ML15203A702
| ML15203A702 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 09/18/2015 |
| From: | Shana Helton Plant Licensing Branch II |
| To: | Waldrep B Progress Energy Carolinas |
| Dennis Galvin, NRR/DORL, 415-6265 | |
| References | |
| TAC MF6053 | |
| Download: ML15203A702 (15) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 Mr. Benjamin C. Waldrep Site Vice President Shearon Harris Nuclear Power Plant 5413 Shearon Harris Rd.
New Hill, NC 27562-0165 September 18, 2015
SUBJECT:
SHEARON HARRIS NUCLEAR POWER PLANT, UNIT 1 RELIEF REQUEST 13R-15 FOR REACTOR VESSEL CLOSURE HEAD PENETRATION NOZZLE REPAIR TECHNIQUE, INSERVICE INSPECTION PROGRAM-THIRD 10-YEAR INTERVAL (TAC NO. MF6053)
Dear Mr. Waldrep:
By letter dated April 2, 2015 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML15092A236), as supplemented by letters dated April 15, April 24, and April 29, 2015, ADAMS Accession Nos. ML15105A521, ML15114A480, and ML15120A406, respectively, Duke Energy Progress, Inc. (the licensee) requested relief from certain requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, related to the repair of degraded reactor vessel closure head (RVCH) penetration nozzle numbers 14, 18, and 23 at Shearon Harris Nuclear Power Plant, Unit 1. The relief request (RR) in the April 29, 2015, supplement that the licensee designated as 13R-15, Revision 2 (hereafter referred to as RR 13R-15), supersedes the April 2,
- and April 15, 2015, submittals, and limits the scope of the requested relief to the three penetration nozzles. The request to the United States Nuclear Regulatory Commission (NRC) applies to the third 10-year lnservice Inspection interval, which is scheduled to end on May 1, 2017.
In the April 2 and April 15, 2015, letters, the licensee requested as an alternative to the requirements of RVCH Code of Construction, ASME Section 111, 1971 including Addenda through winter 1971, to perform the repair of the RVCH nozzle penetrations utilizing the Inside Diameter Temper Bead welding method to restore the pressure boundary of the degraded nozzle penetrations. In the April 29, 2015, letter, the licensee changed the scope of RR 13R-15 to the repair of RVCH penetration nozzle numbers 14, 18, and 23.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR),
Section 50.55a{z)(1 ), the licensee proposed alternatives to the requirements of the ASME Code,Section XI, Article IWA-4000, "Repair/Replacement Activities," on the basis that the alternatives provide an acceptable level of quality and safety.
The 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 1 O CFR 50.55a(z)(1 ). In addition, on May 4, 2015, the NRC staff verbally authorized the use of RR 13R-15. The script for the verbal authorization was issued on May 7, 2015 (ADAMS Accession No. ML15126A542). The enclosed SE documents the NRC staff's detailed technical basis for the verbal authorization.
If you have any questions, please contact the Project Manager, Martha Barillas at 301-415-2760 or Martha. Barillas@nrc.gov.
- Docket No. 50-400
Enclosure:
Safety Evaluation cc w/enclosure: Distribution via ListServ
- sincerely, Shana R. Helton, Chief Plant Licensing Branch 11-2 Division of Operating Reactor Licensing
- Office of Nuclear Reactor.Regulation
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 RELIEF REQUEST 13R-15, REVISION 2: ALTERNATIVE REPAIR OF REACTOR VESSEL CLOSURE HEAD PENETRATION NOZZLES DUKE ENERGY PROGRESS, INC.
SHEARON HARRIS NUCLEAR POWER PLANT, UNIT 1 DOCKET NUMBER 50-400
1.0 INTRODUCTION
By letter dated April 2, 2015, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML15092A236) as supplemented by letters dated April 15, April 24, and April 29, 2015, (ADAMS Accession Nos. ML15105A521, ML15114A480, and ML15120A406, respectively), Duke Energy Progress, Inc. (the licensee) requested relief from certain requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, related to the repair of degraded reactor vessel closure head (RVCH) penetration nozzle numbers 14, 18, and 23 at Shearon Harris Nuclear Power Plant, Unit 1 (Harris). The relief request (RR) in the April 29, 2015, supplement that the licensee
. designated as 13R-15, Revision 2 (hereafter referred to as RR 13R-15), supersedes the April 2 and April 15, 2015, submittals, and limits the scope of the requested relief to the three penetration nozzle repairs. The request to the U. S. Nuclear Regulatory Commission (NRC or the Commission) applies to the third 10-year lnservice Inspection (ISi) interval, which is scheduled to end on May 1, 2017.
In the April 2 and April 15, 2015, letters, the licensee requested as an alternative to the requirements of RVCH Code of Construction, ASME Section Ill, 1971 including Addenda through winter 1971, to perform repairs of the RVCH nozzle penetrations utilizing the Inside Diameter Temper Bead (IDTB) welding method to restore the pressure boundary of the degraded nozzle penetrations. In the April 29, 2015, letter, the licensee changed the scope of RR 13R-15 to the repair of RVCH penetration nozzle numbers 14, 18, and 23.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR)
Section 50.55a(z)(1 ), the licensee proposed alternatives in the repair of degraded RVCH nozzles on the basis that the alternatives provide an acceptable level of quality and safety.
On May 4, 2015 (ADAMS Accession No. ML15126A542), the NRC staff verbally authorized the use of RR 13R-15 for the third 10-year ISi interval because the NRC staff determined that the proposed alternatives are technically justified and provide an acceptable level of quality and safety. This safety evaluation documents the technical basis for the NRC's verbal authorization.
The staff notes by letters dated October 2, 2012, September 13, 2013, and April 11, 2014 (ADAMS Accession Nos. ML12270A258, ML13238A154, and ML14093A075, respectively), the NRC staff previously approved RRs 13R-09, 13R-11, and 13R-13 for similar repairs to Harris RVCH nozzles.
Enclosure
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR 50.55a(z)(1 ), the licensee requested authorization of alternatives to various requirements in IWA-3000, IWA-4000, and IWB-3000 of the ASME Code,Section XI and 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."
Adherence to Section XI of the ASME Code is mandated by 10 CFR S0.55a(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.
Pursuant to 10 CFR 50.55a(g)(6)(ii), the Commission may require the licensee to follow an augmented ISi program for systems and components for which the Commission deems that added assurance of structural reliability is necessary.
As stated in 10 CFR 50.55a(g)(6)(ii)(D), Reactor vessel head inspections, licensees of pressurized water reactors are required to augment their ISi of the RVCH 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, provides requirements for automatic or machine GTAW of Class 1 components without the use of preheat or postweld 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 Commission to authorize the alternative requested by the licensee.
3.0 RELIEF REQUEST 13R-15
3.1 ASME Code Components Affected
The affected components are ASME Class 1, RVCH penetration nozzles, which are made of lnconel SB-167, with a nominal outside diameter of 4 inches.
3.2
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 1971 Edition through winter 1971 Addenda of the ASME Code, Section 111, is the Construction Code for the RVCH. Any discussion of the ASME Code, Sections Ill and XI, and Construction Code, in this safety evaluation will be based on the aforementioned edition and addenda.
3.3 Applicable Code Requirements ASME Code,Section XI, IWA-4221(b) states that "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) 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-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.
I IWB-3420 states: Each detected flaw or group of flaws shall be characterized by the rule~, 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 postweld heat treatment.
- ASME Code Case N-638-1 paragraph 3.0(d) states: The maximum interpass temperature for field applications shall be 350° F 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 paragraph 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 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 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 RVCH nozzle penetrations.
3.4
Reason for Request
During the 2015 refueling outage, the licensee detected indications in a number of RVCH penetration nozzles that required repair. The flaws were in the tube outside diameter surface extending inward toward the tube inside diameter and were axially oriented at the lower toe side of the weld. The licensee requested to repair three nozzles (numbers 14, 18, and 23) under this RR.
The licensee planned to use the same NRC-approved half-nozzle repair technique that was used previously for nozzle Numbers 5, 17, 37, 38, 49, and 63. The proposed half-nozzle repair technique required relief fror:n certain requirements of the ASME Code and code cases.
The licensee stated that because of the risk of damage to the RVCH material properties or dimensions, it was not feasible to apply the post welding heat treatment requirements of the original Construction Code. As an alternative to the requirements of the RVCH Code of Construction, the licensee proposed to perform the repair of 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, utilizing the machine GTAW process and the ambient temperature temper bead method with 50° F minimum preheat temperature and no post weld heat treatment.
3.5 Proposed Alternative In lieu of following the ASME Code, Sections Ill and XI, the licensee proposed to deviate from certain requirements of the ASME Sections Ill and XI, Code Case N-638-1, and Code Case N-729-1 in the repair of degraded RVCH penetration nozzles. The prop6sed repair was described as follows:
- 1. Remove lower portion of existing thermal sleeve assembly, if present, to provide access for the repair.
- 2. Roll expand the existing nozzle above the area of repair to prevent any movement when the nozzle is separated from the J-groove weld.
- 3. Remove a segment of the nozzle from above the J-groove weld to the bottom of the nozzle by machining, including the portions of the nozzle that contains the unacceptable indication.
The machining operation also establishes the preparation area for the new attachment weld.
- 4. Examine the machined area of the nozzle by liquid penetrant testing (PT).
- 5. Weld the remaining portion of the nozzle to the RVCH u*sing primary water stress corrosion cracking (PWSCC) resistant Alloy 52M weld material. Alloy 82 weld material may be used at the interface between the Alloy 182 existing weld and the Alloy 52M new weld if necessary.
- 6. Machine the new attachment weld and nozzle to provide a surface suitable for nondestructive examination (NOE).
- 8. Optional---Apply abrasive water jet machining (AWJM) remediation on the portion of the remaining nozzle most susceptible to PWSCC.
3.6 Basis for Use Triple Point Anomaly' The ASME Code, Section Ill, NB-5330(b) states that "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 weld at the triple point. The triple point is the location in the repair weld where the low alloy steel (LAS)
RVCH base material, the Alloy 600 nozzle, and the Alloy 52M 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 and are assumed to exist, 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 for 40 years.
Flaw Characterization and Successive Examinations The assumptions of the ASME Code,Section XI, IWB-3600 are that cracks are 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 examination requirements 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 that extending through the entire weld and butter material to the interface with the LAS RVCH material. Any growth of the postulated flaw into the LAS RVCH would be by fatigue crack growth under cyclic loading conditions.* Based on an elastic-plastic fracture mechanics analysis, the licensee showed that the postulated flaw from the J~groove weld propagating into ~he RVCH base metal is acceptable for a minimum of 30 years of operation. As an alternative, the licensee analyzed the postulated flaw in the J-groove weld based on the limit load method. The licensee demonstrated that based on the limit load analysis of the postulated flaw, the service life of the RVCH nozzle repair is 15 years.
The licensee stated that it will not perform successive examinations of the J-groove weld as required by the ASME Code,Section XI, IWB-3132.3 in the future because its analytlcal evaluation of the worst-case postulated flaw has* demonstrated the acceptability of continued operation.
General Corrosion of Exposed Low Alloy Steel As a result of the proposed repair,.a small portion of LAS base metal in the bore of the RVCH penetration will be exposed to primary coolant. The licensee evaluated the potential corrosion at the wetted bore surface of the LAS 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 LAS base metal. The licensee noted that general corrosion of the exposed LAS base metal will occur in the area betWeen the new IDTB weld and the J-groove weld. The licensee estimated that the general corrosion of the exposed base metal is acceptable for 40 years from the time the repair is performed.
The licensee also postulated a flaw initiating at the inside surface of the nozzle when AWJM is not applied to the nozzle inside surface as a part of the repair procedures. The licensee estimated that it takes 2.2 effective full power years (EFPYs). for the crack tO. propagate from an undetected flaw of 10 percent of the Alloy 600 nozzle wall thickness to 75 percent of the original RVCH nozzle wall thickness. The 2.2 EFPYs life takes no credit for a delay in PWSCC initiation time, and is based on 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 amongst the weld anomaly analysis, the as-left J-groove analysis.and the PWSCC evaluation of the original Alloy 600 nozzle, which is 2.2 EFPYs.
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. 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 ln any fragments becoming dislodged from a J-groove weld.
Welding ASME Code Case N-638-1 paragraph 3.0(d) states: "The maximum interpass temperature for field applications shall be 350° F regardless of the interpass temperature during qualification.... "
ASME Code Case N-638-1 states that all other requirements of the ASMECode,Section XI, IWA-4000 must be met when using this Case. IWA-4610(a) requires t.hat thermocouples and recording instruments be used to monitor process temperatures. The licensee stated that direct interpass temperature measurement is impractical to perform during welding operations from inside the RVCH nozzle penetration bore. The licensee requested relief from using thermocouples* and recording instruments to verify process temperatures. 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: "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 therefore 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 partial penetration weld; therefore, asked relief from the requirement. In lieu of the requirement, the licensee will perform UT and PT of the new weld and immediate surrounding area within the bore, which will be sufficient to verify that defects have not been induced in the LAS RVCH material due to the welding process and will assure integrity of the 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 Section Ill.
ASME Code Case N-638-1, paragraph 4.0(b) requires that the specified volumetric examination be in accordance with the ASME Code,Section XI, Appendix I. Paragraph 4.0(e) specifies acceptance criteria to be in accordance with ttie ASME Code,Section XI, IWB-3000, which does not have any acceptance criteria that directly apply to the partial penetration weld configuration.
However, the licensee stated that it will follow the acceptance criteria of the ASME Code, Section 111., 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, "lnservice Inspection Code Case Acceptability, ASME Section XI, Division 1," Revision 15, which requires that UT volumetric 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 centerline), it cannot meet the required incremental surface examinations of NB-5245. The licensee requested relief from the.
!ncremental surface examinations. In lieu of this requirement, 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 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 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 RR
- 3. 7 Duration of Proposed Alternative The licensee stated that the design life for the subject repair without using AWJM is 2.2 EFPYs.
The licensee noted that the provisions of this RR are applicable to the third 10-year ISi interval that commenced on May 2, 2007, and will end on May 1, 2017.
4.0 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 evaluated the proposed deviations from the applicable ASME Code requirements included in the proposed alternative.
The licensee identified these deviations as "relief" and the staff used the same.designation for consistency.
4.1 Weld Design The NRC staff notes that the significant cbanges 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 di.d 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.
4.2 Flaw Evaluations The NRC staff evaluated the licensee's analysis of the triple point anomaly, postulated flaw growth from the existing J,.groove weld into the RVCH, corrosion evaluation, and loose parts evaluation.
Triple Point Anomaly The licensee requested relief to permit potential anomalies at the triple point location to remain in service. The NRC staff noted that the ASME Code, Sedion 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 a mockup 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 licensee requested relief from ASME Code,Section XI, IWB-3132.3, which requires subsequent reexaminations of the remnant J-groove weld 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. The licensee postulated a worst-case flaw in the J-groove weld in which the postulated crack extends the entire length of the weld and the crack tip has reached the interface between the butter and the RVCH base metal. The crack is postulated to propagate into the RVCH base metal by fatigue. The licensee's flaw evaluation result shows that th*e flaw is acceptable for 30 years of operation.
.~
The NRC staff finds the licensee's flaw evaluation acceptable because the licensee followed the requirements of the ASME Code,Section XI, IWB-3132.3 and postulated a worst-case flaw in the J-groove. weld.
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. The licensee estimated that the bore of the RVCH penetration will be acceptable for 40 years following the nozzle repair.
The licensee also analyzed a postulated PWSCC crack in a remnant RVCH nozzle. The licensee assumed that PWSCC 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 AWJM will not be applied to the inside surface of the remnant RVCH nozzle. The licensee es~imated that the PWSCC crack would propagate from the inside diameter surface to the allowable depth of 75-percent through wall within 2.2 EFPYs. The licensee concluded that the design life of the proposed repair is 2.2 EFPYs if AWJM is not applied to the remnant nozzle. The NRC staff finds that a design life of 2.2 EFPYs for the proposed repair is acceptable because the licensee is required to inspect every RVCH nozzle, including the repaired nozzles, during every refueling outage, which is about 18 months as discussed further in this safety evaluation. The 18-month inspection interval is shorter than 2.2 EFPYs; therefore, the licensee can monitor appropriately the structural integrity of the RVCH nozzles.
Loose Parts Evaluation The NRC staff is concerned about the potential for fragments of the 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 p~tential 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.
4.3 Welding The licensee stated that ifs vendor has qualified the IDTB w~lding 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 mockup_s will aid in assuring 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 1.14 7, 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 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 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 noted that the 48-hour waiting period is to permit any potential cracking in the weld to emerge so that cracks (fabrication defects) could be repaired prior to placing the weld in service. The licensee stated that Electric P,ower Research Institute (EPRI) Report 1013558, "Temperbead Welding Applic:ations, 48-Hour Hold Requirements for Ambient Temperature Temperbead Welding" (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 t.he UT examination after the 48-hour hold time from the completion of the third temper bead weld layer, rather than the 48-hour ambient temperature requirement in paragraph 4.0(b) of ASME Code Case N-638-1, 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 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 PT on the band around the area to be welded, which includes the exposed surface area of RVCH base metal as presented on Figure 3 of RR 13R-15. 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.
4.4 Examinations The NRC staff believes that the examinations provide significant 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 ISls as discussed below.
Pre-Welding Examination
- The NRC staff noted that prior to making the new weld, the licensee will perform PT examination of the RVCH penetration bore and the inside diameter of the nozzle as shown in Figure 3 of the RR 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
(
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 RR 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 LAS 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 stated 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 re.pair the preservice and I Sis 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 RR In accordance with ASME Code Case N-729-1, Table 1, Item 84.20, the licensee stated that it will perform the surface or volumetric examination of the new attachment weld.
This includes the e*xamination 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 the licensee's proposed preservice and inservice examinations acceptable because the extent of examination area and volume specified in Figure 9 of RR 13R-15 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 previously repaired certain number of degraded RVCH nozzles that the licensee has attributed to PWSCC. The licensee has not asked relief from inspecting all RVCH nozzles during every refueling outage. The NRC staff finds that licensee's inspection frequency of every refueling outage is within the design life of 2.2 EFPYs. Therefore, the structural integrity of the RVCH nozzles is being monitored satisfactorily.
In summary, the _NRC staff determined that RR 13R-15 provides reasonable assurance of the structural integrity of the repaired RVCH penetration nozzles because (a) the licensee has performed necessary flaw analyses to demonstrate the acceptability of the triple point anomaly in the new attachment weld and the worst-case "as-left" flaw in the remnant J-groove weld, (b) the proposed nozzle repair is performed in accordance with the ASME Code, Sections Ill and XI, and Code Case N-638-1 with deviations to which the licensee has satisfactorily addressed, and (c) the licensee will examine all RVCH nozzles every refueling outage in the future in accordance with ASME Code Case N-729-1 as con,ditioned by 1 O CFR 50.55a(g)(6)(ii)(D), which will monitor and provide reasonable assurance of the structural integrity of the RVCH nozzles.
5.0 CONCLUSION
As set forth above, the NRC staff determined that the proposed repairs for RVCH penetration nozzle numbers 14, 18, and 23 in RR 13R-15 will provide an acceptable level of quality and safety. Accordingly, the NRC staff concluded that the licensee 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, Sections Ill and XI, Code Case N-638-1, Code Case N-729-1 as conditioned by 1 O CFR 50.55a(g)(6)(ii)(D) for which relief was not requested. Therefore, the NRC staff authorized the use of RR 13R-15 at Harris for the third 10-year ISi interval, which is scheduled to end on May 1, 2017.
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 herein by the NRC staff remain applicable, including the third party review by the Authorized Nuclear lnservice Inspector.
Principal Contributor: John Tsao Date: September 18, 2015
ML15203A702 RidsNrrLABClayton RidsNrrDeEpnb JTsao, NRR
- by email OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/PM DORL/LPL2-2/LA NAME DGalvin MBarillas BClayton DATE 08/03/15 09/09/15 07/31/15 OFFICE NRR/DE/EPNB/BC NRR/DORL/LPL2-2/BC NAME DAiiey*
SHelton DATE 06/30/15 09/18/15