ML091200040
| ML091200040 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 06/16/2009 |
| From: | Boyce T Plant Licensing Branch II |
| To: | Swafford P Tennessee Valley Authority |
| Brown, E, NRR/DORL, 415-2315 | |
| References | |
| 2-ISI-18R1, TAC MD9359 | |
| Download: ML091200040 (6) | |
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Mr. Preston D. Swafford Chief Nuclear Officer and Executive Vice President Tennessee Valley Authority 3R Lookout Place 1101 Market Street Chattanooga, TN 37402-2801
SUBJECT:
BROWNS FERRY UNIT 2 - SAFETY EVALUATION FOR RELIEF REQUEST 2-ISI-18R1 ASSOCIATED WITH INSERVICE INSPECTION EXAMINATION COVERAGE (TAC NO. MD9359)
Dear Mr. Swafford:
Bya letter dated July 29, 2008, the Tennessee Valley Authority submitted relief request (RR) 2-ISI-18R1 requesting relief from certain inservice inspection (lSI) requirements in Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code for 10 Category R-A Class 1 piping welds. In accordance with Title 10 of the Code ofFederal Regulations (10 CFR)
Section 50.55a(g)(5)(iii), your request proposes relief from the Code Case N-577 requirement (Table I, N-577-2500), Examination Category R-A, Item No. R1.16, to perform essentially 100 percent volumetric examination of the weld and adjacent base material.
Based on our review of your submittal, we have determined that it is impractical for the licensee to meet the examination requirements for the 10 welds identified. The examinations performed should provide reasonable assurance of structural integrity. Therefore, granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life or property, or the common defense and security, and is otherwise in the public interest given due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
These reliefs are authorized for the remainder of the third 10-year ISI interval at Browns Ferry Unit 2, which began May 25, 2001, and ends May 24, 2011.
Sincerely, Thomas H. Boy
,Chief Plant Licensing ranch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-260
Enclosure:
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INSERVICE TESTING PROGRAM RELIEF REQUEST NO. 2-ISI-18R1 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT, UNIT 2 DOCKET NO. 50-260
1.0 INTRODUCTION
Bya letter dated JUly 29,2008, the Tennessee Valley Authority (TVA, the licensee) submitted relief request (RR) 2-ISI-18, Revision 1, requesting relief from certain inservice inspection (lSI) requirements in Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel (ASME) Code for 10 Category R-A Class 1 piping welds. In accordance with Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(g)(5)(iii), the request proposes relief from the Code Case N-577 requirement (Table I, N-577-2500), Examination Category R-A, Item No. R1.16, to perform essentially 100 percent vOlumetric examination of the weld and adjacent base material.
The subject relief request is for the remainder of the third 10-year lSI interval at Browns Ferry Unit 2, which began May 25, 2001, and ends May 24, 2011.
2.0 REGULATORY REQUIREMENTS The lSI of ASME Code Class 1,2, and 3 components is to be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code, and applicable addenda, as required by 10 CFR 50.55a(g), except where specific relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). Section 50.55a(a)(3) of 10 CFR states that alternatives to the requirements of paragraph (g) may be used, when authorized by the U.S. Nuclear Regulatory Commission (NRC), if the licensee demonstrates that (i) the proposed alternatives would provide an acceptable level of quality and safety or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection (lSI) of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the first 1O-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code, which was incorporated by reference in 10 CFR 50.55a(b),
- 2 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
The ASME Code of record for Unit 2, third 1O-year interval lSI program is the 1995 Edition through the 1996 Addenda of ASME Section XI.
ASME Code Case N-460, Alternative Examination Coverage for Class 1 and Class 2 Welds, as an alternative approved for use by the NRC in Regulatory Guide 1.147, Revision 15, Inservice Inspection Code Case Acceptability, states that a reduction in examination cov~rage due to part geometry or interference for any Class 1 and 2 weld is acceptable provided that the reduction is less than 10 percent (Le., greater than 90 percent examination coverage is obtained).
3.0 RELIEF REQUEST NO. 2-ISI-18 3.1 Component Function/Description Table 3.1.1 - Category R-A Welds with Limited Volumetric Coverage Weld System Configuration Coverage Obtained DRHR-2-03 Residual Heat Removal Flued head-to-valve 87.6%
KR-2-03 Recirculation Saddle-to-pipe weld 62.5%
GR-2-38 Recirculation Saddle-to-pipe weld 50%
GR-2-41 Recirculation Saddle-to-pipe weld 50%
GR-2-48 Recirculation Saddle-to-pipe weld 75%
GR-2-15(OL)
Recirculation Saddle-to-pipe weld (overlay) 76%
RCRD-2-50 Reactor Water Cleanup EI bow-to-valve 62.7%
RWCU-2-004-083 Reactor Water Cleanup EI bow-to-valve 81.5%
CRD-2-005-003 Reactor Water Cleanup Pipe-to-valve 64.8%
3.2 Code Requirements for Which Relief is Requested The examination requirements for the subject piping welds at Unit 2 are governed by a Risk-Informed lSI (RI-ISI) program that was approved by the NRC in a Safety Evaluation dated January 19, 2001 (ADAMS ML010190294). The RI-ISI program was developed in accordance with WCAP-14572, Rev. 1-NP-A, Westinghouse Owners Group Application of Risk-Informed Methods to Piping Inservice Inspection Topical Report (WCAP). As part of the NRC-approved program, the licensee has implemented inspection requirements listed in ASME Code Case N-577, Risk-Informed Requirements for Class 1, 2 and 3 Piping, Method A, with more detailed provisions contained in the WCAP. The topical report includes a provision for requesting relief from volumetric examinations if 100 percent of the required volumes cannot be examined.
Table 1 of ASME Code Case N-577 assigns the Examination Category R-A, Item R1.16, to piping inspection elements subject to inter-granular stress corrosion cracking (IGSCC). This table
- 3 requires 100 percent of the examination location volume, as described in Figures IWB-2500-7, 8, 9, 10, or 11, as applicable, be completed for selected Class 1 circumferential piping welds.
3.3 Licensee's Proposed Alternative In lieu of the ASME Code-required essentially 100 percent (Le., greater than 90 percent) volumetric examination, TVA proposes an ultrasonic examination of accessible areas to the maximum extent practical, given the component design configuration of the aforementioned piping welds.
3.4 Licensee's Bases for Alternative (as stated):
The welds were examined with the latest ultrasonic techniques, procedures, equipment, and personnel qualified to the requirements of the Performance Demonstration Initiative (POI) Program, as mandated by 10 CFR 50.55a(g)(4).
An ultrasonic examination was performed on the piping welds and structural weld overlay accessible areas to the maximum extent practical due to the configuration. Credit for the one-sided examination of GR-2-38 and GR-2-41 provided 50 percent coverage because of the requirement mandated in 10 CFR 50.55a(b)(2)(xv)(A)(2), which states in part, "Where examination from both sides is not possible on austenitic welds, full coverage credit from a single side may be claimed only after completing a successful single sided Appendix VIII demonstration using flaw on the opposite side of the weld." At time of the examination, there was no Appendix VIII Program for single sided austenitic welds. Under the original ASME Section XI Code requirements, UT coverage attained was essentially 100 percent.
Credit for the one-sided examinations of KR-2-03 and GR-2-48 provided 62.5 and 75 percent coverage respectively since the requirement mandated in 10 CFR 50.55a(b)(2)(xv)(A)(2), which states in part, "Where examination from both sides is not possible on austenitic welds, full coverage credit from a single side may be claimed only after completing a successful single sided Appendix VIII demonstration using flaw on the opposite side of the weld." At the time of the examination, there was no Appendix VIII Program for single sided austenitic welds. Under the original ASME Section XI Code requirements, UT coverage attained was essentially 100 percent for both welds.
Coverage for the Ultrasonic examination of Weld DRHR-2-03 was limited to the configuration of the components, valve to flued head. Coverage obtained was 87.6 percent.
Coverage for the Ultrasonic examination of Weld GR-2-15(OL) was limited due the configuration of the structural weld overlay covering the pipe to saddle weld.
Coverage obtained was 76 percent. Coverage for the Ultrasonic examination of Weld RCRD-2-50 was limited due the elbow to valve configuration of the weld. Coverage obtained was 62.7 percent.
-4 Coverage for the Ultrasonic examination of Weld RWCU-2-004-083 was limited due the elbow to valve configuration of the weld. Coverage obtained was 81.5 percent. Coverage for the Ultrasonic examination of Weld CRD-2-005-003 was limited due the pipe to valve configuration of the weld. Coverage obtained was 64.8 percent.
The performance of the ultrasonic examination of the subject areas to the maximum extent practical provides an acceptable level of quality and safety because the information and data obtained from the volume examined provide sufficient information to judge-the overall integrity of the piping welds.
3.5 Evaluation The examination requirements for the subject piping welds at Unit 2 are governed by a RI-ISI program that was approved by the NRC in a letter dated January 19, 2001. This program assigns Examination Category R-A, Item R1.16 to piping elements subject to IGSCC, and requires inspection of 100 percent of the examination location volume for Class 1 circumferential piping welds.
TVA has determined that certain Unit 2 welds had ultrasonic examination coverage limitations of less than 100 percent of the ASME Code-required weld and adjacent material volume(s). The limitations encountered during the performance of the ultrasonic examinations on the subject welds were caused by valve-to-pipe, elbow-to-pipe, elbow-to-valve and saddle weld configurations (see Table 3.1.1 above). These configurations severely limit volumetric examinations, and in some cases, access to only a single side of the weld is available. As shown on the sketches and technical descriptions included in the licensee's submittal, examinations of the subject piping welds have been completed to the extent practical with aggregate volumetric coverage ranging from 50 percent to 87.6 percent of the ASME Code-required volumes.
Current technology is not capable of reliably detecting or sizing flaws on the inaccessible side of an austenitic weld for configurations common to U.S. nuclear applications. Instead of a full single-side qualification, PDI offers a best-effort approach, which demonstrates that the best available technology is applied. PDI Performance Demonstration Qualification Summary austenitic piping certificates Jist the limitation that single side examination is performed on a best-effort basis. This requires the inaccessible side of the weld to be listed as an area of no coverage. This examination provides, to the maximum extent practical, an acceptable level of quality and safety based upon the demonstrated and qualified techniques offered.
Ultrasonic personnel, procedures and equipment qualified through the industry's PDI were employed, including 45-, 60-, and 70-degree (as applicable) shear wave and refracted longitudinal wave (L-wave) techniques from the accessible sides of these welds. The L-wave method is capable of detecting planar inside diameter surface-breaking flaws on the far-side of wrought stainless steel welds. Recent studies recommend the use of both shear and L-waves to obtain the best detection results, with minimum false calls, in austenitic welds. No recordable flaw indications were observed during the ultrasonic examinations.
However, the subject piping weld configurations and base materials limit volumetric examinations.
In order to meet the RI-ISI program volumetric coverage requirements, these components would have to be re-designed and modified. The NRC staff considers the redesign and modification to meet the examination requirements impractical for the subject piping welds. The licensee has shown that it is impractical to meet the ASME Code-required 100 percent volumetric examination
- 5 coverage for the subject piping welds due to their design and ultrasonic access restrictions.
Although the ASME Code-required coverage could not be obtained, the ultrasonic methods employed would have provided full volumetric coverage for the near-side of the welds and limited volumetric coverage for the weld fusion zone and base materials on the opposite side of the welds.
Based on the aggregate coverage obtained for the subject welds, and considering the licensee's performance of ultrasonic techniques used to maximize this coverage, it is reasonable to conclude that if significant service-induced degradation were occurring, evidence of it would have been detected by the examinations that were performed.
The NRC staff has reviewed the licensee's submittal and concludes that the ASME Code examination coverage requirements are impractical for the subject welds listed above. Further, based on the volumetric coverage obtained, the staff concluded that, if significant service-induced degradation were occurring, there is reasonable assurance that evidence of it would have been detected by the examinations that were performed, therefore the inspections performed provide reasonable assurance of structural integrity.
4.0 CONCLUSION
Based on the information provided in the licensee's submittal, the NRC staff has determined that examination coverage requirements are impractical for the 10 welds, and the examinations performed, provides reasonable assurance and, therefore, it is authorized pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life or property, or the common defense and security, and is otherwise in the public interest given due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. All other ASME Code,Section XI requirements for which relief was not speci'fically requested and approved in the subject request for relief remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
This authorization is for the third interval that began May 25, 2001 and ends May 24, 2011, and is limited to those components described in Section 3.1 above.
Principal Contributor: Donald Naujock Date:
June 16, 2009