ML082170434
| ML082170434 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 09/09/2008 |
| From: | Chernoff H NRC/NRR/ADRO/DORL/LPLI-2 |
| To: | Christian D Virginia Electric & Power Co (VEPCO) |
| Lamb John G./NRR/DORL, 415-3100 | |
| References | |
| TAC MD6911 | |
| Download: ML082170434 (13) | |
Text
September 9, 2008 Mr. David A. Christian President and Chief Nuclear Officer Virginia Electric and Power Company Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711
SUBJECT:
MILLSTONE POWER STATION, UNIT NO. 2: ISSUANCE OF RELIEF REQUEST REGARDING ALTERNATIVE REQUEST RR-89-64 FOR USE OF A LIMITED ONE-SIDED ULTRASONIC EXAMINATION TECHNIQUE (TAC NO. MD6911)
Dear Mr. Christian:
By letter dated September 27, 2007, as supplemented by letters dated February 18, 2008, March 26, 2008, and June 13, 2008 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML072750402, ML080500519, ML080860589 and ML081650454, respectively), Dominion Nuclear Connecticut, Inc. (DNC) submitted alternative request RR-89-64 for U.S. Nuclear Regulatory Commission (NRC) approval to use a limited one-sided ultrasonic test (UT) examination technique as an alternative to the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code) to be used at Millstone Power Station Unit 2 (MPS2). Alternative Request RR-89-64 will be applicable to a total of eight dissimilar metal welds at the inlet and outlet of the reactor coolant pumps. The eight welds are examined under the MPS2 risk-informed inservice inspection (RI-ISI) program.
The NRC staff has reviewed DNCs submittal and has determined that it is impractical to satisfy the ASME Code required 100-percent examination coverage for the subject welds due to cast austenitic stainless steel material of the safe ends and unsuitable weld configuration for UT.
Therefore, pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.55a(g)(6)(i), the NRC staff grants the use of Alternative Request RR-89-64 for the UT examination of subject welds for the remainder of the third 10-year ISI interval at MPS2. The NRC staff concludes that the use of Alternative Request RR-89-64 for the UT examination of subject welds provides reasonable assurance of structural integrity. 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.
Enclosed is the NRC staffs safety evaluation.
D. Christian If you have any questions, contact John G. Lamb, Senior Project Manager, at 301-415-3100.
Sincerely,
/ra/ (REnnis for)
Harold K. Chernoff, Chief Plant Licensing Branch I-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-336
Enclosure:
Safety Evaluation cc w/encl: See next page
D. Christian If you have any questions, contact John G. Lamb, Senior Project Manager, at 301-415-3100.
Sincerely,
/ra/ (REnnis for)
Harold K. Chernoff, Chief Plant Licensing Branch I-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-336
Enclosure:
Safety Evaluation cc w/encl: See next page DISTRIBUTION:
Public LPL1-2 R/F RidsNrrLAABaxter Resource RidsAcrsAcnw_MailCTR Resource RidsNrrLpl1-2 Resource RidsNrrDciCpnb Resource RidsNrrPMCSanders Resource RidsNrrPMJLamb Resource RidsOgcRp ResourceRidsRgn1MailCenter Resource SWilliams, EDO R-I JTsao, NRR ADAMS ACCESSION NO.: ML082170434
- via memo OFFICE:
LPL1-2/PM LPL1-2/LA DCI/CPNB OGC - NLO LPL1-2BC NAME JLamb ABaxter TChan*
LBS HChernof (REnnis for)
DATE:
08/04/2008 08/13/2008 07/14/2008 08/27/08 9/9/08 OFFICIAL RECORD COPY
Millstone Power Station, Unit No. 2 cc:
Lillian M. Cuoco, Esquire Senior Counsel Dominion Resources Services, Inc.
Building 475, 5th Floor Rope Ferry Road Waterford, CT 06385 Edward L. Wilds, Jr., Ph.D.
Director, Division of Radiation Department of Environmental Protection 79 Elm Street Hartford, CT 06106-5127 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 First Selectmen Town of Waterford 15 Rope Ferry Road Waterford, CT 06385 Charles Brinkman, Director Washington Operations Nuclear Services Westinghouse Electric Company 12300 Twinbrook Pkwy, Suite 330 Rockville, MD 20852 Senior Resident Inspector Millstone Power Station c/o U.S. Nuclear Regulatory Commission P.O. Box 513 Niantic, CT 06357 Mr. J. Alan Price Site Vice President Dominion Nuclear Connecticut, Inc.
Building 475, 5th Floor Rope Ferry Road Waterford, CT 06385 Mr. J. W. "Bill" Sheehan Co-Chair NEAC 19 Laurel Crest Drive Waterford, CT 06385 Mr. Evan W. Woollacott Co-Chair Nuclear Energy Advisory Council 128 Terry's Plain Road Simsbury, CT 06070 Ms. Nancy Burton 147 Cross Highway Redding Ridge, CT 00870 Mr. Chris L. Funderburk Director, Nuclear Licensing and Operations Support Dominion Resources Services, Inc.
Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711 Mr. William D. Bartron Licensing Supervisor Dominion Nuclear Connecticut, Inc.
Building 475, 5th Floor Rope Ferry Road Waterford, CT 06385 Mr. Joseph Roy, Director of Operations Massachusetts Municipal Wholesale Electric Company Moody Street P.O. Box 426 Ludlow, MA 01056 Mr. David A. Sommers Dominion Resources Services, Inc.
5000 Dominion Boulevard Glen Allen, VA 23060-6711 Mr. David A. Christian President and Chief Nuclear Officer Virginia Electric and Power Company Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF THIRD 10-YEAR INTERVAL INSERVICE INSPECTION ALTERNATIVE REQUEST RR-89-64 DOMINION NUCLEAR CONNECTICUT MILLSTONE NUCLEAR POWER STATION UNIT 2 DOCKET NO. 50-336
1.0 INTRODUCTION
By letter dated September 27, 2007, as supplemented by letters dated February 18, 2008, March 26, 2008, and June 13, 2008 (Agencywide Documents Access and Management System (ADAMS) Accession Nos. ML072750402, ML080500519, ML080860589 and ML081650454, respectively), Dominion Nuclear Connecticut, Inc. (DNC) submitted alternative request RR-89-64 for U.S. Nuclear Regulatory Commission (NRC) approval to use a limited one-sided ultrasonic test (UT) examination technique as an alternative to the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code) to be used at Millstone Power Station Unit 2 (MPS2). Alternative Request RR-89-64 will be applicable to a total of eight dissimilar metal welds (DMWs) at the inlet and outlet of the reactor coolant pumps (RCPs). The eight welds are examined under the MPS2 risk-informed inservice inspection (RI-ISI) program.
Alternative Request RR-89-64 is applicable to the third 10-year ISI interval for MPS2. The industry experience has shown that DMWs are susceptible to primary water stress corrosion cracking (PWSCC).
By letter dated February 18, 2008, DNC responded to an NRC staff request for additional information concerning the proposed one-sided UT technique in RR-89-64.
By letter dated March 26, 2008, DNC provided the estimated examination coverage for weld P-8-C-1, which was not available in the letter, dated September 27, 2007. By letter dated June 13, 2008, DNC provided actual examination coverage for the eight subject welds after performing the UT examination in the spring 2008 refueling outage (RFO).
The RI-ISI program requires that the ASME Code Section XI, Figure IWB-2500-8, Examination Category R-A, Item R1.15, 1989 Edition with no Addenda be used in conjunction with the UT examination requirements outlined in the "Westinghouse Owners Group Application of Risk-Informed Methods to Piping Inservice Inspection Topical Report, WCAP-14572, Revision 1-NP-A, dated February 1999 (ADAMS Accession No. ML042610469). DNC states that the subject requirements cannot be met due to the cast austenitic stainless steel (CASS) safe-end base material and the DMW design configuration.
Enclosure In Alternative Request RR-89-64, DNC proposes to perform a one-sided UT examination from the ferritic pipe or elbow side of the DMWs and a bare metal visual examination as an alternative to the ASME Code and Westinghouse Owners Group Topical Report requirements. The proposed alternative method is outlined in the Electric Power Research Institute (EPRI) Internal Report (IR)-2007-277, "EPRI Review of Millstone Unit 2 Dissimilar Metal Weld Walkdown Information," dated June 2007 (ADAMS Accession No. ML072750406).
2.0 REGULATORY EVALUATION
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Section 50.55a(g)(4),
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 requirements, set forth in the ASME Code,Section XI, Rules for Inservice Inspection (ISI) of Nuclear Power Plant Components, to the extent practical within the limitations of design, geometry, and materials of construction of the components. Pursuant to 10 CFR 50.55a(g)(5)(iii), if the licensee determines that conformance with an examination requirement of Section XI of the ASME Code is not practical for its facility, information shall be submitted to the Commission in support of that determination and a request made for relief from the ASME Code requirement. After evaluation of the determination, pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant relief and may impose alternative requirements that are determined to be authorized by law, will not endanger life, property, or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed.
The regulations require that inservice examination 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) twelve months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The Code of record for the current, third 10-year ISI interval at MPS2, which began April 1, 1999, and is scheduled to end March 31, 2010, is the ASME Code,Section XI, 1989 Edition, no Addenda. For the UT examination, the Code of record is ASME Code,Section XI, Appendix VIII, Supplement 10, 1995 Edition through 1996 Addenda.
3.0 MPS2 PROPOSED ALTERNATIVE REQUEST RR-89-64 3.1 Applicable Code Requirement, Edition and Addenda ASME Code,Section XI, Table IWB-2500-8, 1989 Edition, no Addenda is applied to the ISI program and RI-ISI program. The 1995 Edition of Section XI with the 1996 Addenda, Appendix VIII, Supplement 10 is used for UT examination of DMWs including the limitations in 10 CFR 50.55a(b). The UT examination requirements are implemented under the industry Performance Demonstration Initiative (PDI). The UT examination volume shown in Figure IWB 2500-8 of the ASME Code,Section XI, is required to be met under the RI-ISI program. In this figure, the bottom one-third of the weld volume and a small portion of the base materials on each side of the weld must be covered by the UT examination. A similar Figure 2-3, showing the examination volume, is depicted on page 2-2 of the MPS2 RI-ISI program. The required examination volume in Figure 2-3 is shown as C-D-F-E.
3.2 System/Components Affected Category and System Details Code Class: All subject welds are ASME Code Class 1 welds.
System Welds: Welds are located in the Reactor Coolant System (RCS) pressure boundary.
Code Category: Examination Category R-A, "Risk-Informed Piping Examinations."
Code Item No.: R 1.15, "Elements Subject to PWSCC."
Component Descriptions The following safe-end-to-elbow welds are located at the 36-inch outside diameter (OD) inlet (suction) nozzles of the RCP. The welds are made of Alloy 82/182 material. The welds join cast austenitic stainless steel (CASS, P-8) safe ends to ferritic steel (P-1) elbows.
- 1. Weld No. P-4-C-1
- 2. Weld No. P-8-C-1
- 3. Weld No. P-13-C-1
- 4. Weld No. P-17-C-1 The following safe-end-to-elbow welds are located at the 36-inch outside diameter outlet (discharge) nozzles of the RCP. The welds are made of Alloy 82/182 material. The welds join CASS (P-8) safe ends to ferritic steel (P-1) elbows. The pump nozzles are made of CASS.
- 1. Weld No. P-5-C-3
- 2. Weld No. P-9-C-3
- 3. Weld No. P-14-C-3
- 4. Weld No. P-18-C-3 3.3 Reason for the Request Eight DMWs located on the RCP inlet and outlet RCS cold leg piping were scheduled for UT examination in the spring 2008 RFO (2R18) at MPS2. The eight DMWs are required to be examined by the end of RFO (2R19) if the welds could not be examined during the 2R18 outage.
Currently, MPS2 has the UT examination scheduled under the RI-ISI program as these eight DMWs welds are susceptible to PWSCC.
The RI-ISI program refers to the requirements of ASME Code,Section XI, Figure IWB-2500-8, 1989 Edition for volumetric examination and to the requirements of Examination Category R-A, Risk-Informed Piping Examinations within Westinghouse Commercial Atomic Power report (WCAP)-14572, Revision 1-NP-A, "Westinghouse Owners Group Application of RI Methods to Piping ISI Topical Report," Table 4.1-1. ASME Code,Section XI, Figure IWB-2500-8 requires that the bottom one-third of the DMW and some associated base material be volumetrically examined, but does not require examination of the entire DMW end buttering material. The Materials Reliability Program (MRP-139), Primary System Piping Butt Weld Inspection and Evaluation Guidelines, contains industry guidance including the DMW butter in the examination volume. Both the RI-ISI program requirement and the MRP-139 industry guidance require that some of the base material on either side of the DMW and butter be UT examined.
The design configuration of the eight DMWs restricts examination of the base material from the ferritic steel side of the welds. The only possible solution for improving the inspectability of these welds would be to machine the welds. However, machining the welds could result in violating the necessary minimum wall thickness of the pipe and/or elbow. In addition, all of the eight subject welds join safe-ends that are made of CASS. The current UT technique is not qualified to examine the CASS material. DNC requests approval of proposed alternative to allow a limited UT examination of the eight DMW from the ferritic pipe and elbow side only.
3.4 Proposed Alternative and Basis DNC determined that it is possible to examine the DMWs from the ferritic pipe or elbow side only based on: (1) the UT examination volume coverage that can be gained by utilizing multiple search units; (2) scanning the welds in the axial direction; and (3) the calculated coverage depicted and described in the EPRI IR-2007-277. DNCs proposed alternative is applicable for both the RCP inlet and outlet nozzles.
DNC uses conventional UT examination coverage techniques to produce the justification for RR-89-64. No qualified UT technique, to date, has been demonstrated to be consistently reliable for inspection of CASS. Furthermore, no ASME Code requirements exist to perform UT performance demonstrations for CASS.
Susceptibility to PWSCC is the reason that these DMWs were selected for examination under the RI-ISI program. UT examination from the pipe or elbow side of these eight DMWs will cover the full inside diameter of the welds for identification of any suspected circumferential PWSCC that may be present in the Alloy 82/182 DMW material. However, it is possible to miss some axial oriented PWSCC (if it does exist) when scanning these DMWs in the circumferential direction due to the OD configuration.
As an alternative to the ASME Code requirement, DNC proposed to perform: (1) a UT examination of the eight DMWs from the ferritic pipe or elbow side of the welds using a PDI demonstrated/qualified procedure; and (2) a bare metal visual examination to provide the needed defense-in-depth in support of the limited UT for axial PWSCC, when UT examination is not performed on the DMWs during an RFO.
DNC proposes the preceding examinations as an alternative to the UT examination volume coverage requirements in ASME Code,Section XI, Figure IWB-2500-8 of the 1989 Edition and Table 4-1.1 of WCAP-14572 Revision 1-NP-A. DNC states that the proposed bare metal visual examination of the cold leg RCS DMWs exceeds the industry requirements of ASME Code Case N-722, "Additional Examinations for PWR [pressurized-water reactor] Pressure Retaining Welds in Class 1 Components Fabricated with Alloy 600/82/182 Materials Section Xl, Division 1."
DNC states that the proposed alternative will meet the requirements for the RI-ISI program and follow the industry guidance of MRP-139 to close out the current 10-year ISI interval. DNC states further that due to the large size of these welds, additional time will be needed to determine the appropriate mitigation strategy for these welds in the future. According to DNC, the eight DMWs are cold leg RCS welds, which are not expected to be highly susceptible to PWSCC due to lower operating temperature. In addition, industry experience has not shown any cracking in these specific types of welds.
3.5 Duration of the Proposed Request The Alternative Request RR-89-64 will be applicable for the remainder of the third 10-year ISI interval, which is scheduled to end on March 31, 2010.
4.0 STAFF EVALUATION Examination Coverage The NRC staff is concerned with nickel-based Alloy 82/182 metal in the subject welds because recent PWR experience has shown its susceptibility to PWSCC. PWSCC will most likely to occur when a combination of high applied stresses, an adverse environment, and susceptible material is present in the component. The Alloy 82/812 butt welds need to be rigorously monitored for PWSCC.
The subject welds were last ultrasonically examined in the previous 10-year inspection interval during the period between 1989 and 1994 prior to the implementation of the ASME Code,Section XI, Appendix VIII requirements. The examination data reflects that the welds were found to be acceptable with no reportable indications. DNC also performed bare metal visual examination on the subject welds for the previous two RFOs (2R16 and 2R17) and found the subject welds to be acceptable with no evidence of leakage.
In the original submittal dated September 27, 2007, DNC estimated examination coverage of 23-percent to 81-percent for the subject welds (depending on the direction of the UT scan). The low examination coverage estimation was attributed to several factors. The weld configuration would limit the effective examination of the required volume due to the short safe-end and adjacent pump to safe-end weld. This configuration would limit the ability to scan in the axial beam direction (i.e., detection of circumferential reflectors) from only the pipe or elbow side of the weld. The transition from different ODs between the pipe/elbow to the safe-end results in a tapered weld surface. A tapered weld surface would limit effective coupling between the transducer and the surface for both the axial and circumferential scan directions. The type of grain structure in CASS is not favorable for UT. Due to the thickness of these welds, the use of a larger search unit is required. In some cases, the larger search unit would limit the amount of coverage obtainable.
During the NRC staff review of the relief request, the licensee proceeded with UT of the subject welds in the spring 2008 RFO. By letter dated June 13, 2008, the licensee provided the actual examination coverage achieved after the UT inspection was performed. The actual examination coverage data show that the coverage achieved in the spring 2008 RFO has improved from the estimates in the letter, dated September 27, 2007. The above results show that the examination coverage of the required volume of the Alloy82/182 welds and carbon steel base metal is from 83.8-percent to 100-percent. The examination coverage for the required volume of the CASS safe-end is about 46-percent to 50-percent. Because of the low coverage for the CASS safe end, the total achieved examination coverage was from 73.1-percent to 80-percent as shown in Table 2 (examination Volume Coverage Summary) contained in the letter dated June 13, 2008.
DNC reported that no flaw indications were detected in the examined volumes for the eight DMW during the spring 2008 RFO inspection.
The NRC staff finds that, despite an unfavorable weld configuration and CASS safe-ends preventing full examination coverage of the subject welds, the licensee was able to achieve substantial improvement in examination coverage in the Alloy 82/182 welds and carbon steel base metal. The NRC staff confirms that it is impractical to achieve 100-percent volume coverage based on the current unfavorable weld configuration and CASS safe-ends.
Proposed Alternative DNC stated that the inspection procedure has been demonstrated to detect both axial and circumferential oriented flaws based upon proper transducer selection and scan access. The required examination volume can be effectively examined from a single side of the weld when looking for circumferentially-oriented flaws. However, the examination for axially-oriented flaws requires scanning access to the weld crown and adjacent base material on both sides of the weld to effectively examine the required volume. For the subject DMWs, the weld crown and adjacent base material will be scanned in the circumferential direction for axial flaws to the extent possible. However, the weld taper provides a transition between the varying diameters of the safe end and elbow/pipe components that causes the transducer to lose contact when it bridges this transition. The loss of contact restricts the amount of the examination volume that can be effectively examined for axially-oriented flaws. The effects of this bridging have been taken into account with the transducer design and selection to optimize the coverage of the required examination volume in this direction by using a tandem element arrangement where applicable. The use of the narrow tandem element transducer will increase the coverage of the examination volume for axially-oriented flaws.
The NRC staff notes that the industry through EPRI is currently working on qualification for UT of CASS material under the PDI program. The NRC has also funded research programs to study the UT qualification of CASS material in the national laboratories. Once UT is qualified for the examination of the CASS material, DNC should be able to increase the coverage of the percentage of examination volume.
DNC stated that the examination of the subject welds will be performed utilizing UT procedures that are qualified for DMWs with single side scanning access, in accordance with the requirements of the ASME Code,Section XI, Appendix VIII, Supplement 10, as modified by the industry's PDI Program. The same procedure will provide coverage of the CASS material on a best-effort basis for the small portion of the required examination volume that is outside the PDI Program qualified material, (i.e., the CASS safe-end). The PDI-qualified procedure that will be used for these examinations exceeds the ASME Code Section XI, Appendix III, Supplement 4 requirements, considering the use of optimized transducer parameters, (i.e., size, frequency, contouring, focusing, and angle), and the optimized scanning parameters, (i.e., sensitivity, overlap, and coverage), for the configuration of these DMWs with the limited scan access.
Examination coverage of the required volume will be documented as a percentage of volume completely examined with the requirements of the qualified procedure. Best effort coverage obtained will also be documented, where a portion of the volume examined is not necessarily examined with each of the parameters of the qualified procedure, (e.g., for examination of a limited portion of the DMW where only one beam angle in the axial scan direction was achievable, or in the CASS volume with only one direction achievable).
In addition to the UT, DNC will perform a direct visual examination of the bare metal surfaces of the weld during each RFO in which UT is not performed. The examination is performed after plant cooldown following insulation removal for each subject weld. The visual examination is a VT-2 type of examination performed at static system pressure to identify and report any indication of leakage including boric acid deposits or residue. Any indication of through-wall leakage would be found unacceptable for continued service and reported in the Millstone Station Corrective Action Program to evaluate for appropriate corrective measures. Each examination is performed utilizing personnel and procedures that meet the applicable ASME Section XI VT-2 examination requirements.
The UT and the bare metal visual examinations of the subject welds are separate examinations, consistent with current requirements in the MPS2 RI-ISI program and the inspection schedule of MRP-139. MPS2 will meet the industry guidance of MRP-139, which recommends bare metal visual examination of these eight welds once every three RFOs, in outages where UT is not performed, until the weld is mitigated or replaced. UT examination is required under the MPS2 RI-ISI program once every 10-year ISI interval.
Per the requirements of RI-ISI program, these eight welds must be UT examined by the end of the 10-year ISI interval, which is March 31, 2010. Under MRP-139, UT examination of these welds is recommended every 6 years after they are inspected once under MRP-139, and they must be UT examined by December 31, 2010. Thus, MPS-2 RI-ISI program requirements and industry benchmarks have been met by performing UT examination on all the eight subject welds during the spring 2008 RFO. DNC will perform bare metal visual examinations during the fall 2009 RFO.
With regard to the potential of PWSCC in the subject welds, DNC stated that all eight welds are subject only to cold leg temperatures, they are all shop welds, and have never been field weld repaired during service. DNC stated that there is no operating experience at this time to indicate these cold leg welds should be considered at a higher level of susceptibility to PWSCC. DNC has considered applying optimized weld overlay or the mechanical stress improvement process (MSlP TM) on the subject welds to mitigate potential PWSCC.
The NRC staff finds that DNC has demonstrated that it is impractical to satisfy the 100-percent examination coverage of the subject DMWs as required by the ASME Code and RI-ISI program because the weld examination is limited by component geometry (one-sided access) and material properties (CASS grain structure). To meet the 100-percent coverage requirements of the ASME Code based on the current UT technology would require replacing the CASS safe ends and modifying the weld configurations. This replacement would result in an excessive burden to DNC. In lieu of the 100-percent coverage, DNC has performed a best effort UT examination of the required volume. In addition, DNC will perform the bare metal visual examination of the subject welds periodically as a means for defense-in-depth. The NRC staff finds that DNC has taken appropriate steps to consider measures, such as weld overlay or MSIP, for the subject welds to mitigate potential PWSCC. Based on the above evaluation, the staff concludes that the proposed alternative in RR-89-64 is acceptable and provides reasonable assurance of structural integrity.
5.0 CONCLUSION
The NRC staff has reviewed DNCs submittal and has determined that it is impractical to satisfy the ASME Code required 100 percent examination coverage for the subject welds due to CASS material of the safe-ends and unsuitable weld configuration for UT. Imposition of the ASME Code requirements would result in an excessive burden to DNC. Therefore, pursuant to 10 CFR 50.55a(g)(6)(i), the NRC staff grants the use of Alternative Request RR-89-64 for the UT examination of subject welds for the remainder of the third 10-year ISI interval at MPS-2. The NRC staff concludes that the use of Alternative Request RR-89-64 for the UT examination of subject welds provides reasonable assurance of structural integrity. 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.
All other requirements of the ASME Code, for which relief has not been specifically requested and approved remain applicable, including third party review by the Authorized Nuclear Inservice inspector.
Principal Contributor: J. Tsao Date: September 9, 2008