ML12334A549
| ML12334A549 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 12/19/2012 |
| From: | Robert Pascarelli Plant Licensing Branch II |
| To: | Gillespie P Duke Energy Carolinas |
| Thompson, Jon | |
| References | |
| TAC ME8010, TAC ME8036 | |
| Download: ML12334A549 (16) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 December 19, 2012 Mr. Preston Gillespie Site Vice President Oconee Nuclear Station Duke Energy Carolinas, LLC 7800 Rochester Highway Seneca, SC 29672-07S2 SUB..IECT: OCONEE NUCLEAR STATION, UNITS 1 AND 2, RELIEF FROM THE REQUIREMENTS OF THE ASME CODE (TAC NOS. ME8010 THROUGH ME8036)
Dear Mr. Gillespie:
By letter dated December 23, 2011, as supplemented by letter dated September 28, 2012, Duke Energy Carolinas, LLC (Duke Energy, the licensee) submitted a request to the Nuclear Regulatory Commission (NRC) for relief from certain American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, requirements related to inservice inspection (lSI) of welds at Oconee Nuclear Station, Units 1 and 2 (ONS 1 and 2). Relief Request 11-0N-001 was requested for the remainder of ONS 1 and 2 fourth 10-year lSI interval.
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Part SO, Section SO.SSa(g)(S)(iii), the licensee requested relief on the basis that complying with the specified requirement is impractical.
The NRC staff has reviewed the subject request and concludes, as set forth in the enclosed safety evaluation, that granting relief pursuant to 10 CFR SO.SSa(g)(6)(i) is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR SO.SSa(g)(6)(i), and is in compliance with the ASME Code's requirements. Therefore, the NRC staff grants relief for the subject examinations of the components contained in 11-0N-001, Sections 2.0 through 26.0, at ONS 1 and 2 for the duration of the ONS 1 and 2 fourth 1O-year lSI interval, currently scheduled to end on July 1S, 2014.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Sections 27.0 and 28.0 of 11-0N-001, submitted by letter dated December 23, 2011, were subsequently withdrawn by the licensee by letter dated September 28, 2012, and were not evaluated by the NRC staff and relief for the subject examinations of the components in these sections of 11-0N-001 is not granted.
P. Gillespie - 2 If you have any questions, please contact the Project Manager, John Boska, at 301-415-2901, or via email at John.Boska@nrc.gov.
Sincerely, Robert J. Pascarelli, Chief Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-269 and 50-270
Enclosure:
As stated cc w/encl: Distribution via Listserv
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST NO. 11-0N-001 DUKE ENERGY CAROLINAS, LLC OCONEE NUCLEAR STATION, UNITS 1 AND 2 DOCKET NOS. 50-269 AND 50-270
1.0 INTRODUCTION
By letter dated December 23, 2011 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12009A091), as supplemented by letter dated September 28, 2012 (ADAMS Accession No. ML12276A376), Duke Energy Carolinas, LLC (Duke Energy, the licensee), submitted a relief request, 11-0N-001, to the U.S. Nuclear Regulatory Commission (NRC) staff for review and approval. The licensee requested relief from certain inservice inspection (lSI) requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code)Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components for Oconee Nuclear Station." Specifically, the licensee has requested relief from ASME Code requirements pursuant to the regulation at Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.55a(g)(5)(iii) on the basis that complying with the specified requirement is impractical. The relief is requested for several welds where the licensee was not able to achieve essentially 100 percent inspection coverage due to limitations of design, geometry, and materials of construction of the components.
The ASME Code of record for the fourth 1O-year interval lSI interval for both Oconee Nuclear Station, Units 1 and 2 (ONS 1 and 2) is the ASME Code,Section XI, 1998 Edition through the 2000 Addenda, as modified by Code Case 1\1-640. The fourth 1O-year lSI intervals for ONS 1 and 2 are projected to end on July 15, 2014.
In its letter dated September 28, 2012, the licensee withdrew Sections 27 and 28 of the subject relief request 11-0N-001.
2.0 REGULATORY REQUIREMENTS The lSI of ASME Code Class 1, 2, and 3 components is to be performed in accordance with the requirements of Section XI, "Rules for In service Inspection of Nuclear Power Plant Components,"
of the ASME Code and applicable editions and addenda as required by 10 CFR 50.55a(g), except where specific written relief has been granted by the Commission.
Enclosure
-2 Pursuant to 10 CFR SO.SSa(g)(4), ASME Code Class 1, 2, and 3 components (including supports)
"must meet the requirements, except design and access provisions and the preservice examination requirements," set forth in the ASME Code,Section XI," 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 conducted during the first 1O-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 SO.SSa(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein.
The regulation at 10 CFR SO.SSa(g)(S)(iii), states that "If the licensee has determined that conformance with a[n ASME] code requirement is impractical for its facility, the licensee shall notify the NRC and submit, as specified in Section SO.4, information to support the determinations. Determinations of impracticality in accordance with this section must be based on the demonstrated limitations experienced when attempting to comply with the code requirements during the inservice inspection interval for which the request is being submitted.
Requests for relief made in accordance with this section must be submitted to the NRC no later than 12 months after the expiration of the initial or subsequent 120-month inspection interval for which relief is sought."
The regulation at 10 CFR SO.SSa(g)(6)(i), states that "The Commission will evaluate determinations under paragraph (g)(S) of this section that code requirements are impractical. The Commission may grant such relief and may impose such alternative requirements as it determines is authorized by law and will not endanger life or property or the common defense and security and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility."
3.0 LICENSEE'S PROPOSED ALTERNATIVE The information provided by the licensee in support of the request for relief from ASME Code requirements has been evaluated and the basis for disposition is documented below. For clarity, the request has been evaluated in several parts according to ASME Code,Section XI, Examination Category.
3.1 Request for Relief 11-0N-001, Part A, ASME Code,Section XI, Examination Category 8-0, Items 83.110 and 83.1S0, Full Penetration Welded Nozzles in Vessels ASME Code Components Affected The ASME Code components affected by the licensee's proposed alternative are identified in Tables 3.1,1 and 3.1.2 below.
ASME Code Requirement ASME Code,Section XI, Examination Category 8-0, Items 83.110 and 83.1S0, require 100 percent volumetric examination, as defined by ASME Code,Section XI, Figures IW8-2S00-7 (a) through (d). as applicable, of full penetration Class 1 pressurizer (PZR) and heat exchanger (primary side) nozzle-to-vessel welds. ASME Code Case N-460, "Alternative Examination Coverage for Class 1 and Class 2 Welds, Division 1" as an alternative approved for use by the
- 3 NRC in Regulatory Guide (RG) 1.147, Rev. 16, "Inservice Inspection Code Case Acceptability,"
states that "a reduction in examination coverage due to part geometry or interference for any
[ASME Code] Class 1 and 2 weld is acceptable provided that the reduction is less than 10 percent, i.e., greater than 90 percent examination coverage is obtained."
Table 3.1.1, ONS 1 Welds in 11-0N-001. Sections 2.0 through 8.0 11-0N-001 ASME WeldlD Weld Type Coverage Section Code Obtained No. Item Percent 2.0 83.110 1-PZR-WP26-4 PZR Upper Shell-to-Sampling 34.7 Nozzle 3.0 83.110 1-PZR-WP26-5 PZR Upper Shell-to-Sampling 34.7 Nozzle 4.0 83.110 1-PZR-WP26-6 PZR Upper Shell-to-Sampling 34.7 Nozzle 5.0 83.110 1-PZR-WP26-1 PZR Upper Shell-to-Sampling 34.7 Nozzle 6.0 83.110 1-PZR-WP26-2 PZR Upper Shell-to-Sampling 34.7 Nozzle 7.0 83.150 1-51 A-1-53755-V1 Letdown Cooler 18 54.6 Nozzle-to-ChanneI80dy 8.0 83.150 1-51A-1-53755-V2 Letdown Cooler 18 54.6 Nozzle-to-ChanneI80dy Table 3.1.2. ONS 2 Welds in 11-0N-001. Sections 19.0 through 21.0 11-0N-001 ASME WeldlD Weld Type Coverage Section Code Obtained No. Item Percent 19.0 83.110 mZR-WP34 PZR Upper Head-to-Spray Nozzle 76.1
?0.0 83.110 ZR-WP33-3 PZR Upper Head-to-Relief Nozzle 71.2 I 21.0 83.110 2-PZR-WP33-1 PZR Upper Head-to-Relief Nozzle 71.2 Duration of the ASME Relief Request The licensee requested approval of this alternative for the fourth ten-year lSI interval for ONS 1 and 2 currently scheduled to end on July 15, 2014.
Licensee's ASME Code Relief Request In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required volumetric examinations for the PZR and Letdown Cooler nozzle-to-vessel welds listed below in Tables 3.1.1 (ONS 1) and 3.1.2 (ONS 2).
-4 Licensee's Proposed Alternative Examination The licensee did not propose any alternative examinations for the subject welds. However, the licensee's examinations were performed to the maximum extent practical.
Licensee's Basis for Relief Request For the PZR Nozzle-to-Vessel Welds (11-0NS-001, Sections 2.0 through 8.0 and 19.0 through 21.0) the licensee's stated basis for the relief request was that:
The limitation was caused by the design of the [sampling, spray, or relief] nozzle not allowing for scanning from the nozzle side of the weld. In order to scan aI/ of the required volume for this weld, the nozzle would have to be redesigned, which is impractical. "
The Oconee Inservice Inspection Plan allows the use of Code Case N-460, which requires greater than 90% volumetric coverage of examination volume A-B-C-O-E-F-G-H-1. The achieved coverage did not meet the acceptance criteria of this [ASME] Code Case.
For the Letdown Cooler Nozzle-to-Vessel Welds (11-0N-001, Sections 7.0 and 8.0) the licensee's stated basis for the relief request was that:
.. ,The limitation was caused by the weld taper configuration created by the attachment of the nozzle to the channel body [configuration]. In order to scan aI/ of the required volume for this weld, the nozzle to channel body would have to be redesigned to allow scanning from both sides of the weld, which is impractical. There were no recordable indications found during the examination of this weld. This weld was examined using procedures
[equipment,] and personnel qualified in accordance with ASME Section XI, Appendix III.
The Oconee Inservice Inspection Plan allows the use of [ASME] Code Case N-460, which requires greater than 90% volumetric coverage of examination volume A-B-C-O-E-F-G-H-I. The achieved coverage did not meet the acceptance criteria of this
[ASME] Code Case.
NRC Staff Evaluation
The ASME Code requires 100 percent volumetric examination of ASME Code, Class 1 nozzle-to-vessel welds. However, the design configuration of the subject welds and curvature of the nozzle blend radii limit access for ultrasonic (UT) scanning. In order to effectively increase the examination coverage, the nozzle-to-vessel welds would require design modifications. This would place a burden on the licensee; thus, obtaining 100 percent of ASME Code-required volumetric examinations is considered impractical.
The subject PZR nozzle-to-vessel welds in ONS 1 (Table 3.1.1) and ONS 2 (Table 3.1.2) are constructed of carbon steel material with stainless steel inside diameter surface cladding. The Letdown Cooler nozzle-to-vessel welds in ONS 1 (Table 3.1.1) are constructed of wrought stainless steel material. These full penetration butt welds extend the full thickness of the vessel head, and the nozzle configurations are of the "set-in" design, which essentially makes the welds concentric rings aligned parallel with the nozzle axes in the through-wall direction of the vessel.
This nozzle design geometry restricts UT scanning to only the shell side of the welds. In addition,
-5 UT scans cannot be performed from the curved outer diameter (00) surface in the nozzle blend radius regions, further limiting the volumetric examinations.
As shown on the sketches and technical descriptions included in the licensee's submittals, examinations of the subject PZR and Letdown Cooler nozzle-to-vessel welds have been completed to the extent practical with volumetric coverage ranging from approximately 34.7 percent to 7S.1 percent (see Tables 3.1.1 and 3.1.2) of the ASME Code-required volumes. The examination volumes included the weld and base materials near the inside surface of the weld joint, which are high regions of stress, and where one would expect degradation sources to be manifested should they occur. The PZR and Letdown Cooler nozzle-to-vessel weld examinations were performed with manual UT techniques in accordance with the applicable requirements of the ASME Code,Section V, Article 4, and ASME Code Section XI, Appendix III, respectively. The welds were examined using 35-, 45-, SO-degree shear, and 0-, SO-, and 70-degree longitudinal waves (L-waves), as applicable. There were no indications detected on the subject nozzles.
Although UT scans were primarily limited to the vessel side, studies have found that inspections conducted through carbon steel are equally effective whether the UT waves have only to propagate through the base metal, or have to also propagate through the carbon steel weldment. 1 Therefore, it is expected that the UT techniques employed by the licensee on the PZR nozzle-to-vessel welds would detect structurally significant flaws that might occur on either side of the subject welds due to the fine-grained carbon steel microstructures present in these materials.
Additionally, L-waves have been shown to provide enhanced detection on the far-side of austenitic stainless steel welds 2 ,3.4. While the licensee has only taken credit for limited volumetric coverage obtained from primarily one side, it is expected that the techniques employed would have provided coverage beyond the near-side of the Letdown Cooler nozzle-to-vessel welds.
The licensee has shown that it is impractical to meet the ASME Code-required 100 percent volumetric examination coverage for the subject nozzle-to-vessel welds due to nozzle design and curvature of the nozzle blend radii. Based on the volumetric coverage obtained for the subject welds, and considering the licensee's performance of UT techniques employed to maximize this coverage, the NRC staff finds that it is reasonable to conclude that if significant service-induced degradation had occurred, evidence of it would have been detected by the examinations that were performed.
3.2 Request for Relief 11-0N-001, Part B, ASME Code,Section XI, Examination Category B-J, Item B9.11, Pressure Retaining Welds in Piping, ASME Code Components Affected The ASME Code components affected by the licensee's proposed alternative are identified in 1 P. G. Heasler, and S. R. Doctor. Piping Inspection Round Robin, NUREG/CR-5068, PNNL-10475, U.S. NRC, Washington, DC, 1996.
2F. V. Ammirato, X. Edelmann, and S. M. Walker, Examination of Dissimilar Metal Welds in BWR Nozzle-fo-Safe End JOints, 8th International Conference on NDE in the Nuclear Industry, ASM International, 1987.
3 P. Lemaitre, T. D. Koble, and S. R. Doctor, PISC 11/ Capability Study on Wrought-to-Wrought Austenitic Steel Welds:
Evaluation at the Level of Procedures and Techniques, Effectiveness of Nondestructive Examination Systems and Performance Demonstration, PVP-Volume 317, NDE-Volume 14, ASME, 1995.
4 M. T. Anderson, A. A. Diaz, A. D. Cinson, S. L. Crawford, S. E. Cumblidge, S. R. Doctor, K. M. Denslow, and S. Ahmed. An Assessment of Ultrasonic Techniques for Far-Side Examinations of Austenitic Stainless Steel Piping Welds, NUREG/CR-7113. PNNL-19353, U. S. Nuclear Regulatory Commission, Washington, DC, November 2011.
- 6 Tables 3.2.1 and 3.2.2 below.
Table 3.2.1, ONS 1 Welds in 11-0N-001. Sections 9.0 through 11.0 11-0N-001 ASME WeldlD Weld Type Coverage Section No. Code Obtained Item Percent 9.0 89.11 1LP-209-8L Valve 1CF-13-to-Elbow 37.S 10.0 83.110 1PIA2-9 RCP 1A2 Casing Nozzle-to-Safe 36.3 End 11.0 83.110 1PDA2-1 RCP 1A2 Casing Nozzle-to-Safe 37.S End Table 3.2.2, ONS 2 Welds in 11-0N-001, Sections 22.0 through 24.0 11-0N-001 ASME WeldlD Weld Type Coverage Section No. Code Obtained Item Percent 22.0 89.11 2-PIA1-8 RCP 2A1 Casing Nozzle-to-Safe 37.S End 23.0 89.11 2-PDA2-1 RCP 2A2 Casing Nozzle-to-Safe 38.7 End 24.0 89.11 2-PD82-1 RCP 282 Casing Nozzle-to-Safe 39.S End Duration of the ASME Relief Reguest The licensee requested approval of this alternative for the fourth ten-year lSI interval for ONS 1 and 2 currently scheduled to end on July 1S, 2014.
ASME Code Reguirement ASME Code,Section XI, Examination Category 8-J, Item 89.11, requires essentially 100 percent volumetric and surface examinations, as defined by ASME Code,Section XI, Figure IW8-2S00-8, for circumferential piping welds nominal pipe size (NPS) 4 or larger. "Essentially 100%", as clarified by ASME Code Case N-460, is greater than 90% coverage of the examination volume, or surface area, as applicable. ASME Code Case N-460 has been approved for use by the NRC staff in RG 1.147, Rev, 16.
Licensee's ASME Code Relief Reguest In accordance with 10 CFR SO.SSa{g)(S){iii), the licensee requested relief from the ASME Code-required volumetric examination of Class 1 stainless steel piping welds shown in Tables 3.2.1 (ONS 1) and 3.2,2 (ONS 2).
-7 Licensee's Proposed Alternative Examination The licensee did not propose any alternative examinations for the subject welds. However, the licensee's examinations were performed to the maximum extent practical.
Licensee's Basis for Relief Request For the Valve-to-Elbow Weld (11-0N-001, Section 9.0) the licensee's stated basis for the relief request was that:
The limitation was caused by the cast stainless material and the weld taper configuration created by the attachment of the valve to elbow configuration. In order to scan all of the required volume for this weld, the valve would have to be replaced with forged stainless steel and would have to be redesigned to allow scanning from both sides of the weld, which is impractical ....
For the ONS 1 Reactor Coolant Pump (RCP) Casing Nozzle-to-Safe End Welds (11-0N-001, Sections 10.0 and 11.0) the licensee's stated basis for the relief request was that:
The /imitation was caused by the cast stainless material and the weld taper configuration created by the attachment of the nozzle to safe end configuration. In order to scan all of the required volume for this weld, the pump would have to be replaced with forged stainless steel and would have to be redesigned to allow scanning from both sides of the weld, which is impractical. ...
For the ONS 2 RCP Casing Nozzle-to-Safe End Welds (11-0N-001, Sections 22.0 through 24.0) the licensee's stated basis for the relief request was that:
The limitations were caused by the cast stainless steel pump casing material. In order to scan all of the required volume for these welds, the pump casing would have to be redesigned, which is impractical.
NRC Staff Evaluation
The ASME Code requires essentially 100 percent volumetric and surface examinations for selected ASME Code,Section XI, Examination Category B-J pressure retaining welds in piping.
However, complete volumetric examinations are restricted by component design, materials and weld configurations. These conditions preclude the licensee from obtaining full volumetric examinations from both sides of these welds. To gain access for examination, the welds would require design modifications. Imposition of this requirement would create a burden on the licensee, therefore, the ASME Code-required volumetric examinations are considered impractical.
As shown on the sketches and technical descriptions included in the licensee's submittals, examinations of the subject RCP casing nozzle-to-safe end and valve-to-elbow welds have been completed to the extent practical with volumetric coverage ranging from approximately 36.3 percent to 39.5 percent of the ASME Code-required volumes (see Tables 3.2.1 and 3.2.2 above).
The limitations encountered during the performance of the UT examinations were caused by cast
-8 austenitic stainless steel materials, curvature of the taper of the transition region from the nozzle-to-safe end, and curvature of the valve taper in the valve-to-elbow weld configuration.
These configurations limit the volumetric examinations primarily to the wrought stainless steel side of these welds.
Volumetric examinations on the subject welds were conducted with equipment, procedures and personnel that were qualified to a performance demonstration process outlined in ASME Code Section XI, Appendix VIII. These techniques have been qualified for flaws located on the near-side of the welds; far-side detection of flaws is considered to be a "best effort." In addition, no ASME Code,Section XI, Appendix VIII, requirements currently exist for UT scanning through cast stainless steel. The licensee's UT scanning techniques included combinations of 45- and 60-degree shear, and/or 60- and 70-degree refracted longitudinal waves (L-waves), as applicable, for Class 1 piping welds listed in Tables 3.2.1 and 3.2.2 above, from the accessible side of the welds. L-waves have been shown to provide enhanced detection on the far-side of austenitic stainless steel welds 2 , 3. 4, therefore, while the licensee has only taken credit for obtaining less than 50 percent volumetric coverage, it is expected that the techniques employed would have provided coverage beyond the near-side of the welds. The licensee completed the ASME Code-required surface examinations (liquid penetrant) with no limitations on the subject welds listed in Table 3.2.1 for ONS 1 above. For ONS 2, the licensee implemented ASME Code Case N-663, "Alternative Requirements for Classes 1 and 2 Surface Examination" (approved for use in RG 1.147, Rev. 16); therefore, no surface examinations were required for the welds listed in Table 3.2.2 for ONS 2 above. No recordable indications were observed during the UT and surface examinations.
The licensee has shown that it is impractical to meet the ASME Code-required volumetric examination coverage for the subject welds due to the design geometry of the welds and materials of construction. Based on the volumetric coverage obtained, and considering the full surface examination performed for ONS 1 welds, it is reasonable to conclude that, if significant service-induced degradation had occurred in the subject welds, evidence of it would have been detected by the examinations performed.
3.3 Request for Relief 11-0N-001, Part C, ASME Code,Section XI, Examination Category C-F-1, Items C5.11 and C5.21, Pressure Retaining Welds in Austenitic Stainless Steel or High Alloy Piping, ONS 1 and 2, ASME Code Components Affected The ASME Code components affected by the licensee's proposed alternative are identified in Tables 3.3.1 and 3.3,2 below.
Duration of the ASME Relief Request The licensee requested approval of this alternative for the fourth ten-year lSI interval for ONS 1 and 2 currently scheduled to end on July 15, 2014.
- 9 Table 3.3.1, ONS 1 Welds in 11-0N-001, Sections 12.0 through 18.0 I 11-0N-001 ASME WeldlD Weld Type Pipe Size- Coverage Section Code Thickness Obtained No. Item Inches Percent 12.0 C5.11 1-53A-02-65L Pipe-to-Valve 10.0-1.125 37.5 I 1LP-47 13.0 C5.21 1-51A-04-1C Pipe-to-Valve 4.0 -0.674 37.5 1HP-194 14.0 C5.21 1HP-387-118A Elbow-to-Valve 4.0 - 0.531 75.0 1HP-118 15.0 C5.21 1HP-193-17 Pipe-to-Tee 2.5 - 0.375 37.5 16.0 C5.21 1-51A-02-16BH Pipe-to- Flange 4.0 - 0.531 37.5 17.0 C5.21=JHP-0187-184 Pipe-to-Valve 4.0 - 0.531 37.5 18.0 C5.21 HP-0187-185 Pipe-to-Valve 4.0 - 0.531 37.5 Table 3.3.2, ONS 2 Welds in 11-0N-001, Sections 25.0 and 26.0 11-0N-001 ASME WeldlD Weld Type Pipe Size- Coverage Section Code Thickness Obtained No. Item Inches Percent 25.0 C5.11 2LP-215-27 Pipe-to-Valve 10.0-1.0 74.9 2LP-177 26.0 C5.21 2HP-341-V1 Pipe-to-Valve 2.5 - 0.375 62.5 2HP-120 Note: In the licensee's response dated September 28,2012 to the NRC RAI, Duke Energy withdrew Sections 27.0 and 28.0 (preservice pipe-to-valve Welds 2-51A-0029-94, and 2-HP-0396-23, Examination Category C-F-1, Item C5.21) from 11-0N-001. These welds were removed because Duke Energy had determined that preservice examination of these welds was not required and relief was no longer needed.
ASME Code Reguirement ASME Code,Section XI, Examination Category C-F-1, Items C5.11 and C5.21, require 100 percent surface and volumetric examination, as defined by ASME Code,Section XI, Figure IWC-2500-7, of selected ASME Code, Class 2 austenitic stainless steel or high alloy circumferential piping welds. ASME Code Case N-460, as an alternative approved for use by the NRC staff in RG 1.147, Rev. 16, states that "a reduction in examination coverage due to part geometry or interference for any [ASME Code], Class 1 and 2 weld is acceptable provided that the reduction is less than 10 percent, Le., greater than 90 percent examination coverage is obtained."
Licensee's ASME Code Relief Request In accordance with 10 CFR 50.55a(g)(5)(iii), the licensee requested relief from the ASME Code-required 100 percent volumetric examination of the Class 2 austenitic stainless steel welds
- 10 shown in Tables 3.3.1 (ONS 1) and 3.3.2 (ONS 2).
Licensee's Proposed Alternative Examination The licensee did not propose any alternative examinations for the subject welds. However, the licensee's examinations were performed to the maximum extent practical.
Licensee's Basis for Relief Request For the Pipe-to-Valve Weld (11-0N-001, Section 12.0) the licensee's stated basis for the relief request in their RAI response dated September 28,2012, was that:
The impracticality was caused by the cast stainless steel material which cannot be effectively interrogated by ultrasound. There are currently no examination techniques that have been qualified through Appendix VIII. Therefore coverage could not be obtained by scanning from the valve side. In order to scan all of the required volume for this weld, the valve would have to be redesigned and replaced, which is impractical ....
For the Pipe-to-Valve and Elbow-to-Valve Welds (11-0N-001, Sections 13.0 and 14.0) the licensee's stated basis for the relief in their RAI response dated September 28, 2012, was that:
The impracticality was caused by the configuration of the valve body which did not allow access to the full volume of the weld. Therefore coverage could not be obtained by scanning from the valve side. In order to scan all of the required volume for this weld, the valve would have to be redesigned and replaced, which is impractical ....
For the Pipe-to-Tee Weld (11-0N-001, Section 15.0) the licensee's stated basis for the relief request in their RAI response dated September 28, 2012, was that:
The impracticality was caused by the configuration of the tee which did not allow access to the full volume of the weld. Therefore coverage could not be obtained by scanning from the tee side. In order to scan all of the required volume for this weld, the tee would have to be redesigned and replaced, which is impractical ....
For the Pipe-to-Flange Weld (11-0N-001, Section 16.0) the licensee's stated basis for the relief request in their RAI response dated September 28, 2012, was that:
The impracticality was caused by the configuration of the flange which did not allow access to the full volume of the weld. Therefore coverage could not be obtained by scanning from the flange side. In order to scan all of the required volume for this weld, the flange would have to be redesigned and replaced, which is impractical ....
For the Pipe-to-Valve Weld (11-0N-001, Section 17.0) the licensee's stated basis for the relief request was that:
In order to scan all of the required volume for this weld, the valve would have to be redesigned. There were no recordable indications found during the examination of this weld.
- 11 The Oconee Inservice Inspection Plan allows the use of Code Case N-460, which requires greater than 90% volumetric coverage of examination volume C-O-E-F. Therefore, the available coverage will not meet the acceptance criteria of this Code Case.
For the Pipe-to-Valve Weld (11-0N-001, Section 18.0) the licensee's stated basis for the relief request was that:
In order to scan all of the required volume for this weld, the valve would have to be redesigned. There were no recordable indications found during the examination of this weld.
The Oconee In service Inspection Plan allows the use of Code Case N-460, which requires greater than 90% volumetric coverage of examination volume C-O-E-F. Therefore, the available coverage will not meet the acceptance criteria of this Code Case.
For the ONS 2 Pipe-to-Valve Weld (11-0N-001, Section 25.0) the licensee's stated basis for the relief request was that:
The limitation was caused by the taper of the valve body, and a weld-o-Iet. In order to scan all of the required volume for this weld, the valve would have to be redesigned, which is impractical.
The Oconee Inservice Inspection Plan allows the use of Code Case N-460, which requires greater than 90% volumetric coverage of examination volume C-O-E-F. Therefore, the available coverage will not meet the acceptance criteria of this Code Case.
For the ONS 2 Pipe-to-Valve Weld (11-0N-001, Section 26.0) the licensee's stated basis for the relief request was that:
The limitation was caused by the taper of the valve body. In order to scan all of the required volume for this weld, the valve would have to be redesigned, which is impractical.
The Oconee In service Inspection Plan allows the use of Code Case N-460, which requires greater than 90% volumetric coverage of examination volume C-O-E-F. Therefore, the available coverage will not meet the acceptance criteria of this Code Case.
NRC Staff Evaluation
The ASME Code requires 100 percent volumetric and surface examination for selected ASME Code Class 2 pressure-retaining welds in austenitic stainless steel or high alloy circumferential piping. However, volumetric examinations are limited by the design geometry, material of the welds, and associated piping configurations. To gain access for examination, the welds and piping would require design modifications. Imposition of this requirement would create a burden on the licensee, therefore, the ASME Code-required 100 percent volumetric examinations of the welds are considered impractical.
As shown on the sketches and technical descriptions included in the licensee's submittal, access for examination of the subject welds is limited to primarily one side of these welds due to the
- 12 presence of cast stainless steel materials, flange configurations, radius on tees, intrados of elbows, weld-o-Iet, and/or valve taper configurations (see Tables 3.3.1 and 3.3.2 above for specific weld configurations). The UT techniques employed for these welds have been qualified through the industry's Performance Demonstration Initiative (PDI), which meets ASME Code,Section XI, Appendix VIII requirements. These techniques have been qualified for flaws located on the near-side of the welds; far-side detection of flaws is considered to be a "best effort." In addition, no Appendix VIII requirements currently exist for ultrasonic scanning through cast stainless steel. For these reasons, the licensee has only taken credit for obtaining limited volumetric examination coverage. The licensee completed the ASME Code-required liquid penetrant (PT) surface examinations to their full extent for the subject welds listed in Table 3.3.1 above for ONS 1 and no unacceptable indications were noted. For ONS 2, the licensee implemented ASME Code Case N-663; therefore, no surface examinations were required for the welds listed in Table 3.3.2 above for ONS 2. There were two indications detected during volumetric examinations of pipe-to-valve Weld 1-51A-04-1C that were determined to be a result of component geometry and were acceptable without further evaluation.
The licensee's ultrasonic techniques included 38-, 45-, 60-, and/or 70- degree shear waves, and in some cases, 60- and 70-degree refracted longitudinal waves (L-waves), as applicable.
L-waves have been shown to provide enhanced detection on the far-side of austenitic stainless steel welds 2,3,4. While the licensee has only taken credit for limited volumetric coverage obtained from primarily one side, it is expected that the techniques employed would have provided coverage beyond the near-side of the welds.
The licensee has shown that it is impractical to meet the ASME Code-required 100 percent volumetric examination coverage for the subject piping welds due to their configurations and materials. Although the ASME Code-required coverage could not be obtained, the ultrasonic techniques employed would have provided full volumetric coverage for the near-side of the welds and limited volumetric coverage for the weld fusion zone and base materials on the opposite side of the welds. Based on the aggregate coverage obtained for the subject welds, and considering the licensee's performance of a full surface examination for ONS 1 welds, it is reasonable to conclude that if significant service-induced degradation had occurred, evidence of it would have been detected.
4.0 CONCLUSION
As set forth above, the NRC staff has determines that granting relief pursuant to 10 CFR 50.55a(g)(6)(i) is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the facility.
Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(g)(6)(i), and is in compliance with the ASME Code's requirements. Therefore, the NRC staff grants relief for the subject examinations of the components contained in 11-0N-001, Sections 2.0 through 26.0, for the duration of the ONS 1 and 2 fourth 10-year lSI interval, currently scheduled to end on July 15, 2014.
Sections 27.0 and 28.0 of 11-0N-001, submitted by letter dated December 23,2011, were subsequently withdrawn by the licensee by letter dated September 28, 2012, and were not evaluated by the NRC staff and relief for the subject examinations of the components in these sections of 11-0N-001 is not granted.
- 13 All other ASME Code,Section XI requirements for which relief was not specifically requested and approved will remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: T. McLellan, NRR M. Audrain, NRR Date: December 19,2012
P. Gillespie -2 If you have any questions, please contact the Project Manager, John Boska, at 301-415-2901, or via email at John.Boska@nrc.gov.
Sincerely, IRA!
Robert J. Pascarelli, Chief Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-269 and 50-270
Enclosure:
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