ML12270A258
| ML12270A258 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 10/02/2012 |
| From: | Jessie Quichocho Plant Licensing Branch II |
| To: | Hamrick G Progress Energy Carolinas |
| Billoch-Colon, Araceli | |
| References | |
| TAC ME8523 | |
| Download: ML12270A258 (19) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 October 2, 2012 Mr. George Hamrick Vice President Shearon Harris Nuclear Power Plant Progress Energy Carolinas, Inc.
Post Office Box 165, Mail Code: Zone 1 New Hill, NC 27562-0165
SUBJECT:
SHEARON HARRIS NUCLEAR POWER PLANT, UNIT 1 - RELIEF REQUEST 13R-09 FOR REACTOR VESSEL CLOSURE HEAD PENETRATION NOZZLES REPAIR INSERVICE INSPECTION PROGRAM - THIRD 10-YEAR INTERVAL (TAC NO. ME8523)
Dear Mr. Hamrick:
By letter dated May 3, 2012, to the U.S. Nuclear Regulatory Commission (NRC) (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12131A663) as supplemented by letter dated May 18, 2012 (ML12139A407), Carolina Power and Light (the licensee) submitted Relief Request (RR) 13R-09 for Shearon Harris Nuclear Power Plant, Unit 1.
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 four degraded reactor vessel closure head (RVCH) penetration nozzles (Le., Nos. 5, 17,38, and 63).
During the May 2012 refueling outage, the licensee detected flaw indications during the inservice inspection (lSI) examination of the RVCH nozzle penetration tubes, and repair of the degraded nozzles was required. RR 13R-09 was requested for the third 1O-year lSI interval, which commenced on May 2,2007, and will end on May 1, 2017.
Specifically, pursuant to Title 10 of the Code of Federal Regulations 50.55a(a)(3)(i), 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 licensee's submittals and determined that the proposed alternatives are technically justified and provide an acceptable level of quality and safety. On May 21,2012, the NRC staff verbally authorized the use of RR 13R-09. The script for the verbal authorization was issued on May 24,2012 (ADAMS Accession No. ML12144A440).
G. Hamrick -2 The enclosed safety evaluation documents the NRC staff's detailed technical basis for the verbal authorization.
Sincerely, th~~.~Q7U~~Chief lant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-400
Enclosure:
Safety Evaluation cc w/enclosures: Distribution via ListServ
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- 1' SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST 13R-09: REACTOR VESSEL CLOSURE HEAD PENETRATION NOZZLES REPAIR SHEARON HARRIS NUCLEAR POWER PLANT, UNIT 1 DOCKET NUMBER 50-400
1.0 INTRODUCTION
By letter dated May 3, 2012, to the U.S. Nuclear Regulatory Commission (NRC) (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12131A663) as supplemented by letter dated May 18, 2012 (ADAMS Accession No. ML12139A407), Carolina Power and Light (the licensee) submitted relief request (RR) 13R-09 for Shearon Harris Nuclear Power Plant, Unit 1 (Harris). 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 four degraded reactor vessel closure head (RVCH) penetration nozzles (i.e., Nos. 5, 17,38, and 63). During the May 2012 refueling outage, the licensee detected flaw indications during inservice inspection (lSI) examination of the RVCH nozzle penetration tubes, and repair of the degraded nozzles was required. RR 13R-09 was requested for the third 10-year lSI interval, which commenced on May 2, 2007, and will end on May1,2017.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR)
Section 50.55a(a)(3)(i), 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 licensee's submittals and determined that the proposed alternatives are technically justified and provide an acceptable level of quality and safety. On May 21, 2012, the NRC staff verbally authorized the use of RR 13R-09. The script for the verbal authorization was issued on May 24,2012 (ADAMS Accession No. ML12144A440). This safety evaluation documents the staff's detailed technical basis for the verbal authorization.
2.0 REGULATORY EVALUATION
Section 50.55a(g)(4) of 10 CFR specifies that ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements, except the design and access provisions and the pre-service examination (PSI) requirements, set forth in the ASME Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests Enclosure
-2 conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code, incorporated by reference in 10 CFR 50.55a(b), 12-months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
Pursuant to 10 CFR 50.55a(g)(6)(ii), the Commission may require the licensee to follow an augmented lSI program for systems and components for which the Commission deems that added assurance of structural reliability is necessary.
Section 50.55a(g)(6)(ii)(D) of 10 CFR , Reactor vessel head inspections, requires licensees of pressurized water reactors to augment their lSI program 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.
Section 50.55a(a)(3) of 10 CFR states that alternatives to the requirements of paragraph (g) of 10 CFR 50.55a may be used, when authorized by the NRC, if the licensee demonstrates (i) the proposed alternatives would provide an acceptable level of quality and safety or (ii) 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 TECHNICAL EVALUATION
3.1 ASME Code Components Affected (As stated)
ASME Code Class: Class 1 Component: Reactor Vessel Closure Head Penetration Nozzles 5, 17, 38, and 63 Examination Category B-P Item No.: B4.20 (ASME Code Case N-729-1, "Alternative Examination Requirements for PWR Reactor Vessel Upper Heads with Nozzles Having Pressure-Retaining Partial-Penetration Welds," shall be implemented pursuant to 10 CFR 50.55a(g)(6)(ii)(D)
The four RVCH nozzle penetrations, for which a relief is requested, are made of Inconel SB-167 with nominal outside diameter of 4 inches.
3.2 Applicable Code Edition and Addenda The Code of Record for the third 10-year lSI interval at Harris isSection XI of the 2001 Edition through 2003 Addenda of the ASME Code.
The 1971 Edition through Winter 1971 Addenda of the ASME Code,Section III, is the Construction Code for the RVCH at Harris.
-3 3.3 Applicable Code Requirement The 2001 Edition through 2003 Addenda of the ASME Code,Section XI, IWA-4221 (b), states that, "An item to be used for repairlreplacement activities shall meet the Construction Code specified in accordance with (1), (2), or (3) below."
The 2001 Edition throl1gh 2003 Addenda of the ASME Code,Section XI, IWA-4221 (c), states that, 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 III when the Construction Code was not Section III, provided the requirements of IWA-4222 through IWA-4226, as applicable, are met."
The 2001 Edition through 2003 Addenda of the ASME Code,Section XI, IWA-4400, provides welding, brazing, metal removal, and installation requirements related to repairlreplacement activities.
The 2001 Edition through 2003 Addenda of the ASME Code,Section XI, IWA-4411, states that, "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."
The 2001 Edition through 2003 Addenda of the ASME Code,Section XI, IWA-4411 (a), states, in part, that "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)."
The 2001 Edition through 2003 Addenda of the ASME Code,Section XI, IWA-4610(a), states, in part, that "Thermocouples and recording instruments shall be used to monitor the process temperatures. "
The 2001 Edition through 2003 Addenda of the ASME Code,Section XI, IWA-4611.1 (a), states that, "Defects shall be removed in accordance with IWA-4422.1; a defect is considered removed when it has been reduced to an acceptable size."
The 2001 Edition through 2003 Addenda of the ASME Code,Section XI, IWA-3300, specifies requirements for characterization of flaws detected by inservice examination.
The 2001 Edition throl1gh 2003 Addenda of the ASME Code,Section XI, IWB-3420, states that, "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."
The 2001 Edition through 2003 Addenda of the ASME Code,Section XI, IWB-3132.3, states that, "A component whose volumetric or surface examination detects flaws that exceed the acceptance standards of Table IWB-341 0-1 is acceptable for continued service without a repair and/or replacement activity if an analytical evaluation, as described in IWB-3600, meets the
- 4 acceptance criteria of IWB-3600; the area containing the flaw shall be subsequently reexamined in accordance with IWB-2420(b) and (c)."
The licensee adopted ASME Code Case N-638-1, "Similar and Dissimilar Metal Welding USing Ambient Temperature Machine GTAW Temperbead Technique,Section XI, Division 1," for the Harris third 1O-year lSI interval program as an alternative to certain requirements of the Construction Code. This code case provides requirements for automatic or machine gas-tungsten arc welding (GTAW) of ASME Code Class 1 components without the use of pre-heat or post-weld heat treatment. In Regulatory Guide (RG) 1.147, Rev. 15, the NRC approved ASME Code Case N-638-1 for use, with conditions which states that "UT [Ultrasonic Testing] volumetric examinations shall be performed with personnel and procedures qualified for the repaired volume and qualified by demonstration using representative samples which contain construction type flaws. The acceptance criteria of NB-5330 in the 1998 Edition through 2000 Addenda of the ASME Code,Section III, apply to all flaws identified within the repaired volume."
The requirements in paragraph 1.0(d) of ASME Code Case N-638-1 state that, "Prior to welding the area to be welded and a band around the area of at least 11;2 times the component thickness or 5 inches, whichever is less shall be at least 50 of. Paragraph 3.0(d) of ASME Code Case N-638-1 states that, "The maximum interpass temperature for field applications shall be 350 OF regardless of the interpass temperature during qualification." Paragraph 4.0(b) of ASME Code Case N-638-1 states that, 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 hours2 days <br />0.286 weeks <br />0.0658 months <br />; the ultrasonic examination shall be in accordance with Appendix I."
3.4 Licensee's Reason for Relief The licensee stated that flaw indications requiring repair were detected in four RVCH nozzle penetration tubes (Nos. 5, 17,38, and 63) during the lSI examinations during the May 2012 refueling outage. The indications were identified and characterized by the UT performed from the tube inside diameter (10) surface. All flaws are in the tube outside diameter (00) extending inward toward the tube 10 and are approximately parallel with the nozzle axis (axially oriented) at the lower toe side of the weld. Details about the relative locations of degraded nozzles and the characteristics of the detected flaw indications are provided in Figure 10 "Locations of Nozzles Being Repaired" and Table 1 of RR 13R-09, respectively.
To restore the pressure boundary of the degraded nozzle penetration(s), the licensee proposed alternative repair techniques.
3.5 Licensee's Request for Relief. Proposed Alternative, and Basis for Use The licensee stated that the repair and inspection activities will be performed in accordance with requirements of the 2001 Edition through 2003 Addenda of the ASME Code,Section XI, ASME Code Case N-638-1, and ASME Code Case N-729-1. The licensee's proposed repair and inspection activities are described below.
-5 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-weld heat treatment (PWHT) requirements of the original Construction Code. As an alternative to the Code of Construction, the licensee proposed to perform the repair of the RVCH nozzle penetrations utilizing the ID temperbead (IDTB) welding method to restore the pressure boundary of the degraded nozzle penetration(s).
The IDTB welding method will be performed with a remotely operated weld tool utilizing the machine GTAW process and the ambient temperature temper bead method with 50 OF minimum pre-heat temperature and no PWHT. The details of the repair procedure are described in Section 4 of RR 13R-09.
Monitoring of interpass temperature The licensee requested relief from requirements of the ASME Code,Section XI, IWA-4610(a),
and ASME Code Case N-638-1, paragraph 3.0(d), specifically related to use of the thermocouples and recording instruments to monitor welding process temperatures. The licensee stated that relief is requested on the basis that the direct interpass temperature measurement is impractical to perform during welding operations from inside RVCH nozzle penetration bore. As an alternative, the licensee proposed that the maximum interpass temperature be determined by either heat-flow calculations method or measured on a test coupon.
ASME Code Case N-638-1 states that the maximum interpass temperature for field applications shall be 350 OF regardless of the interpass temperature during qualification. Details are provided in Section 5.a. of RR 13R-09. The licensee stated that the proposed measurement methodology is consistent with the associated requirements specified in subsequent versions of ASME Code Case N-638-1, and has previously been approved by the NRC for dissimilar metal (DM) weld overlays in Harris lSI RR 13R-1 (ADAMS Accession No. ML072760737).
Acceptance examination area The licensee requested relief from requirements of ASME Code Case N-638-1, paragraph 4.0(b), specifically related to the surface and volumetric examinations of the final weld surface and the band around the area defined in paragraph 1.0(d) of the code case. The licensee stated that relief is requested on the basis that the required area defined in paragraph 1.0(d) of the code case cannot be examined due to the phYSical configuration of the partial penetration weld.
As an alternative, the licensee proposed that the new weld and immediate surrounding area within the bore identified in Figure 3 "Examination Area" of RR 13R-09, receive liquid penetrant testing (PT) and UT examination. The licensee stated that the alternative is sufficient to verify that defects have not been induced in the RVCH low alloy steel (LAS) material due to the welding process and will assure integrity of the nozzle and the new weld. The licensee stated that the UT examination, performed by scanning from the ID surface of the weld, is qualified to detect construction-type flaws in the new weld and base metal interface beneath the new weld.
The UT examination acceptance criteria will be in accordance with the 2001 Edition through 2003 Addenda of the ASME Code,Section III, NB-5330, and the extent of the examination is consistent with the Construction Code requirements.
-6 The licensee requested relief from the 2001 Edition through 2003 Addenda of the ASME Code,Section III, NB-5245, required incremental surface examination of partial penetration welds.
The licensee stated that relief is requested on the basis that the NB-5245 specific requirements cannot be met due to the welding layer deposition sequence (Le., each layer is deposited parallel to the penetration centerline). The licensee stated that the reason for the original Construction Code requirement for progressive PT examination in lieu of volumetric examination was because the volumetric examination is not practical for the conventional partial penetration weld configurations. As an alternative and for this modification, the licensee stated that the weld, with the exception of the taper transition is suitable for the UT examinations and the final surface examinations by PT (Figure 3 of RR 13R-09 identifies the areas for examination).
The licensee stated that scanning is performed from the inside surface of the new weld and the adjacent portion of the nozzle, excluding the weld taper. The volume of interest for UT examination extends from at least 1-inch above the new weld and into the RVCH LAS base material beneath the weld. to at least one-quarter inch depth. The PT examination area includes the weld surface and extends upward on the nozzle inside surface to include the area required by Figure 2 "Welding" of ASME Code Case N-729-1, and at least 1/2-inch below the new weld. Figure 3 of RR 13R-09 identifies the area for PT examination of the modified nozzle penetration after machining and before welding.
The licensee stated that the UT transducers and delivery tooling are capable of scanning from cylindrical surfaces with IDs near 2.75 inches. The UT equipment is not capable of scanning from the face of the weld taper. The scanning is performed using 0° longitudinal (L)-wave.
45° L-wave. and 70° L-wave transducers. Approximately 70 percent of the weld surface will be scanned by UT. Approximately 83 percent of the RVCH ferritic steel heat affected zone will be covered by UT. The UT examination coverage volumes are shown in Figures 4 through 8 of RR 13R-09 for the various scans. Examination of the area depicted in Figure 3 of RR 13R-09 will assure that all unacceptable flaws associated with the weld repair area have been removed.
48-Hour Hold Period The licensee requested relief from requirements of ASME Code Case N-638-1.
paragraph 4.0(b), specifically related to commencing the 48-hour hold period when the weld reaches ambient temperature. As an alternative, the licensee proposed that the 48-hour hold period will commence upon completion of the third weld layer.
The licensee stated that the potential for hydrogen-induced cracking is greatly reduced by using the machine GTAW process. The extensive research conducted by Electric Power Research Institute (EPRI) and the results documented in EPRI Report 1013558, "Temperbead Welding Applications, 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 temperbead weld layer rather than waiting for the weld to cool to ambient temperature to perform examinations. This approach is permitted by ASME Code Case N-638-4 for austenitic materials and the NRC has conditionally approved the use of this code case in RG 1.147, Rev. 16. In addition, this approach was approved by the NRC for OM weld overlays for Harris Relief Request 13R-1 (ADAMS Accession No. ML072760737). Detailed discussions are provided by the licensee in Section S.c. of RR 13R-09.
-7 Triple point anomaly The licensee requested relief to permit anomalies at the triple point area to remain in service.
The licensee stated that an artifact of ambient temperature temperbead welding is an anomaly in the weld at the triple point. The triple point is the point in the repair weld where the LAS RVCH base material, the Alloy 600 nozzle, and the Alloy 52M weld intersect. The location of the triple point anomaly is shown in Figure 2 of RR 13R-09. 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 stated that a fracture mechanics analysis has been performed for the design configuration to provide justification, in accordance with the ASME Code,Section XI, for operating with the postulated triple point anomaly. The anomaly is modeled as a 0.1 O-inch, circular crack-like, defect extending 360 degrees around the circumference at the triple point location, considering the most susceptible material for propagation. Postulated flaws could be oriented within the anomaly such that there are two possible flaw propagation paths. The results of the analyses demonstrate that the 0.1 O-inch weld anomaly is acceptable for a 40-year design life of the nozzle repair. Details are provided in Section 5.d. of RR 13R-09.
Flaw characterization and successive examinations The licensee requested relief from flaw characterization and subsequent examination requirements. Details are provided in Section 5.e. of RR 13R-09. The licensee stated that the assumptions of the ASME Code,Section XI, IWS-3600, are that cracks are fully characterized in order to compare the calculated parameters to the acceptable parameters addressed in IWS-3500. The original nozzle-to-RVCH J-groove weld is extremely difficult to examine with UT due to the compound curvature and fillet radius around the nozzle circumference. These conditions preclude ultrasonic coupling and control of the sound beam needed to perform flaw sizing with reasonable confidence in the measured flaw dimensions. Therefore, it is impractical to characterize the flaw geometry that may exist.
The licensee stated that because these J-groove welds have not been examined, they are assumed to have unacceptable flaws. The J-groove flaws have been evaluated for acceptance in accordance with the analytical evaluation requirements of the ASME Code,Section XI, IWS-3132.3, using worst-case postulated flaw sizes. The results of this evaluation show that, based on a combination of linear elastic and elastic-plastic fracture mechanics analysis of a postulated remaining flaw in the original Alloy 182 J-groove weld and butter material, the RVCH nozzle repair design configuration is considered to be acceptable for 30 years of operation following an IDTS weld repair. Details are provided in Section 5.e. of RR 13R-09.
The licensee stated that the potential for debris from a cracking J-groove partial penetration weld was considered. Radial cracks were postulated to occur in the weld due to the dominance of hoop stresses at this location. This possibility of 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.
Hence it is unlikely that a series of transverse cracks could intersect a series of radial cracks resulting in any fragments becoming dislodged.
- 8 lSI examination The licensee stated that ASME Code Case N-729-1, Table 1, Item 4.20, permits either volumetric or surface examination. Figure 9 "PSI and lSI weld and Nozzle Base Metal Surface Examination Area (A-B-C-O)" of the RR will be used to establish the area for PSI examination following repair and for future lSI examination. This examination area is equivalent to that required by Figure 2 of the code case, as it examines the nozzle weld and the same area above the nozzle weld, as would be required by Figure 2 of the code case. Therefore, the lSI will comply with ASME Code Case N-729-1 as mandated by 10 CFR SO.SSa(g)(6)(ii)(O).
General corrosion impact on exposed low alloy steel The licensee stated that the IOTB nozzle repair leaves a small portion of LAS in the RVCH exposed to primary coolant. An evaluation was performed for the potential corrosion concerns at the RVCH LAS wetted surface. Galvanic corrosion, hydrogen embrittlement, stress-corrosion cracking (SCC), and crevice corrosion are not expected to be a concern for the exposed LAS base metal.
The general corrosion of the exposed LAS base metal will occur in the area between the IOTB weld and the J-groove weld. The general corrosion rate is conservatively estimated to be 0.0036 inch/year. The corrosion of the exposed base metal has negligible impact on the RVCH and is acceptable for 40 years from the time the modification is installed.
3.6 Duration of Relief The licensee requested relief for Harris for the third 10-year lSI interval that commenced on May 2, 2007, and will end on May 1, 2017. The repairs installed in accordance with the provisions of this relief shall remain in place for the design life expectancy of 14.8 effective full-power years (EFPY) or until the RVCH is replaced, whichever occurs first.
4.0 STAFF EVALUATION The NRC staff issued a request for additional information (RAI) requesting the licensee to clarify why ASME Code Case N-638-4 (approved by the NRC in RG 1.147, Rev. 16, for use, with conditions) has not been used. By letter dated May 18, 2012 (ADAMS Accession No. ML12139A407) in response to the staff's RAI, the licensee clarified that ASME Code Case N-638-1 has already been adopted for Harris, third 10-year lSI interval program.
The NRC staff determined that the licensee is in compliance with 10 CFR SO.SSa(b)(S), because Harris had originally adapted the revision 1 of this code case for the current interval before the later revisions were approved for use by the NRC. According to paragraph (b)(S)(ii) of 10 CFR SO.SSa, the licensee may continue to apply, to the end of the current 120-month interval, the previous version of the code case as authorized or may apply the later version of the code case, including any NRC-specified conditions placed on its use.
-9 Repair Technique and Procedure The ASME Code,Section III, Subarticle NS-4600, "Heat Treatment," provides the requirements for welding pre-heat and post-weld heat treatment. ASME Code Case N-638-1 provides requirements for similar and OM welding using ambient temperature machine GTAW temperbead technique without the specified welding pre-heat or PWHT of the Construction Code, when it is impractical. In RG 1.147, Rev. 15, the NRC approved ASME Code Case N-638-1 for use, with conditions.
The licensee proposed to repair the degraded RVCH nozzle penetrations by the lOTS welding utilizing the machine GTAW temperbead welding technique at ambient temperature (Le., no pre-heat with 50 of minimum temperature) and no PWHT in accordance with ASME Code Case N-638-1. The research conducted by the EPRI and the results documented in Technical Report GC-111050, "Ambient Temperature Preheat for Machine GTAW Temperbead Application," demonstrated that the temperbead repair welds using the machine GTAW technique at ambient temperature (no preheat) with no PWHT produce material properties in LAS components that are equivalent to those produced using required pre-heat and PWHT.
The basis for weld pre-heat and post-weld heat treatment are to minimize any potential for hydrogen induced cracking and weld shrinkage-induced cracking of susceptible materials. The machine GTAWtechnique permits precise and highly controlled application of weld beads. This technique minimizes the introduction of hydrogen into the welding arc. Therefore, the potential risk of inducing hydrogen delayed cracking in LAS is reduced. The potential for the weld shrinkage-induced cracking is also reduced by the machined GTAW due to precision bead placement and control of heat.
To restore the pressure boundary, the licensee will repair the degraded RVCH nozzle penetrations in the following steps.
- 1. Removal of lower portion of existing thermal sleeve assembly at applicable penetrations to provide access for lOTS weld repair.
- 2. Roll expansion above the area of repair. This stabilizes the nozzle to prevent any movement when the nozzle is separated from the nozzle to RVCH J-groove weld.
- 3. Machining to remove the nozzle to above the J-groove weld eliminating the portions of the nozzle containing unacceptable indications. This machining operation also establishes the weld prep area (refer to Figure 1 "Machining" of RR 13R-09).
- 5. Welding the remaining portion of the nozzle to the RVCH using primary water stress corrosion cracking (PWSCC) resistant Alloy 52M weld material (refer to Figure 2 of RR 13R-09).
- 6. Machining the weld and nozzle to provide a surface suitable for nondestructive examination (NOE).
-10
- 8. Abrasive water jet machining remediation on the portion of the remaining nozzle most susceptible to PWSCC. The abrasive water jet machining process removes a small amount of material thickness while imposing compressive residual stress on the nozzle surface.
- 9. Welding a new lower thermal sleeve assembly at applicable locations.
Monitoring of Interpass Temperature ASME Code Case N-638-1, paragraph 3.0(d), requires the maximum interpass temperature for field applications be 350 degrees Fahrenheit CF) regardless of the interpass temperature during qualification. All other requirements of the ASME Code,Section XI, IWA-4000, must be met when using this code case. The ASME Code,Section XI, IWA-4610(a), requires, in part, the use of thermocouples and recording instruments to monitor welding process temperatures.
The licensee proposed an alternative method in lieu of the above to ensure that the ASME Code Case N-638-1, paragraph 3.0(d), required interpass temperature limit is not exceeded. By letter dated May 18, 2012, in response to the staff's RAI, the licensee clarified the use of the heat flow calculation method and provided the heat flow calculation and justifications for not exceeding the required interpass temperature limit. The NRC staff has determined that the licensee's calculation and previous experience all provide assurances that the required interpass temperature limit is not exceed.
Nondestructive Examination The specifics of the NOE examinations required for the weld repair activities are discussed below:
48-hour hold period ASME Code Case N-638-1, paragraph 4.0(b), requires the final weld surface and the band around the area defined in paragraph 1.0(d) be examined by the NOE (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 ASME Code,Section III, NB-4622.11(d)(2), requires surface examination after the completed repair weld has been at ambient temperature for a minimum of 48 hours2 days <br />0.286 weeks <br />0.0658 months <br />. The volumetric examination is required, if practical.
The licensee proposed that the 48-hour hold period commences upon completion of the third temperbead weld layer in lieu of the above requirements. The staff recognizes that this 48-hour hold time is specified to allow sufficient time for hydrogen cracking to occur (if it is to occur) in the heat affected zone (HAZ) of susceptible materials prior to performing NOE, so that if hydrogen cracking does occur, NOE would be able to detect it. However, based on extensive research and industry experience, EPRI has provided a technical basis for starting the 48-hour hold after completion of the third temperbead weld layer rather than waiting for the completed weld to cool to ambient temperature. EPRI has documented its technical basis for this
- 11 conclusion in Topical Report 1013558, Temper Bead Welding Applications - 48 Hour Hold Requirements for Ambient Temperature Temper Bead Welding" (ADAMS Accession No. ML070670060). The NRC staff finds the licensee's proposed alternative acceptable because the licensee's technical basis provides a reasonable assurance that the hydrogen cracking, if it occurs, would be detected by the NDE.
Acceptance Examination Area ASME Code Case N-638-1, paragraph 4.0(b), requires. in part, NDE (surface and volumetric examinations) of the final weld and the band around the area defined in paragraph 1.0(d).
Paragraph 1.0(d) defines the examination area as "the area to be welded and a band around the area of at least 1% times the component thickness or 5 inches, whichever is less."
Paragraph 4.0(a) of ASME Code Case N-638-1 states that "Prior to welding, a surface examination shall be performed on the area to be welded."
Pre-weld examination In lieu of the above, the licensee proposed to perform surface examination using PT on the band around the area to be welded, which includes the exposed surface area of LAS RVCH base material extending 5-inches below the new weld. The LAS RVCH base material extending 5-inches above the new weld will not be examined, because this surface area is behind the Alloy 600 nozzle and not exposed. The purpose of this surface examination is to ensure that all flaws associated with the weld repair area have been removed, or addressed, since these flaws may be associated with the original flaw and may have been overlooked. In addition, the licensee stated that for this modification, the repair welding is performed remotely from the known flaws. The NRC staff finds the licensee's proposed extent of pre-weld surface examination acceptable because the PT examination will be performed to the maximum extent possible and the performance of the examination will provide assurance of structural integrity.
Post-weld examination or pre-service inspection (PSI)
The licensee proposed to perform PT of the new weld surface, weld taper transition, and surrounding area at least 1/2-inch below the new weld and "x" distance above the new weld on the nozzle inside surface, where "x" includes the area required by ASME Code Case N-729-1, Figure 2 ("x" is equal to 1.5 inches for incidence angle less than or equal to 30° to the horizontal plane, or 1 inch for incidence angle greater than 30° to the horizontal plane). The licensee described the area for post-weld PT examination in Figure 3 of the RR.
In addition, the licensee proposed to perform UT examination of the new weld volume extending to a depth of at least 114 inch into the LAS to include HAZ, and the surrounding volume from the highest edge of the weld taper extending up to at least 1 inch above the weld into the nozzle to a depth of nozzle thickness. The licensee described the volume for post-weld UT examination in Figure 3 of the RR. The UT will be performed from ID surface of the nozzle using 0° longitudinal (L)-wave, 45° L-wave, and 70° L-wave transducers. The UT scans provide coverage of approximately 70 percent of the weld surface and approximately 83 percent of the RVCH ferritic steel HAZ surface.
- 12 In the RR, the licensee stated that the weld taper transition region will be excluded from examination. The staff issued RAI requesting the licensee justify the assurance of structural integrity of the weld if taper transition will not be examined. In addition, the NRC staff asked the licensee to discuss the area and volume that will not be examined. By letter dated May 18, 2012, in response to the staff's RAI, the licensee stated that the entire weld including the taper transition will receive PT. The repair weld produces a region that limits the examination volume. The taper transition volume will be examined to the extent possible using 700L- and 45°L-waves and axial scans (looking down). There is no portion of the repair volume that does not receive at least single direction ultrasonic coverage.
Based on the above evaluation, the NRC staff finds the licensee's proposed post-weld examination acceptable, because the UT examination of new weld, weld taper transition, and HAZ will be performed to the maximum extent possible. All portions of the repair volume will receive at least single direction ultrasonic coverage. The entire exposed weld taper transition area will receive surface examination by PT. Furthermore, the performance of PT and UT examinations will provide assurance of structural integrity of the new weld and components.
The licensee requested to deviate from the 2001 Edition through 2003 Addenda of the ASME Code,Section III, NB-5245, requirement related to incremental surface examinations (by the magnetic particle or liquid penetrant methods) of partial penetration welds. This requirement cannot be met due to the welding layer deposition sequence (Le., each layer is deposited parallel to the penetration centerline). The NRC staff found that it is acceptable that in lieu of NB-5245, the licensee will perform surface and volumetric examinations of the final weld to the extent possible because the performance of these examinations will provide assurance of structural integrity of the new weld and components.
Inservice inspection (lSI):
Pursuant to 10 CFR 50.55a(g)(6)(ii)(D), all licensees of PWRs shall augment their lSI program with ASME Code Case N-729-1 subject to the conditions specified in paragraphs (g)(6)(ii)(D)(2) through (g)(6)(ii)(D)(6) of 10 CFR 50.55a. Table 1, Item 4.20, surface and volumetric examination requirements are specified in Figure 2 of ASME Code Case N-729-1.
To comply with the above lSI surface and volumetric examination requirements, the licensee will examine the surface and volume of the new weld including weld taper transition extending up to at least "an distance above the top edge of 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.
ASME Code Case N-729-1, Figure 2, describes the distance "a" as equal to 1.5 inches for incidence angle less than or equal to 30° to the horizontal plane, or 1 inch for incidence angle greater than 30° to the horizontal plane. The licensee described the extent of its surface and volumetric examinations in Figure 9 of the RR. Therefore, the staff finds the licensee's proposed lSI examination acceptable because the extent of surface and volumetric examinations described by Figure 9 of the RR satisfy the examinations required by Figure 2 of ASME Code Case N-729-1.
- 13 Frequency of lSI examination The licensee will comply with the regulatory requirements of 10 CFR 50.55a(g)(6)(ii)(0)(5), that states "If flaws attributed to PWSCC have been identified, whether acceptable or not for continued service under Paragraphs 3130 or 3140 of ASME Code Case N-729-1, the re-inspection interval must be each refueling outage instead of the re-inspection intervals required by Table 1, Note (8) of ASME Code Case N-729-1."
Analvtical Flaw Evaluation The licensee performed an analytical evaluation in accordance with the ASME Code,Section XI, as a part of the technical basis for the proposed weld repair and design configuration. The specifics of the licensee's analyses are evaluated below:
Triple point anomaly evaluation According to the 2001 Edition through 2003 Addenda of the ASME Code,Section III, NB-5330(b), the indications characterized as cracks, lack of fusion, or incomplete penetrations are unacceptable regardless of length.
An artifact common in temperbead welding of the partial penetration joint geometry with OMs is an anomaly in the weld at the triple point (Le., the point in the weld where the LAS RVCH base material, the Alloy 600 nozzle, and the Alloy 52M weld material intersect). Mock-up testing has verified that the triple point anomaly (Le., an irregularly shaped very small void) exits and extends the entire bore (360 degrees), but does not exceed 0.10 inch in depth. In lieu of NB-5330(b), the licensee conducted a fracture mechanics analysis of 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 inservice. The licensee conservatively modeled this anomaly as a 0.1 O-inch deep circular crack-like defect extending 3600 around the circumference of the nozzle tube at the weld triple point location in the most susceptible material. The licensee considered two possible cases in the flaw evaluations.
- 1. The first possible flaw propagation is across the nozzle wall thickness from the 00 to the 10 surface of the nozzle housing. This is the shortest path through the new Alloy 52M weld material. For completeness, the licensee postulated two types of flaws at the outside surface of the nozzle 10TB repair weld. A 360 degree continuous circumferential flaw, lying in a horizontal plane, is considered to be a conservative representation of crack-like defects that may exist in the weld triple point anomaly. This flaw is subjected to axial stresses in the nozzle. An axially oriented semi-circular outside surface flaw is also considered since it would lie in a plane normal to the higher circumferential stresses. Both of these flaws would propagate toward the inside surface of the nozzle.
- 2. The second possible flaw propagation is along the fusion line of the Alloy 52M weld material to the LAS RVCH. A cylindrically oriented flaw is postulated to lie along the weld and the RVCH interface. This flaw is subjected to radial stresses with respect to the nozzle. This flaw may propagate through either the new Alloy 52M weld material or the LAS RVCH base material.
- 14 The licensee stated that the results of the analyses demonstrate that the 0.10 inch weld anomaly (Le .* the triple point anomaly) is acceptable for a 40 year design life of Harris nozzle repair. The NRC staff issued an RAI requesting the licensee provide an explanation on why the final crack size is acceptable. By letter dated May 18. 2012. the licensee responded that the evaluation procedures and acceptance criteria of the ASME Code,Section XI. IWB-3641 and IWB-3642. were followed and a flaw evaluation based on the ASME Code,Section XI, Appendix C, was performed. The licensee stated that its analysis showed that for the postulated circumferential flaw and the axial flaw, the allowable margins of Appendix C are met.
The NRC staff finds the licensee's response acceptable because the licensee followed the required flaw analysis of IWB-3600 and Appendix C. and showed that the margins satisfied the required margins of the ASME Code.Section XI.
Regarding the susceptibility of the triple point anomaly to SCC such as PWSCC, the licensee stated that the triple point crack-like defects are not exposed to the primary coolant and the air environment. Therefore, the time-dependent crack growth rates from PWSCC are not applicable to triple point anomaly.
Based on the above evaluation, the NRC staff finds the licensee adequately demonstrated by the analytical methods in accordance with criteria of the ASME Code.Section XI, IWB-3600.
that the triple point weld anomaly remains stable for the intended service life of the repair and operating with a relevant condition at weld triple point is justified.
Remnant of J-groove weld "as left" flaw evaluation The licensee requested relief from the ASME Code.Section XI, IWB-3132.3. requirements specifically related to subsequent reexamination of the remnant of the J-groove weld. on the basis that any "as-left" flaws in the J-groove weld cannot be sized with reasonable confidence by the currently available NDE examination techniques. As an alternative. the licensee proposed using an analytical evaluation in accordance with the requirements of the ASME Code,Section XI, IWB-3132.3, with the assumption of a worst-case flaw, as a basis for reasonable assurance of RVCH structural integrity.
The licensee evaluated the J-groove weld flaw in accordance with the analytical evaluation requirements of the ASME Code,Section XI, IWB-3132.3, using a postulated worst-case flaw size. By letter dated May 18, 2012, in response to the staffs RAI. the licensee responded that the condition of the remaining J-groove weld is assumed to contain flaws. The licensee conservatively assumed that the worst-case "as-left" flaw in the remaining of the J-groove weld extend through the entire Alloy 82/182 weld and butter materials. The licensee further postulated that the dominant hoop stresses in the J-groove weld would create a situation where the preferential direction for cracking would be radial. A radial crack in the Alloy 82/182 weld metal would propagate by PWSCC through the weld and butter material to the interface with the LAS RVCH material where it would blunt or arrest. Any growth of the postulated as-left flaw into the LAS RVCH would be by fatigue crack growth under cyclic loading conditions. By letter dated May 18, 2012, in response to the staffs RAI, the licensee responded that the combination of linear elastic and elastic-plastic fracture mechanics analyses demonstrated that the RVCH nozzle repair design configuration is acceptable for 30 years of operation following an IDTB
- 15 weld repair. The NRC staff finds the licensee's flaw evaluation acceptable because the analysis requirements of the ASME Code,Section XI, IWS-3132.3, are followed.
Remnant of J-groove weld dislodged debris evaluation The staff determined that the licensee evaluated the potential for fragments dislodged if the remnant J-groove partial penetration weld would crack. The evaluation included postulating the radial cracks to occur in the weld due to the dominance of hoop stresses at this location. 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. Hence, 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 possibility of potential debris from the remnant of the J-groove weld become dislodged and affect the safe operation of the plant is insjgni"ficant.
Corrosion Evaluation As a result of the lOTS nozzle repair, a small portion of the RVCH LAS (the area between the lOTS weld and the J-groove weld) is exposed to primary coolant. The licensee evaluated potential corrosion of the RVCH LAS wetted surface. The licensee determined that general corrosion of the exposed RVCH LAS base metal will occur in the area between the lOTS weld and the J-groove weld. The licensee estimated the general corrosion rate to be 0.0036-inch per year, which has negligible impact on the RVCH and determined to be acceptable for 40-years following an lOTS weld repair. Galvanic corrosion, hydrogen embrittlement, SCC, and crevice corrosion are not expected to be a concern for the exposed RVCH LAS base metal. On the basis of the licensee's evaluation, the staff finds that the general corrosion of the exposed RVCH LAS base metal is acceptable for 40 years because the licensee's evaluation considered a reasonable corrosion rate of RVCH LAS base metal.
Evaluation of Oesign Life of Repair The licensee estimated a design life of 14.8 EFPY for the proposed lOTS repair. The licensee stated that because the design lifetime is sensitive to the length of the Alloy 52M weld ligament and the actual limiting ligament length may vary from nozzle to nozzle depending upon the as-found and as-left conditions, the design life will be re-evaluated if necessary, using the as-built data. The staff issued a RAI requesting the licensee provide its detail description and analysis that result a design life of 14.8 EFPY. Sy letter dated May 18, 2012, the licensee explained that the proposed design life of 14.8 EFPY is based on the PWSCC evaluation of the remnant of Alloy 600 nozzle. The licensee has determined that abrasive water jet machining (AW~IM) performed will create a compressive stress layer (at least 0.003-inch thick) on the surface of the Alloy 600 nozzle in areas adjacent to the lOTS weld and at the roll transition location where elevated tensile stresses may be present. Since the stresses created by the AWJM process are compressive, the licensee has determined that the PWSCC is not expected in this layer. The licensee postulated an undetected flaw, 0.002-inch deep (twice the maximum particle depth of the AWJM abrasive material), which leaves a compressive stress layer
- 16 0.001-inch thick. The licensee has determined that the general corrosion of a 0.001-inch thick compressive layer take about 12.5 EFPY. Once the compressive stress layer is removed by general corrosion, the licensee assumed that the PWSCC would initiate immediately. The licensee has determined that it takes about 2.3 EFPY for the PWSCC crack to propagate to 75 percent of the original Alloy 600 nozzle wall thickness. Therefore, the licensee has estimated the total life of the repair to be 14.8 EFPY and determined to be the most limiting life of the repair design.
On the basis of above evaluation, the NRC staff determined that the licensee has performed flaw analyses of the triple point anomaly in the new weld, the worst-case "as-left" flaw in the remnant of J-groove weld, and the PWSCC evaluation of remaining Alloy-600 nozzle to estimate an acceptable design life of the repair. The NRC staff finds the licensee's proposed life expectancy of 14.8 EFPY for the repair design acceptable because it is based on the most limiting life predicted amongst the flaw analysis.
5.0 CONCLUSION
As set forth above, the NRC staff has determined that RR 13R-09 will provide an acceptable level of quality and safety for the repair of the degraded RVCH penetration nozzles.
Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR SO.S5a(a)(3)(i). Therefore, the NRC staff authorizes the use of RR 13R-09 at Harris for the third 10-year lSI interval, which commenced on May 2, 2007, and will end on May 1, 2017. The RVCH repaired nozzles are acceptable for the design life of the repair which is 14.8 EFPY or until the RVCH is replaced, whichever occurs first.
All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including the third party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: Ali Rezai Date: October 2, 2012
.. ML12270A258 OFFICE LPL2*2/PM LPL2-2/LA NRRlDE/EPNB* LPL2*2/BC(A) LPL2-2/PM NAME ABillochCol6n BClayton JTsao for TLupold JQuichocho ABillochCol6n DATE 09/26/12 10/1112 09/20/12 10/2112 10/2/12