ML20115E352
| ML20115E352 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 05/12/2020 |
| From: | Markley M Plant Licensing Branch II |
| To: | Stoddard D Virginia Electric & Power Co (VEPCO) |
| Thomas V | |
| References | |
| EPID L-2017-LLR-0108 | |
| Download: ML20115E352 (10) | |
Text
May 12, 2020 Mr. Daniel G. Stoddard Senior Vice President and Chief Nuclear Officer Innsbrook Technical Center 5000 Dominion Blvd.
Glen Allen, VA 23060-6711
SUBJECT:
SURRY POWER STATION, UNIT 2 - ALTERNATIVE REQUEST S2-I5-ISI-05 RE: ASME SECTION XI INSERVICE INSPECTION PROGRAM PROPOSED FOR THE USE OF A MECHANICAL CLAMPLING DEVICE FOR MAIN STEAM LINE PRESSURE BOUNDARY REPAIR (EPID L-2017-LLR-0108)
Dear Mr. Stoddard:
By letter dated November 27, 2019, (Agencywide Documents and Access Management System (ADAMS) Accession No. ML19331A916), Virginia Electric and Power Company (Dominion Energy Virginia, the licensee) submitted a request to the U.S. Nuclear Regulatory Commission (NRC) proposing the use of an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Appendix IX, Mechanical Clamping Devices for Class 2 and 3 Piping Pressure Boundary, at Surry Power Station (Surry) Unit 2.
During a November 27, 2019, teleconference (ADAMS Accession No. ML19336A350) between the NRC staff and the licensee, the licensee was granted verbal authorization to use the proposed alternative. Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2), the licensee submitted Alternative Request S2-I5-ISI-05 on the basis that compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. The enclosed safety evaluation provides the technical basis for authoriziaing the use of Alternative Request S2-I5-ISI-05 for Surry Unit 2, until the end of the next refueling outage, 2R29, which is scheduled for spring 2020. All other requirements of ASME Code,Section XI, for which relief was not specifically requested and authorized by the NRC staff, remain applicable, including the third-party review by the Authorized Nuclear In-service Inspector.
If you have any questions, please contact Mr. Vaughn Thomas at (301) 415-5897.
Sincerely, Michael T. Markley, Branch Chief Plant Licensing Branch II-I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-281
Enclosure:
Safety Evaluation cc w/encl: Listserv Michael T.
Markley Digitally signed by Michael T. Markley Date: 2020.05.13 07:22:16 -04'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ALTERNATIVE REQUEST S2-I5-ISI-05 ALTERNATE REPAIR OF AUXILIARY FEEDWATER PUMP STEAM SUPPLY PIPING SURRY POWER STATION UNIT 2 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)
DOCKET NUMBER 50-281
1.0 INTRODUCTION
By letter dated November 27, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19331A916), Virginia Electric and Power Company, Dominion Energy Virginia (the licensee) proposed to use Appendix IX, Mechanical Clamping Devices for Class 2 and 3 Piping Pressure Boundary, of the 2004 Edition of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI to repair a degraded socket weld of the auxiliary feedwater pump steam supply piping at Surry Power Station, Unit 2 (Surry, Unit 2). However, the licensee proposed to deviate from Appendix IX, Subparagraph IX-1000(c)(2) which prohibits the use of a mechanical clamp on the containment boundary and Subparagraph IX-6000(a) which requires periodic volumetric examination after the clamp is installed.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(2), the licensee submitted Alternative Request S2-I5-ISI-05 on the basis that compliance with the requirements of the ASME Code,Section XI would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
On November 27, 2019 (ADAMS Accession No. ML19336A350), the U.S. Nuclear Regulatory Commission (NRC) verbally authorized the use of Alternative Request S2-I5-ISI-05 for Surry, Unit 2, until the end of the next refueling outage, 2R29, which is scheduled for spring 2020. The NRC staff determined that the proposed alterative is technically justified and provides reasonable assurance of structural integrity of the affected piping. This safety evaluation documents the technical basis for the NRC's verbal authorization.
2.0 REGULATORY REQUIREMENTS Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) must 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 of Nuclear Power Plant Components, to the extent practical, within the limitations of design, geometry, and materials of construction of the components.
However, 10 CFR 50.55a(z) states, in part, that alternatives to the requirements of paragraphs (b) through (h) of 10 CFR 50.55a or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate that: (1)
Acceptable level of quality and safety. The proposed alternative would provide an acceptable level of quality and safety; or (2) Hardship without a compensating increase in quality and safety. Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request the use of an alternative and the NRC to authorize the proposed alternative.
3.0 TECHNICAL EVALUATION
3.1 ASME Code Component Affected The components covered in this relief request (RR) is an ASME Code Class 2, 1-inch, SHP-601 main steam piping upstream of valve 2-MS-377. The seamless 1-inch, Schedule 80 pipe is fabricated from A-106, Grade B carbon steel and has a nominal wall thickness of 0.179 inches.
The design pressure and temperature of the subject pipe are 1085 pound per square inch gauge (psig) and 570°F, respectively. The operating pressure and temperature at full power are 811 psig and 520°F, respectively. The normal operating pressure in the subject pipe at the degraded location is in the range of 800 to 1000 psig.
3.2 ASME Code and Requirements The Code of record for the fifth 10-year inservice inspection (ISI) interval is the 2004 Edition of the ASME Code,Section XI. The fifth ISI interval began on May 10, 2014, and ends on May 9, 2024.
The applicable requirements of the ASME Code,Section XI, Appendix IX are as follows:
Subparagraph IX-1000(c)(2) states, in part, "Clamping devices shall not be used on portions of a piping system that forms the containment boundary..."
Subparagraph IX-6000(a) states, in part, "Except as permitted by (b) below, or where precluded by the clamping device configuration, the area immediately adjacent to the clamping device shall be examined using a volumetric method..."
The licensee did not identify any conditions in 10 CFR 50.55a regarding Article IX-1000 of the ASME Code,Section XI, Appendix IX.
3.3 Licensees Proposed Alternative to the ASME Code The licensee proposed to repair the degraded socket weld following provisions of the ASME Code,Section XI, Paragraph IWA-4133 and Appendix IX, with two deviations. The licensee
proposed to deviate from the containment boundary restriction of Subparagraph IX-1000(c) and from the volumetric examinations of Subparagraph IX-6000(a) of Appendix IX.
3.4 Reason for Proposed Alternative On November 22, 2019, during a routine walkdown, the licensee identified a leak of six drops per minute from the insulation just upstream of valve 2-MS-377 which is part of the "C" main steam header, Penetration No. 074. The licensee confirmed a small through-wall pin hole leak with the sound of escaping steam. The location of the pin hole is on an elbow-to-pipe socket weld at approximately the one o'clock position. The licensee estimated that the pin hole diameter was about 1/32-inch or less and was likely caused by a fabrication welding defect (i.e.,
lack of fusion). The licensee stated that the 1/32-inch defect size bounds the limitations of the nondestructive examinations in accordance with Article IX-2000 of the ASME Code,Section XI, Appendix IX. The licensee performed ultrasonic testing of the pipe to obtain wall thickness readings on both sides of the 90-degree elbow next to the welds and extended the testing to areas where a proposed mechanical clamp could be installed. The wall thickness readings ranged from 0.170-inch to 0.186-inch. The licensee did not observe any other degradation, pipe movement or vibration of the affected piping besides the pin hole leak.
The 1-inch piping is located outside the reactor containment in the main steam valve house on the 27-foot elevation at 12 feet off the floor. The subject piping is the bypass line around valve 2-MS-158 which is the steam supply isolation valve associated with the turbine-driven auxiliary feedwater pump (TDAFWP) that takes steam from steam generator C. Valve 2-MS-377 is downstream of the degraded weld and is normally closed during power operations. The steam generator C steam supply line is one of three steam supply lines to the TDAFWP. The steam in the other two steam supply lines is supplied from steam generators A and B. The licensee performed an extent of condition evaluation of the other two steam supply lines through walkdowns. The licensee did not identify any other similar leaks in those two steam supply lines.
Subparagraph IX-1000(c) of the ASME Code,Section XI, Appendix IX prohibits the use of the clamping devices on portions of a piping system that forms the containment boundary. The subject piping is part of the containment boundary. The licensee stated that the steam supply lines to the TDAFWP are within the containment isolation boundary even though they are located outside of containment. The main steam system is considered a closed system (i.e., an extension of the primary containment) as described in the Surry, Units 1 and 2 Updated Final Safety Analysis Report (UFSAR). The licensee reviewed the environmental consequences in the accident analyses of the UFSAR Chapter 14 to assess the potential radiological impact of the pin hole leak. The licensee determined that the steam releases and associated dose consequences for the postulated main steam line break and the steam generator tube rupture (including releases from the TDAFWP exhaust) are of such an insignificant magnitude that the additional release from the pin hole steam leak on the 1-inch line for the duration of the event is negligible.
The ASME Code,Section XI requires a permanent repair of the pin hole leak in the subject piping. However, the licensee stated that it was not possible to perform the ASME Code repair when Surry, Unit 2 was in operation, and the piping leak is unisolable and subject to full steam generator pressure. The licensee explained that performing a permanent ASME Code repair would require the plant to shutdown. A plant shutdown and restart evolution require performing required inspections and Technical Specifications surveillances which would result in radiological dose to personnel. The licensee contended that this evolution would unnecessarily cycles plant systems and components and may result in plant transients. The licensee has
determined that performing a permanent ASME Code repair would results in a hardship without a compensating increase in the level of quality and safety.
- 3. 5 Licensees Basis for Use As a basis for its proposed alternative, the licensee proposed to use a mechanical clamping device to control the leak and ensure structural integrity of the degraded weld and subject piping such that the containment boundary is maintained. The licensee stated that the subject pipe is part of the closed system outside containment and is considered an extension of the containment boundary. The mechanical clamping device will be located on a 1-inch pipe outside containment, and the closed system will continue to provide a passive containment isolation barrier.
In accordance with the ASME Code,Section XI, Appendix IX, Subparagraph IX-1000(d), the licensee developed a repair/replacement plan in accordance with IWA-4150 and identified the defect characterization method, design requirements, and monitoring requirements. The licensee performed a system leakage test at normal operating temperature and pressure in accordance with the ASME Code,Section XI, IWA-5000 on the portion of the piping system containing the mechanical clamping device. The licensee stated that the leakage acceptance criterion for the installed clamping device, post-maintenance testing, is zero leakage. The licensee further stated that should leakage be identified during any of the daily inspections, it will prepare a Condition Report and evaluate the leak.
The licensee designed the mechanical clamping device to comply with the design and materials requirements of Articles IX-3000 and IX-4000 of Appendix IX, respectively. The licensee stated that these requirements meet or exceed the design rating of the piping. The clamp material is carbon steel (SA 516, Grade 70) and the clamp is suitable for the intended application and capable of performing its specified design functions. The licensee calculated pipe stresses using the loading and stress levels for design basis conditions in the original pipe configuration considering the weight of the installed clamp and a new temporary pipe support. According to the licensee, the clamp weighs approximately 60 pounds and is designed to provide more than adequate structural capacity to accommodate the postulated reaction forces in the event the 1-inch socket welded elbow completely separated from the pipe. The licensee evaluated the impact of the additional weight of the sealant and any supporting enclosures, frames, or structures on the ability of the piping system to withstand a seismic event. The licensee stated that the clamp provides more than adequate structural capacity to function as the structural element of the piping and will withstand all design basis loading conditions. The licensees calculation demonstrates that with the clamp and additional vertical pipe support installed, the piping system and pipe restraints remain within the limits of the design code, with margins consistent with those of the original pipe configuration.
The ASME Code,Section XI, Appendix IX, Subparagraph IX-6000(a) requires the area immediately adjacent to the clamping device be examined using a volumetric method every three months. However, Subparagraph IX-6000(a) allows an exception to performing volumetric examinations when the repaired pipe area is precluded by the clamping device. The licensee stated that the proposed clamping device will entirely encapsulate the piping section containing the flaw. This configuration will prevent access to perform the required periodic volumetric examinations of the piping immediately adjacent to the clamping device. The licensee stated that the clamping device is in an area that is readily accessible for visual inspection. As an alternative to the volumetric examinations, the licensee will visually monitor the clamping device for leakage once per day, which significantly exceeds the requirements of Subparagraph IX-6000(c) for weekly monitoring.
- 3. 6 Duration of the Alternative The licensee requested the approval of the proposed alternative until the next refueling outage, 2R29, currently scheduled for spring 2020. In accordance with the ASME Code,Section XI, Appendix IX, Subparagraph IX-1000(a), the licensee stated that the proposed clamping device will not remain in service beyond the next scheduled refueling outage, at which time the defect will be repaired, or the piping replaced.
- 3. 7 NRC Staff Evaluation of the Alternative The NRC staff focused its review on the clamp design and analysis, pipe stress analysis, flaw evaluation, deviations, and hardship justification as follows.
Clamp Design and Analysis The NRC staff finds that, in the clamp design and analysis, the licensee applied the loads from the pipe stress analysis to the clamp components such as cover plates, ears, and studs. The licensee considered the appropriate pipe loads in the clamp design such as thermal, deadweight and seismic. The licensee also considered the thrust force in case the elbow is separated from the pipe, buckling force of the pipe, and bending moments in the clamp design and analysis. The licensee has shown that the clamp components satisfy the allowable stresses in accordance with American National Standards Institute (ANSI)/USA Standard (USAS) B31.1-67, Power Piping. The NRC staff finds that the clamp device is designed to support design basis loading from the subject pipe. In addition, the licensee will inject sealant inside the clamping device to stop leakage. The NRC notes that the clamp is designed and assembled such that there will be no leakage from the degraded socket weld at the elbow.
Pipe Stress Analysis The licensee re-analyzed pipe stresses in accordance with ANSI/USAS B31.1-67 to demonstrate that the additional weight of the clamp will not affect the structural integrity of the subject pipe. The licensees re-analysis has shown that the stresses resulting from the applied loads on the subject pipe are within the allowable of ANSI/USAS B31.1-67. As a result of pipe stress re-analysis, the resultant loads (forces and moments) at some of the pipe restraint locations have changed. The licensee dispositioned differences in resultant loads on the existing pipe restraints between the original and revised pipe stress analyses to determine pipe restraints adequacy. The licensee has appropriately verified that the revised loads at the pipe restraints will not affect the ability of the pipe restraints to support the subject piping. The NRC staff finds that the licensee has appropriated re-analyzed the pipe stresses and verified the capability of the existing pipe restraints to maintain structural integrity of the subject piping.
As part of the temporary repair, the licensee installed a new pipe restraint at about 11.5 inches from the degraded socket weld to support the weight of the installed clamp device. The licensee designed and analyzed the new pipe restraint to ensure that the new pipe restraint components such as the base plate, the attachment fillet weld for the angle plate, and anchor bolts are capable of supporting the pipe loads. The NRC staff found that the stresses at the base plate are within the allowable, the length and size of the fillet weld are acceptable, and the stresses of the anchor bolts are within the allowable. Therefore, the NRC finds that the new pipe restraint is acceptable to support the subject piping.
Flaw Evaluation The licensee analyzed the flaw in the socket weld at the elbow to determine its impact on structural integrity of the subject pipe. The licensee conservatively assumed a 1/2 inch flaw in the socket weld even though the detected flaw is a 1/32-inch diameter pin hole. The licensees flaw evaluation considered all design basis loads including pressure thrust and seismic loads.
The licensee also used a conservative allowable stress. The licensees calculation has shown that the stresses from the pressure thrust and design basis loads on the degraded socket weld are below the allowable stress with sufficient safety margin. The NRC staff finds that the existing flaw in the socket weld of the subject pipe will not significantly affect structural integrity of the subject pipe.
Deviations The licensee requested to deviate from the ASME Code,Section XI, Appendix IX, Subparagraph IX-1000(c)(2). The NRC staff recognizes that the subject piping is part of the containment boundary and that Subparagraph IX-1000(c)(2) prohibits clamping devices to be used on a piping system that forms the containment boundary. However, based on the acceptable clamping design and no leakage is permitted per the proposed alternative, the NRC staff finds that this deviation is acceptable because the NRC staff finds that the clamp will provide reasonable assurance of structural integrity of the containment boundary.
The ASME Code,Section XI, Appendix IX, Subparagraph IX-6000(a) requires the area immediately adjacent to the clamping device be volumetrically examined not exceeding every three months. In lieu of this provision, the licensee proposed to perform daily walkdown of the subject pipe. The NRC staff determines that the proposed daily walkdown is acceptable as an alternative to the 3-month volumetric examination because the frequency of daily monitoring is more effective in monitoring structural integrity of the subject pipe than a 3-month volume examination or a weekly walkdown per Subparagraph IX-6000(c). Therefore, the NRC staff finds that this deviation is acceptable.
Hardship Assessment The NRC staff has determined that if the licensee were required to perform the permanent repair in accordance with the ASME Code,Section XI, IWA-4000, the licensee would have needed to shutdown the plant in mid-cycle. The mid-cycle shutdown would have caused unnecessary loadings on the plant systems and transients. Also, the ASME Code repair would likely have resulted in additional radiological dose on the plant personnel. The NRC staff finds that an ASME Code repair would not achieve a compensating increase in the level of quality and safety. Therefore, the NRC staff finds that the licensees hardship justification is acceptable.
4.0 CONCLUSION
The NRC staff concludes that the proposed alternative provides reasonable assurance of structural integrity and leak tightness of the subject piping and does not adversely affect the containment boundary. The NRC staff determines that complying with the ASME Code requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(2).
Therefore, the NRC authorizes the use of Alternative Request S2-I5-ISI-05 for Surry, Unit 2 until the end of the next refueling outage, 2R29, which is scheduled for spring 2020.
All other requirements of ASME Code,Section XI for which relief was not specifically requested and authorized by the NRC staff remain applicable, including the third-party review by the Authorized Nuclear In-service Inspector.
Principal Contributor: John Tsao, NRR/DNLR/NPHP Date of Issuance: May 12, 2020
- via email OFFICE NRR/DORL/LPL2-1/PM NRR/DORL/LPL2-1/LA NRR/DNRL/NPHP/BC*
NRR/DORL/LPL2-1/BC NAME VThomas KGoldsten MMitchel MMarkley DATE 04/22/2020 04/23/2020 04/17/2020 05/12/2020