ML16343A220
| ML16343A220 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 12/27/2016 |
| From: | Jeanne Johnston Plant Licensing Branch II |
| To: | Hamilton T Duke Energy Progress |
| Barillas Martha | |
| References | |
| CAC MF8487 | |
| Download: ML16343A220 (16) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 December 27, 2016 Ms. Tanya Hamilton Site Vice President Duke Energy Progress, LLC Shearon Harris Nuclear Power Plant 5413 Shearon Harris Rd.
M/C HNP01 New Hill, NC 27562-0165
SUBJECT:
SHEARON HARRIS NUCLEAR POWER PLANT, UNIT 1 RELIEF REQUEST 13R-16 FOR REACTOR VESSEL CLOSURE HEAD PENETRATION NOZZLE REPAIR TECHNIQUE, INSERVICE INSPECTION PROGRAM - THIRD 10-YEAR INTERVAL (CAC NO. MF8487)
Dear Ms. Hamilton:
By letter dated October 19, 2016 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML16294A218), as supplemented by letters dated October 21 and 24, 2016 (ADAMS Accession Nos. ML16295A159 and ML16298A133, respectively), Duke Energy Progress, LLC (the licensee) requested relief from certain requirements of Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) for the repair of degraded reactor vessel closure head (RVCH) penetrations at the Shearon Harris Nuclear Power Plant, Unit 1.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR)
Section 50.55a(z)(1 ), the licensee submitted Relief Request 13R-16 for the repair of degraded RVCH penetration nozzle numbers 30, 40, and 51 on the basis that the alternative provides an acceptable level of quality and safety. The licensee proposed to use the inside diameter temper bead welding method to repair the subject RVCH penetration nozzles.
The U.S. Nuclear Regulatory Commission (NRC) staff reviewed the subject request and concludes, as set forth in the enclosed safety evaluation (SE) that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(1 ). The NRC staff verbally authorized the use of RR 13R-16 for RVCH penetration nozzle numbers 30, 40, and 51 for the remaining period of the third 10-year inservice inspection interval, which ends on May 1, 2017, because the NRC staff determined that the proposed alternative is technically justified and provides an acceptable level of quality and safety. The script for the verbal authorization was issued on October 27, 2016 (ADAMS Accession No. ML16300A180). The enclosed SE documents the NRC staffs detailed technical basis for the verbal authorization.
All other requirements of ASME Code,Section XI, and 10 CFR 50.55a(g)(6)(ii)(D) for which relief was not specifically requested and authorized by the NRC staff remain applicable, including third-party review by the Authorized Nuclear lnservice Inspector.
T. Hamilton If you have any questions, please contact the Project Manager, Martha Barillas at 301-415-2760 or Martha.Barillas@nrc.gov.
Sincerely, c~e-Chief Plant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-400
Enclosure:
Safety Evaluation cc w/enclosure: Distribution via ListServ
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST 13R-16: ALTERNATIVE REPAIR OF REACTOR VESSEL CLOSURE HEAD PENETRATION NOZZLES DUKE ENERGY PROGRESS, LLC SHEARON HARRIS NUCLEAR POWER PLANT, UNIT 1 DOCKET NO. 50-400
1.0 INTRODUCTION
By letter dated October 19, 2016 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML16294A218), as supplemented by letters dated October 21 and 24, 2016 (ADAMS Accession Nos. ML16295A159 and ML16298A133, respectively), Duke Energy Progress, LLC (the licensee), requested relief from certain requirements of Section XI of the American Society of Mechanical Engi.neers Boiler and Pressure Vessel Code (ASME Code) for the repair of degraded reactor vessel closure head (RVCH) penetrations at the Shearon Harris Nuclear Power Plant, Unit 1.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR)
Section 50.55a(z)(1), the licensee submitted Relief Request 13R-16 for the repair of degraded RVCH penetration nozzle numbers 30, 40, and 51 on the basis that the alternative provides an acceptable level of quality and safety. The licensee proposed to use the inside diameter temper bead (IDTB) welding method to repair the subject RVCH penetration nozzles.
On October 27, 2016 (ADAMS Accession No. ML16300A180), the U.S. Nuclear Regulatory Commission (NRC) verbally authorized the use of Relief Request 13R-16 for RVCH penetration nozzle numbers 30, 40, and 51 at Shearon Harris Nuclear Power Plant, Unit 1, for the remaining period of the third 10-year inservice inspection (ISi) interval, which ends on May 1, 2017, because the NRC staff determined that the proposed alternative is technically justified and provides an acceptable level of quality and safety. This safety evaluation documents the technical basis for the NRC's verbal authorization.
2.0 REGULATORY EVALUATION
Adherence to Section XI of the ASME Code is mandated by 10 CFR 50.55a(g)(4), which states, in part, that ASME Code Class 1, 2, and 3 components will meet the requirements, except the design and access provisions and the pre-service examination requirements, set forth in the ASME Code,Section XI.
Enclosure
Pursuant to 10 CFR 50.55a(g)(6)(ii), the NRC may require the licensee to follow an augmented ISi program for systems and components for which the NRC deems that added assurance of structural reliability is necessary.
As stated in 10 CFR 50.55a(g)(6)(ii)(D), Augmented IS/ Requirements: Reactor vessel head inspections, licensees of pressurized-water reactors (PWRs) are required to augment their ISi of the RVCH nozzle penetrations with ASME Code Case N-729-1, "Alternative Examination Requirements for PWR [Pressurized Water Reactor] Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration Welds,Section XI, Division 1," with conditions.
ASME Code Case N-638-1, "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW [Gas Tungsten Arc Welding] Temper Bead Technique,Section XI, Division 1,"
provides requirements for automatic or machine GTAW of Class 1 components without the use of preheat or post-weld heat treatment.
As stated, in part, in 10 CFR 50.55a(z), alternatives to the requirements of paragraph (g) of 10 CFR 50.55a may be used, when authorized by the NRC, if the licensee demonstrates that:
(1) the proposed alternative provides an acceptable level of quality and safety, or (2) compliance with the specified requirements 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 and the NRC to authorize the alternative requested by the licensee.
3.0 TECHNICAL EVALUATION
3.1 Relief Request 13R-16 3.1.1 ASME Code Components Affected The affected components are ASME Class 1, RVCH penetration nozzle numbers 30, 40, and 51, which are made of nickel-based lnconel SB-167 (Alloy 600) with a nominal outside diameter (OD) of 4 inches.
3.1.2 Applicable Code Edition and Addenda The Code of record for the third 10-year ISi interval is the ASME Code,Section XI, 2001 Edition through 2003 Addenda. The Construction Code for the RVCH is the 1971 Edition through winter 1971 Addenda of the ASME Code, Section Ill.
3.1.3 Applicable Code Requirements Th.e ASME Code,Section XI, IWA-4221 (b) states, in part, "An item to be used for repair/replacement activities shall meet the Construction Code .... "
IWA-4221(c) states, in part, "As an alternative to [IWA-4221(b)] above, the item may meet all or portions of the requirements of different Editions and Addenda of the Construction Code, or Section 111. .. provided the requirements of IWA-4222 through IWA-4226, as applicable, are met."
IWA-4400 provides welding, brazing, metal removal, and installation requirements related to repair/replacement activities.
IWA-4411 states, in part, "Welding, brazing, and installation shall be performed in accordance with the Owner's Requirements and, except as modified below, in accordance with the Construction Code of the item."
IWA-4411 (a) states, in part, "Later editions and addenda of the Construction Code, or a later different Construction Code, either in its entirety or portions thereof, and Code Cases may be used, provided the substitution is as listed in IWA-4221 (c)."
IWA-461 O(a) states, in part, "Thermocouples and recording instruments shall be used to monitor the process temperatures."
IWA-4611.1 (a) states, "Defects shall be removed in accordance with IWA-4422.1. A defect is considered removed when it has been reduced to an acceptable size."
IWA-3300 specifies requirements for characterization of flaws detected by inservice examination.
IWB-3420 states, "Each detected flaw or group of flaws shall be characterized by the rules of IWA-3300 to establish the dimensions of the flaws. These dimensions shall be used in conjunction with the acceptance standards of IWB-3500."
IWB-3132.3 states, "A component whose volumetric or surface examination detects flaws that exceed the acceptance standards of Table IWB-3410-1 is acceptable for continued service without a repair/replacement activity if an analytical evaluation, as described in IWB-3600, meets the acceptance criteria of IWB-3600. The area containing the flaw shall be subsequently reexamined in accordance with IWB-2420 (b) and (c)."
ASME Code Case N-638-1 provides requirements for automatic or machine GTAW of Class 1 components without the use of preheat or post-weld heat treatment.
ASME Code Case N-638-1 paragraph 3.0(d) states, The maximum interpass temperature for field applications shall be 350°F [degrees Fahrenheit] regardless of the interpass temperature during qualification."
ASME Code Case N-638-1 paragraph 4.0(b) states, "The final weld surface and the band around the area defined in para. 1.0(d) shall be examined using a surface and ultrasonic methods when the completed weld has been at ambient temperature for at least 48 hours2 days <br />0.286 weeks <br />0.0658 months <br />. The ultrasonic examination shall be in accordance with Appendix I."
ASME Code Case N-729-1, Fig. 2, "Examination Volume for Nozzle Base Metal and Examination Area for Weld and Nozzle Base Metal," is applicable to the subject RVCH penetration nozzles.
3.1.4 Reason for Request During the 2016 refueling outage, the licensee detected indications on RVCH penetration nozzle numbers 30, 40, and 51. The indications are located in the tube OD surface extending inward toward the tube inside diameter (ID) and are axially oriented at the lower toe side of the J-groove weld. The licensee proposed to repair these three nozzles using the subject relief request.
The licensee stated that the repair technique is intended to be the same as was used previously for RVCH penetration nozzle numbers 5, 14, 17, 18, 23, 37, 38, 49, and 63, which is sometimes referred to as a half-nozzle repair. The half-nozzle repair involves machining away the lower section of the nozzle containing the flaw, then welding the remaining portion of the nozzle to the RVCH to form the new pressure boundary.
The licensee stated that because of the risk of damage to the RVCH material properties or dimensions, it is not feasible to apply the post-welding heat treatment requirements of the original Construction Code to the RVCH. As an alternative to the requirements of the RVCH Construction Code, the licensee proposed to repair the RVCH penetration nozzles using the IDTB welding method to restore the pressure boundary of the degraded nozzles. The IDTB welding method is performed with a remotely operated weld tool, using the machine GTAW process and the ambient temperature temper bead method with 50 °F minimum preheat temperature and no post-weld heat treatment.
3.1.5 Proposed Alternative The licensee proposed to deviate from certain requirements of the ASME Code, Sections Ill and XI, Code Case N-638-1, and Code Case N-729-1 in the repair of subject RVCH penetration nozzles. The repair is summarized as follows:
- 1. Remove lower portion of existing thermal sleeve assembly, if present, to provide access for the repair.
- 2. Roll expand the nozzle inside the RVCH penetration bore above the area of repair. This stabilizes the nozzle to prevent any movement when the nozzle is separated from the J-groove weld.
- 3. Remove the nozzle to above the J-groove weld by machining. The machining operation eliminates the portions of the nozzle containing the unacceptable indication and establishes the weld preparation area.
- 4. Examine the machined area by liquid penetrant testing (PT).
- 5. Weld the remnant nozzle to the RVCH using primary water stress-corrosion cracking (PWSCC) resistant Alloy 52M weld material. Alloy 82 weld material may be used at the interface between the existing Alloy 182 weld and the new Alloy 52M weld if necessary.
- 6. Machine the new attachment weld and remnant nozzle to provide a surface suitable for nondestructive examination (NOE).
3.1.6 Basis for Use Repair Welding ASME Code Case N-638-1 paragraph 3.0(d) states, in part, "The maximum interpass temperature for field applications shall be 350°F regardless of the interpass temperature during qualification ... " The Reply section of ASME Code Case N-638-1 states that all other requirements of the ASME Code,Section XI, IWA-4000, must be met. Subarticle IWA-461 O(a) requires that thermocouples and recording instruments be used to monitor process temperatures. The licensee requested relief from using thermocouples and recording instruments to verify process temperatures because direct interpass temperature measurement is impractical during welding operations from inside the RVCH penetration nozzle bore. In lieu of direct temperature measurement, the licensee proposed to use heat flow calculations to determine a maximum anticipated interpass temperature to ensure that interpass temperature limits are not exceeded.
Acceptance Examination ASME Code Case N-638-1 paragraph 4.0(b) states, in part, "The final weld surface and the band around the area defined in paragraph 1.0(d) shall be examined using a surface and ultrasonic methods ... " ASME Code Case N-638-1 paragraph 1.0(d) defines the area requiring preheat and examination as the area to be welded and the band around the area of at least 1.5 times the component thickness or 5 inches, whichever is less. The licensee stated that the band around the area defined in paragraph 1.0(d) cannot be examined due to the physical configuration of the J-groove weld. In lieu of the requirement, the licensee will perform UT and PT of the new attachment weld and immediate surrounding area within the RVCH bore. The licensee stated that this will be sufficient to verify that defects have not been induced in the RVCH material caused by the welding process and will assure integrity of the remnant nozzle and the new weld. The licensee will perform UT examination by scanning from the inner diameter surface of the nozzle. The licensee noted that the UT examination is qualified to detect construction type flaws in the new weld and base metal interface beneath the new weld.
The licensee clarified that UT examination acceptance criteria will follow NB-5330 of the ASME Code, Section Ill.
ASME Code Case N-638-1, paragraph 4.0(b) requires that the UT examination of the final weld surface and the band around the welded area be performed in accordance with the ASME Code,Section XI, Appendix I. Paragraph 4.0(e) requires the use of acceptance criteria for the UT examination in accordance with the ASME Code,Section XI, IWB-3000. The licensee stated that IWB-3000 does not have any acceptance criteria that directly apply to the J-groove weld configuration. However, the licensee stated that it will follow the acceptance criteria of the ASME Code, Section Ill, NB-5330, for all flaws identified within the repaired volume. In addition, the licensee will follow the condition imposed on ASME Code Case N-638-1 in Regulatory Guide (RG) 1.147, Revision 15, "lnservice Inspection Code Case Acceptability, ASME Section XI, Division 1," October 2007 (ADAMS Accession No. ML072070419), which requires that UT examinations be performed with personnel and procedures qualified for the repaired volume and qualified by demonstration using representative samples which contain construction type flaws.
The ASME Code, Section Ill, NB-5245, requires incremental and final surface examination of partial penetration welds. The licensee stated that due to the welding layer deposition sequence (i.e., each layer is deposited parallel to the penetration nozzle centerline), it cannot meet the required incremental surface examinations of NB-5245. In lieu of incremental surface examinations, the licensee will perform UT and PT of the final surface of the attachment weld.
ASME Code Case N-638-1 paragraph 4.0(b) states, in part, that the final weld surface and the surrounding area be examined using a surface and ultrasonic method when the completed weld is cooled to ambient temperature for at least 48 hours2 days <br />0.286 weeks <br />0.0658 months <br />. In lieu of the weld cooling to ambient temperature, the licensee proposed that the 48-hour hold period be commenced upon completion of the third weld layer rather than at ambient temperature.
Preservice and lnservice Inspections The licensee stated that the preservice inspection following repair and future ISls will comply with ASME Code Case N-729-1 as conditioned by 10 CFR 50.55a(g)(6)(ii)(D) and as depicted in Figure 9 of the relief request.
Analyses Triple Point Anomaly The ASME Code, Section Ill, NB-5330(b) states, in part, "Indications characterized as cracks, lack of fusion, or incomplete penetrations are unacceptable regardless of length .... " The licensee stated that an artifact of ambient temperature temper bead welding is an anomaly in the new attachment weld at the triple point. The triple point is the location in the new attachment weld where the low-alloy steel RVCH base material, the remnant Alloy 600 nozzle, and the Alloy 52M attachment weld intersect. This anomaly consists of an irregularly shaped, very small void. Mock-up testing has verified that the anomalies are common and do not exceed 0.10-inch in length. The licensee assumed anomalies, for purposes of analysis, around the entire bore circumference at the triple point elevation.
The licensee requested relief to permit anomalies at the triple point to remain in service based on a fracture mechanics analysis performed in accordance with the ASME Code,Section XI.
The licensee modeled the anomaly as a 0.10-inch, circular crack-like defect, extending 360 degrees around the circumference at the triple point location. The licensee postulated two flaw propagation paths for the triple point anomaly. The licensee demonstrated that the fatigue crack growth of the anomaly is acceptable and it will remain stable in service for 40 years.
Flaw Characterization and Successive Examinations The ASME Code,Section XI, IWB-3600 requires that cracks be fully characterized in order to compare the calculated parameters to the acceptable parameters addressed in IWB-3500. The licensee requested relief from flaw characterization and subsequent examinations of the J-groove weld because it is impractical to characterize the flaw geometry that may exist in the J-groove welds. In lieu of flaw characterization and subsequent examinations, the licensee evaluated a postulated flaw occurring in the remaining J-groove weld extending through the entire J-groove weld and butter material to the interface with the RVCH material. Any growth of the postulated flaw into the RVCH would be caused by fatigue under cyclic loading conditions.
Based on an elastic-plastic fracture mechanics analysis, the licensee showed that the RVCH is acceptable for a minimum of 30 years of operation with the postulated flaw that is propagated from the J-groove weld into the RVCH. Following the detailed elastic-plastic fracture mechanics analysis, the licensee performed a primary stress limits analysis as required per the ASME Code,Section XI, IWB-3610(d)(2). Based on the primary stress limits analysis, the licensee predicted a service life of 5 years for nozzle number 51. The licensee stated that it will take measurements during the 2016 repair activity to confirm that assumed local conditions (head thickness and J-groove weld size) in the primary stress limits analysis are valid for a limiting life greater than or equal to 5 years.
The licensee stated that it will not perform successive examinations in the future of the J-groove weld as required by the ASME Code,Section XI, IWB-3132.3 because its analytical evaluation of the worst-case postulated flaw has demonstrated the acceptability of continued operation of the repaired RVCH nozzles.
General Corrosion of Exposed Low Alloy Steel As a result of the proposed repair, a small portion of low-alloy steel base metal in the bore of the RVCH penetration will be exposed to primary system coolant. The licensee evaluated the potential corrosion at the wetted bore surface of the RVCH base metal. The licensee noted that galvanic corrosion, hydrogen embrittlement, stress-corrosion cracking, and crevice corrosion are not expected to be a concern for the exposed RVCH base metal. The licensee stated that general corrosion of the exposed base metal will occur in the area between the new attachment weld and the remnant J-groove weld. The licensee estimated that the general corrosion of the exposed RVCH base metal is acceptable for 40 years from the time the repair is performed.
Inside Surface Initiated Flaw The licensee postulated a flaw initiating at the inside surface of the remnant RVCH nozzle for the case that abrasive water jet machining is not applied to the nozzle inside surface as a part of the repair. The licensee assumed that the initial flaw depth is 1O percent of the remnant nozzle wall thickness because UT may not be able to detect flaws less than 10 percent of nozzle wall thickness. The depth of the allowable flaw in the nozzle to remain in service is 75 percent
nozzle wall thickness in accordance with the ASME Code,Section XI, IWB-3600. The licensee estimated that it takes 2.2 effective full power years (EFPYs) for the initial flaw to reach to the limit of 75 percent of the wall thickness of the remnant RVCH nozzle. The licensee explained that 2.2 EFPYs was calculated based on taking no credit for a delay in PWSCC initiation time, and PWSCC crack growth of an undetected flaw in the remnant nozzle. The licensee stated that the overall acceptable life of the repair design is based on the most limiting life predicted.
Therefore, the licensee has stated that 2.2 EFPY is the design life of the repaired nozzle numbers 30, 40, and 51.
Loose Parts Evaluation The licensee evaluated the potential for debris from a degraded J-groove weld falling into the reactor vessel. The licensee postulated radial cracks to occur in the J-groove weld due to the dominance of hoop stresses at this location. The licensee stated that the occurrence of transverse cracks that could intersect the radial cracks is considered remote because there are no forces that would drive a transverse crack. The radial cracks would relieve the potential transverse crack driving forces. The licensee concluded that it is unlikely that a series of transverse cracks could intersect a series of radial cracks resulting in any fragments becoming dislodged from a J-groove weld.
3.1. 7 Duration of Proposed Alternative The licensee requested that the relief request is applicable for the third 10-year ISi interval that commenced on May 2, 2007, and will end on May 1, 2017.
3.2 NRC Staff Evaluation The NRC staff evaluated the licensee's proposed alternative, including the weld design, flaw evaluations, welding, and examinations in accordance with ASME Code, Sections Ill and XI, Code Case N-638-1, and Code Case N-729-1. The NRC staff also evaluated the proposed deviations from the applicable ASME Code requirements included in the proposed alternative.
3.2.1 Weld Design The NRC staff notes that the significant changes between the original nozzle and the repaired nozzle are the removal of a portion of the original nozzle and the new attachment weld. The NRC staff finds that the repaired nozzle without a portion of the original nozzle does not affect its structural support to the functionality of the control rod drive mechanism. As for the new attachment weld, the licensee followed the ASME Code, Section Ill design requirements from which it did not ask relief. Nevertheless, the NRC staff performed an independent calculation and determined that the size of the new attachment weld will support all the loads of the repaired nozzle. Therefore, the NRC staff finds that the new weld is designed, in terms of structural support, in accordance with the ASME Code, Section Ill, and therefore, is acceptable.
3.2.2 Flaw Evaluations The NRC staff evaluated the licensee's analyses of the triple point anomaly, postulated flaw growth from the existing J-groove weld into the RVCH, corrosion evaluation, inside nozzle surface initiated flaw, and loose parts evaluation.
Triple Point Anomaly The licensee requested relief from the ASME Code, Section Ill, NB-5000, so that potential anomalies at the triple point location may remain in service. The NRC staff noted that the ASME Code, Section Ill, NB-5330(b), prohibits the existence of indications that are characterized as cracks, lack of fusion, or incomplete penetration regardless of length. As an alternative to NB-5330(b), the licensee analyzed a postulated crack-like anomaly at the triple point in accordance with the ASME Code,Section XI, IWB-3600, to justify operating with the anomaly left in service. The results of the licensee's analyses demonstrate that a postulated 0.10-inch weld anomaly is acceptable for 40 years. The NRC staff finds that the licensee has adequately demonstrated by analysis and by mockup testing that the triple point weld anomaly is acceptable to remain in service without affecting structural integrity of the repaired nozzle for 40 years.
Flaw Evaluation for the J-groove Weld The ASME Code,Section XI, IWB-3132.3 requires that successive examinations be performed on a weld that contains an unacceptable flaw. The licensee proposed not to re-examine the remnant J-groove weld in the future because it is difficult to examine the remnant J-groove weld with reasonable confidence. As an alternative, the licensee analyzed a postulated flaw in the remnant J-groove weld in accordance with the ASME Code,Section XI, IWB-3132.3 and IWB-3610(d)(2). The postulated flaw is the worst-case flaw in the J-groove weld in which the flaw extends the entire length of the weld and the flaw tip has reached the interface between the butter and the RVCH base metal. The flaw is postulated to propagate into the RVCH base metal by fatigue. The licensee's flaw evaluation result shows that the repaired RVCH nozzle is acceptable for a minimum of 5 years of operation after the repair per the ASME Code,Section XI, IWB-3610(d)(2).
The NRC staff finds the licensee's flaw evaluation acceptable because the licensee postulated a worst-case flaw in the J-groove weld propagating into the RVCH and analyzed the flaw growth per the ASME Code,Section XI, IWB-3132.3 and IWB-361 O(d)(2).
Corrosion Evaluation The NRC staff noted that as a result of the nozzle repair, an area in the RVCH nozzle penetration bore is exposed to primary coolant. The NRC staff finds that the licensee considered various corrosion mechanisms and that general corrosion of the exposed RVCH base metal will most likely occur in the affected bore area. Based on the licensee's calculation, the NRC staff finds acceptable that the bore of the RVCH penetration will be acceptable for 40 years following the nozzle repair.
Inside Nozzle Surface Initiated Flaw The licensee also analyzed a postulated PWSCC crack in a remnant RVCH nozzle. The licensee conservatively postulated that the PWSCC crack is initiated on the ID surface of the remnant nozzle as soon as the repair is complete. This assumption is based on the repair option that abrasive water jet machining will not be applied to the inside surface of the remnant RVCH nozzle. The licensee estimated that the PWSCC crack would propagate from the ID surface toward the OD surface to the allowable depth of 75-percent through-wall of the nozzle wall thickness within 2.2 EFPYs. This is the shortest and most conservative design life among various licensee's flaw evaluations. Therefore, the licensee concluded that the design life of the proposed repair is 2.2 EFPYs. Based on the licensee's conservative calculations, the NRC staff finds that a design life of 2.2 EFPYs for the proposed repair is acceptable. The NRC staff notes that the licensee is required to inspect every RVCH nozzle, including the repaired nozzles, during every refueling outage, which occurs every 18 months. The 18-month inspection interval is shorter than 2.2 EFPYs; therefore, the structural integrity of the RVCH nozzles will be monitored appropriately.
Loose Parts Evaluation The NRC staff is concerned about the potential for fragments of the degraded J-groove weld falling into the reactor. To address this concern, the licensee postulated the radial cracks to occur in the J-groove weld due to the dominance of hoop stresses. The licensee determined that the possibility of occurrence of transverse cracks that could intersect the radial cracks is remote because there are no forces that would drive a transverse crack, and the radial cracks would relieve the potential transverse crack driving forces. The licensee stated that it is unlikely that a series of transverse cracks could intersect a series of radial cracks resulting in any fragments becoming dislodged from the remnant J-groove weld. The NRC staff finds that the licensee has adequately demonstrated that the fragments from the remnant J-groove weld are not likely to fall into the reactor vessel to become loose parts.
3.2.3 Welding The licensee stated that its vendor has qualified the IDTB welding technique in repairing RVCH nozzles using mockups since 2001. During these repair evolutions, the site crew performs training on mockups for each of their respective specialties (i.e., machining, welding, and NOE).
The NRC staff finds that the use of the machining, welding and NOE mockups ensure quality fabrication and examinations of the repair.
The licensee stated that in lieu of using direct measurement, it will use heat flow calculations to determine the maximum anticipated interpass temperature to ensure interpass temperature limits are not exceeded. The NRC staff finds that the proposed heat flaw calculations are the same as prescribed in Code Case N-638-4 that the NRC approved in RG 1.147, Revision 17.
The NRC staff finds that the proposed heat flow calculations will provide reasonable assurance that the required interpass temperature limits will not be exceeded.
ASME Code Case N-638-1, paragraph 4.0(b), requires the new attachment weld be examined by surface and ultrasonic methods when the temperature of the completed weld has been at ambient temperature for at least 48 hours2 days <br />0.286 weeks <br />0.0658 months <br />. In lieu of this requirement, the licensee proposed to
start the 48-hour waiting period when the third layer is deposited. The NRC staff notes that the 48-hour waiting period is to permit any potential fabrication defects or cracking in the weld to emerge so that the weld could be repaired prior to placing the weld in service. The licensee stated that Electric Power Research Institute (EPRI) Report 1013558, "Temperbead Welding Applications, 48-Hour Hold Requirements for Ambient Temperature Temperbead Welding,"
December 2006 (ADAMS Accession No. ML070670060), provides justification for starting the 48-hour hold after completing the third temper bead weld layer rather than waiting for the weld to cool to ambient temperature. The NRC staff finds that starting the UT examination after the 48-hour hold time from the completion of the third temper bead weld layer is acceptable because the EPRI research provides reasonable assurance that the completed weld will not be affected by the proposed earlier examination time.
ASME Code Case N-638-1, paragraph 4.0(b) requires that after welding, surface and volumetric examinations be performed on the final weld and the band around the area defined in paragraph 1.0(d) of the code case. As an alternative, the licensee proposed to perform surface examination using liquid penetrant testing on the band around the area to be welded, which includes the exposed surface area of RVCH base metal as shown in Figure 3 of the relief request. The NRC staff finds that the proposed PT and UT examinations will cover the affected area of the new weld satisfactorily. Therefore, the NRC staff finds that the proposed examination coverage is acceptable.
3.2.4 Examinations The NRC staff determined that the examinations provide reasonable assurance that the structural integrity of the repaired nozzle will be maintained. As such, the NRC evaluated the requirements of the pre-welding examination, acceptance examinations, and preservice and inservice inspections as discussed below.
Pre-Welding Examination The NRC staff notes that prior to making the new weld, the licensee will perform PT of the RVCH penetration bore and the ID of the nozzle as shown in Figure 3 of the relief request. The examination coverage will be from the top of the J-groove weld to 1/2 inch above the bottom of the remnant nozzle. The NRC staff finds that the examination coverage is adequate to ensure that the welded surface and machined surface are free of defects prior to welding.
Acceptance Examination The NRC staff notes that after the repair, the proposed acceptance examination consists of UT and PT. The proposed examination coverage for UT and PT is shown in Figure 3 of the relief request. The proposed UT examination will extend from the new weld to at least 1-inch above the new weld and at least 1/4-inch depth into the RVCH base metal underneath the new weld.
In addition, the proposed PT examination area includes the new weld surface and extends upward on the nozzle inside surface to include the area required by ASME Code Case N-729-1, Figure 2, and at least 1/2 inch of the RVCH nozzle bore area below the new weld. The licensee stated that the weld taper transition region will be excluded from UT examination because the UT transducer cannot be positioned to examine the taper transition region. However, the licensee will examine the surface of the taper transition region by PT. The NRC staff finds that
the proposed acceptance examinations are acceptable because PT and UT will cover sufficient examination areas of new weld and the surrounding regions to provide reasonable assurance of structural integrity of the new weld and associated nozzle penetration region.
The licensee requested to deviate from the requirement of the ASME Code, Section Ill, NB-5245, related to incremental surface examinations of the new welds. The licensee explained that it cannot meet this requirement because of the welding layer deposition sequence (i.e., each layer is deposited parallel to the penetration centerline). As an alternative, the licensee proposed to perform PT and UT examinations of the final weld to the extent possible. The NRC staff finds that as long as the licensee performs a PT and UT examination of the completed weld, the incremental surface examinations are not needed because the UT examination and the final PT examination will be able to detect fabrication defects.
Preservice and lnservice Inspections The licensee stated that following the repair, the preservice and inservice inspections will comply with ASME Code Case N-729-1 as conditioned by 10 CFR 50.55a(g)(6)(ii)(D) and as depicted in Figure 9 of the relief request. The licensee stated that it will perform the surface or volumetric examination of the new attachment weld in accordance with ASME Code Case N-729-1, Table 1, Item 84.20. This includes the examination of the weld taper transition extending up to at least the "a" distance above the top edge of the weld taper on the nozzle inside surface, where "a" includes the surface area and volume required by ASME Code Case N-729-1, Figure 2, which defines the distance "a" as equal to 1.5 inches for the nozzle incidence angle less than or equal to 30 degrees to the horizontal plane, or 1 inch for the incidence angle greater than 30 degrees to the horizontal plane. The NRC staff finds that the licensee's proposed preservice and inservice examinations acceptable because the extent of examination area and volume specified in Figure 9 of the relief request satisfies the examinations required by Figure 2 of ASME Code Case N-729-1.
Paragraph 10 CFR 50.55a(g)(6)(ii)(D)(5) specifies that if a flaw attributed to PWSCC has been identified in a RVCH nozzle, even if it is accepted for continued service under paragraph 3130 or 3140 of ASME Code Case N-729-1, all RVCH nozzles, including the repaired nozzles, must be inspected during each refueling outage instead of the re-inspection intervals required by Table 1, Note (8) of ASME Code Case N-729-1. The licensee has not asked relief from inspecting all RVCH nozzles during every refueling outage. As long as the subject repaired nozzles are found to have no degradation during each refueling outage inspection, the repaired nozzles are permitted to remain in service for the next 2.2 EFPY. The clock for the 2.2 EFPY starts immediately after the inspection is performed during each subsequent refueling outage.
The fuel cycle for the plant is 18 months and, therefore, the inspection interval for each repaired nozzle is 18 months. The NRC staff finds that the inspection interval of 18 months for the repaired nozzles is acceptable because it is shorter than the design life of 2.2 EFPY.
In summary, the NRC staff determines that the proposed alternative provides reasonable assurance of the structural integrity of the repaired RVCH penetration nozzles because (a) the weld design and the proposed repair are performed in accordance with the ASME Code, Sections Ill and XI, Construction Code, and Code Case N-638-1 with deviations to which the licensee has satisfactorily addressed, (b) the licensee has performed necessary analyses to demonstrate the acceptability of the RVCH and repaired nozzles containing postulated flaws to
remain in service, and (c) the licensee will examine the repaired RVCH nozzles every refueling outage in the future in accordance with ASME Code Case N-729-1 as conditioned by 10 CFR 50.55a(g)(6)(ii)(D).
4.0 CONCLUSION
The NRC staff concludes that Relief Request 13R-16 will provide an acceptable level of quality and safety for the repaired RVCH nozzle numbers 30, 40, and 51. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(1) and is in compliance with the requirements of the ASME Code,Section XI, ASME Code Case N-638-1 as conditioned in Regulatory Guide 1.147, and ASME Code Case N-729-1, as conditioned by 10 CFR 50.55a(g)(6)(ii)(D). Therefore, the NRC authorizes the use of Relief Request 13R-16 at Shearon Harris Nuclear Power Plant, Unit 1, for the remaining period of the third 10-year ISi interval, which ends on May 1, 2017.
The NRC notes that although the third 10-year ISi interval ends on May 1, 2017, the repaired RVCH nozzle numbers 30, 40, and 51 are acceptable to remain in service for the remaining life of the plant.
All other requirements of ASME Code,Section XI, and 10 CFR 50.55a(g)(6)(ii)(D) for which relief was not specifically requested and authorized by the NRC staff remain applicable, including third-party review by the Authorized Nuclear lnservice Inspector.
Principal Contributor: John Tsao Date: December 27, 2016
T. Hamilton If you have any questions, please contact the Project Manager, Martha Barillas at 301-415-2760 or Martha. Barillas@nrc.gov.
Sincerely,
/RA/
Jeanne D. Johnston, Acting Chief Plant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-400
Enclosure:
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PUBLIC LPL2-2 R/F RidsNrrPMShearonHarris Resource RidsACRS_MailCenter Resource RidsNrrLABClayton Resource RidsRgn2MailCenter Resource RidsNrrDeEpnb Resource RidsNrrDorllpl2-2 Resource JTsao, NRR ADAMS A ccess1on N o.: ML16343A220 *b1yema1*1 OFFICE NRR/DORL/LPL2-2/PM DORL/LPL2-2/LA NRR/DE/EPNB/BC NAME MBarillas BClayton (JBurkhardt for) RWolfgang*
DATE 12/27/16 12/23/16 11/30/16 OFFICE NRR/DORL/LPL2-2/BC NAME JJohnston
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