ML18283B544
| ML18283B544 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 11/20/2018 |
| From: | Undine Shoop Plant Licensing Branch II |
| To: | Hamilton T Duke Energy Progress |
| Barillas M, 301-415-2760 | |
| References | |
| EPID L-2018-LLR-0053 | |
| Download: ML18283B544 (14) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 November 20, 2018 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 FROM THE REQUIREMENTS OF THE ASME CODE, SECTION XI, RE: REACTOR VESSEL CLOSURE HEAD PENETRATION NOZZLE REPAIR TECHNIQUE (EPID L-2018-LLR-0053)
Dear Ms. Hamilton:
By letter dated April 18, 2018 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML18108A094), as supplemented by letter dated April 20, 2018 (ADAMS Accession No. ML18110A292), Duke Energy Progress, LLC (the licensee) requested relief from certain requirements of Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code for the repair of a degraded reactor vessel closure head (RVCH) penetration at the Shearon Harris Nuclear Power Plant, Unit 1.
Specifically, pursuant to Title 10 of the Code of Federal Regulations ( 10 CFR) 50.55a(z)( 1), the licensee submitted Relief Request 14R-18 for the repair of degraded RVCH penetration nozzle 33 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 nozzle.
The U.S. Nuclear Regulatory Commission (NRC) staff reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, 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 Relief Request 14R-18 for RVCH penetration nozzle 33 for the remaining period of the fourth 10-year inservice inspection interval, which ends on September 8, 2027, after determining 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 April 30, 2018 (ADAMS Accession No. ML18116A116). The enclosed safety evaluation documents the NRC staff's detailed technical basis for the verbal authorization.
T. Hamilton If you have any questions, please contact the Project Manager, Martha Barillas at 301-415-2760 or Martha.Barillas@nrc.gov.
Undine Shoop, Branch Chief Plant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-400
Enclosure:
Safety Evaluation cc: Listserv
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST 14R-18 REGARDING ALTERNATIVE REPAIR OF REACTOR VESSEL CLOSURE HEAD PENETRATION NOZZLE DUKE ENERGY PROGRESS, LLC SHEARON HARRIS NUCLEAR POWER PLANT, UNIT 1 DOCKET NO. 50-400
1.0 INTRODUCTION
By letter dated April 18, 2018 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML18108A094), as supplemented by letter dated April 20, 2018 (ADAMS Accession No. ML18110A292), Duke Energy Progress, LLC (the licensee), requested relief from certain requirements of Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (B&PV Code) for the repair of a degraded reactor vessel closure head (RVCH) penetration at the Shearon Harris Nuclear Power Plant (Shearon Harris), Unit 1.
Specifically, pursuant to Title 10 of the Code of Federal Regulations ( 10 CFR) 50.55a(z)( 1), the licensee submitted Relief Request 14R-18 for the repair of degraded RVCH penetration nozzle 33 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 nozzle.
On April 26, 2018 (ADAMS Accession No. ML18116A116), the U.S. Nuclear Regulatory Commission (NRC) verbally authorized the use of Relief Request 14R-18 for RVCH penetration nozzle 33 at Shearon Harris, Unit 1, for the remaining period of the fourth 10-year inservice inspection (ISi) interval, which is scheduled to end on September 8, 2027, because the NRC staff determined that the proposed alternative is technically justified and provides an acceptable level of quality and safety. Details of the verbal authorization are documented in the memorandum dated April 30, 2018, which attached the April 26, 2018, verbal authorization document. This safety evaluation documents the technical basis for the NRC's verbal authorization.
2.0 REGULATORY EVALUATION
Adherence to Section XI of the ASME B&PV 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 ISi Requirements: Reactor vessel head_inspection:
(1) Implementation. Holders of operating licenses or combined licenses for pressurized-water reactors as of or after August 17, 2017 shall implement the requirements of ASME BPV Code Case N-729-4 instead of ASME BPV Code Case N-729-1, subject to the conditions specified in paragraphs (g)(6)(ii)(D)(2) through (4) of this section, by the first refueling outage starting after August 17, 2017.
ASME Code Case N-638-6, "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division 1," provides requirements for automatic or machine gas tungsten arc welding (GTAW) of Class 1 components without the use of preheat or post-weld heat treatment. Code Case N-638-6 is listed in Regulatory Guide (RG) 1.147, Revision 18, "lnservice Inspection-Code Case Acceptability, ASME Section XI, Division 1," dated March 2017 (ADAMS Accession No. ML16321A336), as acceptable for use with one condition.
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 14R-18 3.1.1 ASME Code Components Affected The affected component is ASME Class 1, RVCH penetration nozzle 33, which is made of nickel-based alloy lnconel SB-167 (Alloy 600) with a nominal outside diameter of 4 inches.
3.1.2 Applicable Code Edition and Addenda The Code of record for the fourth 10-year ISi interval is the ASME Code,Section XI, 2007 Edition through 2008 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 The 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 (b) [IWA-4221] 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-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-4610(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)."
The ASME Code, Section Ill, NB-5245, requires progressive surface examination of partial penetration welds. NB-5331 (b) states, "indications characterized as cracks, lack of fusion, or incomplete penetration are unacceptable regardless of length.
ASME Code Case N-638-6 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-729-4, "Alternative Examination Requirements for PWR Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration WeldsSection XI, Division 1," Figure 2, "Examination Volume for Nozzle Base Metal and Examination Area for Weld and Nozzle Base Metal," is applicable to the subject RVCH penetration nozzle.
3.1.4 Reason for Request During the 2018 refueling outage, the licensee detected unacceptable flaws on RVCH penetration nozzle 33. The flaws are located in the tube outside the diameter surface extending inward toward the tube inside diameter and are axially oriented at the lower toe side of the J-groove weld. The licensee proposed to repair the nozzle 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 nozzles 5, 14, 17, 18, 23, 30, 37, 38, 40, 49, 51, 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 nozzle using the IDTB welding method to restore the pressure boundary of the degraded nozzle penetration.
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 degrees Fahrenheit
(°F) minimum preheat temperature and no post-weld heat treatment.
3.1.5 Proposed Alternative The licensee proposed to perform the repair in accordance with the requirements of the ASME Code, Sections Ill and XI, Code Case N-638-6 and Code Case N-729-4, with the alternatives discussed below. 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 lower 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.
3.1.6 Basis for Use Repair Welding The licensee's alternative implements Code Case N-638-6 with no deviations noted. In addition to complying with the code case, the licensee complies with the condition imposed on Code Case N-638-6 in RG 1.147, Revision 18, which states, "Demonstration for ultrasonic examination of the repaired volume is required using representative samples which contain construction type flaws."
Acceptance Examination 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 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 flaws in the new weld and base metal interface in the repair region to the extent practical. The licensee clarified that UT examination acceptance criteria will follow NB-5330 of the ASME Code, Section Ill, for all flaws identified within the repaired volume.
Preservice and lnservice Inspections The licensee stated that the preservice inspection following repair and future IS ls will comply with ASME Code Case N-729-4 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-5331(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.
Mockup 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 from the acceptance criteria specified in NB-5331(b) 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 0.1 O 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 (PSLA), as required per the ASME Code,Section XI, IWB-3610(d)(2), to demonstrate the service life of the RVCH, considering 12 previously repaired nozzles and nozzle 33., The results of the licensee's PSLA show an overall RVCH service life of 5 years from the April 2018 outage. The licensee stated that it will take measurements of nozzle 33 during the 2018 repair activity to confirm that assumed local conditions (head thickness and J-groove weld size) used in the PSLA 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 nozzle.
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.
Alloy 600 PWSCC Evaluation The licensee stated that the* most limiting life of the repair design is the PWSCC evaluation of the remaining portion of the original Alloy 600 nozzle material. The licensee's PWSCC evaluation supports a maximum examination interval of 2.2 effective full power years (EFPY) or 803 effective full power days for continued plant operation. The 2.2 EFPY examination interval starts at the time of the repair and is reset to an additional 2.2 EFPY upon demonstration of acceptable results from examinations performed each refueling outage ( 18 months) on repaired RVCH nozzles.
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 fourth 10-year ISi interval that is scheduled to end on September 8, 2027.
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 the ASME Code, Sections Ill and XI; Code Case N-638-6; and Code Case N-729-4. 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. 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-5331(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-5331(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 0.1 O 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. However, current technology does not permit accurate characterization of flaws in J-groove welds. 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-3610(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 By letter dated April 29, 2015 (ADAMS Accession No. ML15105A521 ), the licensee submitted a flaw growth calculation of a postulated PWSCC crack in the remnant nozzle as part of NRG-approved Relief Request 13R-15. In that flaw evaluation, which is also applicable to the current Relief Request 14R-18, the licensee conservatively postulated that the PWSCC crack is initiated on the inside diameter 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 allowable depth for the postulated flaw is 75 percent through-wall, based on the provision of the ASME Code,Section XI, IWB-3643. The licensee estimated that the PWSCC crack would propagate from the inside diameter surface toward the outside diameter 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. 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, if a flaw exists, the ISi will be able to detect the flaw in time, and the licensee would take corrective actions before the nozzle reaches the design life of 2.2 EFPY. The NRC staff finds that with an
inspection frequency of 18 months, 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 nondestructive examination). The NRC staff finds that the use of the machining, welding, and nondestructive examination mockups ensure quality fabrication and examinations of the repair.
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 staff evaluated the requirements of the pre-welding examination, acceptance examinations, and preservice and 1Sls, 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 inside diameter 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-729-4, 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 ISls will comply with ASME Code Case N-729-4, 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-729-4, 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-729-4, 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 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-729-4.
Code Case N-729-4 specifies that if a flaw attributed to PWSCC has been identified in an RVCH nozzle, even if it is accepted for continued service under paragraphs 3130 or 3140 of ASME Code Case N-729-4, all RVCH nozzles, including the repaired nozzles, must be inspected during each refueling outage. 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 new 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 nozzle 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 nozzle 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-638-6, 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 nozzle containing postulated flaws to remain in service; and (c) the licensee will examine the repaired RVCH nozzle every refueling outage in the future in accordance with ASME Code Case N-729-4, as conditioned by 10 CFR 50.55a(g)(6)(ii)(D).
4.0 CONCLUSION
The NRC staff concludes that Relief Request 14R-18 will provide an acceptable level of quality and safety for the repaired RVCH nozzle 33. 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-638-6, as conditioned in RG 1.147, and ASME Code Case N-729-4, as conditioned by 10 CFR 50.55a(g)(6)(ii)(D). Therefore, the NRC authorizes the use of Relief Request 14R-18 at Shearon Harris, Unit 1, for the remaining period of the fourth 10-year ISi interval, which is scheduled to end on September 8, 2027.
All other requirements of the 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: Robert Davis Da~: November 20, 2018
ML182838544 *b email OFFICE NRR/DORULPL2-2/PM DORL/LPL2-2/LA NRR/DMLR/MPHB/BC*
NAME MBarillas PTalukdar/LRonewicz SRuffin (SCumblidge for)
DATE 10/11/2018 10/18/2018 08/09/2018 OFFICE NRR/DORULPL2-2/BC NAME UShoop (RSchaaf for)
DATE 11/20/2018