ML101610306
| ML101610306 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 06/28/2010 |
| From: | Stang J Plant Licensing Branch II |
| To: | Repko R Duke Energy Carolinas |
| Thompson, Jon 415-1119 | |
| References | |
| TAC ME1822 | |
| Download: ML101610306 (8) | |
Text
June 28, 2010 Mr. Regis T. Repko Vice President McGuire Nuclear Station Duke Energy Carolinas, LLC 12700 Hagers Ferry Road Huntersville, NC 28078
SUBJECT:
MCGUIRE NUCLEAR STATION, UNIT 1 (MCGUIRE 1) - RELIEF REQUEST 09-MN-003 FOR EXTENSION OF THE REACTOR VESSEL INSERVICE INSPECTION (ISI) DATE TO THE YEAR 2020 (PLUS OR MINUS ONE OUTAGE) (TAC NO. ME1822)
Dear Mr. Repko:
By letter dated June 29, 2009, as supplemented by letter dated November 23, 2009, Duke Energy Carolinas, LLC (the licensee), proposed an alternative to the American Society of Mechanical Engineers (ASME), Boiler and Pressure Vessel Code (the Code), inservice inspection interval requirements for the reactor vessel. Relief request 09-MN-003 proposes to extend the ISI interval for reactor vessel examination category B-A and B-D welds from 10 to 20 years for McGuire 1. This would extend the date for the next reactor vessel ISI for these components in McGuire 1 to the year 2020 (plus or minus one outage).
The NRC staff has reviewed the licensee's submittal and, based on the information provided, the NRC staff has determined that the proposed alternative provides an acceptable level of quality and safety. Therefore, pursuant to Title 10 of the Code of Federal Regulations, Part 50, Section 50.55a(a)(3)(i), the NRC staff authorizes the use of the proposed alternative to extend the reactor vessel ISI date to the year 2020 (plus or minus one outage), thus extending the third ISI interval for McGuire 1 Category B-A and B-D components from 10 to 20 years. In addition, this approval is dependent upon the licensee changing the date for the Oconee 3 reactor vessel ISI to the year 2014 (plus or minus one outage) as discussed in the application.
All other requirements of ASME Code,Section XI, for which relief has not been specifically requested remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Sincerely,
/RA/
John Stang, Acting Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-369
Enclosure:
Safety Evaluation cc w/encl: Distribution via Listserv
ML101610306 *concurrence via email dated 3/30/10 ML100890514 OFFICE NRR/LPL2-1/PM NRR/LPL2-1/LA NRR/CVIPNB/BC NRR/LPL2-1/BC(A)
NRR/LPL2-1/PM NAME JThompson MOBrien MMitchell*
JStang JThompson DATE 06/14/10 06/14/10 03/30/10 06/28/10 06/14/10
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF THIRD 10-YEAR INTERVAL INSERVICE INSPECTION RELIEF NO. 09-MN-003 DUKE ENERGY CAROLINAS, LLC MCGUIRE NUCLEAR STATION, UNIT 1 DOCKET NO. 50-369
1.0 INTRODUCTION
By letter dated June 29, 2009 (Agencywide Documents Access and Management System (ADAMS), Accession No. ML091880423), as supplemented by letter dated November 23, 2009 (ADAMS Accession No. ML093350526), Duke Energy Carolinas, LLC (Duke or the licensee),
submitted relief request 09-MN-003 to the U.S. Nuclear Regulatory Commission (NRC) to request approval to use a proposed alternative to meet certain requirements of the 1998 Edition of Section XI of the American Society of Mechanical Engineers (ASME), Boiler and Pressure Vessel Code (Code), for McGuire Nuclear Station, Unit 1 (McGuire 1). The licensee requested the proposed alternative under the provisions of Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.55a(a)(3)(i). The proposed alternative 09-MN-003 requested approval of an alternative to extend the third inservice inspection (ISI) interval from 10 years to approximately 20 years for the examination of reactor vessel (RV) Category B-A welds and Category B-D nozzle-to-vessel welds and nozzle inner radius sections. Under this request, the proposed McGuire 1 RV ISI date of 2011 (plus or minus one outage) would be extended to 2020 (plus or minus one outage). In exchange for moving the McGuire 1 RV ISI date to 2020 (plus or minus one outage), Duke would change the next proposed Oconee Nuclear Station, Unit 3 (Oconee 3), RV ISI date to 2014 (plus or minus one outage), as opposed to the previous 2024 (plus or minus one outage) as indicated in the Pressurized Water Reactor (PWR) Owners Group letter dated October 31, 2006, OG-06-356, Plan for Plant Specific Implementation of Extended Inservice Inspection Service Interval per WCAP-16168-NP, Revision 1, Risk-Informed Extension of the RV In-Service Inspection Interval (ADAMS Accession No. ML082210245).
The NRC staff verbally authorized the licensee's requested alternative in a teleconference on December 9, 2009. This Safety Evaluation (SE) documents the basis for the NRC staff's verbal authorization and is written consistently with the information available at the time the verbal authorization was given.
2.0 REGULATORY EVALUATION
ISI of ASME Code Class 1, 2, and 3 components is performed in accordance with Section XI of the ASME Code and applicable addenda as required by 10 CFR 50.55a(g), except where specific relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). The
regulation at 10 CFR 50.55a(a)(3) 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.
The regulation at 10 CFR 50.55a(g)(4) states further that ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements, except design and access provisions and preservice examination requirements, set forth in 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 ISI 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 applicable ISI Code of Record for McGuire 1 is the 1998 Edition with the 2000 Addenda of ASME Code,Section XI.
ASME Code,Section XI, Article IWB-2000 establishes an ISI interval of 10 years for the inspection of pressure-retaining RV welds. In the proposed alternative, the licensee requested extension of the ISI for category B-A and B-D RV welds from 10 to 20 years based upon the Westinghouse Electric Company (Westinghouse) Topical Report (TR) WCAP-16168-NP-A, Rev. 2, submitted by letter dated January 26, 2006 (ADAMS Accession No. ML060330504), as supplemented by letter dated June 8, 2006 (ADAMS Accession No. ML0616004311).
WCAP 16168-NP-A, Rev. 2, was approved by the NRC staff by letter dated May 8, 2008 (ADAMS Package No. ML081060053). The proposed alternative used the provisions of 10 CFR 50.55a(a)(3)(i), stating that the alternative inspection interval (20 years) would provide an acceptable level of quality and safety. In the proposed alternative the licensee identified 2020 (plus or minus one outage) as the year to which the future interval for the examination of Categories B-A and B-D RV welds would be deferred.
2.1 Background
The ISI of Category B-A and B-D components consists of visual and ultrasonic examinations intended to discover whether flaws have initiated, whether pre-existing flaws have extended, and whether pre-existing flaws may have been missed in prior examinations.
2.2 Summary of WCAP-16168-NP, Revision 2 In 2006, the PWR Owners Group submitted TR WCAP-16168-NP, Rev. 2, to the NRC in support of making a risk-informed assessment of extensions to the ISI intervals for Category B-A and B-D components. In the report, the PWR Owners Group took data associated with three different PWR plants (referred to as the pilot plants), one designed by each of the main contractors for nuclear power plants in the USA, and performed the necessary studies on each of the pilot plants required to justify the proposed extension for the ISI interval for Category B-A and B-D components from 10 to 20 years.
The analyses in the TR used probabilistic fracture mechanics tools and inputs from the work described in the NRC staffs pressurized thermal shock (PTS) risk re-evaluation: NUREG-1806
(ADAMS Accession No. ML061580318) and NUREG-1874 (ADAMS Accession No. ML070860156). The PWR Owners Group analyses incorporated the effects of fatigue crack growth and ISI. Design basis transient data was used as input to the fatigue crack growth evaluation. The effects of the ISI were modeled consistently with the previously approved probabilistic fracture mechanics codes in TR WCAP-14572-NP-A (ADAMS Accession Nos.
ML012630327, ML012630349, and ML12630313). These effects were put into evaluations performed with the Fracture Analysis of Vessels-Oak Ridge (FAVOR) code, ONRL/NRC/LTR0418 (ADAMS Accession No. ML042960391). All other inputs were identical to those used in the PTS risk re-evaluation.
From the results of the studies, the PWR Owners Group concluded that the ASME Code,Section XI, 10-year inspection interval for Category B-A and B-D components in PWR RVs can be extended to 20 years. Their conclusion from the results for the pilot plants was considered to apply to any plant designed by the three vendors (Westinghouse, Combustion Engineering, and Babcock and Wilcox) as long as the critical, plant-specific parameters (defined in Appendix A of TR WCAP-16168-NP, Rev. 2) are bounded by the pilot plants.
2.3 Summary of NRC SE for TR WCAP-16168, Rev. 2 The NRC staffs conclusion in its SE for TR WCAP-16168, Rev. 2, dated May 8, 2008, indicates that the methodology presented in the TR WCAP-16168, Rev. 2, in concert with the guidance provided by Reg. Guide 1.174, Rev. 1 (ADAMS Accession No. ML023240437), is acceptable for referencing in requests to implement alternatives to ASME Code inspection requirements for PWR plants in accordance with the limitations and conditions in the SE. In addition to showing that the subject plant is bounded by the pilot plants information from Appendix A in TR WCAP-16168, Rev. 2, the key points of the SE relevant to McGuire 1 are summarized below:
- 1.
The dates identified in the request for the alternative should be within plus or minus one refueling cycle of the dates identified in the implementation plan provided to the NRC staff. Any deviations from the implementation plan contained in the PWR Owners Group Letter OG-06-356 should be discussed in detail in the request for alternative. The maximum proposed ISI interval is 20 years.
- 2.
Calculation of T30 for the purpose of demonstrating plant-specific consistency with material property values cited in TR WCAP-16168, Rev. 2, must be carried out via an NRC-approved methodology.
- 3.
The SE for TR WCAP-16168, Rev. 2, called for a license condition related to the evaluation of future ISI results. The submittal of a license condition is no longer necessary in conjunction with this requested alternative (see discussion in Section 4.1 of this SE); however, subsequent updated alternatives to seek to extend an ISI interval from 10 to 20 years for the subject component examinations should include the evaluation of the most recent ISI data in accordance with the criteria in the final alternative PTS Rule, 10 CFR 50.61a.
3.0 TECHNICAL EVALUATION
3.1 Description of Proposed Alternatives In the proposed alternative, the licensee proposed to defer the ASME Code-required Category B-A and B-D weld ISI for McGuire 1 until 2020 (plus or minus one outage). As indicated in PWR Owners Group Letter OG-06-356, the next proposed McGuire 1 RV ISI date is 2011 (plus or minus one outage). The licensee proposes that in exchange for moving the McGuire 1 RV ISI date to 2020 (plus or minus one outage), the next proposed Oconee 3 RV ISI date will be 2014 (plus or minus one outage), as opposed to 2024 (plus or minus one outage) as indicated in the PWR Owners Group Letter OG-06-356.
3.2 Components for Which Relief is Requested The affected components are the subject plant RV and its interior attachments and core support structure. The following examination categories and item numbers from IWB-2500 and Table IWB-2500-1 of the ASME Code,Section XI, are addressed in this request:
Examination Category Item Number Description B-A B1.11 Circumferential Shell Weld B-A B1.12 Longitudinal Shell Welds B-A B1.21 Circumferential Head Weld B-A B1.22 Meridional Head Weld B-A B1.30 Shell-to-Flange Weld B-D B3.90 Nozzle-to-Vessel Welds B-D B3.100 Nozzle Inner Radius Areas 3.3 Basis for Proposed Alternatives The basis for the proposed alternative is found in the NRC-approved version of TR WCAP-16168, Rev. 2. Plant-specific parameters for the subject plant are summarized in the attachment to the licensees letter of June 29, 2009. The format of the information is patterned after that found in Appendix A of TR WCAP-16168, Rev. 2, and the critical parameters listed in Tables 1, 2, and 3, of the attachment are bounded by this TR.
4.0 NRC STAFFS TECHNICAL EVALUATION The NRC staff has reviewed the attachment to the licensees letter dated June 29, 2009, as supplemented by letter dated November 23, 2009, to make this evaluation. The Frequency and Severity of Design Transients for McGuire 1 were found to be bounded by the TR WCAP-16168, Rev. 2. Also, the McGuire 1 RV is single-layer clad and therefore was bounded by the analyses in TR WCAP-16168, Rev. 2.
Table 2 of the submittal includes additional information pertaining to previous RV inspections and the schedule for future ones. The proposed third ISI interval inspection for McGuire 1 is scheduled to be performed in 2011 (plus or minus one outage), according to PWR Owners Group Letter OG-06-356. The licensee proposed that in exchange for moving the McGuire 1
RV ISI date to 2020 (plus or minus one outage), the next proposed Oconee 3 RV ISI date will be 2014 (plus or minus one outage), as opposed to 2024 (plus or minus one outage) as indicated in the PWR Owners Group Letter OG-06-356. There were a total of 64 indications detected in the most recent ISI. Thirty-five of these 64 indications were within the inner 3/8ths of the RV thickness and they were further assessed and found acceptable per Table IWB-3510-1 of Section XI of the ASME Code. Six of these 35 indications were within the 1/10th (or 1) of the RV thickness and were further assessed. Five of the six indications were in the weld material.
One circumferential indication in plate material B5012-1 did not meet the requirements in SECY-07-0104. Circumferential flaws were shown in NUREG-1874 to have a very small contribution to the calculation of through-wall crack frequency (TWCF). Further analysis found that this material has a maximum RTNDT + T30 of 118°F and is not the limiting material in the beltline region. The total number of flaws detected in the inner 1/10th of the McGuire 1 beltline is far lower than those allowed in Tables 2 and 3 of SECY-07-0104. Additional information was provided in the licensees letter of November 23, 2009, containing details of the inspection technologies used by the examiners. The NRC staff agrees that the detection of the flaw in plate material B5012-1 can be attributed to the improvement in inspection technology and that the subsurface flaw is judged to be due to fabrication and not attributable to a service-related degradation mechanism.
The calculation of TWCF95-TOTAL was performed using Table 3 of the November 23, 2009, submittal as a basis. The request uses the NUREG-1874 methodology to calculate T30. The calculations were independently verified via NRC staff calculation and the difference between the licensees and NRC staffs calculations were found to be insignificant. In addition, the NRC staff calculated T30 values according to Regulatory Guide (RG) 1.99, Revision 2, Radiation Embrittlement of Reactor Vessel Materials, May 1988, to compare this to the methodology used in NUREG-1874; the NUREG-1874 values were similar to those calculated using RG 1.99, Rev. 2. The TWCF95-TOTAL was found to be acceptably low as calculated through the methodology prescribed in the TR WCAP-16168, Rev. 2 and detailed in Table 3 of the letter dated November 23, 2009.
At the time of issuance of the safety evaluation for TR WCAP-16168, Rev. 2, it was the NRC staffs intent to establish a process by which licensees could receive approval to implement 20-year ISI intervals for the subject component examinations through the end of their facilitys current operating license. This objective led to the provision, as discussed in Section 4 of the SE for TR WCAP-16168, that the licensee would submit a license amendment which required the licensee to evaluate future volumetric ISI data in accordance with the criteria in the draft and/or final alternative PTS Rule, 10 CFR 50.61a. The NRC staff has since determined that the appropriate process for requesting further extensions of the ISI interval, beyond this granting of relief in response to the licensees application of June 29 and November 23, 2009, is through 10 CFR 55a for each subsequent ISI interval. Accordingly, the NRC staff considers that such a license condition as discussed above is not necessary and that requirements for future evaluation of ISI data will be addressed as part of the review of further requests for extension of the ISI interval for the subject components.
The NRC staff will grant ISI interval extensions for the subject components on an interval-by-interval basis, i.e., only a facilitys current ISI interval will be extended for up to 20 years.
Licensees will have to submit updated alternatives to the NRC staff for review and approval to extend each following ISI interval from 10 years to 20 years, as needed. Accordingly, the
requirement in TR WCAP-16168, Rev. 2, for a license condition to address the evaluation of future ISI data (see Section 2.3, item 3) is no longer necessary in conjunction with this requested alternative. However, in order to obtain NRC staff approval, a subsequent updated alternative that seeks to extend an ISI interval from 10 to 20 years for the subject component examinations should include the evaluation of a facilitys most recent ISI data in accordance with the criteria in the final alternative PTS Rule, 10 CFR 50.61a. For purposes of technical and regulatory consistency, the NRC staffs SE for TR WCAP-16168, Rev. 2, will be revised to reflect these changes in NRC staff position regarding the implementation of ISI interval extensions based on TR WCAP-16168, Rev. 2. Therefore, the NRC staff will only approve the proposed alternative 09-MN-003 for the third ISI interval that will now end on 2020 (plus or minus one outage) for the subject component examination.
In summary, the licensee has demonstrated through the submittal dated June 29 and November 23, 2009, that the RV for McGuire 1 is bounded by the analyses in TR WCAP-16168, Rev. 2. The submittal demonstrates that there is no significant additional risk associated with extending the ISI interval for Category B-A and B-D components from 10 years to 20 years.
5.0 CONCLUSION
The NRC staff has completed its review of the June 29 and November 23, 2009, submittal for 09-MN-003 regarding McGuire 1. The NRC staff concludes that increasing the ISI interval for Category B-A and B-D components from 10 years to 20 years shows no appreciable increase in risk. The NRC staff comes to this conclusion based on the fact that the plant-specific information provided by the licensee is bounded by the data supplied in TR WCAP-16168, Rev. 2, and the request dated June 29 and November 23, 2009, including the additional change in the ISI schedule for Oconee 3, meets all the conditions and limitations described in the TR WCAP-16168, Rev. 2. Therefore, the proposed alternative in relief request 09-MN-003 provides an acceptable level of quality and safety and the alternative is granted pursuant to 10 CFR 50.55a(a)(3)(i) until the end of the third interval for Categories B-A and B-D components at McGuire 1 in 2020 (plus or minus one outage).
All other requirements of ASME Code,Section XI, not specifically included in the request for the proposed alternatives, remain in effect.
Principal Contributor: C. Fairbanks, NRR Date: June 28, 2010