworth, TX 77483 C. M. Canady City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 J. J. Nesrsta/R. K. Temple E. Alercon/Kevin Pollo City Public Service Board P.O. Box 1771 San Antonio, TX 78296 INPO Records Center 700 Galleria Parkway Atlanta, GA 30339-3064 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011 Steve Winn/Christie Jacobs Eddy Daniels/Marty Ryan NRC Energy, Inc.
211 Carnegie Center Princeton, NJ 08540 Judge, Matagorda County Matagorda County Courthouse 1700 Seventh Street Bay City, TX 77414 A. H. Gutterman, Esq.
Morgan, Lewis & Bockius 1111 Pennsylvania Avenue, NW Washington, DC 20004 E. D. Halpin Site Vice President STP Nuclear Operating Company South Texas Project Electric Generating Station P.O. Box 289 Wadsworth, TX 77483 S. M. Head, Manager, Licensing STP Nuclear Operating Company P.O. Box 289, Mail Code: N5014 Wadsworth, TX 77483 C. T. Bowman General Manager, Oversight STP Nuclear Operating Company P.O Box 389 Wadsworth, TX 77483 Marilyn Kistler Sr. Staff Specialist, Licensing STP Nuclear Operating Company P.O. Box 289, Mail Code 5014 Wadsworth, TX 77483 Environmental and Natural Resources Policy Director P.O. Box 12428 Austin, TX 78711-3189 Jon C. Wood Cox, Smith, & Matthews 112 East Pecan, Suite 1800 San Antonio, TX 78205 Director Division of Compliance & Inspection Bureau of Radiation Control Texas Department of State Health Services 1100 West 49th Street Austin, TX 78756
March 2007 South Texas Project, Units 1 & 2 cc:
Mr. Ted Enos 4200 South Hulen Suite 422 Ft. Worth, TX 76109 Brian Almon Public Utility Commission William B. Travis Building P.O. Box 13326 1701 North Congress Avenue Austin, TX 78701-3326 Susan M. Jablonski Office of Permitting, Remediation and Registration Texas Commission on Environmental Quality MC-122 P.O. Box 13087 Austin, TX 78711-3087 Ken Coates Plant General Manager STP Nuclear Operating Company South Texas Project Electric Generating Station P.O. Box 289 Wadsworth, TX 77483 Mr. Terry Parks, Chief Inspector Texas Department of Licensing and Regulation Boiler Division P.O. Box 12157 Austin, TX 78711
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO EXTENSION OF TYPE A TESTING INTERVAL STP NUCLEAR OPERATING COMPANY SOUTH TEXAS PROJECT, UNIT 1 AND UNIT 2 DOCKET NOS. 50-498 AND 50-499
1.0 INTRODUCTION
By letter dated February 28, 2006 (Agencywide Document Access and Management System (ADAMS) Accession No. ML062910349) (Reference 1), STP Nuclear Operating Company (STPNOC), the licensee for South Texas Project (STP), Units 1 and 2, submitted to the U.S. Nuclear Regulatory Commission (NRC) an application pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Section 50.90. The licensee requested changes to STP, Units 1 and 2, Technical Specifications (TSs) to allow a one time extension of the integrated leakage rate (Type A) test (ILRT) interval from 15 years to 20 years. The NRC staff has completed its evaluation of the proposed one-time extension of the Type A test interval, as outlined in this safety evaluation.
The NRC staff previously approved a one-time extension of the performance-based ILRT interval from 10 years to 15 years for Type A tests, on September 17, 2002 (Reference 2). This evaluation discusses the licensees procedures and activities to determine the feasibility of extending the Type A test interval again from 15 years to 20 years, while adequately testing the impact of the aging degradation of the containment pressure boundary components on the containments structural integrity.
2.0 REGULATORY EVALUATION
The test requirements of 10 CFR Part 50, Appendix J, are intended to provide assurance that leakage from the containment, including systems and components that penetrate the containment, does not exceed allowable leakage rates specified in the TSs. This limitation on containment leakage provides assurance that adequate integrity of the containment structure is maintained during its service life. The regulations in 10 CFR Part 50, Appendix J, were revised, effective October 26, 1995, to allow licensees to perform containment leakage tests in accordance with the requirements of either Option A, Prescriptive Requirements, or Option B, Performance-Based Requirements. The STP adopted Option B of Appendix J to comply with containment leak-rate test requirements of 10 CFR 50.54(o). The performance-based leakage test requires that a Type A test be conducted at periodic intervals based on the historical performance of the overall containment system as a barrier against the accidental release of fission products to the outside environment. Also, the Type A test is to be augmented by general visual examination of the accessible interior and exterior surfaces of the containment system for structural degradation.
Regulatory Guide (RG) 1.163, Performance-Based Containment Leak Test Program, specifies a method acceptable to the NRC staff for complying with Option B by approving the use of Nuclear Energy Institute (NEI) 94-01 and American National Standards Institute/American Nuclear Society (ANSI/ANS) 56.8-1994 guidance documents, subject to several regulatory positions in the guide. The surveillance frequency for a Type A test in NEI 94-01 considers the performance factors in NEI 94-01, Section 11.3. The test frequency is based upon an evaluation that looks at the ?as found leakage history to determine the frequency for leakage testing, which would provide assurance that leakage limits will be maintained. Guidance on the risk impact assessment of extending ILRT intervals is provided in RG 1.174, ?An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis.
As stated above, on August 2, 2001, STPNOC proposed an amendment to STPs TS Section 6.8.3.j to allow a one-time extension of the interval between the Type A test from 10 to 15 years, utilizing as a basis the sequence of historical test performance. The NRC staff approved the proposed amendment in a safety evaluation dated September 17, 2002.
3.0 PROPOSED CHANGE
STP, Units 1 and 2, TS Section 6.8.3.j currently states:
A program shall be established to implement the leakage rate testing of the primary containment as required by 10 CFR 50.54(o) and 10 CFR 50, Appendix J, Option B, as modified by approved exemptions. This program shall be in accordance with the guidelines contained in Regulatory Guide 1.163, "Performance-Based Containment Leak-Test Program," dated September 1995. The current ten-year interval between performance of the integrated leakage rate (Type A) test, beginning September 24, 1991, for Unit 2, and March 10, 1995, for Unit 1, has been extended to 15 years (a one-time change).
The proposed change would state:
... The current interval between performance of the integrated leakage rate (Type A) test, beginning September 24, 1991, for Unit 2, and March 10, 1995, for Unit 1, has been extended to 20 years (a one-time change).
4.0 TECHNICAL EVALUATION
To demonstrate acceptable performance of its containment, STPNOC cites the results of its American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)
Section XI, Subsection IWE/IWL, inspection findings. The licensee reports that during these visual inspections, no recordable indications of liner plate degradation or damage or degradation of the concrete surfaces were identified. The licensee states that it has not experienced any containment conditions that would require an augmented inspection.
To address the effect of aging on a pre-stressing force, the licensee performed a regression analysis which indicates that for the four groups of tendons, the pre-stress loss will remain within the acceptable range for the life of the plant.
Similarly, to demonstrate the leak-tightness of the containment system, the licensee has cited the success in performing five ILRT tests between the two units over a span of 8 years. The licensee has stated that these early successes are adequate in providing assurance that the ILRT test interval can be extended to 20 years from the last test, which for Unit 1 would be March 2015 and for Unit 2 would be September 2011.
However, the industry-wide experience at a number of plants suggests that given the normal construction materials, i.e., concrete, steel reinforcement, and pre-stressing tendons, and the quality of construction, containment systems are subject to various types of degradation. STP containment components are not immune to the potential for such degradation. Additionally, the proximity of the plant to the marine environment would cause acceleration of degradation mechanisms relative to other plants not subject to a marine environment.
Recently, the NRC staff has witnessed evidence of liner corrosion in a number of plants. In some cases, the evidence was discovered by ASME Code visual examinations only after the full depth of the liner was corroded. In other plants, the corrosion was detected when the containment concrete was removed during steam generator replacement. It is clear from these experiences that the visual examination of the containment system is not adequate for predicting the progress of any liner corrosion until it has penetrated the entire depth of the liner or the concrete is removed from the liner. In many cases, where the corrosion started from outside of the liner and progressed inside the liner, the past visual examinations provided no indication of the ongoing incipient liner degradation or perforation. The containments at STP, Units 1 and 2, are not immune to the above degradations.
The licensee has also provided its analysis of the risk associated with not performing the test at the interval specified in the TSs. The risk associated with not performing a test or inspection can be assessed using a probabilistic risk assessment (PRA) process. Such an assessment has been made for STP by the licensee.
The current risk methodology, based on NEIs Interim Guidance, is adequate for the limited ILRT extensions of up to 15 years as used to address one-time extensions. The results of risk assessments are driven by a few input assumptions that have significant uncertainty. The probability of a small leak (0.027), the probability of large leak (0.0027), and leakage rate have associated uncertainty, in the case of a large leak. In the licensees analysis, the treatment of external events is generally limited and, in the case of STP, Units 1 and 2, it was omitted. The treatment of corrosion is based on a series of unsupportable assumptions regarding flaw likelihood, rate of increase of flaws, and probability of detection.
Based on the above discussion and recognizing the insensitivity of the risk-informed criterion (i.e., delta large early release frequency (LERF)) used in the licensees analyses of the ILRT interval extension, and uncertainties in these analyses, the NRC staff has made a determination that performing ILRTs at an interval greater than 15 years is not consistent with ensuring the expected essentially leak-tight condition of the containments.
However, the NRC staff is considering the industry-wide experience on ILRTs and local leak-rate tests, and insights from the NRC staffs previous reviews of one-time extensions to a 15-year interval, as a basis for considering granting a permanent ILRT interval extension to 15 years for containments of all plants.
5.0 CONCLUSION
Based on the above discussion of operating experience with containment liner performance and the limitations of existing PRA methodologies, the NRC staff concludes that the licensee has not shown that the proposed extension of ILRT interval to 20 years will not endanger the health and safety of the public. Accordingly, the licensees request for extension of ILRT interval at STP, Units 1 and 2 is denied.
6.0 REFERENCES
1.
Letter from T. J. Jordan, STP Nuclear Operating Company, to the NRC, Proposed Amendment to Technical Specification 6.8.3.j for a One-Time Extension of the Integrated Leakage Rate Test Interval to 20 Years, dated February 28, 2006.
2.
Letter from Mohan C. Thadani, NRC, to William T. Cottle, STP Texas Project Nuclear Operating Company, South Texas Project, Units 1 and 2 - Issuance of Amendments Re: Revising the Appendix J Integrated Leak Rate Testing Interval, dated September 17, 2002.
Principal Contributors: S. Samaddar Z. Cruz-Perez Date: May 29, 2007