ML12250A401
| ML12250A401 | |
| Person / Time | |
|---|---|
| Site: | Mcguire, McGuire  |
| Issue date: | 09/13/2012 |
| From: | Robert Pascarelli Plant Licensing Branch II |
| To: | Capps S Duke Energy Carolinas |
| Thompson J | |
| References | |
| TAC ME7268, TAC ME7269, TAC ME7270, TAC ME7271, TAC ME7272, TAC ME7273, TAC ME7274 | |
| Download: ML12250A401 (16) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 September 13, 2012 Mr. Steven D. Capps Vice President McGuire Nuclear Station Duke Energy Carolinas, LLC 12700 Hagers Ferry Road Huntersville, NC 28078
SUBJECT:
MCGUIRE NUCLEAR STATION, UNITS 1 AND 2, PROPOSED RELIEF REQUEST 11-MN-001 (TAC NOS. ME7268, ME7269, ME7270, ME7271, ME7272, ME7273, AND ME7274)
Dear Mr. Capps:
By letter dated September 21, 2011, as supplemented by letter dated June 4,2012, Duke Energy Carolinas, LLC (the licensee) submitted a request, RR 11-MN-001, to the Nuclear Regulatory Commission (NRC) for the use of alternatives to certain requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code),
Section XI, related to inservice inspection (lSI) of welds. RR 11-MN-001 was requested for the remainder of McGuire Nuclear Station, Units 1 and 2 (McGuire 1 and 2), third 10-year lSI interval. Pursuant to Title 10 of the Code of Federal Regulations (1 0 CFR), Part SO, Section SO.SSa(g)(S)(iii), the licensee requested to use alternatives on the basis that complying with the specified requirement is impractical.
The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that the proposed alternatives for weld lSI would provide reasonable assurance of leak-tightness and structural integrity of the piping and component segments identified in RR 11-MN-001, and that complying with the specified ASME Code,Section XI, requirements is impractical. Therefore, pursuant to 10 CFR SO.SSa{g){6){i), the NRC staff authorizes the licensee's proposed alternatives as described in RR 11-MN-001, Section 2.0, Section 4.0 and Section S.O, for the duration of the McGuire 1 third 1O-year lSI interval, which ended on December 1, 2011. The NRC staff also authorizes the licensee's proposed alternatives as described in RR 11-MN-001, Sections 6.0 through 12.0 for the duration of the McGuire 2 third 10-year lSI interval, currently scheduled to end on July 1S, 2014.
All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including the third party review by the Authorized Nuclear Inservice Inspector.
S. Capps - 2 If you have any questions, please contact the Project Manager, Jon H. Thompson at 301-415-1119 or via e-mail at jon.thompson@nrc.gov.
Sincerely,
~;{J~
Robert J. Pascarelli, Chief Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-369 and 50-370
Enclosure:
Safety Evaluation cc w/encl: Distribution via ListServ
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST NO. 11-MN-001 REGARDING ALTERNATIVE REQUIREMENTS FOR LIMITED WELD EXAMINATIONS DUKE ENERGY CAROLINAS, LLC MCGUIRE NUCLEAR STATION, UNITS 1 AND 2 DOCKET NOS. 50-369 AND 50-370
1.0 INTRODUCTION
By letter dated September 21,2011, (Agencywide Documents Access and Management System (ADAMS) at Accession No. ML11279A035), as supplemented by letter dated June 4, 2012 (ADAMS Accession No. ML12173A061), Duke Energy Carolinas, LLC. (Duke, the licensee) submitted relief request (RR) 11-MN-001 to the U.S. Nuclear Regulatory Commission (NRC) staff for review and approval. RR 11-MN-001 requested the use of alternatives to certain requirements of the American Society of Mechanical Engineers (ASME) Boifer and Pressure Vessel Code (Code), Section Xl. Specifically, the licensee has requested relief from ASME Code requirements pursuant to the regulation at Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.55a(g)(5)(iii). The RR requests relief for several welds where the licensee was not able to achieve essentially 100% inspection coverage due to limitations of design, geometry, and materials of construction of the components.
The ASME Code of record for the third 10-year interval inservice inspection (lSI) program for both McGuire 1 and 2 is the ASME Code,Section XI, 1998 Edition through the 2000 Addenda.
The third 10-year interval lSI for McGuire 1 ended on December 1, 2011. The third 10-year interval lSI for McGuire 2 is scheduled to end on July 15, 2014.
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) "must meet the requirements, except design and access provisions and preservice examination requirements, set forth in Section XI of editions and addenda of the ASME [Boiler and Pressure Vessel] B&PV Code .,. to the extent practical within the limitations of design, geometry, and materials of construction of the components."
Enclosure
-2 The regulation at 10 CFR SO.SSa(g}(S}(iii), states that "If the licensee has determined that conformance with a code requirement is impractical for its facility, the licensee shall notify the NRC and submit, as specified in 10 CFR SO.4, information to support the determinations.
Determinations of impracticality in accordance with this section must be based on the demonstrated limitations experienced when attempting to comply with the code requirements during the inservice inspection interval for which the request is being submitted. Requests for relief made in accordance with this section must be submitted to the NRC no later than 12 months after the expiration of the initial or subsequent 120-month inspection interval for which relief is sought."
The regulation at 10 CFR SO.SSa(g)(6)(i), states that "The Commission will evaluate determinations under paragraph (g)(S) of this section that code requirements are impractical.
The Commission may grant such relief and may impose such alternative requirements as it determines is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility."
3.0 TECHNICAL EVALUATION
3.1 Background By letter dated September 21, 2011, the licensee sent RR 11-MN-001, which included Sections 2.0 through 17.0, to the NRC staff for approval. By letter dated June 4,2012, the licensee determined that the welds described in Sections 3.0, 1S.0, 16.0, and 17.0 no longer required relief and requested that these welds be removed from the NRC staff evaluation of RR 11-MN-001. Therefore, the NRC staff is not evaluating or approving Sections 3.0, 1S.0, 16.0 and 17.0 of RR 11-MN-001 in this safety evaluation. In addition, Duke Energy did not include responses to the RAI questions from the NRC staff with respect to these sections.
The safety evaluation is structured so that for each applicable section of RR 11-MN-001 (sections sharing the same examination category were evaluated together), the following are described and/or evaluated: the ASME Code components, the ASME Code requirements, the licensee's proposed alternative and the licensee's basis for requesting relief, along with the NRC staff's evaluation of that section of RR 11-MN-001.
3.2 Sections 2.0 and 14.0 of RR 11-MN-001 ASME Code Components McGuire 1 Nozzle to Pipe Weld, Weld #1 NC1 F-3613-3092, Summary Number M1.R1.11.0390.
McGuire 2, Nozzle to Pipe Weld, Weld #2 NC2FW2-2, Summary Number M2.R1.11.1730.
- 3 ASME Code Requirement The licensee was granted permission to use a risk-informed lSI (RI-ISI) program for the third 10 -year lSI interval by the NRC staff in a letter dated June 12, 2002 (ADAMS Accession No. ML021480421). The RI-ISI program was developed in accordance with the Westinghouse Owners Group Topical Report WCAP-14572, Revision 1-NPA. The welds are assigned Examination Category R-A, Item R1.11, and are either subject to Thermal Fatigue/Stratification or defaulted to 'Thermal Fatigue" as the most likely degradation mechanism.
The ASME Code,Section XI, and the licensee's RI-ISI program require "essentia"y" 100%
volumetric examinations of the Category R-A, Item Number R1.11. ASME Code Case N-460, "Alternative Examination Coverage for Class 1 and Class 2 welds,Section XI, Division 1," is an alternative approved for use by the NRC staff in Regulatory Guide (RG) 1.147, Revision 16, "Inservice Inspection Code Case Acceptability," which states that a reduction in examination coverage due to part geometry or interference for any Class 1 and 2 weld is acceptable provided that the reduction is less than 10% (i.e., greater than 90% examination coverage is obtained).
Licensee's Proposed Alternatives (as stated)
No alternative examinations are planned for the weld during the current inspection interval. Radiography (RT) is not a desired option because RT is limited in the ability to detect expected degradation mechanisms such as thermal fatigue cracking and stress corrosion crack initiating at the pipe inside surface. Additiona"y, radiography has not been qualified through performance demonstration.
Licensee's basis for requesting relief The licensee has examined the welds to the maximum extent possible utilizing approved examination techniques and equipment. Ultrasonic examination of each of the welds was conducted using personnel, equipment, and procedures qualified in accordance with ASME Code Section XI, 1998 Edition, with the 2000 Addenda.
The system leakage tests were performed each refueling outage in accordance with Table IWB-2500-1; Examination Category B-P. Examination Category B-P requires a VT-2 visual examination to detect evidence of leakage.
In addition to the above ASME Code required examinations (volumetric and pressure test),
Reactor Building Normal Sump monitoring provided assurance that, in the event that leakage did occur through this weld, it would be detected and proper action taken.
NRC Staff Evaluation of the Proposed Alternative in RR 11-MN-001, Sections 2.0 and 14.0 Pressurizer Surge Line-to-Nozzle Welds, Weld #1 NC 1F-3613-3092 and Weld #2 NC2FW2-2, are both 14-inch diameter Class 1 stainless steel welds joining a stainless steel pressurizer surge line to the hot legs in McGuire 1 and 2. The ASME Code,Section XI and the licensee's
4 The RI-ISI program requires essentially 100% volumetric coverage of the welds. However, volumetric examinations are limited by the geometry of the welds and the associated piping configurations, which restrict scanning to one side only.
To gain access for examination, the welds and piping would require design modifications.
Imposition of this requirement would create a burden on the licensee.
The NRC staff has determined that the licensee was able to obtain coverage values of 62.5%
for Weld #1 NC1F-3613-3092 and 63.9% for Weld #2 NC2FW2-2. This coverage was obtained using 60° shear and longitudinal waves for the axial scans for circumferential flaws and 45° longitudinal and shear waves for the circumferential scans for axial flaws. The entire length of the weld was examined on one side of the pipe side for circumferential flaws and the entire weld width was scanned for axial flaws.
Although the essentially 100% ASME Code-required coverage could not be obtained, the UT techniques employed provided 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. The NRC staff has determined that there is no known operational experience showing cracking in similar stainless steel welds and the only form of cracking that is expected to occur is thermal fatigue. It is expected, given the location of these components, that thermal fatigue cracking would progress relatively slowly though the weld. Considering the coverage obtained, it is expected that axial cracking would likely be detected and circumferential cracking on the near side or initiating near the weld root should also be detected.
Based on the above evaluation, the NRC staff concludes that, if significant service-induced degradation had occurred, there is reasonable assurance that evidence of degradation would have been detected by the ultrasonic and visual examinations performed by the licensee within the examined area. Based on the above determinations, the NRC staff considers achieving 100% volumetric examination coverage to be impractical. The NRC staff, therefore, concludes that relief should be granted pursuant to 10 CFR 50.55a(g)(6)(i) for McGuire 1 Nozzle to Pipe Weld, Weld #1 NC1F 3613-3092, and McGuire 2 Nozzle to Pipe Weld, Weld #2 NC2FW2-2, as described in Sections 2.0 and 14.0, respectively, of RR 11-MN-001.
3.3 Sections 4.0 and 13.0 of RR 11-MN-001 ASME Code Components McGuire 1 Pipe to Valve Weld, Weld #1 NV1 FW53-27, Summary Number M1.R1.11.2170.
McGuire 2 Nozzle to Pipe Weld, Weld #2 NV2FW180-1, Summary Number M2.R1.11.1566.
ASME Code Requirement The licensee was granted permission to use an RI-ISI program for the third 1O-year lSI interval by the NRC staff in a letter dated June 12, 2002 (ADAMS Accession No. ML021480421). The RI-ISI program was developed in accordance with the Westinghouse Owners Group Topical
-5 Report WCAP-14572, Revision 1-NPA. The welds are assigned Examination Category R-A, Item R1.11, and are either subject to Thermal Fatigue/Stratification or defaulted to "Thermal Fatigue" as the most likely degradation mechanism.
The ASME Code,Section XI, and the licensee's RI-ISI program require "essentially" 100%
volumetric examinations of the Category R-A, Item Number R1.11. ASME Code Case N-460, "Alternative Examination Coverage for Class 1 and Class 2 Welds,Section XI, Division 1," is an alternative approved for use by the NRC in RG 1.147, Revision 16, "Inservice Inspection Code Case Acceptability," which states that a reduction in examination coverage due to part geometry or interference for any Class 1 and 2 weld is acceptable provided that the reduction is less than 10% (Le., greater than 90% examination coverage is obtained).
Licensee's Proposed Alternative (as stated)
No alternative examinations are planned for the weld during the current inspection interval. Radiography (RT) is not a desired option because RT is limited in the ability to detect expected degradation mechanisms such as thermal fatigue cracking and stress corrosion crack initiating at the pipe inside surface. Additionally, radiography has not been qualified through performance demonstration.
Licensee's basis for requesting relief The licensee has examined the welds to the maximum extent possible utilizing approved examination techniques and equipment. Ultrasonic examination of each of the welds was conducted using personnel, equipment, and procedures qualified in accordance with ASME Code Section XI, 1998 Edition with the 2000 Addenda.
The system leakage tests were performed each refueling outage in accordance with Table IWB-2500-1; Examination Category B-P. Examination Category B-P requires a VT-2 visual examination to detect evidence of leakage.
In addition to the above ASME Code required examinations (volumetric and pressure test),
Reactor Building Normal Sump monitoring provided assurance that, in the event that leakage did occur through this weld, it would be detected and proper action taken.
NRC Staff Evaluation of the Proposed Alternative in RR 11-MN-001! Sections 4.0 and 13.0 The welds described in RR 11-MN-001, Sections 4.0 and 13.0, are Chemical Volume and Control System Piping welds, Weld #1 NV1 FW53-27 and Weld #2 NV2FW180-1. These welds are 2-inch diameter Class 1 stainless steel welds in the chemical volume and control systems in McGuire 1 and 2.
ASME Code and the Licensee's RI-ISI program require essentially 100% volumetric coverage of the welds. The volumetric examinations were limited by the geometry of the welds and the associated piping configurations, which restricted scanning to one side only. To gain access for essentially 100% examination coverage, the welds and piping would require design modifications. Imposition of this requirement would create a burden on the licensee.
-6 The NRC staff has determined that the licensee was able to obtain coverage values of 37.50%
for Weld #1 NV1FW53-27 and 50% for Weld #2 NV2FW180-1. This coverage was obtained using 60° and 70° shear waves for the axial scans for circumferential flaws and 45° longitudinal and shear waves for the circumferential scans for axial flaws. The inspection coverage for Weld #1 NV1 FW53-27 was restricted by the weld geometry and the cast material of the valve.
The entire lengths of the welds were examined on the pipe sides for circumferential flaws and the half of the welds widths were scanned for axial flaws.
Although the essentially 100% ASME Code-required coverage could not be obtained, the UT techniques employed provided 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. The NRC staff has determined that there is no known operational experience showing cracking in similar stainless steel welds, and the only form of cracking that is expected to occur is thermal fatigue. It is expected, given the location of these components, that thermal fatigue cracking would progress relatively slowly though the weld. Considering the coverage obtained, one would expect that axial cracking would likely be detected and circumferential cracking on the near side or initiating near the weld root should also be detected.
Based on the above evaluation, the NRC staff concludes that the examinations performed provide reasonable assurance of structural integrity of the subject components. Therefore, considering the burden on the licensee, the NRC staff considers that the ASME Code-required essentially 100% volumetric examination from both sides of Weld #1 NV1 FW53-27 and Weld #2 NV2FW180-1 is impractical. The NRC staff, therefore, concludes that relief should be granted pursuant to 10 CFR 50.55a(g)(6)(i) for-McGuire 1, Pipe to Valve Weld, Weld #1 NV1 FW53-27, and McGuire 2, Nozzle to Pipe Weld, Weld #2 NV2FW180-1, as described in Sections 4.0 and 13.0, respectively, of RR 11-MN-001.
3.4 Section 5.0 of RR 11-MN-001 ASME Code Component McGuire 1 Heat Exchanger Tubesheet to Shell Weld, Weld #1 BCSHX-SH-48, Summary Number M1.C1.30.0005.
ASME Code Requirement The ASME Code,Section XI, Table IWC-2500-1, Examination Category C-A, Item No. C1.30, Fig. IWC-2500-2, 100% Volume Coverage of Examination Volume E-F-G-H.
Licensee's Proposed Alternative Examination The licensee stated that no viable alternatives exist to credibly increase the coverage; specifically that the use of RT is impractical due to a lack of access for film placement. As an alternative, the licensee proposes to accept the performed examinations as sufficient.
The licensee further stated that the examination as performed achieved coverage of 44.29%.
-7 Licensee's Basis for Requesting Relief The licensee stated that the design configuration of the subject weld precludes 100%
examination due to obstruction by attached permanent hanger supports. Achieving 100%
coverage would require a substantial redesign of the heat exchanger. The licensee continued with a discussion that leakage from this weld would be detected by periodic system leakage tests, visual observations, and general leakage monitoring.
NRC Staff Evaluation of the Proposed Alternative in RR 11-MN-001! Section 5.0 The ASME Code requirement for the subject weld requires an examination of "essentially 100%
of the weld length" as illustrated in Figure IWC-2500-2 of ASME Code,Section XI. The licensee achieved an aggregate coverage of 44.29%. The licensee provided a diagram in the submittal clarifying the weld design as well as a full limitation report. The examined weld length included the full through-thickness weld volume, however, obstructions limited the amount of examinable weld-length.
The licensee stated that attached permanent hanger supports obstructed the examination; citing eight separate permanent supports obstructing a total of 97.5 inches of weld length.
Redesigning the supports to increase coverage would be highly impractical. Alternative examination techniques would be unlikely to increase surety of the weld condition.
The NRC staff requested that the licensee report examination experience with similar welds in the context of Section 9.0 of RR 11-MN-001. The licensee reported in their RAI response sent by letter dated June 4, 2012, that this McGuire 1 weld was similar to the McGuire 2 Weld #2 ACSHX-SH-48. This examination was more limited, with coverage of only 23.4%. The greater coverage for the McGuire 1 weld was due to a difference in support design, with eight smaller supports allowing greater coverage than the four large supports near Weld #2 ACSHX-SH-48. The licensee further reported that no recordable indications have been found in either weld, no repairs or replacements have been conducted, and that additional opportunities to identify degradation exist through leak-tests and VT-2 examinations existed.
The NRC staff concludes that if significant service-induced degradation had occurred, then there is reasonable assurance that evidence of degradation would have been detected by the ultrasonic and visual examinations performed by the licensee within the examined area. Based on the above determinations, the NRC staff considers achieving 100% coverage to be impractical. The NRC staff, therefore, concludes that, pursuant to 10 CFR 50.55a(g){6){i), relief should be granted for McGuire 1 Heat Exchanger Tubesheet to Shell Weld, Weld #1 BCSHX-SH-48, as described in Section 5.0 in RR 11-MN-001.
3.5 Sections 6.0,7.0, and 8.0 of RR 11-MN-001 ASME Code Components McGuire 2 Pressurizer Safety/Relief Nozzle to Upper Head Weld, Weld #2 PZR-13, Summary Number M2.B3.110.0003.
- 8 McGuire 2 Pressurizer Safety/Relief Nozzle to Upper Head Weld, Weld #2 PZR-14, Summary Number M2.B3.11 0.0004.
McGuire 2, Pressurizer Safety/Relief Nozzle to Upper Head Weld, Weld #2 PZR-15, Summary Number M2.B3.1110.0005.
ASME Code Requirement The ASME Code,Section XI, Table IWB-2500-1, Item No. B3.11 0, component examinations require a volumetric examination of the pressurizer nozzle-to-vessel welds. The extent of the examination is illustrated in Figure IWB-2500-7(a). ASME Code Case N-460 effectively states that 90% coverage is adequate to meet the ASME Code requirement.
Licensee's Proposed Alternative Examination The licensee stated that no viable alternatives exist to credibly increase the coverage; specifically that the use of RT is impractical due to a lack of access for film placement. As an alternative, the licensee proposes to accept the performed examinations as sufficient.
The licensee further stated that the examination as performed achieved coverage of 78.7%.
Licensee's Basis for Requesting Relief The licensee stated that the design configuration of the subject welds precludes 100%
examination due to the weld taper configuration. Achieving 100% coverage would require a substantial redesign of the welds. The licensee continued with a discussion that leakage from these welds would be detected by periodic system leakage tests, and Reactor Building Normal Sump monitoring.
NRC Staff Evaluation of the Proposed Alternative in RR 11-MN-001, Sections 6.0.7.0 and 8.0 The ASME Code requirement for the subject welds requires an examination of "essentially 100%" of the volume illustrated in Figure IWB-2500-7(a) of ASME Code,Section XI.
The licensee achieved an aggregate coverage of 78.7%. This is not unusual for pressurizer nozzle-to-vessel welds in plant designs such as McGuire 2. The licensee documented the examinations in several diagrams provided in the submittal, clearly marking the examined volumes. Most of the weld volumes were scanned at several angles in both the axial and circumferential scans.
The licensee cited the weld taper as limiting the examination volume. Redesigning the subject welds to increase coverage would be highly impractical. Alternative examination techniques would be unlikely to increase surety of the weld condition.
The NRC staff concludes that, if significant service-induced degradation had occurred, there is reasonable assurance that evidence of degradation would have been detected by the ultrasonic and visual examinations performed by the licensee within the examined areas. Based on the above determinations, the NRC staff considers achieving 100% coverage to be impractical. The
-9 NRC staff, therefore, concludes that pursuant to 10 CFR SO.SSa(g)(6)(i), relief should be granted for McGuire 2 Pressurizer Safety/Relief Nozzle to Upper Head Welds, Weld #2 PZR-13, Weld #2 PZR-14, and Weld #2 PZR-1S, as described in Sections 6.0,7.0, and 8.0, respectively, of RR 11-MN-001.
3.6 Section 9.0 of RR 11-MN-001 ASME Code Components McGuire 2, Exchanger Shell to Tubesheet Weld, Weld #2 ACSHX-SH-48, Summary Number M2.C1.30.0006.
ASME Code Requirement The ASME Code,Section XI, Table IWC-2S00-1, Item No. C1.30 component examinations require a volumetric examination of the tubesheet-to-shell welds. The extent of the examination is "essentially 100% of the weld length," specifically the volume illustrated in Figure IWC-2S00-2.
ASME Code Case N-460 effectively states that 90% coverage is adequate to meet the ASME Code requirement.
Licensee's Proposed Alternative Examination The licensee stated that no viable alternatives exist to credibly increase the coverage; specifically that the use of RT is impractical due to a lack of access for film placement. As an alternative, the licensee proposes to accept the performed examinations as sufficient.
The licensee further stated that the examination as performed achieved 23.4% coverage.
Licensee's Basis for Requesting Relief The licensee stated that the design configuration of the subject weld precludes 100%
examination due to obstruction by welded supports. Achieving 100% coverage would require the welded supports to be removed. The licensee continued with a discussion that leakage from this weld would be detected by periodic leakage tests and visual observations.
NRC Staff Evaluation of the Proposed Alternative in RR 11-MN-001. Section 9.0 The ASME Code requirement for the subject weld requires an examination of "essentially 100%
of the weld length" as illustrated in Figure IWC-2S00-2 of ASME Code,Section XI. The licensee achieved an aggregate coverage of 23.4%. The licensee documented the examination in diagrams provided in the submittal, illustrating the examined volume.
The licensee cited that welded supports obstructed most of the weld length, specifically the obstruction of 123.S inches of weld length due to four permanent welded supports. Redesigning the subject weld and welded supports to increase coverage would be highly impractical.
Alternative examination techniques would be unlikely to increase surety of the weld condition.
- 10 The NRC staff requested that the licensee report examination experience with similar welds.
The licensee reported in their RAI response sent by letter dated June 4,2012, that while McGuire 2 had no similar welds, McGuire 1 had two similar welds, only one of which is required to be examined. This examination was similarly limited, with coverage of only 22% during the previous interval and coverage of 44.3% during the interval of interest (this weld was submitted for relief in Section 5.0 of RR 11-MN-001). The greater coverage for the McGuire 1 weld was due to a difference in support design, with eight smaller supports allowing greater coverage than the four large supports near Weld #2 ACSHX-SH-48.
In addition, the NRC staff requested that the licensee discuss the operating experience regarding these welds as well as the likely consequence of failure in this weld. The licensee reported in their RAI response sent by letter dated June 4,2012, that no unacceptable indications have been detected in this weld, that no repair activities have been performed in this weld or the other two similar welds. The licensee stated that any failure in this weld would result in detectable leakage followed by the corresponding leg of the Containment Spray System being isolated and declared inoperable. The licensee would then have 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to restore the system to operability before having to bring the unit to Mode 3 within a further six hours. The NRC staff considered this to be adequate.
The NRC staff concludes that, if significant service-induced degradation had occurred, there is reasonable assurance that evidence of degradation would have been detected by the ultrasonic and visual examinations performed by the licensee within the examined area, or should the weld begin leaking, the leakage would be detected and proper compensatory action be taken to (a) repair or restore the system, or (b) bring the plant to Mode 3. Based on the above determinations, the NRC staff considers achieving 100% coverage to be impractical. The NRC staff therefore concludes that relief should be granted pursuant to 10 CFR 50.55a(g)(6)(i) for McGuire 2, Exchanger Shell to Tubesheet Weld, Weld #2 ACSHX-SH-48, as described in Section 9.0 of RR 11-MN-001.
3.7 Section 10.0,11.0, and 12.00fRR 11-MN-001 ASME Code Components McGuire 2, Nozzle to Pipe Weld, Weld #2 NC2FW39-1, Summary Number M2.R1.11.0048.
McGuire 2, Nozzle to Pipe Weld, Weld #2 NC2FW40-1 1, Summary Number M2.R1.11.0049.
McGuire 2, Nozzle to Pipe Weld, Weld #2 NC2FW43-1, Summary Number M2.R1.11.0050.
ASME Code Requirement The licensee was granted permission to use an RI-ISI program for the third 10-year lSI interval by the NRC staff in a letter dated June 12, 2002 (ADAMS Accession No. ML021480421). The RI-ISI program was developed in accordance with the Westinghouse Owners Group Topical
- 11 Report WCAP-14572, Revision 1-NPA. The welds are assigned Examination Category R-A, Item R1.11, and are either subject to Thermal Fatigue/Stratification or defaulted to "Thermal Fatigue" as the most likely degradation mechanism.
The ASME Code,Section XI, and the licensee's RI-ISI program require "essentially" 100%
volumetric examinations of the Category R-A, Item Number R1.11. ASME Code Case N-460, "Alternative Examination Coverage for Class 1 and Class 2 welds,Section XI, Division 1," is an alternative approved for use by the NRC in RG 1.147, Revision 16, "Inservice Inspection Code Case Acceptability," which states that a reduction in examination coverage due to part geometry or interference for any Class 1 and 2 weld is acceptable provided that the reduction is less than 10% (i.e., greater than 90% examination coverage is obtained).
Licensee's Proposed Alternatives (as stated)
No alternative examinations are planned for the weld during the current inspection interval. Radiography (RT) is not a desired option because RT is limited in the ability to detect expected degradation mechanisms such as thermal fatigue cracking and stress corrosion crack initiating at the pipe inside surface. Additionally, radiography has not been qualified through performance demonstration.
Licensee's basis for requesting relief The licensee has examined the welds to the maximum extent possible utilizing approved examination techniques and equipment. Ultrasonic examination of each of the welds was conducted using personnel, equipment, and procedures qualified in accordance with ASME Code Section XI, 1998 Edition, with the 2000 Addenda.
The system leakage tests were performed each refueling outage in accordance with Table IWB 2500-1; Examination Category B-P. Examination Category B-P requires a VT-2 visual examination to detect evidence of leakage.
In addition to the above ASME Code required examinations (volumetric and pressure test),
Reactor Building Normal Sump monitoring provided assurance that, in the event that leakage did occur through this weld, it would be detected and proper action taken.
NRC Staff Evaluation of the Proposed Alternative in RR 11-MN-001, Sections 10.0, 11.0 and 12.0 The safety injection to cold leg nozzle welds described in these sections are 1.5-inch diameter stainless steel welds joining the safety injection line with the cold leg via a nozzle in the McGuire 2. The ASME Code and the licensee's RI-ISI program require essentially 100%
volumetric coverage of the welds. The volumetric examinations must be applied from both sides of the weld to maximize coverage. However, volumetric examinations are limited by the geometry of the welds and the associated piping configurations, which restrict scanning to one side only. To gain access for examination, the welds and piping would require design modifications. Imposition of this requirement would create a burden on the licensee.
- 12 The NRC staff has determined that the licensee was able to obtain coverage values of 26.3S%
for Weld #2 NC2FW39-1, and 37.S% for Weld #2 NC2FW40-11 and Weld #2 NC2FW43-1. This coverage was obtained using 4So and 70° shear waves for the axial scans for circumferential flaws and 38° longitudinal and shear waves for the circumferential scans for axial flaws. The entire lengths of Weld #2 NC2FW40-11 and Weld #2 NC2FW43-1 were examined on the pipe sides for circumferential flaws and the half of the welds widths were scanned for axial flaws.
The NRC staff has determined that Weld #2 NC2FW39-1 has SO% coverage for circumferential flaws from the pipe side of the weld and very little coverage for axial flaws. This lack of coverage for axial flaws means that the only method of detecting axial cracking is by leakage monitoring and visual testing for leakage. The safety significance of the low coverage for axial flaws is mitigated by the fact that axial cracks would almost certainly cause detectable leakage prior to the weld failing and that leakage from an axial crack would not prevent the safety injection system from functioning.
Although the essentially 100% ASME Code-required coverage could not be obtained, the UT techniques employed would have provided 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. There is no known operational experience showing cracking in similar stainless steel welds, and the only form of cracking that is expected to occur is thermal fatigue.
It is expected, given the location of these components, that thermal fatigue cracking would progress relatively slowly through the welds. Considering the coverage obtained, one would expect that axial cracking would likely be detected for Weld #2 NC2FW40-11 and Weld #2 NC2FW43-1 and circumferential cracking on the near side or initiating near the weld roots should also be detected for all welds.
Based on the above evaluation, the NRC staff concludes that the examinations performed provide reasonable assurance of structural integrity of the subject components. Therefore, considering the burden on the licensee, the NRC staff considers that the ASME Code-required essentially 100% volumetric examination from both sides of Weld #2 NC2FW39-1, Weld #2 NC2FW40-11, and Weld #2 NC2FW43-1 is impractical. The NRC staff, therefore, concludes that relief should be granted pursuant to 10 CFR SO.SSa(g)(6)(i) for McGuire 2 Nozzle to Pipe Welds, Weld #2 NC2FW39-1, Weld #2 NC2FW40-11, and Weld #2 NC2FW43-1, as described in Sections 10.0, 11.0, and 12.0, respectively, of RR 11-MN-001.
4.0 CONCLUSION
As set forth above, the NRC staff determines that granting the relief requested in RR 11-MN-001 pursuant to 10 CFR SO.SSa(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 giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR SO.SSa(g)(6)(i), and is in compliance with the ASME Code's requirements. Therefore, the NRC staff authorizes the licensee's proposed alternatives as described in RR 11-MN-001, Section 2.0, Section 4.0 and Section S.O, for the duration of the McGuire 1 third 1O-year lSI interval, which ended on December 1, 2011. The NRC staff also
- 13 authorizes the licensee's proposed alternatives as described in RR 11-MN-001, Sections 6.0 through 12.0 for the duration of the McGuire 2 third 10-year lSI interval, currently scheduled to end on July 15, 2014.
All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including the third party review by the Authorized Nuclear In-service Inspector.
Principal Contributors: D.. Widrevitz, NRR S. Cumblidge, NRR Date: September 13,2012
S. Capps - 2 If you have any questions, please contact the Project Manager, Jon H. Thompson at 301-415-1119 orvia e~mail at jon.thompson@nrc.gov.
Sincerely, IRA!
Robert J. Pascarelli, Chief Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-369 and 50-370
Enclosure:
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