RS-17-054, Supplement to Request for Relief for Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surfaces (RS-16-049)

Supplement to Request for Relief for Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surfaces (RS-16-049)

ML17128A031
Person / Time
Site:	Byron
Issue date:	04/28/2017
From:	Gullott D Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
Shared Package
ML17128A021	List: RS-17-054, Supplement to Request for Relief for Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surfaces (RS-16-049)
References
RS-17-054
Download: ML17128A031 (55)

Text

4300 Winfield Road Warrenville. IL 60555 Exelon Generation re 630 657 2000 Office Proprietary information contained in Attachment 2 Withhold from public disclosure under 10 CFR 2.390 When separated, the cover letter and Attachments 1, 3 and 4 are Non-Proprietary RS-17-054 10 CFR 50.55a April 28, 2017 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Byron Station, Unit 2 Renewed Facility Operating License No. NPF-66 NRC Docket No. STN 50-455

Subject:

Supplement to Request for Relief for Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surfaces (RS-16-049)

References:

1. Letter from David M. Gullett (Exelon Generation Company, LLC) to U.S.

NRC, "Request for Relief for Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surfaces in Accordance with 10 CFR 50. 55a(z)( 1), " dated December 16, 2016(ML16356A019)

2. Electric Power Research Institute (EPRI) , Materials Reliability Program:

Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement (MRP-335 Revision 3-A), EPRI Publication No.

3002009241 , Final Report, dated November 2016

3. Letter from Kevin Hsueh , (U .S. NRC) to Matthew Sunseri, (EPRI), "Final Safety Evaluation of the Electric Power Research Institute MRP-335, Revision 3, 'Materials Reliability Program: Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement

[Peening],"' dated August 24, 2016(ML16208A485)

In accordance with 10 CFR 50.55a , "Codes and standards," paragraph (a)(z)(1) , Exelon Generation Company, LLC (EGC), submitted a request for relief (Reference 1) from the current examination requirements of Reactor Pressure Vessel Head Penetration Nozzles (RPVHPN) performed in accordance with 10 CFR 50.55a(g)(6)(ii)(D), which specifies the use of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, "Rules for lnservice Inspection of Nuclear Power Plant Components," Code Case N-729-1 on the basis that the proposed alternative would provide an acceptable level of quality and safety. The basis of the request was the implementation of the Ultra High Pressure Cavitation Peening (UH PCP) process at Byron Station Unit 2 during the refueling outage in Spring 2016 (B2R19).

Proprietary information contained in Attachment 2 Withhold from public disclosure under 10 CFR 2.390 When separated, the cover letter and Attachments 1, 3 and 4 are Non-Proprietary U.S . Nuclear Regulatory Commission April 28, 2016 Page 2 Specifically, EGC requested a change to the examination interval of the follow-up inspections for peened RPVHPNs and associated welds in accordance with References 2 and 3; including relief from the Reference 3 Condition 5.4 (b) requirement for inspection in the first refueling outage after peening. The request was supported by an EPRI technical evaluation (Reference 2) which developed a revised volumetric or surface inspection frequency interval for Alloy 600 RPVHPNs and Alloy 82/182 partial-penetration (J-groove) attachment welds that have received peening application . This technical basis demonstrates that for any peening surface stress improvement process meeting the performance criteria of section 4 .3.8 of Reference 2, the inspection frequency interval can be changed.

The purpose of this letter is to supplement the Reference 1 request with a revision to the Reference 1 Attachment 1 Relief Request, a revision to the Reference 1 Attachment 2 Summary Report and a revision to the supporting Summary Report affidavit (i.e., Reference 1 ) . The revised attachments are the result of recently identified input errors and editorial corrections as further described below. The revised attachments supersede the Reference 1 attachments in their entirety.

Two legacy peening implementation issues impacting the Byron Station Unit 2 reactor head peening campaign results during the spring 2016 outage (B2R19) were recently identified during the Spring 2017 Byron Station Unit 1 outage (B 1R21 ). The implementation issues were evaluated per AREVA's 10 CFR Appendix B program via the Condition Reporting (CR) Process as discussed in Attachment 1, Attachment 2 or summarized below. In addition to the recently identified issues in 81 R21 , other peening implementation issues have been identified and are described below due to their effect on the essential variables/critical parameters of the peening process which in some cases resulted in those nozzles not meeting the required specifications.

The following CRs were determined to impact UHP cavitation peening results requiring a future reapplication of the peening process for specific nozzles:

CR-2016-3427, 2016-3423 and 2016-3356 Nozzles 68, 69, 74, 75 and 77 Unable to Form Inner Diameter (ID) Seal:

While cavitation peening the ID of nozzles 68 , 69 , 74, 75 and 77 there was significant leakage from the seal of the ID annulus tool and/or adapters and system backpressure could not be achieved . Backpressure is an essential variable and a minimum of 35 psi is required (see section 3.0 of Attachment 2) . Since an ID seal could not be formed to achieve the required back pressure, peening the ID of these nozzles was abandoned during B2R 19 Reactor Head Peening campaign per CR-2016-3431.

CR-2017-1767 - Nozzles 67, 69, 71 and 73 (Tier 148) OD Peening Rotation Axis Start Position is Incorrect:

This CR identified a legacy software input error with OD peening rotational starting position for Tier 148 nozzles 67, 69 , 71 and 73 not meeting Reference 2 requirements during 81 R21 . The correct rotation axis start position for Tier 148 is +22 .5 degrees. However, a rotation axis start position of -22.5 degrees was entered into the motion profile program since the start position input value was incorrectly specified per the Operating Instruction (01). Therefore, the Byron

Proprietary information contained in Attachment 2 Withhold from public disclosure under 10 CFR 2.390 When separated, the cover letter and Attachments 1, 3 and 4 are Non-Proprietary U.S. Nuclear Regulatory Commission April 28, 2016 Page 3 Station Unit 2 Tier 14B nozzles were peened during B2R19 with the incorrect input values since the Byron Station Unit 2 01 and motion profile parameters report carried over the same input error.

CR-2017-1944 - Vent Line Vertical Home Start Value (Py )for the Almen Strip was not correct:

This CR is also a legacy software input error and impacts the vent line. During the process of reviewing the 30 models and data for the open penetration and vent line tools as part of a review for Byron Station Unit 1 CR-2017-1767 (i.e., the CR noted above) , the +14.593 Py value for the Vent Line Almen Strip was discovered to be incorrect. The correct Py is +13.593.

Therefore, the Byron Station Unit 2 01 and motion profile parameters report carried over the same input error.

No credit will be taken for extension of examination interval for nozzles not peened in accordance with Reference 2 (i.e., 67, 68, 69, 71 , 73, 74, 75, 77 and the vent line as described above) . These nozzles are planned to be re-peened during a future outage Reactor Head Peening campaign and will be re-evaluated for compliance with Reference 2 once complete.

The evaluation for compliance with Reference 2 will be will be documented in a subsequent revision to the Attachment 2 summary report and the impacted nozzles will be evaluated for acceptability for inclusion in the population of the Attachment 1 Relief Request by the Engineering Change evaluation process. Specifically, once these nozzles are evaluated to meet the requirements of Reference 2, they will be included in the population of the Attachment 1 Relief Request, as allowed per Note 1 of Attachment 1.

In addition to the changes described above, corrections and various editorial changes were made throughout the Attachment 1 Relief Request. Corrections were made for consistency with the Attachment 2 Summary Report. A copy of the Attachment 1 Relief Request with track changes is included as Attachment 4 for information only. contains proprietary information as defined by 10 CFR 2.390, "Public inspection, exemption, requests for withholding ." AREVA, Inc, (AREVA) as the owner of proprietary information has executed the enclosed affidavit, which identifies that the enclosed proprietary information has been handled and classified as proprietary, is customarily held in confidence, and has been withheld from public disclosure. The proprietary information was provided to EGC by AREVA as referenced by the affidavits. The proprietary information has been faithfully reproduced in the attached information such that affidavits remain applicable. AREVA hereby requests that the attached proprietary information be withheld, in its entirety, from public disclosure in accordance with the provisions of 10 CFR 2.390 and 10 CFR 9.17. The affidavit supporting the proprietary nature of the information is contained in Attachment 3.

EGC requests approval of the revised proposed alternative Attachment 1 Relief Request by September 25, 2017, in support of the Fall Byron Unit 2 Refueling Outage (B2R20).

Proprietary information contained in Attachment 2 Withhold from public disclosure under 10 CFR 2.390 When separated, the cover letter and Attachments 1, 3 and 4 are Non-Proprietary U.S. Nuclear Regulatory Commission April 28, 2016 Page4 There are no regulatory commitments contained within this letter.

Should you have any questions concerning this letter, please contact Ms. Jessica Krejcie at (630) 657-2816.

Respectfully, David M. Gullett Manager - Licensing Exelon Generation Company, LLC : 10 CFR 50.55a Request Number 14R-14 Revision 1, Request for Relief for Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surfaces in Accordance with 10 CFR 50.55a(z)(1) : AREVA Document# 51-8092600-001 , "Summary Report, RVCH Peening Implementation, Byron Unit 2" (PROPRIETARY) (NOTE: This report is included through Appendix A. The remaining Appendices (i.e., B, C, and D) are not included) : AREVA Inc., Affidavit for 51-8092600-001 , "Summary Report, RVCH Peening Implementation, Byron Unit 2" dated March 27, 2017 : 10 CFR 50.55a Request Number 14R-14 Revision 1, Request for Relief for Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surfaces in Accordance with 10 CFR 50.55a(z)(1) with TRACK CHANGES SHOWN-FOR INFORMATION ONLY Cc: Regional Administrator - NRC Region Ill NRC Senior Resident Inspector - Byron Station Illinois Emergency Management Agency

ATTACHMENT 3 AREVA Inc., Affidavit for 51-8092600-001, "Summary Report, RVCH Peening Implementation, Byron Unit 2" dated March 27, 2017

AFFIDAVIT COMMONWEAL TH OF VIRGINIA SS .

CITY OF LYNCHBURG

1. My name is Gayle Elliott. I am Deputy Director, Licensing & Regulatory Affairs, for AREVA Inc. (AREVA) and as such I am authorized to execute this Affidavit.

2. I am familiar with the criteria applied by AREVA to determine whether certain AREVA information is proprietary. I am familiar with the policies established by AREVA to ensure the proper application of these criteria.

3. I am familiar with the AREVA information contained in Engineering Information Record 51-8092600-001 entitled, "Summary Report, RVCH Peening Implementation, Byron Unit 2" dated March 2017 and referred to herein as "Document." Information contained in this Document has been classified by AREVA as proprietary in accordance with the policies established by AREVA for the control and protection of proprietary and confidential information.

4. This Document contains information of a proprietary and confidential nature and is of the type customarily held in confidence by AREVA and not made available to the public. Based on my experience, I am aware that other companies regard information of the kind contained in this Document as proprietary and confidential.

5. This Document has been made available to the U.S. Nuclear Regulatory Commission in confidence with the request that the information contained in this Document be withheld from public disclosure. The request for withholding of proprietary information is made in accordance with 10 CFR 2.390. The information for which withholding from disclosure is requested qualifies under 10 CFR 2.390(a)(4) "Trade secrets and commercial or financial information ."

6. The following criteria are customarily applied by AREVA to determine whether information should be classified as proprietary:

(a) The information reveals details of AREVA's research and development plans and programs or their results .

(b) Use of the information by a competitor would permit the competitor to significantly reduce its expenditures, in time or resources , to design, produce, or market a similar product or service.

(c) The information includes test data or analytical techniques concerning a process, methodology, or component, the application of which results in a competitive advantage for AREVA.

(d) The information reveals certain distinguishing aspects of a process, methodology, or component, the exclusive use of which provides a competitive advantage for AREVA in product optimization or marketability.

(e) The information is vital to a competitive advantage held by AREVA, would be helpful to competitors to AREVA, and would likely cause substantial harm to the competitive position of AREVA.

The information in this Document is considered proprietary for the reasons set forth in paragraphs 6(c) , 6(d) and 6(e) above.

7. In accordance with AREVA's policies governing the protection and control of information , proprietary information contained in this Document has been made available, on a limited basis, to others outside AREVA only as required and under suitable agreement providing for nondisclosure and limited use of the information.

8. AREVA policy requires that proprietary information be kept in a secured file or area and distributed on a need-to-know basis.

9. The foregoing statements are true and correct to the best of my knowledge, information, and belief.

~ ' ***.* * * ..**

SUBSCRIBED before me this dayof ~ I 2017.

Sherry L. McFaden NOTARY PUBLIC, COMMONWEALTH OF VIRGINIA MY COMMISSION EXPIRES: 10/31/18 Reg.# 7079129 S.HEARV L. MCfADEN NoJiry Public Qon'lmon~111th or Virginia 7079U9 M commlnlon ~xplr11Oct31, 2018

ATTACHMENT 1 10 CFR 50.55a Request Number 14R-14 Revision 1, Request for Relief for Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surfaces in Accordance with 10 CFR 50.55a(z)(1)

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 1 of 22)

Request for Relief Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surfaces in Accordance with 10 CFR 50.55a(z)(1) 1.0 ASME CODE COMPONENTS AFFECTED:

Component Numbers: Unit 2, Reactor Vessel 2RC01 R

Description:

Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles (RPVHPNs) Having Pressure-Retaining Partial-Penetration J-groove Welds with Mitigated Alloy 600/82/182 Peened Surfaces Code Class: Class 1 Examination Category: ASME Code Case N-729-1 Code Item: 84.20 Identification: RPVHPN Numbers 1 through 78 and vent, (P-1 through P-78 and vent) 1 Reference Drawing : Closure Head Assembly: 185282E Size: 4 Inch Nominal Outside Diameter, 2.75 Inch Nominal Inside Diameter (Vent Nozzle NPS 1)

Material : SB-167 UNS N06600 (Alloy 600) , ENiCrFe-3 (Alloy 182),

and ERNiCr-3 (Alloy 82) 2.0 APPLICABLE CODE EDITION AND ADDENDA:

lnservice Inspection (ISi) and Repair/Replacement Programs: American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI , 2007 Edition including 2008 Addenda [1] . Examinations of the RPVHPNs are performed in accordance with 10 CFR 50.55a(g)(6)(ii)(D), which specifies the use of ASME Code Case N-729-1 with conditions .

Code of Construction [Reactor Pressure Vessel (RPV)] : ASME Section Ill , 1971 Edition through Summer 1973 Addenda .

1 Applies to RPVHPNs mitigated in accordance with section 4.3.8 of MRP-335, R3-A [16]

/SI Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 2 of 22) 3.0 APPLICABLE CODE REQUIREMENT:

ASME Code Case N-729-1 contains requirements for the inspection of RPVHPNs, with or without flaws , as conditioned by 10 CFR 50.55a(g)(6)(ii)(D). The specific Code requirements for which use of the proposed alternative is being requested are as follows:

Code of Federal Regulations (CFR) 10 CFR 50.55a(g)(6)(ii)(D)(1) requires (in part):

"All licensees of pressurized water reactors must augment their inservice inspection program with ASME Code Case N-729-1 , subject to the conditions specified in paragraphs (g)(6)(ii)(D)(2) through (6) of this section. Licensees of existing operating reactors as of September 10, 2008 must implement their augmented inservice program by December 31 , 2008."

10 CFR 50.55a(g)(6)(ii)(D)(3) conditions ASME Code Case N-729-1 by stating:

"Instead of the specified 'examination method' requirements for volumetric and surface examinations in Note 6 of Table 1 of Code Case N-729-1 , the licensee must perform volumetric and/or surface examination of essentially 100 percent of the required volume or equivalent surfaces of the nozzle tube, as identified by Figure 2 of ASME Code Case N-729-1 . A demonstrated volumetric or surface leak path assessment through all J-groove welds must be performed. If a surface examination is being substituted for a volumetric examination on a portion of a penetration nozzle that is below the toe of the J-groove weld (Point Eon Figure 2 of ASME Code Case N-729-1 ), the surface examination must be of the inside and outside wetted surface of the penetration nozzle not examined volumetrically."

ASME Code Case N-729-1 , Alternative Examination Requirements for PWR Reactor Vessel Upper Heads with Nozzles Having Pressure-Retaining Partial-Penetration Welds,Section XI , Division 1 [2], Figure 2, "Examination Volume for Nozzle Base Metal and Examination Area for Weld and Nozzle Base Metal," is applicable to the RPVHPNs.

ASME Code Case N-729-1 , Paragraph -241 O specifies that the reactor vessel upper head penetrations shall be examined on a frequency in accordance with Table 1 of the code case (Refer to [2], hereafter known as N-729-1). However, 10 CFR 50.55a(g)(6)(ii)(D)(5) states "If flaws attributed to PWSCC have been identified, whether acceptable or not for continued service under Paragraphs -3130 or -3140 of ASME Code Case N-729-1 , the re-inspection interval must be each refueling outage instead of the re-inspection intervals required by Table 1, Note (8) , of ASME Code Case N-729-1 ." Since flaws attributed to Primary Water Stress Corrosion Cracking (PWSCC) have been identified at Byron Station Unit 2, the RPVHPNs are examined every fuel cycle in accordance with 10 CFR 50.55a(g)(6)(ii)(D)(5).

As an alternative to the requirements above, required inspections will be conducted in accordance with the inspection requirements for Alloy 600 RPVHPNs mitigated by peening , based on Table 4-3 in MRP-335, Revision 3-A, "Materials Reliability Program:

Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement," November 2016, (16] ; including relief from Final Safety Evaluation

[3] Condition 5.4 requirement for inspection in the first refueling outage post peening application (i.e., N+1 outage) which is reflected in MRP-335 Table 4-3 Note (11)(b) (16] .

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 3 of 22) 4.0 REASON FOR REQUEST:

Exelon Generation Company, LLC (EGC) has implemented the Ultra High Pressure Cavitation Peening (UHPCP) process at Byron Station Unit 2 and is requesting a change to the reexamination interval of the follow-up inspections for peened RPVHPNs and associated welds in accordance with MRP-335 Table 4-3 [16] with an additional request for relief from the Table 4-3 Note (11)(b) requirement for follow-up inspection in the first refueling outage after peening .

As discussed in section 3.0, N-729-1 as conditioned by 10 CFR 50.55a(g)(6)(ii)(D)(5) requires volumetric and/or surface examination of the Byron Station Unit 2 RPVHPNs and associated welds of all nozzles every refueling outage or one fuel cycle, nominally every 18 months. The examination schedule of N-729-1 does not address the effects of Surface Stress Improvement (SSI) by peening or the associated inspection frequency for RPVHPNs in this mitigated state. Electric Power Research Institute (EPRI) developed, using appropriate analytical tools, a volumetric or surface re-examination interval for Alloy 600 RPVHPNs and Alloy 82/182 partial-penetration (J-groove) attachment welds that have received peening application. This technical basis demonstrates that for any peening SSI process meeting the performance criteria of section 4.3.8 of MRP-335 [16] ,

the re-examination interval can be changed to the Table 4-3 inspection schedule.

As described in detail in section 5.0 below, the UHPCP process implemented at Byron Station Unit 2 meets or exceeds the SSI residual plus operating stress, the coverage area and the depth of compression requirements specified in MRP-335. In addition ,

considering the deterministic analysis work described by EPRI [16] and by ASME in section 5.4.7 of this relief, EGC is requesting a change from the Final Safety Evaluation Condition 5.4 requirement for follow-up inspection in N+1 , which is reflected in MRP-335 Table 4-3 Note (11)(b) [16] .

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE:

5.1. Introduction The peening process was developed by the peen ing vendor (AREVA) as a Special Process in accordance with 10 CFR 50 Appendix B. Qualification of the AREVA UHPCP process on RPVHPNs for the purpose of PWSCC mitigation is documented in the Qualification Report [7] .

Peening Mechanism for PWSCC Mitigation When the applicable MRP-335 performance criteria are met, peening mitigation prevents initiation of PWSCC [16] . The possibility of pre-existing flaws that are not detected in the pre-peening Non Destructive Examination (NOE) is addressed through the required follow-up inspection that is performed during the second refueling outage (N+2) after application of peening. Peening also has the benefit of arresting PWSCC growth of shallow surface flaws that are located in regions at the surface where the residual plus normal operating stress is now compressive [16][15] . This secondary benefit is not

/SI Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 4 of 22) credited in the main analyses of MRP-335 because these analyses conservatively assume that the bounding stress effect meeting the performance criteria is achieved .

In order to prevent the initiation of new PWSCC, the application of peening has to result in the peak tensile stresses at the wetted surface of material being less than the "threshold" stress for initiation of PWSCC. Based on laboratory testing , a tensile stress of +20 ksi is a conservative lower bound of the stress level below which PWSCC initiation will not occur over plant time scales per MRP-95 [5]. This applies to steady-state stresses during normal operation since stress corrosion cracking (SCC) initiation is a long-term process, and does not apply to transient stresses that occur only for relatively short periods of time . Additional conservatism is provided by the MRP-335 performance criterion limiting the surface stress to +10 ksi (tensile) for the case of RPVHPNs when normal operating stresses are considered [16] .

The potential for growth of small flaws too shallow to be reliably detected in the pre-peening ultrasonic (UT) examination , or for flaws located in the J-groove weld metal, is addressed by the follow-up UT examination , and by the ongoing visual examinations for evidence of leakage performed at the same schedule as prior to peening. The N+2 and subsequent program of inspections addresses growth of any flaws via PWSCC that may not have been detected in the pre-peening examination. For the cold head operating conditions of the Byron Station RPVHPNs and 18 month refueling cycle, the bases described in MRP-335 section 5.2.3.2 [16] supports the 36-month follow-up inspection time.

Stress Effect to Prevent Future PWSCC Initiations The compressive residual stress depth required by the performance criteria ensures that the stress improvement effect extends a significant distance into the material. The Byron Station Unit 2 peening met or exceeded the MRP-335 depth of compression requirements. The deterministic and probabilistic analyses in MRP-335 that form the basis for the requested inspection relief show that it is not necessary for growth of shallow pre-existing flaws to be arrested by the post-peening stress field . Pre-existing flaws are effectively addressed by the combination of pre-peening and follow-up inspections. In cases when a shallow pre-existing flaw is located within a region of compressive residual plus operating stress, PWSCC growth of the pre-existing flaw would be arrested [16] . In the event of a pre-existing flaw that exists below the depth of peening application , probabilistic and deterministic evaluations show that the flaw growth and detection in N+1 is unlikely due to the Tcold head environment. The probability of flaw detection supports performing inspection in N+2 ([16], section 5.1).

Effect of Pre-Existing Residual Stresses High residual tensile stresses do not interfere with the ability of peening to develop the stress effect needed to be effective [6] . The peening effect is self-normalizing with regard to the level of pre-peening residual stresses [16][7] . A study was performed by AREVA (Item 9 of Attachment 1 of [11]) to verify that the unpeened residual stress state of the material does not have a significant effect on the final peened surface compressive stress and depth of compression . Testing supports that regardless of the initial stress state i.e., high tension or high compression, the final compressive stresses ended up within a -63 ksi to -81 ksi range [16] . Theory and test data show that peening

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 5 of 22) results in high compressive residual stresses regardless of the starting state of the residual stresses.

5.1.1 Proposed Alternative EGC is requesting relief from the examination frequency requirements of 10 CFR 50.55a(g)(6)(ii)(D)(5), for performing volumetric and/or surface examinations of the Byron Station Unit 2 RPVHPNs each refueling outage.

Specifically, relief is requested to allow an alternative inspection frequency consistent with requirements of MRP-335 Revision 3-A, Table 4-3 with an additional request for relief from the Table 4-3 Note (11 )(b) requirement for follow-up inspection in the first refueling outage after peening.

The alternative inspection frequency requirements for Item B4.60 RPVHPNs mitigated by peening SSI per MRP-335 Table 4-3 [16] require a pre-peening baseline inspection, follow-up inspection, and subsequent in-service inspection ,

as summarized below.

Pre-Peening Baseline Inspection Prior to performance of peening but during the same outage, examinations are to be performed in accordance with the requirements in MRP-335 Table 4-3, Note ( 13) [16] . Examinations include volumetric or surface examinations of essentially 100% of the required volume or equivalent surfaces of the nozzle tube as identified in Figure 2 of N-729-1 , and a demonstrated volumetric or surface leak path assessment through all J-groove welds. The leak path examination detects through-wall cracking by checking for areas at the interface (annulus) between the nozzle tube and low-alloy steel head where leakage has caused a loss of interference fit. The analyses in Section 5 and Appendix B of MRP-335 conservatively do not take credit for the leak path examination.

Follow-Up Inspection During the follow-up inspection , a volumetric examination of 100% of the required volume or equivalent surfaces of the nozzle tube is to be performed and a leak path examination is also to be performed. EGC proposes to follow the inspection interval specified in MRP-335 Table 4-3 [16] with an additional request for relief from the Table 4-3 Note (11 )(b) requirement for follow-up inspection in the first refueling outage after peening . The follow-up inspection schedule is based on the value of the effective degradation year (EDY) parameter (defined in N-729-1) at the time of peening . EGC's proposed alternative is consistent with the MRP-335 Table 4-3 Note (11)(b) [16]

requirement, "For plants where EDY < 8 at the time of peening and containing pre-existing flaws a follow-up inspection is to be performed in the second (N+2) refueling outage subsequent to peening" (EDY=3.249 at the time of peening for Byron Station Unit 2). Furthermore, for the cold head operating conditions of the Byron Station RPVHPNs and 18 month refueling cycle, the bases described in MRP-335 section 5.2.3.2 supports the 36-month follow-up inspection time.

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 6 of 22)

Subsequent ISi Program The ISi program interval examinations take effect after completion of the follow-up inspection per Item 84.60, Table 4-3 [16] . Examinations include volumetric or surface examinations of peened penetrations at an interval not to exceed one inspection interval (nominally 10 calendar years) , and a demonstrated volumetric or surface leak path assessment through all J-groove welds each time the periodic volumetric or surface examination is performed .

5.2. Description of Application Specific Process PWSCC is mitigated via surface remediation by inducing a compressive stress layer in the surface of each nozzle and J-groove weld at the Byron Station Unit 2 RPVHPNs through the application of water jet UHPCP as qualified in the Special Process Qualification Report (SPQR) [7] by AREVA. This compressive stress layer has been demonstrated to prevent PWSCC initiation [15] .

5.2.1 Description of Peened Components and Selection of Peened Area UH PCP was applied to the outer and inner surfaces of the Alloy 600/182/82 materials. Peening of the OD of the nozzle and outer weld surface was performed using an OD tool that rotates the water jet around the outer circumference of the nozzle and weld material (Figure 5.2 .1-1). Note that a shoulder area of the Core Exit Thermocouple (CETC) funnel (upper collar) , that when seated to the CETC nozzle penetration tube, physically blocked access to the required surface area to be peened . The portion of the funnel upper collar that was covering the

+20 ksi area on the downhill side of the CETC nozzles was removed to permit peening of the +20 ksi area. Electrical Discharge Machining was used to remove this piece of the funnel , which allowed the guide funnels to remain in place while the required high stress (+20 ksi) mitigation area was peened (Figure 5.2.1-2).

Figure 5.2 .1-1 Figure 5.2.1-2

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 7 of 22)

Accessibility of the nozzle OD and J-groove weld surfaces is sufficient to permit UHPCP to meet and exceed the 0.04 inch minimum depth of compression for RPVHPNs. Peening the ID surface of the nozzle was performed using an ID tool that rotates the water jet around the inner circumference of the nozzle. For open penetrations and the vent line, the ID open penetration/vent line tool rotates the water jet around the inner circumference of the nozzle as the water jet is applied directly from inside the nozzle. For nozzles with thermal sleeves, the ID annulus tool moves the thermal sleeve to one side to allow the water jet access to fit into the annulus region between the OD of the thermal sleeve and ID of the nozzle. This allows the water jet to peen the inner circumference of the nozzle from inside the annulus region. The ID annulus tool has sufficient clearance to meet and exceed the 0.01 inch minimum depth of compression for RPVHPNs. See SPQR section 4.0 [7] .

The outer surface (nozzle OD and weld) and nozzle ID peening mitigation coverage was based on Figure 2 of N-729-1 , which is also the extent of the ISi inspection area. The extent of peening coverage on the nozzle and weld outer surface is zone G-F-E-C. The extent of peening coverage on the nozzle ID surface is zone A-D. Note: the surfaces required to be peened are defined in Figures 4-1 , 4-2 and 4-3 of MRP-335, wh ich is less OD surface area than that identified in Figure 2 of N-729-1 . Thus, the Byron Station Unit 2 nozzle OD peened surface area exceeded the MRP-335 peening area mitigation requirement. This margin is discussed in section 5.4 of this rel ief request with additional detail provided in the post peening Summary Report [14) .

Peening of Previously Repaired RPVHPNs Exceptions to the above RPVHPNs are nozzles that have been previously repaired e.g., nozzles that were repaired by weld overlay. Th is type of repair is known as an embedded flaw repair. Byron Station Unit 2 penetrations 6 and 68 were previously repaired by weld overlay. For these penetrations, peening of the weld repair area is not required since this weld material is PWSCC resistant (J-groove weld area and portions of the nozzle tube OD that are covered by the repair weld). However, peening of the ID and the portion of the nozzle tube OD surfaces not having weld repair material is required from the weld overlay to the top of the threads.

The Byron Station Unit 2 nozzle 6 J-groove weld and top portion of the nozzle OD has been mitigated with a weld overlay. The OD of the nozzle below the weld overlay to the top of the threads was peened and the requ ired nozzle ID area was peened.

The Byron Station Unit 2 nozzle 68 J-groove weld and top portion of the OD has been mitigated with a weld overlay. There is no area of the nozzle OD below the weld overlay to consider peening since that portion of the nozzle and threaded section was removed (Figure 5.2.1-3). The ID of the nozzle was not peened during B2R19 due to excess leakage preventing a good seal.

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Figu re 5.2.1-3 The exposed areas of Alloy 52 weld metal (overlay) are not required to be peened since Alloy 52 is PWSCC resistant per MRP-375 [8] and section 4.3.7 of MRP-335 [16] . Therefore , from the perspective of susceptibility to PWSCC degradation, a penetration repa ired using the embedded flaw repair technique (i. e., with an Alloy 52 repair weld applied to the J-groove weld area and portion of the nozzle tube OD) is mitigated . Subsequent to peening the unrepaired OD and ID, the nozzle areas with Alloy 600 material in contact with reactor coolant, will have a residua l plus operating surface stress well below that necessary to initiate PWSCC per the residual plus operating stress analysis [13].

If the requ irements of section 4.3 of MRP-335 are satisfied, a RPVHPN with flaws that has been corrected and subsequently peened using a process meeting the performance criteria of section 4.3.8 of MRP-335 may be identified as Item 84.60 in Table 4-3 Note (12) of MRP-335. Thus, follow-up and ISi program examinations for weld overlay repaired nozzles subsequent to peening are equivalent to the follow-up and ISi program exam inations for unrepaired nozzles subsequent to peening i. e., may be identified as Item 84.60.

5.2.2 Process Description Performance demonstration is the method used to ensure that peening fully covers all of the areas that requ ire peen ing , and achieves the desired magnitude and depth of residual compressive stresses. The critical parameters to be controlled ensure that peening develops the intended levels of compressive residual stresses in each peened area [7][14] . The SPQR is the Qualification Report that demonstrates desired results are achieved per MRP-335 with a bounded set of parameters. The UHPCP procedure implements the process per the requirements defined in the SPQR. During the implementation process, essential variables are recorded for each nozzle. Completed procedural enclosures and data output files are provided in the Summary Report [14] to document and log the performance results of the UH PCP process. The post peening Summary Report [14] confirms performance demonstration of peening at each nozzle and summarizes the essential variables/critical parameters.

Surface Condition Considerations There are no limitations imposed by surface cond itions on water jet UHPCP. No preparations of the surfaces to be peened are requ ired before peening is

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 9 of 22) performed. In addition , there are no limitations on the peening caused by irregularities or undulations of the surface, such as those associated with weld beads, local grinding, or from initial forging [7] .

Pre-Peening NOE The pre-peening baseline RPVHPN inspection was performed in accordance with N-729-1 as conditioned by 10 CFR 50.55a and found no conditions requiring repair.

Contingencies If critical parameters go outside of the specified range during the peening process, the issue is displayed on the peening controls system and evaluated or the process is shut down automatically. If peening is stopped for any reason the process is restarted in accordance with the approved peening process procedures to ensure adequate peening coverage. A Condition Report (CR) is issued if corrective action is required that is outside of the approved peening process procedures and appropriately evaluated by AREVA and EGC.

5.3. Performance Criteria The following is an overview of MRP-335 [16] performance criteria requirements for RPVHPN peening . The Byron Station Unit 2 UHPCP implementation demonstrated meeting or exceeding these criteria is addressed in detail in section 5.4.

Stress Magnitude The stress prior to consideration of operating stresses must be compressive on all peened surfaces. The residual stress plus operating stress on peened surfaces must not exceed +10 ksi (tensile) .

Peening Coverage The required coverage is the full wetted area of the susceptible material with surface stress (residual plus operating stress) of at least +20 ksi (tensile), which is a conservative measure of the threshold for PWSCC initiation [16][5] . The susceptible material locations to be considered are the wetted surface of the Alloy 82/182 J-groove weld and butter material and the surfaces of the Alloy 600 nozzle tube material in the region of the J-groove weld as defined in Figures 4-1 , 4-2 and 4-3 of MRP-335 [16] .

Depth of Effect The compressive residua l stress field extends a nominal minimum depth of:

• 0.04 inch on the susceptible area of the outer nozzle and weld surfaces

• 0.01 inch on the susceptible area of the inner nozzle surface

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Sustainability of Effect The mitigation process is effective for at least the remaining service life of the component i.e., the residual plus operating surface stress state after considering the effects of thermal relaxation and load cycling (i .e. , shakedown) must remain no greater than +10 ksi (tensile).

lnspectability The capability to perform UT examinations of the relevant volume of the Alloy 600 nozzle tube material is not adversely affected , and the relevant volume or surface of the J-groove weld and Alloy 600 nozzle tube material is inspectable using a qualified process.

Lack of Adverse Effects As verified by analysis or testing , the mitigation process is not to have degraded the component, caused detrimental surface conditions, or adversely affected other components in the system.

5.4. Reactor Vessel CROM UHPCP Implementation Results and Margins This section provides detail on the AREVA Qualification Program , summarizes the Byron Station Unit 2 peening performance margin achieved in meeting or exceeding MRP-335 performance criteria, and hig hlights additional technical rigor performed to validate the peening process.

5.4.1 Qualification as a Special Process Surface stress improvement by peening affects the performance of nuclear safety-related systems and components, thus, it shall be performed in accordance with a quality assurance program meeting the requirements of 10 CFR 50 Appendix B. Further, since peening is a special process, it is required to be controlled in a manner consistent with Append ix B Criterion IX, "Control of Special Processes."

Per Criterion IX, the personnel and procedures involved are required to be appropriately qualified. Since there are no industry standards that apply to peening , these qualifications shall be done to peening vendor requirements developed and documented per the vendor's 10 CFR 50 Appendix B quality assurance program .

The Qualification Program for the UHPCP process covered in this relief request was developed by AREVA and is documented in the Qualification Report [7] .

The qualification program addresses both the generic process and, by use of representative test coupons , the effectiveness of the peening process when applied to the specific geometries of the components covered by this relief request.

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Technical justification is included in the SPQR based on MRP-335 section 6.3.

The specific process used has been demonstrated to be effective, including surface stress magnitude, compressive residual stress depth, and sustainability of the stress effect. Included is a description of the demonstration testing of peening of coupons representative of the geometry, material, accessibility, and surface condition of the component to be peened (see section 5.4.2 of this relief) . The specific process has been demonstrated to result in no adverse effects (see section 5.4.6 of this relief) . Essential variables with associated ranges of acceptable values are determined for the specific application, plus a description of the process controls is included which ensure essential variables remain within acceptable ranges (see sections 5.2 .2 and 5.4.2 of this relief).

Specific process controls were provided ensuring coverage requirements are met with a high degree of confidence, including what overlap of peening beyond the susceptible material is required (see section 5.2.2 and 5.4.2 of this relief).

Disposition of non-conforming issues encountered are included (see section 5.2.2 of this relief).

Critical Process Parameters and Acceptable Values MRP-335 Performance Criterion 4.3.8.1 requires testing be performed "to demonstrate the critical process parameters and [to] define acceptable ranges of the parameters needed to ensure that the required residual stress field (exclusive of normal operating stresses) has been produced on the mitigated surface."

Demonstration that the stress improvement parameters are met is provided, in part, by verification that all of the control process parameters (essential variables) were maintained within the specified ranges during the application of UHPCP. The peening process parameters were maintained and verified within acceptable ranges [14]. The critical process parameters were monitored and recorded as described in the SPQR [7] . The data is reviewed and verified by AREVA's quality control. The essential variables/critical parameters and acceptable ranges for UHPCP implementation for Byron Station Unit 2 Reactor Vessel Closure Head (RVCH) nozzle penetrations is provided in section 3.0 of the Summary Report [14] .

5.4.2 Demonstration that Required Stress Effect is Achieved In accordance with the performance criteria , testing and analysis demonstrate that the required stress improvement effect exceeded over 100% of the required area and that the required effect will be sustained for at least the remaining service life of the peened components. The stress effect is quantified to be conservative relative to that required in MRP-335 in terms of the residual plus operating stress at the peened surface and the depth of the compressive residual stress. The requested testing and analysis are documented in the Qualification Report [7] and summarized below.

Residual Stress Measurements Using Representative Test Coupons Per the Qualification Report, demonstration testing has been performed in accordance with MRP-335 Performance Criterion 4.3.8.1 to determine the

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 12 of 22) residual stress state at peened surfaces. Residual stress measurements were made for full scale peened test coupons representative of the geometry, material, accessibility, and surface condition of the components to be peened (see Figure 5.4.2-1 and Figure 5.4.2-2).

Figure 5.4.2-1 , Representative Full Scale Coupon Figure 5.4.2-2, Representative Full Scale Coupon The residual stress measurements satisfied the nominal depth requirement for the compressive residual stress of MRP-335 Performance Criterion 4.3.8.1.2.

The magnitude of the residual stress at the surface was combined with the operating stress at the surface to demonstrate compliance with MRP-335 Performance Criterion 4.3.8.1.1. Key aspects of demonstration testing are provided below.

Site specific geometry is identified and validated through mockup testing . A total of 18 mockup coupons were peened as part of the qualification testing activity that included various RVCH penetration tiers and the head vent. A summary matrix of the qualification coupon peened surfaces is provided in the Qualification Report, Table 3-1 [7) . The test coupons were peened within control parameters that were recorded . As discussed in section 5.4.1 "Critical Process Parameters and Acceptable Values," this testing was used to determine the ranges of acceptable values for the critical process parameters for application in the plant.

As simulated in the Qualification testing, UHPCP achieved the performance requirements despite the geometric limitations associated with the application of peening to RVCH penetrations, such as limited access associated with ID annulus peen ing or CETC downhill nozzle to RVCH head clearance.

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The residual stress measurements ensure that the required stress effect was achieved in each portion of the component area required to be peened, including areas with different materials, curvature or accessibility. For RPVHPNs, the nozzle tube ID, nozzle tube OD, and weld surfaces are addressed . The actual peening coverage was checked during examination of the test coupons using X-ray Diffraction (XRD) of the peened surface. XRD testing confirmed that the compressive residual stress depth measurements met the requirement of the performance criteria. For each of the peened areas, the magnitude and depth of the compressive residual stresses that would be developed by lower bound allowable values of the critical peening parameters were identified . As analyzed ,

the post peening surface stress is not adversely affected by the effects due to operating stresses, load cycling (shakedown) and thermal stress relaxation [13] .

Verification and validation of the residual stress measurements on Alloy 600 and Alloy 182 materials used for the qualification mockups was demonstrated. As reported in the SPQR [7], the accuracy of each XRD measurement is recorded on the applicable laboratory data sheet. Typically, the highest accuracy is on the surface of the Alloy 600 base material with reduced accuracy at full depth (0.04 inch and deeper) in the Alloy 182 weld material. Using AREVA provided representative Byron RVCH test coupons (lnconel 600 nozzle I J-groove weld filler metals 82/182) , the XRD vendor (PROTO) performed validation testing based on criteria from the ASM handbook publication (section G.2 of [7]). A report was generated by PROTO to document their results, as well as the independent verification of results as performed by the University of Manchester (independent laboratory}, which confirmed repeatability and reproducibility.

AREVA peened six identical flat plates (same lot). Three were sent to PROTO for XRD and three were sent to Manchester for XRD, to provide data from two different independent labs for comparison . Both labs followed the XRD validation process procedure and are ISO/IEC 17025:2005 accredited laboratories. The test report addresses uncertainty in XRD residual stress measurements, documents compliance with accepted international standards and meets MRP-335, section 2.3.6 requirements (16] .

Mock-up testing demonstrated the effects that cavitation peening has to the ID of the nozzle penetration surfaces at thermal sleeve centering tab locations. The thermal sleeve centering tabs produce cold working during cavitation peening that reduces tensile stresses at the thermal sleeve centering tab wear groove locations. Thus, peening at wear groove locations produces higher conservative compressive stresses at these locations and is bounding for nozzle surfaces without wear grooves. Site specific wear groove geometry due to centering tabs is not required since deeper wear grooves would produce conservative compressive stress results . XRD results further confirmed that cavitation peening near the thermal sleeve centering tabs creates a compressive stress that is greater in the localized area than the results produced by the cavitation peening process per the SPQR [7] , section 7.7.4.1 and A.6 .

Motion profiles were created within parameters for controlling the water jet application for the various RPVHPN geometries. The specific motion profile

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 14 of 22) parameters required to peen each nozzle for Byron Station Unit 2 were defined by the special process to achieve the requ ired peening stresses and depth of compression per the SPQR, section 4.0.

Post Peening Residual Plus Operating Stress Stress analyses document the levels of operating stress that occur in the peened RPVHPNs [12][13]. The analysis approach included Finite Element Analysis (FEA) modeling with operating pressure and temperature applied to the model.

The residual plus operating stress at the peened surface exceeds the surface stress MRP-335 Performance Criterion 4.3.8.1.1.

In accordance with MRP-335 Performance Criterion 4.3.8.2, sustainability of the stress effect induced by the application specific water jet UH PCP process used is demonstrated to last the life of the plant by the testing included in the Qualification Report [7] and analyzed in the peening residual plus operating stress analysis [13] . The effects of both thermally induced stress relaxation and load cycling (shakedown) induced stress relaxation are evaluated in the stress analysis.

The post peening residual plus operating surface stress levels achieved are below the MRP-335 requirement of +10 ksi tensile. The nozzle (Alloy 600) OD stress range is -42.7 to -47.3 ksi for a margin of 52.7 to 57.3 ksi . The J-groove weld (Alloy 182) OD stress range is -11 .1 to -41 .6 ksi for a margin of 21 .1 to 51 .6 ksi . The nozzle (Alloy 600) ID stress range is 0 to -34 ksi for a margin of 10 to 44 ksi. The post peening residual plus operating stress levels and demonstrated margin for UHPCP implementation for Byron Station Unit 2 RVCH nozzle penetrations is provided in section 5.0 of the Summary Report [14] .

The increased margin to the residual plus operating stress to the + 10 ksi requirement places the nozzles in an increased compressive state that reduces the susceptibility to initiation and increases the duration before a small pre-existing flaw may be detectable. Therefore, the increased margin supports the conclusion that a follow-up inspection in the N+1 outage is not necessary.

5.4.3 Peening Coverage Area The peening coverage area was determined in accordance with MRP-335 Performance Criterion 4.3.8.1 . The required stress improvement effect was obtained over the area required to be peened . As stated in section 5.2.1 ,

UHPCP was applied to the standard RPVHPN inspection area per N-729-1 Figure 2, which exceeded the MRP-335 coverage requirements.

MRP-335 Performance Criterion 4.3.8.1 does not require RPVHPN threaded areas to be peened . Therefore, threaded areas near the end of the RPVHPNs that are within the area normally required to be peened, but which are impractical to peen using the method being applied , were not peened . These nozzles include the CETCs where portions of the threaded area were covered by the CETC funnel.

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Controls used to ensure the required coverage area is peened to achieve the required stress improvement effect are described in section 5.2.2. Measures that ensured complete coverage of the required area include the following :

• Complete coverage of the area designated for peening is assured by use of overlapping passes and by extending the peening out beyond the edge of the designated area .

• Critical parameters with acceptable ranges were established to ensure full peening coverage and depth of compression is achieved when all parameters are at both the maximum or minimum limits.

• Process controls are used to ensure the required surface areas are peened for the required length of time. Peening coverage area is programmed into the peening process via motion profiling.

• Process control document records are reviewed by independent reviewer{s) and Quality Assurance to assure accuracy.

The Summary Report documents where the post peening coverage area for the nozzle OD, nozzle ID and J-groove weld surfaces contained margin (e.g.,

exceeded MRP-335 requirements) due to the peening process and site specific FEA model. The FEA model determined that the actual +20 ksi stress region on the OD and ID nozzle surfaces did not extend down below the J-groove weld as far as the coverage region shown in Figures 4-1 and 4-2 of MRP-335. Five cases were run which bound the CROM penetration angles for the Byron RVCH .

The FEA model determined the actual nozzle OD downhill side +20 ksi stress region extends 0.44 to 0.48 inch below the toe of the weld . The FEA model determined the actual nozzle OD uphill side +20 ksi stress region extends 0.46 to 0.61 inch below the toe of the weld . The FEA model determined the actual nozzle ID downhill side +20 ksi stress region extends 0.47 to 1.26 inch below the toe of the weld . The FEA model determined the actual nozzle ID uphill side +20 ksi stress region extends 0.93 to 1.22 inch above the J-groove weld .

The nozzle OD downhill side peening process margin is 0.06 to 0.64 inch below the MRP-335 identified +20 ksi region . The nozzle OD uphill side peening process margin is 0.24 to 4.25 inch below the MRP-335 identified +20 ksi region.

The nozzle ID, below the weld toe, downhill side peening process margin is 0.07 to 1.20 inch below the MRP-335 identified +20 ksi region . The nozzle ID, above the weld toe, uphill side peening process margin is 0.44 to 5.54 inch above the MRP-335 identified +20 ksi region. The J-groove weld was peened to a minimum of 0.25 inch beyond the cladding/buttering interface.

The OD area of the CETC nozzle with +20 ksi and greater weld residual stress is conservatively peened with margin. A portion of the CETC guide funnel was removed to expose the required SSI area in accordance with MRP-335 with a minimum clearance of 0.5 inch [14]. The ID surface of the CETC nozzle was peened in accordance with MRP-335 with conservative margin. UHPCP implementation coverage data for Byron Station Unit 2 is provided in section 4.0 of the Summary Report applicable for RPVHPN Tiers 1-15 [14] .

Peening the full inspection area beyond the +20 ksi region area in combination with the plant specific actual FEA +20 ksi region being smaller than that specified

/SI Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 16 of 22) in the MRP-335 and the peening process margin places a larger area of the nozzles in an increased compressive state giving further assurance of a low probability that a flaw would initiate. Therefore, supporting the conclusion that a follow-up inspection in the N+1 outage is not necessary.

5.4.4 Depth of Compression The minimum OD and ID depth of compression per MRP-335 is 0.04 inch and 0.01 inch respectively. UHPCP consistently achieved a demonstrated depth of compression that met or exceeded MRP-335 requirements per section 6.0 of the Summary Report [14] . The depth of OD compression was from 0.04 to 0.06 inch for RPVHPNs. The depth of ID compression was from 0.01 to 0.05 inch for open penetrations. The depth of ID compression was from 0.01 to 0.02 inch for annulus penetrations (containing thermal sleeves) and the vent penetration.

The depth of compression results meet and exceed the requirements specified in the MRP-335 and therefore provide compressive stresses to a deeper level of the nozzles. This increased compressive state reduces the potential that a small pre-existing flaw would grow to a detectable size in one cycle. Therefore, supporting the conclusion that a follow-up inspection in the N+1 outage is not necessary.

5.4.5 XRD Accuracy and Effect on Cavitation Peening The post peening stress accuracy is documented in the Qualification Report and typically within +/-1 to +/-3 ksi for the nozzle (Alloy 600) and +/- 5 to+/- 13 ksi for the J-groove weld (Alloy 182). The internationally recognized best practices for instrument calibration and validation of results as defined in the ASM Handbook was used for XRD measurements per the Summary Report, section 7.0 [14] .

The stress results were repeatable for nozzle material (Alloy 600) with a standard deviation of +/-0.9 ksi and repeatable with a standard deviation of +/-0.7 ksi for J-groove weld material (Alloy 182). Likewise, the stress results were reproducible for nozzle material (Alloy 600) with a standard deviation of +/-0.3 ksi and reproducible with a standard deviation of +/-0.3 ksi for J-groove weld material (Alloy 182).

In accordance with MRP-335 Performance Criterion 2.3.6, residual stress measurement uncertainty has been considered when assessing the surface stress after peening and presented in the Special Process Qualification Report

[7] . XRD was performed using the multiple exposure technique with a minimum of 22 4J (psi) angles to increase accuracy of results per SAE HS784 with the best accuracy on the surface of the nozzle (Alloy 600) . In addition , an independent third party laboratory confirmed the XRD methodology used by AREVA and validated process repeatability and reproducibility . Since the Special Process Qualification Report used median surface stress XRD values, the reported measurement error (i.e., +/-3 ksi for Alloy 600 and +/- 13 ksi for Alloy 182) is bounded . Thus, XRD uncertainty associated with AREVA UHPCP does not impact the residual plus operating stresses on peened nozzles as qualified in the SPQR [7] . This is attributed to the highly accurate XRD process that was selected .

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The highly accurate and reproducible XRD results increase the confidence that the residual stresses and depth of compression are representative of actual stress conditions of the nozzles and weld materials. Therefore, supporting the increased compressive state that reduces the potential that a small pre-existing flaw would grow to a detectable size in one cycle and that a follow-up inspection in the N+1 outage is not necessary.

5.4.6 Technical Rigor Additional technical rigor was applied to the peening process beyond the requirements of MRP-335 through additional testing to ensure peening does not adversely affect the RVCH nozzles.

Demonstration of No Adverse Effects Qualification testing and analysis verifying the lack of adverse effects including the items covered by MRP-335 Performance Criterion 4.3.8.4 are documented in the Qualification Report and MRP-335. A summary of the specific testing and analysis is documented in Reference 7 and is provided below:

The effect of peening on surface roughness and inspectability was evaluated.

Surface roughness measurements were compared before and after peening on representative mock-up test coupons, using bounding values of peening parameters. The testing confirmed that the surface roughness was not significantly increased by the bounding values of peening parameters, and that the maximum surface roughness does not affect the capability to perform qualified NOE methods i.e., UT Time of Flight Diffraction , Penetrant Testing (PT) and Eddy Current Testing . Refer to the Special Process Qualification Report, Appendix A and section 11 .10.

The effect of peening to induce surface cracking is evaluated . The absence of peening-induced cracks in the surface, after exposure to bounding values of peening parameters is confirmed. Refer to the Special Process Qualification Report, Appendix A The effect of transitions from peened to unpeened conditions on the magnitude of surface tensile stresses and on the likelihood of developing sec cracks is evaluated. Testing verifies that the tensile stresses on the surfaces in transition regions from peened to unpeened conditions are not high enough to raise the risk of inducing PWSCC initiation. Refer to the Special Process Qualification Report, Appendix A The effect of flow induced vibration (FIV) on peened components or nearby components is evaluated. For water jet UHPCP of RPVHPNs with thermal sleeves, the integrity of the thermal sleeve and its connection to the nozzle will not be adversely affected by FIV. Likewise, there is no adverse impact to nearby components due to FIV. Refer to the Special Process Qualification Report section 11.4 and Appendix B.

The effect of over peening is evaluated . Erosion Testing demonstrates the margin , beyond the maximum allowed peening conditions required to result in

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 18 of 22) adverse effects such as erosion , roughening , or development of cracks. By demonstrating a large margin factor prior to unacceptable damage, there is confidence that unacceptable damage will not occur. Results showed that continuous peening of a location would be required for over eight times (8X) exposure time prior to experiencing any detectable detrimental surface conditions. The peening process is controlled to ensure that such over peening does not occur. Refer to the Special Process Qualification Report, Appendix A.

The potential for adverse effects due to UHPCP is evaluated per 10 CFR 50.59.

The evaluation determined that peening the wetted RPVHPN surfaces has no adverse effects on maintaining leak tight integrity. It was concluded that peening increases the surface resistance to PWSCC.

Performance of the erosion testing confirmed that peening will not adversely affect the RVCH. This additional rigor was completed to increase the understanding of the enterprise risk impact related to implementation of the peening process.

Corrosion Testing to Confirm PWSCC Mitigated Effectiveness Corrosion testing for crack initiation and growth performed for the peening process is described in the SPQR [7] . Alloy 600 specimens were exposed to simulated nominal PWR primary environment to determine the extent of SCC of peened vs non-peened samples. The peened samples were peened to a compressive depth of 0.01 inch, which meets the minimum nozzle ID depth requirements. After the test period , all of the non-peened specimens were heavily cracked (crack indications and through wall cracks) . The peened specimens were visually examined , PT examined , cross sectioned and examined by scanning electron microscopy. None of the peened specimens revealed any evidence of PWSCC indications or significant change in grain boundary [7] .

Based on the above corrosion testing , the samples that were peened to the required nozzle ID depth of 0.01 inch did not exhibit any PWSCC; which is a depth of only one fourth (1/4) of the outer surface peened depth requirement of 0.04 inch.

5.4.7 Deterministic Technical Basis A fully deterministic technical basis paper [17] has been published supplementing MRP-395 [9] with additional deterministic crack growth analyses , demonstrating the acceptability of a 36-month UT interval for heads with previously detected PWSCC that operate at Tcold . This new analysis extends the deterministic analysis in MRP-395 by applying the 95th percentile factor, rather than the standard 75th percentile per ASME Section XI. This new analysis exceeds the ASME approach and supports the 36-month inspection interval without crediting peening . On the basis of this technical analysis, a 36-month interval would continue to ensure that the nuclear safety and leakage (for defense in depth) concerns are conservatively addressed to support the additional request for relief from the MRP-335 Table 4-3 Note (11)(b) [16] requirement for inspection in the first refueling outage after peening.

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The following issue pertains to essential variables I critical parameters that were outside of qualified range during implementation of the B2R19 Reactor Head Peening . This issue was evaluated per AREVA's 10 CFR Appendix B program via the CR Process and determined to not impact UHPCP results, providing assurance that nozzle 57 was peened in accordance with MRP-335 [16] .

Although there is a Condition Report Appendix contained in the post peening Summary Report (14], this CR is further discussed here since this CR pertains to essential variables I critical parameters that were outside of qualified ranges.

CR-2016-3107 - Nozzle 57 High Pressure Transducer Signal Errors:

While cavitation peening the OD of nozzle 57, system high pressure was shown to fluctuate between -53,000 psi to 0 psi and back to -53,000 psi over a period of seconds. High pressure is an essential variable and a minimum of 50,000 psi is required . By physical system design, high pressure cannot rapidly fluctuate in this short period of time, therefore the fluctuation in pressure was determined to be a signal error due to electrical equipment malfunction and not an actual drop in system high pressure. When the system high pressure fluctuations were occurring , the tool backpressure remained constant, which further confirmed that system high pressure was not fluctuating and the issue was related to an electrical equipment failure. The tool backpressure data output files were reviewed and confirmed that the tool backpressure remained constant and did not fluctuate. Therefore, this issue does not impact UHPCP results for nozzle 57.

5.5. Conclusions On the basis of the above, the applicable peening performance criteria of MRP-335 section 4.3.8 are satisfied and exceeded with significant margin considering coverage area and post peened residual plus operating stresses. The detailed qualification work shows that the required SSI is achieved , and that the required operating stress effect and depth of compression is sustained with sufficient margin for the remaining service life of the peened component. The N-729-1 inspection area was peened compared to the MRP-335 required +20 ksi region , thus demonstrating margin. A highly accurate XRD methodology was used that provided repeatable and reproducible results, supporting the stress measurements in the Qualification Report.

A 36-month inspection interval is demonstrated as acceptable by ASME deterministic crack-growth rate analysis confirming inspection during N+1 is not required , which is consistent with industry approved inspection requirements per Code Case N-729-5 (18]. Code Case N-729-5 has been approved by ASME to credit peening RPVHPNs consistent with MRP-335 [4] . In addition , the increased margins demonstrated in the Byron Station Unit 2 peening application support the conclusion that a follow-up inspection in the N+1 outage is not necessary.

On the basis that the MRP-335 section 4.3.8 performance criteria were met or exceeded in accordance with MRP-335 requirements, demonstrates that inspection of the peened RPVHPNs at the alternative schedule requested will provide an acceptable level of quality and safety. Pending follow-up examination (i.e ., N+2 inspection) confirming no previous PWSCC present, the life of the peened RVCH penetrations is

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 20 of 22) acceptable for a 60-year plant license [15]. Thus, in accordance with 10 CFR 50.55a(z)(1), it is requested that NRC authorize this proposed alternative.

6.0 DURATION OF PROPOSED ALTERNATIVE:

The proposed Alternative is requested for the remainder of the 4th lnservice Inspection Interval for Byron Station, Unit 2, currently scheduled to end on July 15, 2025.

7 .0 PRECEDENT:

None

8.0 ACRONYMS

ASM American Society of Metals ASME American Society of Mechanical Engineers CFR Code of Federal Regulations CETC Core Exit Thermocouple Column CR Condition Report CRDM Control Rod Drive Mechanism EDY Effective Degradation Year EPRI Electric Power Research Institute FEA Finite Element Analysis FIV Flow Induced Vibration ID Inner Diameter ISi lnservice Inspection MRP [EPRI] Materials Reliability Program NDE Nondestructive Examination OD Outer Diameter PT [Liquid] Penetrant Testing PWR Pressurized Water Reactor PWSCC Primary Water Stress Corrosion Cracking RPV Reactor Pressure Vessel RPVHPN Reactor pressure vessel [upper] head penetration nozzle RVCH Reactor Vessel Closure Head SCC Stress Corrosion Cracking SPQR Special Process Qualification Report SSI Surface Stress Improvement UHP Ultra High Pressure UHPCP Ultra High Pressure Cavitation Peening UT Ultrasonic Testing XRD X-ray Diffraction

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 21 of 22)

9.0 REFERENCES

1. ASME Boiler and Pressure Vessel Code,Section XI, "Rules for lnservice Inspection of Nuclear Power Plant Components, " 2007 Edition including 2008 Addenda

2. ASME Code Case N-729-1, "Alternative Examination Requirements for PWR Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration Welds,Section XI, Division 1," Approved March 28, 2006.

3. Final Safety Evaluation of The Electric Power Research Institute MRP-335, Revision 3, "Materials Reliability Program: Topical Report For Primary Water Stress Corrosion Cracking Mitigation By Surface Stress Improvement [Peening]," (TAC NO. MF2429)

4. Materials Reliability Program: Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement (MRP-335 Revision 3) , EPRI ,

Palo Alto, CA: 2016. 3002007392 . [available at www.epri. com ]

5. Materials Reliability Program Generic Evaluation of Examination Coverage Requirements for Reactor Pressure Vessel Head Penetration Nozzles, Revision 1 (MRP-95R1), EPRI, Palo Alto, CA: 2004. 1011225. [Non-proprietary version: NRG ADAMS Accession No. ML043200602]

6. Materials Reliability Program: Technical Basis for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement (MRP-267, Revision 1), EPRI, Palo Alto, CA: 2012. 1025839. [available at www.epri.com]

7. AREVA Document No. 150-8086004-001, Special Process Qualification Record (SPQR), "SPQR, Qualification of the Cavitation Peening Process for RVCH Nozzles, " (EC 401061)

8. Materials Reliability Program: Technical Basis for Reexamination Interval Extension for Alloy 690 PWR Reactor Vessel Top Head Penetration Nozzles (MRP-375),

EPRI, Palo Alto, CA: 2014. 3002002441 . [available at www.epri.com]

9. Materials Reliability Program: Reevaluation of Technical Basis for Inspection of Alloy 600 PWR Reactor Vessel Top Head Nozzles (MRP-395) , EPRI, Palo Alto, CA:

2014. 3002003099.

10. Section titled "Shot Peening," page 131, ASM Handbook, Volume 5, "Surface Engineering ", ASM, 1994.

11 . MRP Letter 2014-027, "Response to the NRG Request for Additional Information (RAJ) related to Electric Power Research Institute (EPRI) MRP-335, Revision 1,

'Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement [Peening]' (TAC No. MF2429), " dated October 10, 2014. [NRG ADAMS Accession No. ML14288A370]

12. AREVA Analysis No. 32-9238505-001 , "Byron/Braidwood RVCH Nozzle and Penetration Original Configuration Stresses, " (Calculation B YR15-088)

13. AREVA Analysis No. 32-9241722-001 , "Byron & Braidwood Peening Residual Plus Operating Stress Analysis," (Calculation BYR15-090)

14. AREVA Document No. 51-8092600-001 , Engineering Information Record, "Summary Report, RVCH Peening Implementation, Byron Unit 2" (EC 400682)

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1 (Page 22 of 22)

15. AREVA Evaluation No. 51-9238120-002, "PWSCC Evaluation of UHP Cavitation Peening for Byron and Braidwood Reactor Vessel Head Penetrations," (Calculation BYR15-091)

16. Materials Reliability Program: Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement (MRP-335 Revision 3-A) , EPRI ,

Palo Alto, CA: 2016. 3002009241 . [available at www.epri.com ]

17. Deterministic Technical Basis for Re-Examination Interval of Every Second Refueling Outage for PWR Reactor Vessel Heads Operating at Tcotd with Previously Detected PWSCC, No. PVP2016-64032, Copyright 2016 by ASME.

18. ASME Code Case N-729-5, "Alternative Examination Requirements for PWR Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration Welds,Section XI, Division 1, "Approved October 7, 2015.

ATTACHMENT 4 10 CFR 50.55a Request Number 14R-14 Revision 1, Request for Relief for Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surfaces in Accordance with 10 CFR 50.55a(z)(1) with TRACK CHANGES SHOWN FOR INFORMATION ONLY

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 1 of 23)

Request for Relief Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surfaces in Accordance with 10 CFR 50.55a(z)( 1) 1.0 ASME CODE COMPONENTS AFFECTED:

Component Numbers: Unit 2, Reactor Vessel 2RC01 R Description : Extension of Examination Interval for Reactor Pressure Vessel Head Penetration Nozzles (RPVHPNs) Having Pressure-Retaining Partial-Penetration J-groove Welds with Mitigated Alloy 600/82/182 Peened Surfaces Code Class: Class 1 Examination Category: ASME Code Case N-729-1 Code Item: 84.20 Identification: RPVHPN Numbers 1 through 78 and vent, (P-1 through P-78 and vent) 1 Reference Drawing: Closure Head Assembly: 185282E Size: 4 Inch Nominal Outside Diameter, 2.75 Inch Nominal Inside Diameter (Vent Nozzle NPS 1)

Material: SB-167 UNS N06600 (Alloy 600), ENiCrFe-3 (Alloy 182),

and ERNiCr-3 (Alloy 82) 2.0 APPLICABLE CODE EDITION AND ADDENDA:

lnservice Inspection (ISi) and Repair/Replacement Programs: American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code,Section XI ,

2007 Edition including 2008 Addenda [1] . Examinations of the RPVHPNs are performed in accordance with 10 CFR 50.55a(g)(6)(ii)(D) , which specifies the use of ASME Code Case N-729-1 with conditions.

Code of Construction [Reactor Pressure Vessel (RPV)]: ASME Section Ill , 1971 Edition through Summer 1973 Addenda .

1 Applies to RPVHPNs mitigated in accordance with section 4.3.8 ofMRP-335 , R3-A [16]

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 2 of 23) 3.0 APPLICABLE CODE REQUIREMENT:

ASME Code Case N-729-1 contains requirements for the inspection of RPVHPNs, with or without flaws, as conditioned by 10 CFR 50.55a(g)(6)(ii)(D). The specific Code requirements for which use of the proposed alternative is being requested are as follows:

Code of Federal Regulations (CFR) 10 CFR 50.55a(g)(6)(ii)(D)( 1) requires (in part):

"All licensees of pressurized water reactors must augment their inservice inspection program with ASME Code Case N-729-1 , subject to the conditions specified in paragraphs (g)(6)(ii)(D)(2) through (6) of this section. Licensees of existing operating reactors as of September 10, 2008 must implement their augmented inservice program by December 31 , 2008."

10 CFR 50.55a(g)(6)(ii)(D)(3) conditions ASME Code Case N-729-1 by stating :

"Instead of the specified 'examination method' requirements for volumetric and surface examinations in Note 6 of Table 1 of Code Case N-729-1 , the licensee must perform volumetric and/or surface examination of essentially 100 percent of the required volume or equivalent surfaces of the nozzle tube, as identified by Figure 2 of ASME Code Case N-729-1 . A demonstrated volumetric or surface leak path assessment through all J-groove welds must be performed. If a surface examination is being substituted for a volumetric examination on a portion of a penetration nozzle that is below the toe of the J-groove weld (Point Eon Figure 2 of ASME Code Case N-729-1 ), the surface examination must be of the inside and outside wetted surface of the penetration nozzle not examined volumetrically."

ASME Code Case N-729-1 , Alternative Examination Requirements for PWR Reactor Vessel Upper Heads with Nozzles Having Pressure-Retaining Partial-Penetration Welds,Section XI , Division 1 [2], Figure 2, "Examination Volume for Nozzle Base Metal and Examination Area for Weld and Nozzle Base Metal ," is applicable to the RPVHPNs .

ASME Code Case N-729-1 , Paragraph -2410 specifies that the reactor vessel upper head penetrations shall be examined on a frequency in accordance with Table 1 of the code case (Refer to Reference [2], hereafter known as N-729-1 ). However, 10 CFR 50.55a(g)(6)(ii)(D)(5) states "If flaws attributed to PWSCC have been identified, whether acceptable or not for continued service under Paragraphs -3130 or-3140 of ASME Code Case N-729-1 , the re-inspection interval must be each refueling outage instead of the re-inspection intervals required by Table 1, Note (8), of ASME Code Case N-729-1 ." Since flaws attributed to Primary Water Stress Corrosion Cracking (PWSCC) have been identified at Byron Station Unit 2, the RPVHPNs are examined every fuel cycle in accordance with 10 CFR 50.55a(g)(6)(ii)(D)(5).

As an alternative to the requirements above, required inspections will be conducted in accordance with the inspection requirements for Alloy 600 RPVHPNs mitigated by peening , based on Table 4-3 in MRP-335, Revision 3-A, "Materials Reliability Program:

Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement, November 2016, -[16](Reference 16); including relief from Final Safety Evaluation [3] Condition 5.4 requirement for inspection in the first refueling outage

IS/ Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 3 of 23) post peening application (i.e., N+1 outage) which is reflected in Referenoe 16MRP-335 Table 4-3 Note (11 )(b) [16] .

4.0 REASON FOR REQUEST:

Exelon Generation Company, LLC (EGC) has implemented the Ultra High Pressure Cavitation Peening (UHPCP) process at Byron Station Unit 2 and is requesting a change to the reexamination interval of the follow-up inspections for peened RPVHPNs and associated welds in accordance with Referenoe 16MRP-335 Table 4-3 [16] with an additional request for relief from the Table 4-3 Note (11)(b) requirement for follow-up inspection in the first refueling outage after peening.

As discussed in section 3.0, N-729-1 as conditioned by 10 CFR 50.55a(g)(6)(ii)(D)(5) requires volumetric and/or surface examination of the Byron Station Unit 2 RPVHPNs and associated welds of all nozzles every refueling outage or one fuel cycle, nominally every 18 months. The examination schedule of N-729-1 does not address the effects of Surface Stress Improvement (SSI) by peening or the associated inspection frequency for RPVHPNs in this mitigated state. Electric Power Research Institute (EPRI) developed, using appropriate analytical tools , a volumetric or surface re-examination interval for Alloy 600 RPVHPNs and Alloy 82/182 partial-penetration (J-groove) attachment welds that have received peening application. This technical basis demonstrates that for any peening SSI process meeting the performance criteria of section 4.3.8 of Referenoe MRP-335 [16], the re-examination interval can be changed to the Table 4-3 inspection schedule.

As described in detail in section 5.0 below, the UHPCP process implemented at Byron Station Unit 2 meets or exceeds the SSI residual plus operating stress, the coverage area and the depth of compression requirements specified in MRP-335. In addition ,

considering the deterministic analysis work described by EPRI [16] and by ASME in section 5.4.7 of this relief, EGC is requesting a change from the Final Safety Evaluation Condition 5.4 requirement for follow-up inspection in N+1 , which is reflected in Referenoe MRP-335 4-e-Table 4-3 Note (11 )(b) [16].

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE:

5.1. Introduction The peening process was developed by the peening vendor (AREVA) as a Special Process in accordance with 10 CFR 50 Appendix B. Qualification of the AREVA UHPCP process on RPVHPNs for the purpose of PWSCC mitigation is documented in the Qualification Report [7] .

Peening Mechanism for PWSCC Mitigation When the applicable MRP-335 performance criteria are met, peening mitigation prevents initiation of PWSCC [16]. The possibility of pre-existing flaws that are not detected in the pre-peening Non Destructive Examination (NOE) is addressed through the required follow-up inspection that is performed during the second refueling outage (N+2) after application of peening. Peening also has the benefit of arresting PWSCC growth of

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 4 of 23) shallow surface flaws that are located in regions at the surface where the residual plus normal operating stress is now compressive [16][15] . This secondary benefit is not credited in the main analyses of MRP-335 because these analyses conservatively assume that the bounding stress effect meeting the performance criteria is achieved.

In order to prevent the initiation of new PWSCC, the application of peening has to result in the peak tensile stresses at the wetted surface of material being less than the

"~threshold"~ stress for initiation of PWSCC. Based on laboratory testing, a tensile stress of +20 ksi is a conservative lower bound of the stress level below which PWSCC initiation will not occur over plant time scales per MRP-95 [5]. This applies to steady-state stresses during normal operation since stress corrosion cracking (SCC) initiation is a long-term process, and does not apply to transient stresses that occur only for relatively short periods of time. Additional conservatism is provided by the MRP-335 performance criterion limiting the surface stress to +10 ksi (tensile) for the case of RPVHPNs when normal operating stresses are considered [16].

The potential for growth of small flaws too shallow to be reliably detected in the pre-peening ultrasonic (UT) examination , or for flaws located in the J-groove weld metal, is addressed by the follow-up UT examination , and by the ongoing visual examinations for evidence of leakage performed at the same schedule as prior to peening . The N+2 and subsequent program of inspections addresses growth of any flaws via PWSCC that may not have been detected in the pre-peening examination. For the cold head operating conditions of the Byron Station RPVHPNs and 18 month refueling cycle, the bases described in Reference 16 MRP-335 section 5.2.3.2 [16] supports the 36- month follow-up inspection time.

Stress Effect to Prevent Future PWSCC Initiations The compressive residual stress depth required by the performance criteria ensures that the stress improvement effect extends a significant distance into the material. The Byron Station Unit 2 peening met or exceeded the MRP-335 depth of compression requirements. The deterministic and probabilistic analyses in MRP-335 that form the basis for the requested inspection relief show that it is not necessary for growth of shallow pre-existing flaws to be arrested by the post-peening stress field . Pre-existing flaws are effectively addressed by the combination of pre-peening and follow-up inspections. In cases when a shallow pre-existing flaw is located within a region of compressive residual plus operating stress, PWSCC growth of the pre-existing flaw would be arrested [16] . In the event of a pre-existing flaw that exists below the depth of peening application, probabilistic and deterministic evaluations show that the flaw growth and detection in N+1 is unlikely due to the Tcold head environment. The probability of flaw detection supports performing inspection in N+2 ([16]Reference 16, section 5.1).

Effect of Pre-Existing Residual Stresses High residual tensile stresses do not interfere with the ability of peening to develop the stress effect needed to be effective [6] . The peening effect is self-normalizing with regard to the level of pre-peening residual stresses [16][7] . A study was performed by AREVA (Item 9 of Attachment 1 of Reference 11[11 ]) to verify that the unpeened residual stress state of the material does not have a significant effect on the final peened surface compressive stress and depth of compression. Testing supports that regardless

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 5 of 23) of the initial stress state i.e., high tension or high compression , the final compressive stresses ended up within a -63 ksi to -81 ksi range [16] . Theory and test data show that peening results in high compressive residual stresses regardless of the starting state of the residual stresses.

5.1.1 Proposed Alternative EGC is requesting relief from the examination frequency requirements of 10 CFR 50.55a(g)(6)(ii)(D)(5) , for performing volumetric and/or surface examinations of the Byron Station Unit 2 RPVHPNs each refueling outage.

Specifically, relief is requested to allow an alternative inspection frequency consistent with requirements of MRP-335 Revision 3-A, Table 4-3 with an additional request for relief from the Table 4-3 Note (11)(b) requirement for follow-up inspection in the first refueling outage after peening.

The alternative inspection frequency requirements for Item B4.60 RPVHPNs mitigated by peening SSI per MRP-335 Table 4-3 [16] require a pre-peening baseline inspection , follow-up inspection, and subsequent in-service inspection, as summarized below.

Pre-Peening Baseline Inspection Prior to performance of peening but during the same outage, examinations are to be performed in accordance with the requirements in Reference 16MRP-335 Table 4-3, Note f( 13) [16] . Examinations include volumetric or surface examinations of essentially 100% of the required volume or equivalent surfaces of the nozzle tube as identified in Figure 2 of N-729-1, and a demonstrated volumetric or surface leak path assessment through all J-groove welds. The leak path examination detects through-wall cracking by checking for areas at the interface (annulus) between the nozzle tube and low-alloy steel head where leakage has caused a loss of interference fit. The analyses in Section 5 and Appendix B of MRP-335 conservatively do not take credit for the leak path examination .

Follow-Up Inspection During the follow-up inspection, a volumetric examination of 100% of the required volume or equivalent surfaces of the nozzle tube is to be performed and a leak path examination is also to be performed. EGC proposes to follow the inspection interval specified in MRP-335 Reference 16 Table 4-3 [16] with an additional request for relief from the Table 4-3 Note (11 )(b) requirement for follow-up inspection in the first refueling outage after peening . The follow-up inspection schedule is based on the value of the effective degradation year (EDY) parameter (defined in N-729-1) at the time of peening . EGC's proposed alternative is consistent with the Reference 4MRP-335 Table 4-3 Note (11 )(b)

[16] requirement, "For plants where EDY< 8 at the time of peening and containing pre-existing flaws a follow-up inspection is to be performed in the second (N+2) refueling outage subsequent to peening" (EDY=3.249 at the time of peening for Byron Station Unit 2). Furthermore, for the cold head operating

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 6 of 23) conditions of the Byron Station RPVHPNs and 18 month refueling cycle, the bases described in Referenoe 16MRP-335 section 5.2.3.2 supports the 36-month follow-up inspection time.

Subsequent ISi Program The ISi program interval examinations take effect after completion of the follow-up inspection per Item B4.60, Table 4-3 [16] . Examinations include volumetric or surface examinations of peened penetrations at an interval not to exceed one inspection interval (nominally 10 calendar years) , and a demonstrated volumetric or surface leak path assessment through all J-groove welds each time the periodic volumetric or surface examination is performed .

5.2. Description of Application Specific Process PWSCC is mitigated via surface remediation by inducing a compressive stress layer in the surface of each nozzle and J-groove weld at the Byron Station Unit 2 RPVHPNs through the application of water jet UH PCP as qualified in the Special Process Qualification Report (SPQR) [7] by AREVA. This compressive stress layer has been demonstrated to prevent PWSCC initiation [15].

5.2.1 Description of Peened Components and Selection of Peened Area UH PCP was applied to the outer and inner surfaces of the Alloy 600/182/82 materials. Peening of the OD of the nozzle and outer weld surface was performed using an OD tool that rotates the water jet around the outer circumference of the nozzle and weld material (Figure 5.2.1-1). Note that a shoulder area of the Core Exit ThermocGouple (CETC) funnel (upper collar) ,

that when seated to the CETC nozzle penetration tube, physically blocked access to the required surface area to be peened . The portion of the funnel upper collar that was covering the

+20 ksi area on the downhill side of the CETC nozzles was removed to permit peening of the +20 ksi area. Electrical Discharge Machining (EDM) was used to remove this piece of the funnel , which allowed the guide funnels to remain in place while the required high stress (+20 ksi) mitigation area was peened (Figure 5.2.1-2).

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 7 of 23)

Figure 5.2.1-1 Figure 5.2.1-2 Accessibility of the nozzle OD and J-groove weld surfaces is sufficient to permit UHPCP to meet and exceed the 0.04 inch minimum depth of compression for RPVHPNs . Peening the ID surface of the nozzle was performed using an ID tool that rotates the water jet around the inner circumference of the nozzle. For open penetrations and the vent line, the ID open penetration/vent line tool rotates the water jet around the inner circumference of the nozzle as the water jet is applied directly from inside the nozzle. For -ID-nozzles with thermal sleeves, the ID annulus tool moves the thermal sleeve to one side to allow the water jet access to fit into the annulus region between the OD of the thermal sleeve and ID of the nozzle. This allows the water jet to peen the inner circumference of the nozzle from inside the annulus region . The ID annulus tool has sufficient clearance to meet and exceed the 0.01 inch minimum depth of compression for RPVHPNs . See SPQR section 4.0 [7] .

The outer surface (nozzle OD and weld) and nozzle ID peening mitigation coverage was based on Figure 2 of N-729-1 , which is also the extent of the ISi inspection area. The extent of peening coverage on the nozzle and weld outer surface is zone G-F-E-C. The extent of peening coverage on the nozzle ID surface is zone A-D. Note: the surfaces required to be peened are defined in Figures 4-1 , 4-2 and 4-3 of MRP-335, which is less OD surface area than that identified in Figure 2 of N-729-1 . Thus, the Byron Station Unit 2 nozzle OD peened surface area exceeded the MRP-335 peening area mitigation requirement. This margin is discussed in section 5.4 of this relief request with additional detail provided in the post peening Summary Report [14] .

Peening of Previously Repaired RPVHPNs Exceptions to the above RPVHPNs are nozzles that have been previously repaired e.g., nozzles that were repaired by weld overlay. This type of repair is known as an embedded flaw repair. Byron Station Unit 2 penetrations 6 and 68 were previously repaired by weld overlay. For these penetrations, peening of the weld repair area is not required since this weld material is PWSCC resistant

/SI Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 8 of 23)

(J-groove weld area and portions of the nozzle tube OD that are covered by the repair weld). However, peening of the ID and the portion of the nozzle tube OD surfaces not having weld repai r material is required from the weld overlay to the top of the threads.

The Byron Station Unit 2 nozzle 6 J-groove weld and top portion of the nozzle OD has been mitigated with a weld overlay. The OD of the nozzle below the weld overlay to the top of the threads was peened and the required nozzle ID area was peened.

The Byron Station Unit 2 nozzle 68 J-groove weld and top portion of the OD has been mitigated with a weld overlay. There is no area of the nozzle OD below the weld overlay to consider peening since that portion of the nozzle and threaded section was removed (Figure 5.2.1-3). The ID of the nozzle was not peened during 82R19 due to excess leakage preventing a good seal.

Figure 5.2.1-3 The exposed areas of Alloy 52 weld metal (overlay) are not required to be peened since Alloy 52 is PWSCC resistant per MRP-375 [8] and section 4.3.7 of MRP-335 [16] . Therefore, from the perspective of susceptibility to PWSCC degradation , a penetration repai red using the embedded flaw repair technique (i.e., with an Alloy 52 repair weld applied to the J-groove weld area and portion of the nozzle tube OD) is mitigated . Subsequent to peening the unrepaired OD and ID, the nozzle areas with Alloy 600 material in contact with reactor coolant, will have a residual plus operating surface stress well below that necessary to initiate PWSCC per the residual plus operating stress analysis [13] .

If the requ irements of section 4.3 of MRP-335 are satisfied, a RPVHPN with flaws that has been corrected and subsequently peened using a process meeting the performance criteria of section 4.3.8 of MRP-335 may be identified as Item 84.60 in Table 4-3 f Note (12) of MRP-335. Thus, follow-up and ISi program examinations for weld overlay repaired nozzles subsequent to peening are equivalent to the follow-up and ISi program examinations for unrepaired nozzles subsequent to peening i.e. , may be identified as Item 84.60.

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 9 of 23) 5.2.2 Process Description Performance demonstration is the method used to ensure that peening fully covers all of the areas that require peening , and achieves the desired magnitude and depth of residual compressive stresses. The critical parameters to be controlled ensure that peening develops the intended levels of compressive residual stresses in each peened area [7][14] . The SPQR is the Qualification Report that demonstrates desired results are achieved per MRP-335 with a bounded set of parameters. The UHPCP procedure implements the process per the requirements defined in the SPQR. During the implementation process, essential variables are recorded for each nozzle. Completed procedural enclosures and data output files are provided in the Summary Report [14] to document and log the performance results of the UH PCP process. The post peening Summary Report [14] confirms performance demonstration of peening at each nozzle and summarizes the essential variables/critical parameters.

Surface Condition Considerations There are no limitations imposed by surface cond itions on water jet UHPCP. No preparations of the surfaces to be peened are requ ired before peening is performed. In addition , there are no limitations on the peening caused by irregularities or undulations of the surface, such as those associated with weld beads, local grinding, or from initial forging [7].

Pre-Peening NOE The pre-peening base-line RPVHPN inspection was performed in accordance with N-729-1 as conditioned by 10 CFR 50. 55a and found no conditions requiring repair.

Contingencies If critical parameters go outside of the specified range during the peening process, the issue is displayed on the peening controls system and evaluated or the process is shut down automatically. If peening is stopped for any reason the process is restarted in accordance with the approved peening process procedures to ensure adequate peening coverage. A Condition Report (CR) is issued if corrective action is required that is outside of the approved peening process procedures and appropriately evaluated by AREVA and EGOEeleR.

5.3. Performance Criteria The following is an overview of MRP-335 [16] performance criteria requirements for RPVHPN peening . The Byron Station Unit 2 UHPCP implementation demonstrated meeting or exceeding these criteria is addressed in detail in section 5.4.

Stress Magnitude

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 1O (Page 1Oof23)

The stress prior to consideration of operating stresses must be compressive on all peened surfaces. The residual stress plus operating stress on peened surfaces must not exceed +10 ksi (tensile).

Peening Coverage The required coverage is the full wetted area of the susceptible material with surface stress (residual plus operating stress) of at least +20 ksi (tensile), which is a conservative measure of the threshold for PWSCC initiation [16][5]. The susceptible material locations to be considered are the wetted surface of the Alloy 82/182 J-groove weld and butter material and the surfaces of the Alloy 600 nozzle tube material in the region of the J-groove weld as defined in Figures 4-1 , 4-2 and 4-3 of MRP-335

[Reference 11 6].

Depth of Effect The compressive residual stress field extends a nominal minimum depth of:

• 0.04 inch on the susceptible area of the outer nozzle and weld surfaces

• 0.01 inch on the susceptible area of the inner nozzle surface Sustainability of Effect The mitigation process is effective for at least the remaining service life of the component i.e., the residual plus operating surface stress state after considering the effects of thermal relaxation and load cycling (i.e. , shakedown) must remain no greater than +10 ksi (tensile) .

lnspectability The capability to perform UT examinations of the relevant volume of the Alloy 600 nozzle tube material is not adversely affected, and the relevant volume or surface of the J-groove weld and Alloy 600 nozzle tube material is inspectable using a qualified process.

Lack of Adverse Effects As verified by analysis or testing , the mitigation process is not to have degraded the component, caused detrimental surface conditions, or adversely affected other components in the system .

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 11 of 23) 5.4. Reactor Vessel CROM UHPCP Implementation Results and Margins This section provides detail on the AREVA Qualification Program, summarizes the Byron Station Unit 2 peening performance margin achieved in meeting or exceeding MRP-335 performance criteria , and highlights additional technical rigor performed to validate the peening process.

5.4.1 Qualification as a Special Process Surface stress improvement by peening affects the performance of nuclear safety-related systems and components, thus, it shall be performed in accordance with a quality assurance program meeting the requirements of 10 CFR 50 Appendix B. Further, since peening is a special process, it is required to be controlled in a manner consistent with Appendix B Criterion IX,

":'.Control of Special Processes. "~

Per Criterion IX, the personnel and procedures involved are required to be appropriately qualified. Since there are no industry standards that apply to peening , these qualifications shall be done to peening vendor requirements developed and documented per the vendor's 10 CFR 50 Appendix B quality assurance program.

The Qualification Program for the UHPCP process covered in this relief request was developed by AREVA and is documented in the Qualification Report [7].

The qualification program addresses both the generic process and , by use of representative test coupons, the effectiveness of the peening process when applied to the specific geometries of the components covered by this relief request.

Technical justification is included in the SPQR based on MRP-335 section 6.3.

The specific process used has been demonstrated to be effective, including surface stress magnitude, compressive residual stress depth, and sustainability of the stress effect. Included is a description of the demonstration testing of peening of coupons representative of the geometry, material, accessibility, and surface condition of the component to be peened (see section 5.4.2 of this relief) . The specific process has been demonstrated to result in no adverse effects (see section 5.4.6 of this relief) . Essential variables with associated ranges of acceptable values are determined for the specific application, plus a description of the process controls is included which ensure~ essential variables remain within acceptable ranges (see sections 5.2.2 and 5.4.2 of this relief) . Specific process controls were provided ensuring coverage requirements are met with a high degree of confidence, including what overlap of peening beyond the susceptible material is requ ired (see section 5.2.2 and 5.4.2 of this relief). Disposition of non-conforming issues encountered are included (see section 5.2.2 of this relief).

Critical Process Parameters and Acceptable Values MRP-335 Performance Criterion 4.3.8.1 requires testing be performed ":'.to demonstrate the critical process parameters and [to] define acceptable ranges of the parameters needed to ensure that the required residual stress field

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 12 of 23)

(exclusive of normal operating stresses) has been produced on the mitigated surface . "~

Demonstration that the stress improvement parameters are met is provided, in part, by verification that all of the control process parameters (essential variables) were maintained within the specified ranges during the application of UHPCP. The peening process parameters were maintained and verified within acceptable ranges [14] . The critical process parameters were monitored and recorded as described in the SPQR [7] . The data is reviewed and verified by AREVA's quality control. The essential variables/critical parameters and acceptable ranges for UHPCP implementation for Byron Station Unit 2 Reactor Vessel Closure Head (RVCH) nozzle penetrations is provided in section 3.0 of the Summary Report [14] .

5.4.2 Demonstration that Required Stress Effect is Achieved In accordance with the performance criteria, testing and analysis demonstrate that the required stress improvement effect exceeded over 100% of the required area and that the required effect will be sustained for at least the remaining service life of the peened components. The stress effect is quantified to be conservative relative to that required in MRP-335 in terms of the residual plus operating stress at the peened surface and the depth of the compressive residual stress. The requested testing and analysis are documented in the Qualification Report [7] and summarized below.

Residual Stress Measurements Using Representative Test Coupons Per the Qualification Report, demonstration testing has been performed in accordance with MRP-335 Performance Criterion 4.3.8.1 to determine the residual stress state at peened surfaces. Residual stress measurements were made for full scale peened test coupons representative of the geometry, material, accessibility, and surface condition of the components to be peened (see Figure 5.4.2-1 and Figure 5.4.2-2).

Figure 5.4.2-1 , Representative Full Scale Coupon

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Figure 5.4.2-2, Representative Full Scale Coupon The residual stress measurements satisfied the nominal depth requirement for the compressive residual stress of MRP-335 Performance Criterion 4.3.8.1.2.

The magnitude of the residual stress at the surface was combined with the operating stress at the surface to demonstrate compliance with MRP-335 Performance Criterion 4.3.8.1.1. Key aspects of demonstration testing are provided below.

Site specific geometry is identified and validated through mockup testing . A total of 18 mockup coupons were peened as part of the qualification testing activity that included various RVCH penetration tiers and the head vent. A summary matrix of the qualification coupon peened surfaces isai:e provided in the Qualification Report, Table 3-1 [7]. The test coupons were peened with in control parameters that were recorded . As discussed in section 5.4.1 "~Critical Process Parameters and Acceptable Values ,".'.'. this testing was used to determine the ranges of acceptable values for the critical process parameters for application in the plant. As simulated in the Qualification testing , UHPCP achieved the performance requirements despite the geometric limitations associated with the application of peening to RVCH penetrations, such as limited access associated with ID annulus peening or CETC downhill nozzle to RVCH head clearance.

The residual stress measurements ensure that the required stress effect was achieved in each portion of the component area requ ired to be peened , including areas with different materials, curvature or accessibility. For RPVHPNs, the nozzle tube ID, nozzle tube OD, and weld surfaces are addressed. The actual peening coverage was checked during examination of the test coupons using X-ray Diffraction (XRD) of the peened surface. XRD testing confirmed that the compressive residual stress depth measurements met the requirement of the performance criteria. For each of the peened areas, the magnitude and depth of the compressive residual stresses that would be developed by lower bound allowable values of the critical peening parameters were identified. As analyzed ,

the post peening surface stress is not adversely affected by the effects due to operating stresses, load cycling (shakedown) and thermal stress relaxation [13].

Verification and validation of the residual stress measurements on Alloy 600 and Alloy 182 materials used for the qualification mockups was demonstrated. As reported in the SPQR [7] , the accuracy of each XRD measurement is recorded

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 14 of 23) on the applicable laboratory data sheet. Typically, the highest accuracy is on the surface of the Alloy 600 base material with reduced accuracy at full depth (0.04 inch and deeper) in the Alloy 182 weld material. Using AREVA provided representative Byron RVCH test coupons (lnconel 600 nozzle I J-groove weld filler metals 82/182) , the XRD vendor (PROTO) performed validation testing based on criteria from the ASM handbook publication (section G.2 of Reference[-?]). A report was generated by PROTO to document their results, as well as the independent verification of results as performed by the University of Manchester (independent laboratory) , which confirmed repeatability and reproducibility. AREVA peened six identical flat plates (same lot). Three were sent to PROTO for XRD and three were sent to Manchester for XRD, to provideconfirm data from two different independent labs for comparison . Both labs followed the XRD validation process procedure and are ISO/IEC 17025:2005 accredited laboratories. The test report addresses uncertainty in XRD residual stress measurements, documents compliance with accepted international standards and meets MRP- 335, section 2.3.6 requirements [16] .

Mock-up testing demonstrated the effects that cavitation peening has of thermal sleeve tab wear to the ID- of the nozzle penetration surfaces at thermal sleeve centering tab locations. due to centeringThe thermal sleeve centering tabs produces cold working during cavitation peening that reduces tensile stresses at the thermal sleeve centering tab wear groove locations. Thus, peening at wear groove locations produces higher conservative compressive stresses at these locations and is bounding for nozzle surfaces without wear grooves. Site specific wear groove geometry due to centering tabs is not required since deeper wear grooves would produce conservative compressive stress results . XRD results further confirmed that cavitation peening near the thermal sleeve centering tabs wear does creates a compressive stress on the surfaoe from cold working and that is greater in the localized area than the results produced by the cavitation peening process per the SPQR [7], section 7.7.4.1 and A.6.

Motion profiles were created within parameters for controlling the water jet application for the various RPVHPN geometries. The specific motion profile parameters required to peen each nozzle for Byron Station Unit 2 were defined by the special process to achieve the required peening stresses and depth of compression per the SPQR, section 4.0.

Post Peening Residual Plus Operating Stress Stress analyses document the levels of operating stress that occur in the peened RPVHPNs [12][13] . The analysis approach included Finite Element Analysis (FEA) modeling with operating pressure and temperature applied to the model.

The residual plus operating stress at the peened surface exceeds the surface stress MRP-335 Performance Criterion 4.3.8.1.1 .

In accordance with MRP-335 Performance Criterion 4.3.8.2, sustainability of the stress effect induced by the application specific water jet UHPCP process used is demonstrated to last the life of the plant by the testing included in the Qualification Report [7] and analyzed in the peening residual plus operating stress analysis [13] . The effects of both thermally induced stress relaxation and

/SI Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 15 of 23) load cycling (shakedown) induced stress relaxation are evaluated in the stress analysis.

The post peening residual plus operating surface stress levels achieved are below the MRP-335 requirement of +10 ksi tensile. The nozzle (Alloy 600) OD stress range is -42 . 7~ to -47.3 ksi for a margin of 52 . 7~ to 57.3 ksi. The J-groove weld (Alloy 182) OD stress range is -11 .1 to -41.6 ksi for a margin of 21 .1 to 51 .6 ksi. The nozzle (Alloy 600) ID stress range is 0 to -34 ksi for a margin of 10 to 44 ksi. The post peening residual plus operating stress levels and demonstrated margin for UHPCP implementation for Byron Station Unit 2 RVCH nozzle penetrations is provided in section 5.0 of the Summary Report [14] .

The increased margin to the residual plus operating stress to the + 10 ksi requirement places the nozzles in an increased compressive state that reduces the susceptibility to initiation and increases the duration before a small pre-existing flaw may be detectable. Therefore, the increased margin supportsffi9 the conclusion that a follow-up inspection in the N+1 outage is not necessary.

5.4.3 Peening Coverage Area The peening coverage area was determined in accordance with MRP-335 Performance Criterion 4.3.8.1. The required stress improvement effect was obtained over the area required to be peened . As stated in section 5.2.1, UHPCP was applied to the standard RPVHPN inspection area per N-729-1 Figure 2, which exceeded the MRP-335 coverage requirements.

MRP-335 Performance Criterion 4.3.8.1 does not require RPVHPN threaded areas to be peened . Therefore, threaded areas near the end of the RPVHPNs that are within the area normally required to be peened , but which are impractical to peen using the method being applied , were not peened. These nozzles include the CETCs where portions of the threaded area were covered by the CETC funnel.

Controls used to ensure the required coverage area is peened to achieve the required stress improvement effect are described in section 5.2.2. Measures that ensured complete coverage of the required area include the following:

• Complete coverage of the area designated for peening is assured by use of overlapping passes and by extending the peening out beyond the edge of the designated area.

• Critical parameters with acceptable ranges were established to ensure full peening coverage and depth of compression is achieved when all parameters are at both the maximum or minimum limits.

• Process controls are used to ensure the required surface areas are peened for the required length of time. Peening coverage area is programmed into the peening process via motion profiling.

• Process control document records are reviewed by independent reviewer(s) and Quality Assurance to assure accuracy.

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The Summary Report documents where the post peening coverage area for the nozzle OD, nozzle ID and J-groove weld surfaces contained margin (e.g.,

exceeded MRP-335 requirements) due to the peening process and site specific finite element analysis (FEAj model. The FEA model determined that the actual

+20 ksi stress region on the OD and ID nozzle surfaces did not extend down below the J-groove weld as far as the coverage region shown in Figures 4-1 and 4-2 of MRP-335. Five cases were run which bound the CROM penetration angles for the Byron RVCH. The FEA model determined the actual nozzle OD downhill side +20 ksi stress region extends 0.44 to 0.48 inch below the toe of the weld . The FEA model determined the actual nozzle OD uphill side +20 ksi stress region extends 0.46 to 0.61 inch below the toe of the weld . The FEA model determined the actual nozzle ID downhill side +20 ksi stress region extends 0.47 to 1.26 inch below the toe of the weld . The FEA model determined the actual nozzle ID uphill side +20 ksi stress region extends 0.93 to 1.22 inch above the J-groove weld .

The nozzle OD downhill side peening process margin is 0.06G,.GS to 0.64G-4G inch below the MRP-335 identified +20 ksi region . The nozzle OD uphill side peening process margin is 0.24 to 4.2~ inch below the MRP-335 identified

+20 ksi region . The nozzle ID, below the weld toe , downhill side peening process margin is 0.07~ to 1 . 20~ inch below the MRP-335 identified +20 ksi region .

The nozzle ID, above the weld toe, uphill side peening process margin is 0.44 to 5.54 inch above the MRP-335 identified +20 ksi region. The J-groove weld was peened to a minimum of 0.250.060 to o.aga inch beyond the cladding/buttering interface.

The OD area of the CETC nozzle with +20 ksi and greater weld residual stress is conservatively peened with margin. A portion of the CETC guide funnel was removed to expose the required SSI area in accordance with MRP-335 with a minimum clearance of 0.5 inch [14]. The ID surface of the CETC nozzle was peened in accordance with MRP-335 with conservative margin. UHPCP implementation coverage data for Byron Station Unit 2 is provided in section 4.0 of the Summary Report applicable for RPVHPN Tiers 1-15 [14] .

Peening the full inspection area beyond the +20 ksi region area in combination with the plant specific actual FEA +20 ksi regionlocation being smaller than that specified in the MRP-33~5 and the peening process margin places a larger area of the nozzles in an increased compressive state giving further assurance of a low probability that a flaw would initiate. Therefore, supporting the conclusion that a follow-up inspection in the N+1 outage is not necessary.

5.4.4 Depth of Compression The minimum OD and ID depth of compression per MRP-335 is 0.04 inch and 0.01 inch respectively. UHPCP consistently achieved a demonstrated depth of compression that met or exceeded MRP-335 requirements per section 6.0 of the Summary Report [14] . The depth of OD compression was from 0.04 to 0.06 inch for RPVHPNs. The depth of ID compression was from 0.01 to 0.05 inch for open penetrations. The depth of ID compression was from 0.01 to 0.02 inch for annulus penetrations (containing thermal sleeves) and the vent penetration.

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The depth of compression results meet and exceed the requirements specified in the MRP-33-95 and therefore provide compressive stresses to a deeper level of the nozzles. This increased compressive state reduces the potential that a small pre-existing flaw would grow to a detectable size in one cycle. Therefore, supporting the conclusion that a follow-up inspection in the N+1 outage is not necessary.

5.4.5 XRD Accuracy and Effect on Cavitation Peening The post peening stress accuracy is documented in the Qualification Report and typically within +/-1 to +/-3 ksi for the nozzle (Alloy 600) and+/- 5 *8f-to +/- 13 ksi for the J-groove weld (Alloy 182). The internationally recognized best practices for instrument calibration and validation of results as defined in the ASM Handbook was used for XRD measurements per the Summary Report, section 7.0 [14] .

The stress results were repeatable for nozzle material (Alloy 600) with a standard deviation of +/-0.9 ksi and repeatable with a standard deviation of +/-0.7 ksi for J-groove weld material (Alloy 182). Likewise, the stress results were reproducible for nozzle material (Alloy 600) with a standard deviation of +/-0.3 ksi and reproducible with a standard deviation of +/-0.3 ksi for J-groove weld material (Alloy 182).

In accordance with MRP-335 Performance Criterion 2.3.6, residual stress measurement uncertainty has been considered when assessing the surface stress after peening and presented in the Special Process Qualification Report

[7] . XRD was performed using the multiple exposure technique with a minimum of 22 4J (psi) angles to increase accuracy of results per SAE HS784 with the best accuracy on the surface of the nozzle (Alloy 600). In addition , an independent third party laboratory confirmed the XRD methodology used by AREVA and validated process repeatability and reproducibility . Since the Special Process Qualification Report used median surface stress XRD values, the reported measurement error (i.e., - -+/-3 ksi for Alloy 600 and +/-13 ksi for Alloy 182) is bounded. Thus, XRD uncertainty associated with AREVA UHPCP does not impact the residual plus operating stresses on peened nozzles as qualified in the SPQR [7] . This is attributed to the highly accurate XRD process that was selected .

The highly accurate and reproducible XRD results increase the confidence that the residual stresses and depth of compression are representative of actual stress conditions of the nozzles and weld materials. Therefore, supporting the increased compressive state that reduces the potential that a small pre-existing flaw would grow to a detectable size in one cycle and that a follow-up inspection in the N+1 outage is not necessary.

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 18 of 23) 5.4.6 Technical Rigor Additional technical rigor was applied to the peening process beyond the requirements of MRP-335 through additional testing to ensure peening does not adversely affect the RVCH nozzles.

Demonstration of No Adverse Effects Qualification testing and analysis verifying the lack of adverse effects including the items covered by MRP-335 Performance Criterion 4.3.8.4 are documented in the Qualification Report and MRP-335. A summary of the specific testing and analysis is documented in Reference 7 and is provided below:

The effect of peening on surface roughness and inspectability was evaluated.

Surface roughness measurements were compared before and after peening on representative mock-up test coupons, using bounding values of peening parameters. The testing confirmed that the surface roughness was not significantly increased by the bounding values of peening parameters, and that the maximum surface roughness does not affect the capability to perform qualified NDE methods i.e., UT Time of Flight Diffraction+Gm, Penetrant Testing (PT) and Eddy Current Testing+. Refer to the Special Process Qualification Report, Appendix A and section 11 .10.

The effect of peening to induce surface cracking is evaluated. The absence of peening-induced cracks in the surface, after exposure to bounding values of peening parameters is confirmed . Refer to the Special Process Qualification Report, Appendix A.

The effect of transitions from peened to unpeened conditions on the magnitude of surface tensile stresses and on the likelihood of developing SCC cracks is evaluated. Testing verifies that the tensile stresses on the surfaces in transition regions from peened to unpeened conditions are not high enough to raise the risk of inducing PWSCC initiation. Refer to the Special Process Qualification Report, Appendix A.

The effect of flow induced vibration (FIV) on peened components or nearby components is evaluated. For water jet UH PCP of RPVHPNs with thermal sleeves, the integrity of the thermal sleeve and its connection to the nozzle will not be adversely affected by FIV. Likewise, there is no adverse impact to nearby components due to FIV. Refer to the Special Process Qualification Report section 11.4 and Appendix B.

The effect of over peening is evaluated . Erosion Testing demonstrates the margin , beyond the maximum allowed peening conditions required to result in adverse effects such as erosion , roughening , or development of cracks. By demonstrating a large margin factor prior to unacceptable damage, there is confidence that unacceptable damage will not occur. Results showed that continuous peening of a location would be required for over eight times (8X) exposure time prior to experiencing any detectable detrimental surface conditions. The peening process is controlled to ensure that such over peening does not occur. Refer to the Special Process Qualification Report, Appendix A.

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(Page 19 of 23)

The potential for adverse effects due to UHPCP is evaluatedhas also boon addressed by a safety evaluation per 10 CFR 50.59. The safety evaluation determined that peening the wetted RPVHPN surfaces has no adverse effects on maintaining leak tight integrity. It was concluded that ?peening i.vas oonoludod to increases the surface resistance to PWSCC on these surfaces.

Performance of the erosion testing confirmed that peening will not adversely affect the RVCH . This additional rigor was completed to increase the understanding of the enterprise risk impact related to implementation of the peening process.

Corrosion Testing to Confirm PWSCC Mitigated Effectiveness Corrosion testing for crack initiation and growth performed for the peening process is described in the SPQR [7] . Alloy 600 specimens were exposed to simulated nominal PWR primary environment to determine the extent of SCC of peened vs non-peened samples. The peened samples were peened to a compressive depth of 0.01 inch, which meets the minimum nozzle ID depth requirements. After the test period , all of the non-peened specimens were heavily cracked (crack indications and through wall cracks) . The peened specimens were visually examined , PT examined , cross sectioned and examined by scanning electron microscopy. None of the peened specimens revealed any evidence of PWSCC indications or significant change in grain boundary [7] .

Based on the above corrosion testing , the samples that were peened to the required nozzle ID depth of 0.01 inch did not exhibit any PWSCC; which is a depth of only one fourth (1/4) of the outer surface peened depth requirement of 0.04 inch .

5.4.7 Deterministic Technical Basis A fully deterministic technical basis paper [17] has been published supplementing MRP-395 [9] with additional deterministic crack growth analyses , -demonstrating the acceptability of a 36-month UT interval for heads with previously detected PWSCC that operate at Tcold . This new analysis extends the deterministic analysis in MRP-395 by applying the 95th percentile factor, rather than the standard 75th percentile per ASME Section XI. This new analysis exceeds the ASME approach and supports the 36-month inspection interval without crediting peening. On the basis of this technical analysis, a 36-month interval would continue to ensure that the nuclear safety and leakage (for defense in depth) concerns are conservatively addressed to support the additional request for relief from the Roforonoo 16MRP-335 Table 4-3 Note (11)(b) [16] requirement for inspection in the first refueling outage after peening .

5.4.8 Implementation Issues - fAREVA Condition Reporting (CR)

The following issue pertains to essential variables I critical parameters that were outside of qualified range during implementation of the B2R 19 Reactor Head Peening. This issue was evaluated per AREVA's 10 CFR Appendix B program via the CR Process and determined to not impact UHPCP results, providing assurance that nozzle 57 was peened in accordance with MRP-335 [16] .

Although there is a Condition Report Appendix contained in the post peening

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Summary Report [14], this CR is further discussed here since this CR pertains to essential variables I critical parameters that were outside of qualified ranges.

CR-2016-3107 - Nozzle 57 High Pressure Transducer Signal Errors:

While cavitation peening the OD of nozzle 57, system high pressure was shown to fluctuate between -53 ,000 psi to 0 psi and back to -53,000 psi over a period of seconds. High pressure is an essential variable and a minimum of 50,000 psi is required. By physical system design, high pressure cannot rapidly fluctuate in this short period of time, therefore the fluctuation in pressure was determined to be a signal error due to electrical equipment malfunction and not an actual drop in system high pressure. When the system high pressure fluctuations were occurring , the tool backpressure remained constant, which further confirmed that system high pressure was not fluctuating and the issue was related to an electrical equipment failure. The tool backpressure data output files were reviewed and confirmed that the tool backpressure remained constant and did not fluctuate. Therefore, this issue does not impact UHPCP results for nozzle 57.

5.5. Conclusions On the basis of the above, the applicable peening performance criteria of MRP-335 section 4.3.8 are satisfied and exceeded with significant margin considering coverage area and post peened residual plus operating stresses. The detailed qualification work shows that the required SSI is achieved , and that the required operating stress effect and depth of compression is sustained with sufficient margin for the remaining service life of the peened component. The N-729-1 inspection area was peened compared to the MRP-335 required +20 ksi region , thus demonstrating margin. A highly accurate XRD methodology was used that provided repeatable and reproducible results, supporting the stress measurements in the Qualification Report.

A 36-month inspection interval is demonstrated as acceptable by ASME deterministic crack-growth rate analysis confirming inspection during N+1 is not required, which is consistent with industry approved inspection requirements per Code Case N-729-5 [18] . Code Case N-729-5 has been approved by ASME to credit peening RPVHPNs consistent with MRP-335 [4] . In addition , the increased margins demonstrated in the Byron Station Unit 2 peening application support the conclusion that a follow-up inspection in the N+1 outage is not necessary.

On the basis that the MRP-335 section 4.3.8 performance criteria were met or exceeded in accordance with MRP-335 requirements, demonstrates that inspection of the peened RPVHPNs at the alternative schedule requested will provide an acceptable level of quality and safety. Pending follow-up examination (i.e., N+2 inspection) confirming no previous PWSCC present, the life of the peened RVCH penetrations is acceptable for a 60-year plant license [15] . Thus, in accordance with 10 CFR 50.55a(z)(1 ), it is requested that NRC authorize this proposed alternative.

6.0 DURATION OF PROPOSED ALTERNATIVE:

The proposed Alternative is requested for the remainder of the 4th lnservice Inspection Interval for Byron Station , Unit 2, currently scheduled to end on July 15, 2025.

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None

8.0 ACRONYMS

A LARA As Low As Reasonably Aohievable ASM American Society of Metals ASME American Society of Mechanical Engineers B&PV Boiler and Pressure Vessel CFR Code of Federal Regulations CETC Core Exit Thermocouple Column CR Condition Report CROM Control Rod Drive Mechanism EDM Eleotrioal Disoharge Maohining EDY Effective Degradation Year EPRI Electric Power Research Institute ET Eddy Current Testing FEA Finite Element Analysis FIV Flow Induced Vibration ID Inner Diameter ISi lnservice Inspection MRP [EPRI] Materials Reliability Program NOE Nondestructive Examination OD Outer Diameter PT [Liquid] Penetrant Testing PWR Pressurized Water Reactor PWSCC Primary Water Stress Corrosion Cracking RPV Reactor Pressure Vessel RPVHPN Reactor pressure vessel [upper] head penetration nozzle RVCH Reactor Vessel Closure Head sec Stress Corrosion Cracking SPQR Special Process Qualification Report SSI Surface Stress Improvement TOFD Time of Flight Diffraotion UHP Ultra High Pressure UHPCP Ultra High Pressure Cavitation Peening UT Ultrasonic Testing XRD X-ray Diffraction

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9.0 REFERENCES

1. ASME Boiler and Pressure Vessel Code,Section XI, "!:!R ules for lnservice Inspection of Nuclear Power Plant Components!!," 2007 Edition including 2008 Addenda

2. ASME Code Case N-729-1, ".!!Alternative Examination Requirements for PWR Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration Welds,Section XI, Division 1!!, " Approved March 28, 2006.

3. Final Safety Evaluation of The Electric Power Research Institute MRP-335, Revision 3, ".!!-Materials Reliability Program: Topical Report For Primary Water Stress Corrosion Cracking Mitigation By Surface Stress Improvement [Peening]!:,"

(TAC NO. MF2429)

4. Materials Reliability Program: Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement (MRP-335 Revision 3), EPRI ,

Palo Alto, CA: 2016. 3002007392. [available at www.epri.com]

5. Materials Reliability Program Generic Evaluation of Examination Coverage Requirements for Reactor Pressure Vessel Head Penetration Nozzles, Revision 1 (MRP-95R1), EPRI, Palo Alto, CA: 2004. 1011225. [Non-proprietary version: NRG ADAMS Accession No. ML043200602]

6. Materials Reliability Program: Technical Basis for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement (MRP-267, Revision 1), EPRI, Palo Alto, CA : 2012. 1025839. [available at www.epri.com)

7. AREVA Document No. 150-8086004-001, Special Process Qualification Record (SPQR), .! .SPQR, Qualification of the Cavitation Peening Process for RVCH Nozzles,"!! (EC 401061)

8. Materials Reliability Program: Technical Basis for Reexamination Interval Extension for Alloy 690 PWR Reactor Vessel Top Head Penetration Nozzles (MRP-375),

EPRI, Palo Alto, CA: 2014. 3002002441 . [available at www.epri.com]

9. Materials Reliability Program: Reevaluation of Technical Basis for Inspection of Alloy 600 PWR Reactor Vessel Top Head Nozzles (MRP-395) , EPRI, Palo Alto, CA:

2014. 3002003099.

10. Section titled .! .Shot Peening!!," page 131, ASM Handbook, Volume 5, "Surface Engineering", ASM, 1994.

11 . MRP Letter 2014-027, .! .Response to the NRG Request for Additional Information (RA/) related to Electric Power Research Institute (EPRI) MRP-335, Revision 1,

'Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement [Peening]' (TAC No. MF2429), "!! dated October 10, 2014. [NRG ADAMS Accession No. ML14288A370]

12. AREVA Analysis No. 32-9238505-001, .! .Byron/Braidwood RVCH Nozzle and Penetration Original Configuration Stresses!!, (Calculation B YR15-088)

II

13. AREVA Analysis No. 32-9241722-001, ' .!!.Byron & Braidwood Peening Residual Plus Operating Stress Analysis!!," (Calculation BYR15-090)

ISi Program Plan Unit 2, Fourth Interval 10 CFR 50.55a RELIEF REQUEST Byron Station 14R-14 Revision 10 (Page 23 of 23)

14. AREVA Document No. 51-8092600-001fl, Engineering Information Record,

"!!Summary Report, RVCH Peening Implementation, Byron Unit 2"!! (EC 400682)

15. AREVA Evaluation No. 51-9238120-002, "!!PWSCC Evaluation of UHP Cavitation Peening for Byron and Braidwood Reactor Vessel Head Penetrations!!," (Calculation BYR15-091)

16. Materials Reliability Program: Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement (MRP-335 Revision 3-A) , EPRI ,

Palo Alto, CA: 2016 . 3002009241 . [available at www.epri.com]

17. Deterministic Technical Basis for Re-Examination Interval of Every Second Refueling Outage for PWR Reactor Vessel Heads Operating at Tcold with Previously Detected PWSCC, No. PVP2016-64032, Copyright 2016 by ASME.

18. ASME Code Case N-729-5, "!!Alternative Examination Requirements for PWR Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration Welds,Section XI, Division 1!!, " Approved October 7, 2015.