ML20147A663

Proposed Alternative Requirements for ASME Code Preservice Inspection Acceptance of Volumetric and Surface Examinations

ML20147A663
Person / Time
Site:	Vogtle
Issue date:	09/17/2020
From:	Omar Lopez-Santiago NRC/NRR/VPOB
To:	Whitley B Southern Nuclear Operating Co
Billy Gleaves x5848
References
EPID L-2020-LLR-0080
Download: ML20147A663 (12)

Text

September 17, 2020 Mr. Brian H. Whitley, Director Regulatory Affairs Southern Nuclear Operating Company, Inc.

3535 Colonnade Parkway, Bin N-226-EC Birmingham, AL 35243

SUBJECT:

PROPOSED ALTERNATIVE REQUIREMENTS FOR ASME CODE PRESERVICE INSPECTION ACCEPTANCE OF VOLUMETRIC EXAMINATIONS, VOGTLE ELECTRIC GENERATING PLANT, UNITS 3 AND 4 (EPID L-2020-LLR-0080)

Dear Mr. Whitley:

By letter dated June 12, 2020, and subsequently replaced in its entirety by letter dated July 28, 2020 (Revision 1), Southern Nuclear Operating Company (SNC or licensee) submitted a request to the Nuclear Regulatory Commission (NRC) to use an alternative to certain American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (B&PV),Section XI, 2007 Edition and 2008 Addenda, and ASME Code,Section III, 1998 Edition including the 2000 Addenda requirements at the Vogtle Electric Generating Plant (VEGP), Units 3 and 4. SNC stated that the basis for the submitted alternative (PSI/ISI-ALT-14R1) was in accordance with Title 10 of the Code of Federal Regulations (10 CFR):

10 CFR 50.55a(z)(1), the licensee requested to use the proposed alternative on the basis that the alternative provides an acceptable level of quality and safety.

As set forth in the attached safety evaluation, the NRC staff determined that the proposed alternative to use the flaw evaluation acceptance requirements of IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition to Section XI of the ASME Code, is acceptable in order to place components with flaws into service in lieu of meeting the requirements of NCA-3252 and NB-5332(b) of the 1998 Edition, including the 2000 Addenda, of ASME Code,Section III and IWB-3112(c) and IWC-3112(c) in the 2007 Edition, including the 2008 Addenda, of ASME Code,Section XI that would require repairing flaws which would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety. The NRC staff finds there is reasonable assurance of adequate protection on the use of this alternative based on the conditions in the alternative that includes limitation on the number of welds, limitation on depth of the flaws, analyzing flaws for the service life of the component, using the proximity limits in Section XI of the ASME Code, and reexamination of the actual flaws during the first inservice inspection period as stated in the licensees letter dated July 28, 2020. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(2), and otherwise is in compliance with the ASME Code requirements. Therefore, the NRC staff authorizes PSI/ISI-ALT-14R1 for the preservice inspection, and the first inservice inspection intervals at VEGP, Units 3 and 4. All other requirements of ASME Code, Sections III and XI and 10 CFR 50.55a, for which an alternative has not been specifically requested and authorized, remain applicable including third party review by the Authorized Nuclear Inspector and Authorized Nuclear Inservice Inspector.

B. Whitley If you have any questions, please contact the Senior Project Manager, Billy Gleaves, at (301) 415-5848.

Sincerely,

/RA/

Omar R. Lpez-Santiago, Chief Vogtle Project Office Office of Nuclear Reactor Regulation Docket No(s).: 52-025 52-026

Enclosure:

Safety Evaluation cc: See next page

ML20147A663 *Via email NRO-008 OFFICE NRR/VPO:LA NRR/VPO:PM NRR/VPO:PM NRR/DEX:BC NRR/VPO:BC OLopez-NAME RButler* WGleaves* CSantos* MMitchell* Santiago*

DATE 9/15/2020 9/15/2020 9/17/2020 9/15/2020 9/17/2020 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR ALTERNATIVE VEGP 3&4-PSI/ISI-ALT-14R1 REGARDING PRESERVICE INSPECTION ACCEPTANCE OF VOLUMETRIC EXAMINATIONS COMBINED LICENSE NOS. NPF-91 AND NPF-92 SOUTHERN NUCLEAR OPERATING COMPANY, INC.

GEORGIA POWER COMPANY OGLETHORPE POWER CORPORATION MEAG POWER SPVM, LLC MEAG POWER SPVJ, LLC MEAG POWER SPVP, LLC CITY OF DALTON VOGTLE ELECTRIC GENERATING PLANT, UNITS 3 AND 4 DOCKET NOS.52-025 AND 52-026

1.0 INTRODUCTION

By letter dated June 12, 2020 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20164A174), replaced in its entirety by Revision 1, dated July 28, 2020, (ADAMS Accession No. ML20211L786), Southern Nuclear Operating Company Inc. (SNC or the licensee) requested U.S. Nuclear Regulatory Commission (NRC) approval of an alternative, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1) of, to the requirements of American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME B&PV Code), Sections III and XI, for acceptance of preservice inspection (PSI) volumetric examination flaws for ASME Code Class 1 and 2 welds. The proposed alternative Enclosure

(PSI/ISI-ALT-14R1) would allow SNC to use the flaw evaluation acceptance requirements of IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition to Section XI of the ASME Code, in order to place components with flaws into service in lieu of meeting the requirements of NCA-3252 and NB-5332(b) of the 1998 Edition, including the 2000 Addenda, of ASME Code,Section III and IWB-3112(c) and IWC-3112(c) in the 2007 Edition, including the 2008 Addenda, of ASME Code,Section XI. The use of IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition of ASME Code,Section XI, with provisions for accepting flaws by analytical evaluation during preservice inspection, is prohibited by 10 CFR 50.55a(b)(2)(xli). The licensee has requested approval of this alternative as a contingency for evaluating flaws in welds found during PSI.

Although the licensee requested NRC authorization pursuant to 10 CFR 50.55a(z)(1), for the use of a proposed alternative on the basis that the alternative provides an acceptable level of quality and safety, the NRC staff evaluated the licensees submittal and determined that the request would be reviewed pursuant to 10 CFR 50.55a(z)(2), in that the applicable requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

2.0 REGULATORY EVALUATION

10 CFR 50.55a(a)(1) incorporates by reference approved Editions and Addendas of the ASME Code.

10 CFR 50.55a(b)(2) specifies conditions on the use of the ASME B&PV Code,Section XI for the inspection of applicable components.

10 CFR 50.55a(b)(2)(xli) prohibits the use of the flaw evaluation acceptance requirements of ASME Code,Section XI, IWB-3112(a)(3) and IWC-3112(a)(3) in the 2013 through 2017 Edition.

10 CFR 50.55a(c)(1), 10 CFR 50.55a(d)(1) and 10 CFR 50.55a(e)(1) require systems and components to meet the requirements for ASME Code Class 1, 2, and 3, respectively, in Section III of the ASME Code.

10 CFR 50.55a(g)(2)(ii) requires that systems and components that are classified as ASME Code Class 1, Class 2, and Class 3 and supports for components that are classified as ASME Code Class 1, 2, and 3 must be designed and be provided with the access necessary to perform the required preservice and inservice examinations set forth in the Editions and Addenda of Section III or Section XI of the ASME Code incorporated by reference in paragraph (a)(1) of 10 CFR 50.55a.

10 CFR 50.55a(g)(3)(ii) states that ASME Code Class 1, Class 2, and Class 3 components and supports for components that are classified as ASME Code Class 1, 2, and 3 must meet the preservice examination requirements set forth in the editions and addenda of Section III or Section XI of the ASME BPV Code incorporated by reference in paragraph (a)(1) of 10 CFR 50.55a applied to the construction of the particular component.

Per 10 CFR 50.55a(z), alternatives to the requirements of paragraphs (b) through (h) of 10 CFR 50.55a or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. In proposing alternatives, the licensee must demonstrate that:

(1) the proposed alternative would provide an acceptable level of quality and safety; or (2) compliance would result in hardship or unusual difficulty without a compensating increase in quality and safety.

Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request, and the NRC to authorize, the alternative requested by the licensee.

3.0 TECHNICAL EVALUATION

3.1 SNCs Alternative Pursuant to 10 CFR 50.55a(z)(1), the licensee submitted this alternative requesting NRC approval to allow the use of the flaw evaluation acceptance requirements of IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition to Section XI of the ASME Code, in order to place components with flaws into service in lieu of meeting the requirements of the 1998 Edition, including the 2000 Addenda, of ASME Code,Section III and the 2007 Edition, including the 2008 Addenda, of ASME Code,Section XI. The use of IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition of ASME Code,Section XI is prohibited by 10 CFR 50.55a(b)(2)(xli). The licensee has requested approval of this alternative for use during the PSI and the first period of the first interval of the inservice inspections (ISI) for re-examination of vessel welds at VEGP, Units 3 and 4.

The ASME Code of Record for the construction of VEGP, Units 3 and 4 is the 1998 Edition, including the 2000 Addenda, of ASME Code,Section III. The ASME Code of Record for the PSI and ISI of VEGP, Units 3 and 4 is the 2007 Edition, including the 2008 Addenda, of ASME Code,Section XI. The inspection requirements for ASME Code Class 1 and 2 components are provided in ASME Code,Section XI, Subsection IWB and Subsection IWC, respectively.

The components affected by this request are ASME Code Class 1 welds in Table IWB-2500-1 examination Category B-A, B-B, B-D, B-F, and B-J of Section XI, and ASME Code Class 2 welds in Table IWC-2500-1 examination Category C-A, C-B, C-C, C-F-1, and C-F-2 of Section XI. These specific welds are those that require PSI and are listed in the PSI program plan which includes the corresponding weld class, weld category and nondestructive examination method to be used for each unit at VEGP, Units 3 and 4. This alternative is to be used as a contingency, if flaws are detected that exceed the acceptance criteria in Sections III and XI of the ASME Code.

During PSI of the Core Make-up Tank (CMT) inlet and outlet nozzle-to-head welds for VEGP, Unit 3, flaws were detected in three welds that exceeded the acceptance standards in Table IWB-3410-1 of ASME Code,Section XI. SNC proposes to use the flaw evaluation acceptance requirements in IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition of ASME Code,Section XI for these three welds and for an additional, limited number of welds for both VEGP, Units 3 and 4, if necessary. The NRC staff notes that if this alternative is used for the three CMT welds for VEGP, Unit 3, the limit on number of welds for VEGP, Unit 3 would be reduced accordingly. Limited use of the flaw evaluation criteria in IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition to Section XI of the ASME Code would allow disposition of these flaws without weld repairs that could be detrimental to the component welds.

SNC stated that, as of May 27, 2020, approximately 432 Class 1 welds have undergone Ultrasonic Testing (UT) PSI out of 607 for VEGP Unit 3, leaving approximately 175 welds to be examined. The approximate total number of Class 2 welds that are being examined using UT PSI is 128 in each unit. For Unit 3, approximately 49 out of 128 Class 2 welds have UT PSI

performed, with about 79 remaining. The number of UT PSI completed welds for VEGP, Unit 4 is smaller than VEGP, Unit 3.

SNC stated that experience has shown that local weld repair of flaws can result in high weld residual stresses that can lead to stress corrosion cracking in service. Studies have also shown that such weld repairs can reduce weld reliability, as compared to using flaw evaluation techniques to leave embedded flaws in welds. This is relevant when considering repairs of embedded flaws in component welds, which often are larger thickness welds, as compared to piping system welds. In order to maintain the integrity of plant components, particularly fabricated vessels, the use of flaw evaluation with the conditions cited in the alternative below, establishes the optimal conditions for maintaining weld integrity for the construction of VEGP, Units 3 and 4.

SNC also stated that the flaw evaluation methods, which have been developed for use under the fracture mechanics methods described in ASME Code,Section XI, allow for very accurate assessment of the impact of such embedded flaws on the integrity of the component. SNC stated that the use of analytical flaw evaluation, in accordance with the provisions of IWB-3132.3 as described in IWB-3600, is consistent with the requirements for flaws identified during ISI and is therefore considered an acceptable method to demonstrate weld integrity for operating nuclear plants.

SNC proposed additional conditions on the use of IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition to Section XI of the ASME Code as summarized below:

• This alternative can be applied to a maximum of twelve Class 1 welds and seven Class 2 welds. These limits are applicable to each unit. The total number of welds and initial individual flaw depth (T%) shall be limited to the following for each unit:

Code Maximum T% 50%* 50%<T% 55%* 55%<T%

Class Number of 60%*

Welds Class 1 12 9 2 1 Class 2 7 4 2 1

• Unused weld count from higher depth limits can be used in these columns.

• This alternative is not applicable to the steam generator to reactor coolant pump (SG-to-RCP) welds.

• The flaw evaluation shall demonstrate that the flaw is predicted to remain non-surface-connected (embedded) for the entire service life of the component.

• Subsequent examination for each vessel weld that has been evaluated using this alternative shall be conducted during the first ISI period.

• IWB-3640 flaw evaluation will account for proximity of flaws, as described in ASME Section XI, including Nonmandatory Appendix C of ASME Code,Section XI.

The above conditions limit the use of this alternative to less than 2 percent of Class 1 and 6 percent of Class 2 welds, for each unit, which require UT PSI. If additional application of analytical flaw evaluation is needed beyond these limits, then it is intended that this restriction will assure that the process of accepting such evaluations is an iterative one, by requiring an additional request for alternative.

It should be noted that the limits for Class 1 and Class 2 in the above table is modified by the note that states, Unused weld count from higher depth limits can be used in these columns.

This clarifies that unused weld counts for higher depth limits can be used to allow evaluation of a lower depth limit. For example, if there are no welds in the 55 percent to 60 percent range, then there can be three welds evaluated in the 50 percent to 55 percent range, but the total number of welds is always limited to 12 Class 1 welds and seven Class 2 welds, for each unit.

The NRC staff notes that unused weld counts are to be used within each class and cannot be transferred between classes of welds or between the units at VEGP, Units 3 and 4.

The proposed additional limitations provide assurance that the use of this alternative will ensure that weld integrity is maintained and provide conservative limitations on the number of welds that can be subjected to flaw evaluation under IWB-3600 and IWC-3600. Also, it is noted that IWB-3640 states, The procedures shall be the responsibility of the Owner and shall be provided to the regulatory authority having jurisdiction at the plant site. Therefore, this information will be available to the NRC, as required.

SNC stated that the proposed alternative provides an acceptable level of quality and safety in accordance with 10 CFR 50.55a(z)(1) based on limits on the number of welds this alternative can be used, along with limits on depth of embedded flaws, inservice reexamination to verify the flaw evaluation is bounding, and operating experience research on weld residual stresses. The duration of the proposed alternative is the preservice examinations and until the end of the first period in the first inservice inspection interval of Section XI of the ASME Code.

3.2 NRC Staff Evaluation The ASME Code of Record for the construction of VEGP, Units 3 and 4 is the 1998 Edition, including the 2000 Addenda, of ASME Code,Section III. The ASME Code of Record for inspection requirements for ASME Code Class 1 and 2 components are provided in the 2007 Edition, including the 2008 Addenda of the ASME Code,Section XI, Subsection IWB and Subsection IWC, respectively, which is the ASME Code of Record for the PSI and ISI at VEGP, Units 3 and 4.

10 CFR 50.55a requires that components of nuclear power plants meet the requirements of the ASME Code, except where alternatives have been authorized by the Director, Office of Nuclear Reactors Regulation, pursuant to 10 CFR 50.55a(z). 10 CFR 50.55a(g)(ii) states that ASME Code Class 1, 2 and 3 systems and components (including supports) of boiling and pressurized water-cooled nuclear power reactors must meet the requirements for PSI and ISI of the ASME Code Sections III or XI incorporated by reference in paragraph (a)(1) of 10 CFR 50.55a. In addition, 10 CFR 50.55a(g)(3)(v) states that all components (including supports) may meet the preservice examination requirements set forth in subsequent Editions and Addendas of the ASME Code or portions thereof that are incorporated by reference in paragraph (a) of 10 CFR 50.55a, subject to the conditions listed therein. 10 CFR 50.55a(b)(2)(xli) conditioned the 2013 through the 2017 Edition of the ASME Code,Section XI by prohibiting the use of flaw evaluation acceptance for PSI in IWB-3112(a)(3) and IWC-3112(a)(3).

The ASME Code,Section III, NCA-3252(a) provides that the design specification shall contain sufficient detail to provide a complete basis for construction in accordance with ASME Code,Section III. The ASME Code,Section III, NCA-3252(c) further specifies that the design specification shall identify those components and/or parts that require a PSI and shall include the edition and addenda of Section XI to be used; the examination category (e.g., B-D, C-D, D-A, etc.); the examination method to be used; qualifications of personnel, procedures, and

equipment; and (for welds) surface conditioning requirements and the identification marking system to be used. The PSI method required for any specific weld is based on what ISI method is required in accordance with ASME Code,Section XI to be performed during operation.

IWB-2200 and IWC-2200 in ASME Code,Section XI requires PSI to be completed prior to initial plant startup, while IWB-3111(a) and IWC-3111(a) specifies that the PSI be evaluated to the acceptance standards specified in Table IWB-3410-1, including IWB-3112 and Table IWC-3410-1, including IWB-3112, respectively, for ASME Code Classes 1 and 2. IWB-3112(c) and IWC-3112(c) in the 2007 Edition, including the 2008 Addenda, of ASME Code,Section XI further state that flaws that exceed the standards are unacceptable for service unless the component is repaired to the extent necessary to meet the acceptance standards prior to placement of the component in service. This is also consistent with NB-5332(b) of ASME Code,Section III for Class 1 which states that flaws exceeding those specified in IWB-3000 of ASME Code,Section XI are not acceptable for service and shall be repaired. Therefore, PSI of welds and adjacent base material are required to be performed and must meet the acceptance criteria in ASME Code,Section III and Section XI to be considered acceptable for service.

The 2007 Edition, including the 2008 Addenda, of ASME Code,Section XI does not allow the use of flaw evaluation for flaws detected during PSI in welds. The 2013 through 2017 Edition of the ASME Code,Section XI included new IWB-3112(a)(3) and IWC-3112(a)(3) that allowed the use of flaw evaluation for PSI, but was prohibited in 10 CFR 50.55a(b)(2)(xli). The NRC prohibited the use of flaw evaluation for PSI because it would allow flaws sizes up to 75 percent through wall in Class 1 and 2 systems that could reduce the structural margin and thereby, increase the potential for challenging the structural integrity of safety-related Class 1 and 2 welds as discussed in the final rule dated May 4, 2020 (85 FR 26540). The NRC further stated in the final rule dated May 4, 2020 (85 FR 26540) that a preservice flaw detected in a weld that exceeds the acceptance standards of Table IWB-3410-1 demonstrates poor workmanship and/or inadequate welding practice and procedures. The NRC found that such an unacceptable preservice flaw must be removed and the weld repaired before it is placed in service.

Therefore, to allow the use of IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition to Section XI of the ASME Code proposed in this alternative, the licensee would have to demonstrate that the use of Table IWB-3410-1/IWB-3112 and IWC-3410-1/IWB-3112, would either result in hardship or unusual difficulty without a compensating increase in the level of quality and safety, or provides an acceptable level of quality and safety, while addressing the basis for the conditions in 10 CFR 50.55a(b)(2)(xli).

In regards to NRC authorization pursuant to 10 CFR 50.55a(z), the NRC staff evaluated the licensees submittal and determined that the request would be reviewed pursuant to 10 CFR 50.55a(z)(2), in that the current code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety based on the following, and not per 10 CFR 50.55a(z)(1) as stated in the alternative. Since the components at VEGP, Units 3 and 4 are either installed or at the site, any repairs necessary to these components, if flaws detected during PSI did not meet the acceptance criteria in either Section III or XI, would necessitate field repairs or removal of the component to be sent back to the initial fabricator for repairs. Depending on the material or extent of the flaws, other processes such as post weld heat treatment would be necessary. Post weld heat treatment for field repairs could be difficult or impossible depending on the component size or heat treatment temperatures required to ensure adequate post weld heat treatment. Neither the removal of these flaws nor the removal of the components for further repairs would provide a compensating increase in the level of quality and safety, and may introduce weld residual stresses that could be detrimental to the

long term function of the components as it would increase the susceptibility of some of the materials to stress corrosion cracking. Weld repairs made on the surface of a component that is in contact with the reactor coolant produces weld residual stresses that have caused stress corrosion cracking in operating plants. Therefore, the NRC staff determined that the possible repairs to the small subset of Class 1 and 2 components specified in this alternative would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety pursuant to 10 CFR 50.55a(z)(2).

In regard to the conditions in 10 CFR 50.55a(b)(2)(xli), the basis forwarded by SNC is that the use of analytical flaw evaluation is consistent with the requirements for flaws identified during ISI and is considered an acceptable method to demonstrate weld integrity for operating nuclear plants. However, the NRC staff notes that acceptance of flaws found during ISI is different than those during PSI for a new plant with no operating experience. For example, the numbers of welds that have been accepted by flaw evaluation during ISI is small compared to the overall number of welds in a system. Part of this small number of flaws found during ISI is based on having initially constructed the welds to a standard which required unacceptable PSI flaws to be repaired. Flaws not meeting the acceptance criteria of the ASME Code Sections III and XI were required to be repaired until provisions for acceptance by analysis were included in recent editions of the ASME Code,Section XI, which led to the staffs prohibition on the use of those provisions in the final rule dated May 4, 2020 (85 FR 26540). Without the staffs prohibition on the use of those IWB-3112(a)(3) and IWC-3112(a)(3) provisions in the final rule dated May 4, 2020 (85 FR 26540), a larger number of welds with PSI flaws could be accepted in a newly designed component of a new reactor without operating experience that could comprise the integrity of the system before adequate operating experience is gained.

Typically, it takes years, if not decades, for inservice degradation to produce unacceptable ISI flaws, which allows for operating experience to be gained of the system. When these flaws are found in operating reactors, there are various methods of dealing with these flaws that have been used other than acceptance by flaw evaluation for the life of the plant (IWB/IWC-3600),

such as weld overlays, partial repairs or replacements. Permitting flaws, that could be up to 75 percent through wall as allowed by IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition to Section XI of the ASME Code, in a large number of Class 1 and Class 2 welds would create uncertainty regarding the structural integrity of the pipe component and system because there is no operating experience where flaws that did not meet the ASME Code Section III criteria were allowed to go into service in newly constructed plants.

Hence, the alternative proposed by SNC limited the number of welds that could use this alternative to 12 Class 1 welds and seven Class 2 welds in each unit, and included further conditions in the proposed alternative that would limit the number of welds that could have flaws over 50 percent through wall in depth, and would prohibit flaws over 60 percent through wall in depth. By limiting the depth of the flaws, and the number of welds with larger flaws, the cumulative effects of having numerous welds with preservice flaws in a system is reduced, thereby reducing the risk that would impact the structural integrity of safety-related Class 1 and 2 systems and their performance of their safety function. Therefore, from an overall risk perspective, the NRC staff can approve a limited number of welds that have flaws that exceed those specified by the acceptance criteria of Sections III and XI. As noted in the public meeting summary with SNC on July 23, 2020 (ADAMS Accession No. ML20216A636), there are currently no welds at VEGP, Unit 3 that exceed the 55 percent through wall limitation, although there are flaws that exceed the 50 percent through wall limitation. Since most of the larger through wall flaws for VEGP, Unit 3 are already located and characterized based on the current

PSI examinations performed, including those for the CMT, the limitations in the number of welds and size of flaws included in the alternative are reasonable.

SNC also included a limitation that the alternative does not apply to the SG-to-RCP weld. The NRC staff finds this particular limitation to be acceptable since this is a unique weld, where the location of two significant components are welded together could have significant safety consequences.

Also, the flaws would be thoroughly analyzed, using the proximity limits in Section XI of the ASME Code, which provides conservatism by increasing the size of the flaw to be analyzed if multiple flaws are within close proximity to account for possible flaw growth that would connect these multiple flaws. The proximity limits also provide conservatism by requiring a flaw [that] is subsurface, but within the proximity limit of IWA-3340 from the surface of the component, the flaw shall be considered a surface flaw. This assures that subsurface flaws that are evaluated using the criteria in IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition to Section XI of the ASME Code. The SNC condition that the flaws be analyzed for the life of the component and demonstrated to remain subsurface further reduces the risk of having a surface flaw that could propagate due to other degradation mechanisms and affect the structural integrity of the component or require repair during operation.

In addition, other limitations proposed in the alternative add assurance that structural integrity of the welds will not be compromised, including having to reexamine the welds with flaws subject to this alternative to verify that the actual flaw is not propagating beyond what was analyzed in the flaw evaluation so that the flaw will remain subsurface. The 2017 Edition to Section XI of the ASME Code, IWB-3112(a)(3) states that when volumetric examination detects flaws that are confirmed by surface or volumetric examination to be non-surface-connected and that are accepted by analytical evaluation in accordance with the provisions of IWB-3132.3 to the end of the service lifetime of the component, they are to be reexamined in accordance with the requirements of IWB-2420(b) and IWB-2420(d). IWC-3112(a)(3) of the 2017 Edition to Section XI of the ASME Code, has similar requirements including that reexamination must be in accordance with the requirements of IWB-2420(b) and IWB-2420(d), in lieu of IWC-2420(b) and IWC-2420(d). IWB-2420(b) and IWB-2420(d) require reexamination during the next three periods of the ISI interval of all welds with flaws that have been accepted by evaluation, except for vessel welds. SNC included a condition in the proposed alternative to require reexamination of Class 1 and 2 vessel welds similar to those required for other components during the first period of the first ISI interval. The NRC staff finds this condition acceptable as it provides assurance that the actual flaw in vessel welds will be verified to remain essentially unchanged, or that flaw growth is within the growth predicted by the analytical evaluation, which is already required for other component welds.

Therefore, the NRC staff finds that the use of this alternative for Class 1 and 2 welds, with the limitation on the number of welds, the limits on depth of the flaws, the requirement to analyze flaws for the service life of the component, using the proximity limits in Section XI of the ASME Code, and reexamination of the actual flaws during ISI is acceptable as stated above, in lieu of repairing flaws as has been previously discussed which would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety, to be acceptable.

4.0 CONCLUSION

As set forth above, the NRC staff determined that the proposed alternative to use the flaw evaluation acceptance requirements of IWB-3112(a)(3) and IWC-3112(a)(3) in the 2017 Edition

to Section XI of the ASME Code, is acceptable in order to place components with flaws into service in lieu of meeting the requirements of NCA-3252 and NB-5332(b) of the 1998 Edition, including the 2000 Addenda, of ASME Code,Section III and IWB-3112(c) and IWC-3112(c) in the 2007 Edition, including the 2008 Addenda, of ASME Code,Section XI that would require repairing flaws which would result in a hardship or unusual difficulty without a compensating increase in the level of quality and safety. The NRC staff finds there is reasonable assurance of adequate protection on the use of this alternative based on the conditions in the alternative that includes limitation on the number of welds, limitation on depth of the flaws, analyzing flaws for the service life of the component, using the proximity limits in Section XI of the ASME Code, and reexamination of the actual flaws during the first inservice inspection period as stated in the licensees letter dated July 28, 2020. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(2),

and otherwise is in compliance with the ASME Code requirements. Therefore, the NRC staff authorizes PSI/ISI-ALT-14R1 for the preservice inspection, and the first inservice inspection intervals at VEGP, Units 3 and 4. All other requirements of ASME Code, Sections III and XI and 10 CFR 50.55a, for which an alternative has not been specifically requested and authorized, remain applicable including third party review by the Authorized Nuclear Inspector and Authorized Nuclear Inservice Inspector.

5.0 REFERENCES

1. VEGP 3&4 PSI/ISI-ALT-14, Request for Alternative: Requirements for Preservice Inspection Acceptance of Volumetric Examinations, dated June 12, 2020 (ADAMS Accession No. ML20164A174).

2. VEGP 3&4 PSI/ISI-ALT-14R1, Revision to Request for Alternative: Requirements for Preservice Inspection Acceptance of Volumetric Examinations, dated July 28, 2020 (ADAMS Accession No. ML20211L785)

3. Summary of Public Meeting with Southern Nuclear Operating Company on July 23, 2020, (ADAMS Accession No. ML20216A636)