ML13129A298
| ML13129A298 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 05/30/2013 |
| From: | Markley M Plant Licensing Branch IV |
| To: | Entergy Operations |
| Kalyanam N | |
| References | |
| TAC MF0331 | |
| Download: ML13129A298 (10) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 May 30,2013 Vice President, Operations Arkansas Nuclear One Entergy Operations, Inc.
1448 S.R. 333 Russellville, AR 72802
SUBJECT:
ARKANSAS NUCLEAR ONE, UNIT 2 - REQUEST FOR ALTERNATIVE AN02-ISI-007, ASME CODE CASE N-770-1 BASELINE EXAMINATION (TAC NO. MF0331)
Dear Sir or Madam:
By letter dated December 4,2012, as supplemented by letter dated December 17, 2012, Entergy Operations, Inc. (the licensee), submitted for the U.S. Nuclear Regulatory Commission (NRC) review and authorization of "Revised Request for Alternative AN02-ISI-007 Code Case N-770-1 Baseline Examination," for Arkansas Nuclear One, Unit 2 (ANO-2). The request is associated with the use of an alternative to the requirements of the ASME Boiler and Pressure Vessel Code, Code Case N-770-1 in accordance with Title 10 of the Code of Federal Regulations, Part 50 (10 CFR 50), paragraph 55a(g)(6)(ii)(F)(3), dated June 21, 2011. The licensee also stated that the alternative is for the current fourth 10-year lSI interval, which began on March 26, 2010, and is scheduled to end on March 25, 2020.
Specifically, the licensee is proposing to credit a previous examination of nickel-based Alloy 82/182 dissimilar metal butt welds to satisfy the baseline examination requirement of ASME Code Case N-770-1. The licensee requested authorization to use the proposed alternative pursuant to 10 CFR 50.55a(a)(3)(ii) on the basis that complying with the specified requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
The NRC staff determined that proposed alternative AN02-ISI-007 provides reasonable assurance of structural integrity and leak tightness until the scheduled refueling outage in the spring of 2014, and that complying with the specified requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Accordingly, the NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(a)(3)(ii) and, therefore, recommends authorization to use the proposed alternative at ANO-2, until the scheduled refueling outage in the spring of 2014. Verbal authorization for use of the proposed alternative was given in a conference call between the NRC staff and the licensee's representatives on December 18, 2012.
All other ASME Code,Section XI requirements for which relief was not specifically requested and authorized in the subject proposed alternative remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
-2 The NRC staffs safety evaluation is enclosed.
Sincerely.
Michael T. Markley. Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-368
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 USE OF ALTERNATE ASME CODE CASE N-770-1 BASELINE EXAMINATION ENTERGY OPERATIONS, INC.
ARKANSAS NUCLEAR ONE. UNIT 2 DOCKET NO. 50-368
1.0 INTRODUCTION
By letter dated December 4,2012 (Reference 1), as supplemented by letter dated December 17,2012 (Reference 2), Entergy Operations, Inc. (the licensee), submitted "Revised Request for Alternative AN02-ISI-007, Code Case N-770-1 Baseline Examination" for Nuclear Regulatory Commission (NRC) review and authorization. Specifically, the licensee requested relief from the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code) Case N-770-1, "Alternative Examination Requirements and Acceptance Standards for Class 1 PWR [Pressurized-Water Reactor] Piping and Vessel Nozzle Butt Welds Fabricated With UNS N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation Activities," as conditioned by paragraph 50.55a(g)(6)(ii) of Title 10 of the Code of Federal Regulations (10 CFR), to permit the use of an ultrasonic (UT) examination performed at Arkansas Nuclear One, Unit 2, in the fall of 2009 to fulfill the dissimilar metal butt weld (DMBW) baseline examination requirement of 10 CFR 50.55a(g)(6)(ii){F). The licensee's request for alternative has been submitted pursuant to 10 CFR 50.55a(a)(3)(ii) on the basis that conformance to the requirements would result in hardship without a compensating increase in the level of quality or safety.
Acceptance of the fall 2009 examination coverage for the subject welds was previously addressed in the safety evaluation dated November 27,2012 (Reference 3). At that time, the NRC staff concluded that the information supplied by the licensee demonstrated structural integrity and leak tightness of the subject welds for a limited period of time and, accordingly, the NRC staff authorized the use of the fall 2009 examination as the baseline until January 1, 2013.
In this revised request for alternative, the licensee has submitted information to support use of the fall 2009 examination as the baseline examination until the scheduled refueling outage in the spring of 2014.
Verbal authorization for use of the proposed alternative was given in a conference call between the NRC staff and licensee representatives on December 18, 2012 (Reference 4).
2.0 REGULATORY EVALUATION
Paragraph 55a{g)(6)(ii)(F) of 10 CFR 50 requires that licensees of existing operating pressurized-water reactors (PWRs) implement the requirements of ASME Code Case N-770-1, Enclosure
-2 subject to the conditions specified in paragraphs (g)(6)(ii)(F)(2) through (g)(6)(ii)(F)( 10), by the first refueling outage after August 22, 2011.
Paragraph 55a(g)(6)(ii)(F}(3) of 10 CFR 50 states that Baseline examinations for welds in Table 1, Inspection Items A-1, A-2, and B, shall be completed by the end of the next refueling outage after January 20, 2012. Previous examinations of these welds can be credited for baseline examinations if they were performed within the re-inspection period for the weld item in Table 1 using Section XI. Appendix VIII requirements and met the Code required examination volume of essentially 100 percent. Other previous examinations that do not meet these requirements can be used to meet the baseline examination requirement, provided NRC approval of alternative inspection requirements in accordance with paragraphs (a)(3)O) or (a)(3)(ii) of this section is granted prior to the end of the next refueling outage after January 20, 2012.
Paragraph 10 CFR 50.55a(a)(3) states, in part, that alternatives to the requirements of 10 CFR 50.55a(g) may be used when authorized by the NRC if the applicant demonstrates that:
(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 analysis of the regulatory requirements, the NRC staff concludes that regulatory authority exists to authorize the proposed alternative pursuant to 10 CFR 50.55a(a)(3)(ii).
3.0 TECHNICAL EVALUATION
3.1 Licensee's Request for Alternative 3.1.1 Components Affected ASME Code Class 1 dissimilar metal piping welds containing Alloy 82/182, ASME Code Case N-770-1 Inspection Item 8, unmitigated butt weld at cold leg operating temperature.
Reactor Coolant Pump (RCP) suction nozzle elbow-to-safe end (SE) welds08-014, 10-014,12-014 and 14-014 RCP discharge nozzle SE-to-pipe welds09-008, 11-008,13-008 and 15-008 3.1.2 Code Requirements The Arkansas Nuclear One, Unit 2, inservice inspection (lSI) Code of record for the fourth 10-year lSI interval, which began on March 26, 2010, and is scheduled to end on March 25, 2020, isSection XI of the ASME Code, 2001 Edition through the 2003 Addenda.
- 3 The subject welds are classified as Inspection Item "B", "Unmitigated butt weld at Cold Leg operating temperature ~ 525 0 F and < 580 F" for which visual and essentially 100 percent Q
volumetric examinations are required.
3.1.3 Licensee's Reason for Request The licensee stated that the UT examination of the subject welds in fall 2009 did not obtain essentially 100 percent of the required examination volume coverage, and to obtain additional coverage would necessitate modification or replacement of the component.
3.1.4 Licensee's Proposed Alternative and Basis for Use The licensee proposes that the scan coverage attained during the UT examination performed in fall 2009 in accordance with Electric Power Research Institute (EPRI) technical report, "Material Reliability Program: Primary System Piping Butt Weld Inspection and Evaluation Guideline (IVIRP-139, Revision 1)," December 2008 (Reference 5), be credited for the 10 CFR 50.55a(g)(6)(ii)(F)(3) required baseline examination until the scheduled spring 2014 refueling outage. The licensee stated that the manually delivered ultrasonic phased-array examination was performed using ASME Code,Section XI, Appendix VIII requirements employing the best available technology for maximizing examination coverage of these types of welds, and that the examinations performed on the subject areas demonstrate an acceptable level of integrity.
Furthermore, the actions required to obtain the required degree of coverage would result in hardship without a compensating increase in the level of quality and safety.
3.2 NRC Staff Evaluation Primary water stress-corrosion cracking (PWSCC) of nickel-based pressure boundary materials is a safety concern. Operational experience has shown that PWSCC can occur as the result of the combination of susceptible material, corrosive environment. and tensile stresses, resulting in leakage and the potential for loss of structural integrity. The subject DMBWs meet these conditions and therefore may be susceptible to PWSCC. The examination requirements of ASME Code Case N-770-1, as conditioned by 10 CFR 50.55a(g)(6)(ii)(F), are intended to ensure the structural integrity and leak tightness of DMBWs through nondestructive examination.
The licensee is proposing to credit the fall 2009 UT examinations to fulfill the baseline examination requirement until the scheduled refueling outage in the spring of 2014. The licensee states that the previous UT examinations were performed using ASME Code,Section XI, Appendix VIII, requirements, but could not obtain essentially 100 percent coverage of the required examination volume for axial flaws due to the weld taper and the presence of the cast austenitic stainless steel (CASS) safe-ends. The 2009 examination of the CASS material could not be credited for any coverage because the qualification requirements for cast austenitic piping welds (ASME Code,Section XI, Appendix VIII, Supplement 9) is in the course of preparation. Because CASS is not known to be susceptible to PWSCC or other service-related cracking in the pressurized-water reactor coolant system environment, the NRC staff concludes that the lack of ASME Code,Section XI, Appendix VIII compliant coverage of the CASS material is not a structural integrity concern.
- 4 In the previous safety evaluation concerning examination of the subject welds dated November 27, 2012 (Reference 3), the NRC staff determined that fulfilling the essentially 100 percent examination requirement for axial flaws in the susceptible weld material is not possible using currently available technology and procedures, and that weld 10-014 is bounding for the subject welds. In addition, the NRC staff also determined that achieving the required examination coverage would require modification and/or replacement of the components, which would constitute a hardship.
By letter dated September 10, 2012 (Reference 6), in response to the NRC staff's previous request for additional information (RAI), the licensee proposed that the largest undetected flaw that could exist in the unexamined volume is 0.5 inches deep with a depth to length ratio of 1:2.
The NRC staff, however, concluded that the licensee did not provide a sufficient basis for the ability to detect the proposed flaw size with the UT examination that was performed. In its evaluation, the NRC staff added 15 percent of the wall thickness to the licensee's 0.5-inch depth to address conservatively flaw detectability. The NRC staff used the licensee's plot of projected flaw depth with time (Reference 7) to determine that the NRC staff's assumed initial flaw size would reach the ASME Code limit of 75 percent of the wall thickness in 44 months. The NRC staff also performed independent confirmatory analyses using the assumed hypothetical flaw size and reference weld residual stress (WRS) values for a 50 percent weld repair performed from the inside diameter (ID). The results of this analysis supported the prOjected 44-month period to reach the ASME Code limit. The NRC staff concluded that the baseline examination performed in fall 2009 provided reasonable assurance of structural integrity and leak tightness for approximately 44 months, and authorized use of the baseline until January 1, 2013.
In the present submissions (References 1 and 2), the licensee has provided additional information concerning the growth of a hypothetical axial flaw in weld 10-014. The licensee's present analysis includes the effects of the WRS corresponding to an ID weld repair of 50 percent wall thickness without a subsequent post-repair heat treatment. The NRC staff concludes that the assumed 50 percent weld repair will likely bound any undocumented weld repair and that the absence of subsequent post-weld heat treatment reflects the condition of the weld, thus concludes the parameters acceptable. The NRC staff has compared the WRS values used in the calculation to reference WRS values and concludes that the licensee's WRS values are reasonable. Therefore, the NRC staff accepts these WRS values for use in axial flaw growth analysis in weld 10-014.
In the present submission, the licensee proposes that the largest undetected axial flaw that can exist due to the examination limitations is 10 percent through wall (0.33 inches) in depth. In response to the discussions with the NRC staff, the licensee provided bases (Reference 2) for acceptance of a hypothetical 10 percent through wall flaw. The licensee has stated that the UT scans were performed in accord with the Performance Demonstration Initiative-approved UT procedure SI-UT-130 (Reference 8). The circumferential UT scans for axial flaws were performed from the ferritic nozzle using manual and electronic skewing of the phased-array probe assembly in accord with the provisions of SI-UT-130. The NRC staff notes that there is no standard guidance or procedure for performing a determination of flaw detectability, but that the UT procedure and personnel have been qualified in blind demonstration for scanning to 10 percent depth, as documented in Section XI of the ASME Code, 2001 Edition, Appendix VIII, Supplement 10, paragraph 1.2(c)(1).
-5 The NRC staff understands that the weld volume has been ensonified by the circumferential scans in two scan directions from the carbon steel side of the weld, as well as by circumferential scans in two scan directions from the weld crown. The NRC staff requested that Pacific Northwest National Laboratory (PNNL) model the UT response in the susceptible weld material for scans performed from the weld crown. The evaluation included theoretical modeling of the sound beams based on actual phased-array design parameters and component geometry provided by the licensee. The PNNL methodology models sound field extents and intensities for isotropic material, actual grain sizes and structures, velocity ranges, and other material variables that will affect sound beam attenuation, re-direction, and signal-to-noise values have not been applied. The phased-array UT examination was modeled with focal laws defined to produce steered beams from 0 to 80 degrees, at one-degree increments, each focused at approximately 122 millimeter of metal path after exiting the probe (Reference 9). It is generally assumed that adequate volumetric coverage exists for sound field intensity greater than or equal to -6 decibels (dB). PNNL determined that a volume exists at the 10 of weld 10-014 that had a UT sound field of less than -6 dB due to the outside diameter (00) taper and wall thickness. In order for the lower scan angles to extend to their maximum -6 dB depth, electronic lateral skewing was required. While focal laws were produced to laterally skew the beam by 10 degrees, modeling showed that the actual array matrix would only produce an approximate 4-degree skew because only two elements exist in the passive direction of the array. Although the PNNL model did not indicate that there was an adequate sound field to interrogate the weld material at the 10, the model predicted that the extent of coverage with greater than -6dB sound field extended deeper than the uppermost tip of the assumed hypothetical flaw. Based on the multiple scans from the ferritic side of the weld as well as those from the weld crown, the NRC staff concludes that there is a high likelihood of finding the hypothetical flaw size proposed by the licensee, and thus, concludes that the proposed hypothetical flaw size is acceptable.
In the proposed alternative, the licensee submitted a flaw growth calculation for weld 10-014 for a hypothetical axial flaw growing by PWSCC in response to operational stress and the WRS that would result from a repair of 50 percent of the wall thickness. The licensee's flaw growth calculation shows that a 16.7 percent through wall flaw, significantly deeper than the proposed hypothetical 10 percent flaw through wall flaw, would grow to the ASME Code allowable flaw size of 75 percent through wall in approximately 54 months.
The NRC staff has performed independent confirmatory analyses using the proposed 10 percent through wall hypothetical flaw size. The NRC staffs analysis used the licensee's calculated values for WRS for a 50 percent repair as well as reference WRS values for a 50 percent weld repair. The results of the NRC staff's analyses support the licensee's 54-month lifetime calculation for the bounding RCP weld,10-014.
In summary, the NRC staff concludes that compliance with the requirements of 10 CFR 50.55a(g}(6)(ii}(F)(3) for performing an ASME Code-compliant baseline examination would result in hardship. The NRC staff further concludes that the PWSCC-susceptible weld material has been examined by ASME Code-compliant examinations in the axial scan direction for detection of safety significant circumferential flaws, and that the hypothetical bounding axial flaw in the susceptible material has a calculated time in excess of 54 months to grow by PWSCC to reach ASME Code limits. The NRC staff concludes that the UT examination, which was previously performed in fall 2009, provides a reasonable assurance of structural integrity and
-6 leak tightness until the scheduled refueling outage in the spring of 2014. The NRC staff therefore concludes that complying with the requirements of 10 CFR SO.SSa(g)(6)(ii)(F)(3) would result in hardship without a compensating increase in the level of quality and safety.
4.0 CONCLUSION
Based on the above, the NRC staff concludes that the proposed alternative provides reasonable assurance of structural integrity and leak tightness of the subject reactor coolant pump welds, and that complying with the specified requirement would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR SO.SSa(a)(3)(ii). The NRC staff therefore authorizes use of the proposed alternative crediting the DMBW examination performed at Arkansas Nuclear One, Unit 2, in the fall of 2009, for the baseline examination required by 10 CFR SO.SSa(g)(6)(ii)(F)(3) until the scheduled refueling outage in the spring of 2014.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in the subject request for relief remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
S.O REFERENCES
- 1. Pyle, S. L., Entergy Operations, Inc., letter to U.S. Nuclear Regulatory Commission, "Revised Request for Alternative AN02-ISI-007, Code Case N-770-1 Baseline Examination," dated December 4,2012 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12340A449), with proprietary Attachment 1: "Westinghouse Calculation Note Number CN-MRCDA-12-27, Revision 1, ANO-2 PWSCC Analysis for RCP Dissimilar Metal Weld," dated October 29,2012.
- 2. Pyle, S. L., Entergy Operations, Inc., letter to U.S. Nuclear Regulatory Commission, "Clarification on Initial Flaw Size and Qualified Examination Area Revised Request for Alternative AN02-ISI-007 Code Case N-770-1 Baseline Examination," dated December 17,2012 (ADAMS Accession No. ML 123S4A203).
- 3. Markley, M. T., U.S. Nuclear Regulatory Commission, letter to Entergy Operations, Inc.,
"Arkansas Nuclear One, Unit 2 - Relief Request AN02-ISI-007, Alternative to Use ASME Code Case N-770-1 Baseline Examination, Fourth 10-Year Inservice Inspection Interval (TAC No. ME7646)," dated November 27,2012 (ADAMS Accession No. ML12319A367).
- 4. Kalyanam, N., U.S. Nuclear Regulatory Commission, memorandum to file, "Waterford Steam Electric Station, Unit 3, Verbal Authorization ofW3-ISI-020," dated December 18, 2012 (ADAMS Accession No. ML 1308SA12S).
S. Electric Power Research Institute, "Material Reliability Program: Primary System Piping Butt Weld Inspection and Evaluation Guideline (MRP-139, Revision 1)," December 2008 (ADAMS Accession No. ML100970671).
-7
- 6. Pyle, S. L., Entergy Operations, Inc., letter to U.S. Nuclear Regulatory Commission, "Response to Second Request for Additional Information, Request for Alternative AN02-ISI-007, Code Case N-770-1 Baseline Examination," dated September 10, 2012 (ADAMS Accession No. ML12255A388).
- 7. Pyle, S. L., Entergy Operations, Inc., letter to U.S. Nuclear Regulatory Commission, "Transmittal of Westinghouse Calculation Note CN-MRCDA-12-27 in Support of Response for Additional Information Related to Request for Alternative AN02-ISI-007,"
dated September 10,2012 (ADAMS Accession No. ML12255A386), with proprietary Attachment 1: Westinghouse Calculation Note Number CN-MRCDA-12-27 Entitled "ANO-2 PWSCC Analysis for RCP Dissimilar Metal Welds (Proprietary)," dated August 16, 2012.
- 8. Mason, M. E., Entergy Operations, Inc., letter to U.S. Nuclear Regulatory Commission, "Waterford 3 Response to an NRC Request for Additional Information (RAI) Associated with W3-ISI-020, Request for Alternative to ASME Code Case N-770-1 Baseline Examination [TAC No. ME9801]," dated November 15,2012 (ADAMS Accession No. ML12324A170).
- 9. Pacific Northwest National Laboratory, Technical Letter Report, "Evaluation of Licensee's Alternative to 10 CFR 50.55a{g)(6)(ii)(F) for Limitations to Volumetric Examinations of Dissimilar Metal Welds, Entergy Operations, Inc., Arkansas Nuclear One, Unit 2," dated April 23, 2013 (ADAMS Accession No. ML13113A218).
Principal Contributor: Jay Wallace, NRR/DE/EPNB Date: May 30,2013
ML13129A298 *SE email dated 4/25/2013 OFFICE NRR/DORLlLPL4/PM NRR/DORLlLPL4/LA NRR/D EIE P N B/BC NRR/DORLlLPL4/BC I NAME NKalyanam JBurkhardt TLupold* MMarkley Ii i DATE 5/20/13 5/16/13 4/25/13 5/30/13 II