ML102870030
| ML102870030 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 11/16/2010 |
| From: | Kulesa G Plant Licensing Branch II |
| To: | Ajluni M Southern Nuclear Operating Co |
| Martin R, NRR/DORL, 415-1493 | |
| References | |
| TAC ME3752, TAC ME3753, VEGP-ISI-ALT-03 | |
| Download: ML102870030 (10) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 November 16, 2010 Mr. Mark J. Ajluni Manager, Nuclear Licensing Southern Nuclear Operating Company, Inc 40 Inverness Center Parkway Birmingham, Alabama 35201
SUBJECT:
VOGTLE ELECTRIC GENERATING PLANT, UNITS 1 AND 2, SAFETY EVALUATION OF RELIEF REQUEST VEGP-ISI-ALT-03, VERSION 3.0, FOR REACTOR VESSEL NOZZLE TO SAFE-END DISSIMILAR METAL WELD AND ADJACENT AUSTENITIC SAFE-END WELD EXAMINATIONS (TAC NOS.
ME3752 AND ME3753)
Dear Mr. Ajluni:
By letters to the U.S. Nuclear Regulatory Commission (NRC), dated April 7, 2010, and September 7,2010, Southern Nuclear Operating Company, Inc. (SNC, the licensee) submitted request for relief at the Vogtle Electric Generating Plant (VEGP), Units 1 and 2, for VEGP-ISI ALT-03 from certain examination qualification requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code).
Based on the proposed alternatives and information provided in SNC's submittal, the NRC staff has determined that requiring SNC to qualify procedures, personnel, and equipment to meet the maximum error of 0.125 inch root mean square error (RMSE) for crack depth sizing is not feasible at the present time. The SNC's proposal of adding the difference between the ASME Code-required RMSE and the demonstrated RMSE to the measured through-wall extent, in addition to the use of the appropriate ASME Code Section XI acceptance standards, provides reasonable assurance of structural integrity of the subject welds. Additionally, SNC's proposal to use surface geometry profiling combined with eddy current examination provides reasonable assurance that the axial flaws in the presence of rough surfaces will be detected, thus providing a reasonable assurance of structural integrity of the subject welds. Therefore, granting relief pursuant to Title 10 of the Code of Federal Regulations 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.
Relief is granted for the third 10-year lSI interval for the VEGP, which began on May 31,2007, and is scheduled to end on May 30,2017.
M. Ajluni
- 2 All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
Docket Nos. 50-424 and 50-425
Enclosure:
Safety Evaluation cc w/encl: Distribution via Listserv Sincerely, j°J;J4.f;J~
I I
,/
r-c9 Gloria Kulesa, Branch Chief Plant Licensing Branch 11-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RELIEF REQUEST NO. ISI-ALT-03, VERSION 3.0, THIRD 10-YEAR INSERVICE INSPECTION INTERVAL SOUTHERN NUCLEAR OPERATING COMPANY, INC.
VOGTLE ELECTRIC GENERATING PLANT (VEGP), UNITS 1 AND 2 DOCKET NOS. 50-424 AND 50-425
1.0 INTRODUCTION
By letter dated April 7, 2010 (Agencywide Documents Access and Management System (ADAMS) ML100970408), Southern Nuclear Operating Company (SNC, the licensee) submitted VEGP-ISI-ALT-03, Version 2.0, to request relief from certain examination requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code). In response to the U.S. Nuclear Regulatory Commission staff's (NRC) Request for Additional Information, the licensee submitted a revised version of the relief request, VEGP-ISI-ALT-03, Version 3.0, dated September 7,2010 (ADAMS Accession No. ML102500097). In that letter, the licensee requested, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(a)(3)(i), that the NRC staff approve relief request VEGP ISI-ALT-03, Version 3.0, that relates to the inservice inspection (lSI) of reactor vessel nozzle to safe-end dissimilar metal (DM) welds as well as the adjacent austenitic safe-end welds during the third 10-year lSI interval which began on May 31,2007, and is scheduled to end on May 30, 2017.
2.0 REGULATORY REQUIREMENTS The NRC regulations in 10 CFR 50.55a(g) specify that lSI of nuclear power plant components shall be performed in accordance with the requirements of the ASME Code,Section XI, except where specific written relief has been granted by the NRC pursuant to 10 CFR 50.55a(g)(6)(i).
In 10 CFR 50.55a(g)(6)(i) it states that the NRC 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, given the consideration of the burden upon the licensee. In 10 CFR 50.55a(a)(3) it states that alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (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. In 10 CFR 50.55a(g)(5)(iii) it states that if the licensee has determined that conformance with certain code requirements is impractical for its facility, the licensee shall notify the NRC and submit, as specified in Section 50.4, information to support the determinations.
Enclosure
- 2 Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and preservice examination 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 lSI of components and system pressure tests 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.
3.0 TECHNICAL EVALUATION
3.1
Applicable Code Edition and Addenda
The code of record for the third 10-year lSI program at VEGP, Units 1 and 2, is the 2001 Edition through the 2003 addenda of the ASME Code,Section XI. In addition, as required by 10 CFR 50.55a(b)(2)(xv), licensees who use later editions and addenda than the 2001 Edition of the ASME Code shall use the 2001 Edition of Appendix VIII, "Performance Demonstration for Ultrasonic Examinations Systems." The third 10-year lSI interval for VEGP, Units 1 and 2, began on May 31,2007, and is scheduled to end on May 30,2017.
3.2 Components for Which Relief is Requested The affected components are the Class 1, Category R-A, Item R1.15, Reactor Pressure Vessel (RPV) nozzle to safe-end DM butt welds and the adjacent Category R-A, Item 81.20, austenitic safe-end welds.
3.3
Applicable Code Requirement
Examination Category R-A, Item R1.15, "RPV nozzle to safe-end DM butt welds" and Examination Category R-A, Item R1.20, "austenitic safe-end welds" specify volumetric examination. IWA-2232, "Ultrasonic Examination," requires that ultrasonic (UT) examinations be performed per Appendix I. Appendix I, 1-2220 requires that UT examination procedures, equipment, and personnel be qualified by performance demonstration in accordance with Appendix VII/. Instead of the Appendix VIII qualification requirements, the licensee is using NRC-approved Code Case N-695, "Qualification Requirements for Dissimilar Metal Piping Welds" and NRC-approved Code Case N-696, "Qualification Requirements for Appendix VIII Piping Examinations Conducted From the Inside Surface." (In accordance with 10 CFR 50.55a(b), Code Cases N-695 and N-696 are approved for use since these code cases have been included in Revision 16 of Regulatory Guide (RG)1.147 on lSI code case acceptability.)
Code Case N-695 provides an alternative to the Appendix VIII, Supplement 10 requirements for the qualification requirements of DM welds. Paragraph 3.3(c) indicates examination procedures, equipment, and personnel are qualified for depth-sizing when the root mean square error (RMSE) of the flaw depth measurements, as compared with true depths, does not exceed 0.125 inches.
Code Case N-696, provides an alternative to the Appendix VIII, Supplements 2 and 10, qualification requirements for piping welds that are examined from the inside surface.
- 3 Paragraph 3.3(d) indicates that examination procedures, equipment, and personnel are qualified for depth-sizing when the RMSE of the flaw depth measurements, as compared to the true depths, does not exceed 0.125 inches.
3.4 Licensee Proposed Alternative and Basis for Use 3.4.1 Variation to 0.125 RMSE The licensee stated that a request for relief from the required RMSE in depth-sizing is needed because, to date, examination vendors have not met the established RMSE of 0.125 inch for depth-sizing. The licensee proposes to use a contracted examination vendor that has demonstrated ability to meet a depth-sizing qualification requirement with an RMSE of 0.189 inch instead of the 0.125 inch required for Supplement 10 and an RMSE of 0.245 inch instead of the 0.125 inch for Supplements 10 and 2 combined.
The licensee stated that in the event an indication is detected that requires depth-sizing, the difference between the required RMSE and the demonstrated RMSE will be added to the measured through-wall depth. This amended through-wall depth will then be used to determine the acceptability of the indication. For planar indications that are not connected to the inside surface, the amended through-wall depth will be compared with the Section IWB-3500 acceptance criteria. For planar indications that are connected to the inside surface, an IWB-3600 evaluation will be performed per Section 7 of MRP-139, Revision 1 (or per future NRC Rulemaking which supersedes MRP-139 requirements).
The licensee also stated that if the examination vendor demonstrates an improved depth-sizing RMSE prior to the examination, the excess of that improved RMSE over the 0.125 inch RMSE requirement, if any, will be added to the measured value for comparison with the applicable acceptance criteria.
3.4.2 Inside Diameter UT Examinations Supplemented by Eddy Current The following is extracted from SNC's alternative and basis, as described in its submittal:
SNC states that the examination vendor for the VEGP reactor vessel nozzle examinations has qualified for detection of axial flaws in accordance with Appendix VIII, Supplements 10 and 2, as demonstrated through the Electric Power Research Institute (EPRI) Performance Demonstration Initiative (PDI) Program, for DM nozzle-to-safe end and austenitic safe-end welds examined from the inside diameter (ID) surface provided the surface is machined or ground smooth with no exposed root reinforcement or counter-bore. However, surface roughness may be present that could call into question the ultrasonic qualifications demonstrated for detection of axial flaws. (SNC notes that the examination vendor has qualified for detection of circumferential flaws in accordance with Appendix VIII, Supplements 10 and 2, as demonstrated through the EPRI PDI Program for DSM nozzle-to-safe end and austenitic safe-end welds examined from the ID surface.)
SNC proposes using surface geometry profiling software (profilometry) in conjunction with a focused immersion ultrasonic transducer positioned to permit accurate profile data across the examination volume, to help the examiner confirm locations where the raw
- 4 data indicates lack of transducer contact due to problematic surface geometry.
Subsequently, eddy current examination will be used to supplement ultrasonic examination where there is sufficient surface roughness to call into question the applicability of the ultrasonic examination qualification to detect axial flaws. The ultrasonic examinations, supplemented by eddy current examinations and profilometry, will be conducted to the maximum extent practical.... It is anticipated that all OM nozzle to-safe-end welds and all safe-end welds could be examined using this process.
To supplement the UT examinations for rough surface detection coverage, the following eddy current techniques will be utilized:
Up to two plus point probes applied circumferentially on the inside surface in scan increments of 0.08 inches circumferentially (for axial flaws) and 0.25 inches axially.
Automated systems for data collection and analysis.
The target flaw size for the eddy current procedure is 0.28 inches long, well within the ASME Code linear flaw acceptance standards of 0.45 inches for austenitic material, and 0.625 inches for ferritic material (defined for the outside surface in the Code Tables).
The eddy current technique was first used in the V. C. Summer reactor vessel primary nozzle examinations of 2000. The procedure was refined by applying it to the V. C. Summer hot-leg dissimilar metal weld section removed from service.
The removed section had a number of primary water stress corrosion cracking flaws along with non-relevant indications resulting from metallurgical interface and surface geometry. Using these actual flaws and geometric conditions in the removed section to refine the technique, the vendor developed reliable flaw screening criteria which allowed for the successful use of the procedure in the V. C. Summer 2002 and 2003 examinations.
Subsequently, the technique was successfully blind tested for the Swedish authority SQC Kvalificeringscentrum AS (SQC NOT Qualification Center) under the program, "Qualification of Equipment, Procedure and Personnel for Detection, Characterization and Sizing of Defects in Areas in Nozzle to Safe End Welds at Ringhals Unit 3 and 4," Hakan Soderstrand 7-10-03. The important qualification parameters for eddy current in the SQC blind tests (Ref. SQC Qualification Report No. 019AN03) were as follows:
Defect types: fatigue and stress corrosion cracks, surface initiated Tilt: +/-10 degrees; Skew: +/-10 degrees Detection target size: IDSCC 6mm (0.25 inches) long Flaw Location: within 10mm (13/32 inch)
Length of the planar flaw within a 70% confidence interval: +/- 9mm (3/8 inch)
False call rate: less than or equal to 20% for the personnel qualification tests
- 5 The use of ultrasonic profilometry and eddy current examination, with procedures and personnel qualified through the sac blind tests to supplement Appendix VIII qualified ultrasonic procedures and personnel, provides additional assurance that surface-breaking flaws (that may be present) will be detected in the presence of potential surface roughness. This process will assure that there is reasonable assurance of structural integrity and thus, will provide an acceptable level of quality and safety.
3.4.3 Duration of Proposed Alternative The proposed alternative is requested for the third 1O-year lSI interval for VEGP, Units 1 and 2, which began on May 31,2007, and is scheduled to end on May 30, 2017.
4.0 STAFF EVALUATION 4.1 Variation to 0.125 RMSE In ASME Code,Section XI, Appendix VIII, Supplement 10, it states that examination procedures, equipment, and personnel are qualified for depth-sizing when the RMSE of the flaw depth measurements, as compared to true depths, do not exceed 0.125 inch. Supplement 2 also requires that the RMSE or of the flaw depths estimated by UT examination, as compared with true depths, shall not exceed 0.125 in. Code Case N-696, which combines the requirements of Supplements 10 and 2, states that Supplement 2 examination procedures, equipment, and personnel are qualified for depth-sizing when the flaw depths estimated by UT examination, as compared with the true depth, do not exceed 0.125 inch RMS, when they are combined with a successful Supplement 10 qualification. (Note: Code Cases N-695 and N-696 are identified as Acceptable Section XI Code Cases in Revision 16 of the NRC RG 1.147, "lnservice Inspection Code Case Acceptability ASME Section XI, Division 1.")
The nuclear industry is in the process of qualifying personnel to Supplement 10 as implemented by the POI [Performance Demonstration Initiative] program. However, for demonstrations performed from the inside surface of a pipe weld, personnel have been unsuccessful at achieving the ASME Code-required 0.125 inch RMSE flaw depth-sizing criterion. At this time, the NRC staff concludes that achieving the 0.125 inch RMSE for depth-sizing does not appear to be feasible as personnel have only been capable of achieving an accuracy of 0.189 inch RMSE to size any detected flaws. The vendor contracted by the licensee has proposed to use an RMSE of 0.189 inch instead of the 0.125 inch required for Supplement 10 and an RMSE of 0.245 inch instead of the 0.125 inch for Supplements 10 and 2 combined, as per approved Code Case N-696. In the event an indication is detected that requires depth-sizing, the difference between the required RMSE and the demonstrated RMSE (e.g., 0.245 inch - 0.125 inch = 0.120 inch for Supplements 10 and 2 combined) will be added to the measured through wall extent. This amended through-wall depth will then be assessed against the applicable acceptance criteria specified in ASME Code,Section XI, for flaw evaluation. For planar indications that are not connected to the inside surface, the amended through-wall depth will be compared with the Section IWB-3500 acceptance criteria. For planar indications that are connected to the inside surface, an IWB-3600 evaluation will be performed per Section 7 of MRP-139, Revision 1 (or per future NRC Rulemaking which supersedes MRP-139 requirements).
- 6 Additionally, the licensee proposes that, if the examination vendor demonstrates an improved depth-sizing RMSE prior to the examination, the excess of that improved RMSE over the 0.125 inch RMSE requirement, if any, will be added to the measured value for flaw evaluation with applicable acceptance criteria specified in Section XI of the ASME Code.
The NRC staff finds that compliance with the ASME Code-required RMS error value is not feasible at this time and that adding the difference between the ASME Code-required RMSE and the demonstrated RMSE to the measured through-wall extent, in addition to the use of the appropriate acceptance standards specified in Section XI of the ASME Code, provides reasonable assurance of structural integrity of the subject welds.
4.2 Inside Diameter UT Examinations Supplemented by Eddy Current The licensee's examination vendor did not fully meet the qualification requirements of ASME Code,Section XI, Appendix VIII, Supplements 10 and 2. The vendor is qualified for detection of axial flaws for nozzle-to-safe end DM welds and austenitic safe-end welds examined from the inside diameter (lD) surface provided the surface is machined or ground smooth with no exposed root reinforcement or counter-bore. However, where surface roughness may be present, the ultrasonic qualifications demonstrated for detection of axial flaws is called into question due to the UT transducer's lift-off from the rough surface/unfavorable ID geometry.
The NRC staff notes that the PDI program is not successful in qualifying examiners to detect axial flaws in the presence of rough surfaces. Therefore, the NRC staff has determined that to fully comply with the subject ASME Code qualification requirement is not possible at this time.
The licensee proposed the use of surface geometry profiling software (profilometry) in conjunction with a focused immersion ultrasonic transducer positioned to permit accurate profile data across the examination volume to help the examiner confirm locations where the raw UT data indicates lack of transducer contact due to problematic surface geometry. The NRC staff finds that the use of profilometry to confirm the presence of rough surfaces acceptable as it provides additional information as to the condition of the surface of the examination volume.
In addition to profilometry, the licensee proposed the use of eddy current examination to supplement the UT examination for the nozzle-to-safe end and safe end-to-pipe welds having sufficient surface roughness to call into question the applicability of the UT examination qualification to detect axial flaws. Profilometry will confirm the presence of rough surfaces and the eddy current examination will assure the detection of surface breaking flaws. The licensee stated that the eddy current methodology to be used is similar to that used in the V. C. Summer Nuclear Station (VCSNS) Unit 1 outages in 2000, 2002, and 2003. The technique was refined based on examinations performed on a hot-leg dissimilar metal weld section removed from VCSNS during the 2000 refueling outage. The removed section contained primary water stress corrosion cracking flaws and nonrelevant indications resulting from surface geometry and metallurgical interfaces. The NRC staff finds that the licensee's proposed alternative, which combines ultrasonic and eddy current techniques in examining for axial flaws in the presence of rough surfaces, will provide an acceptable level of detectability and sensitivity. Therefore, the NRC staff concludes that the licensee's proposed alternative provides reasonable assurance of structural integrity of the subject welds.
- 7
5.0 CONCLUSION
Based on the above review, the NRC staff has determined that requiring the licensee to qualify procedures, personnel, and equipment to meet the maximum error of 0.125 inch RMSE for crack depth-sizing is not feasible at the present time. The licensee's proposal of adding the difference between the ASME Code-required RMSE and the demonstrated RMSE to the measured through-wall extent, in addition to the use of the appropriate ASME Code,Section XI, acceptance standards provides reasonable assurance of structural integrity of the sUbject welds. Additionally, the licensee's proposal to use surface geometry profiling combined with eddy current examination provides reasonable assurance that the axial flaws in the presence of rough surfaces will be detected, thus providing a reasonable assurance of structural integrity of the subject welds. Therefore, 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.
Relief is granted for the third 1O-year lSI interval for the VEGP I which began on May 31, 2007, and is scheduled to end on May 30,2017.
All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal contributor: Carol Nove, NRR/DCI/CPNB Date of issuance: November 16, 2010
- memo transmitted SE dated OFFICE NRRlLPL2-1/PM NRRlLPL2-1/LA NRRlCPNB/BC OGC NRRlLPL2-1/BC NAME RMartin SRohrer TLupold*
Waived ML091380595 GKulesa (PBoyle for)
DATE 11/15/10 10/18/10 10/12/10 11/16/10