ULNRC-06420, Request 14R-05 for Relief from Requirements of ASME Code Case N-770-2 Regarding Inspection Intervals for Reactor Vessel Nozzle Dissimilar Metal Welds

Request 14R-05 for Relief from Requirements of ASME Code Case N-770-2 Regarding Inspection Intervals for Reactor Vessel Nozzle Dissimilar Metal Welds

ML18099A120
Person / Time
Site:	Callaway
Issue date:	04/09/2018
From:	Wink R Ameren Missouri, Union Electric Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Case N-770-2, ULNRC-06420
Download: ML18099A120 (18)

Text

Amerell Callaway Phint MISSOURI April 9.2018 ULNRC-06420 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington. DC 20555-0001 10 CFR 50.55a Ladies and Gentlemen:

DOCKET NUMBER 50-483 CALLAWAY PLANT UNIT 1 UNION ELECTRIC CO.

RENEWED FACILITY OPERATING LICENSE NPf-30 REQUEST 14R-05 FOR RELIEF FROM REQUIREMENTS OF ASME CODE CASE N-770-2 REGARDING INSPECTION INTERVALS FOR REACTOR VESSEL NOZZLE DISSIMILAR METAL WELDS Pursuant to 10 CFR 50.55a(z)(1). Union Electric Company (Ameren Missouri) hereby requests NRC approval of the enclosed relief recJuest 14R-05.

The requested relief is intended for the fourth 10-year inseiwice inspection interval of the Callaway Plant. Unit I (Callaway) inservice Inspection (151) Program. With regard to the American Society of Mechanical Engineers (ASME) Boilet and Pressure Vessel Code. i.e..Section XI. Rules and Inservice Inspection of Nuclear Power Plant Components, the Code Edition and Addenda applicable to Callaways fourth 10-year ISI interval is the 2007 Edition through 2008 Addenda.

Relief is requested from the inspection frequency requirements. as incorporated by reference in 1 0 CFR 50.55a(g)(6)(ii)(f), of ASME Code Case N-770-2. Inspection Item A-2. Unmitigated butt weld at Hot Leg operating temperature 625°F (329°C), and Inspection Item B, Unmitigated butt weld at Cold Leg operating temperature. As an alternative to the inspection fiequency requirements above, Arneren Missouri proposes that the inspections be conducted in accordance with the inspection requirements for Alloy 82/182 dissimilar metal welds mitigated by water-jet peening. based on hem L of Table 4-1 in MRP-335, Revision 3A, Materials Reliability Program: Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement. (November 2016) on the basis that the proposed alternative provides an acceptable level of quality and safety.

P.O. Box 620 Fulton, MO 65251 AmerenMissouncOrn

ULNRC-06420 April 9,2018 Page 2 of4 Supporting information and essential details. including proposed alternative and basis for use. is provided in the attached relief request. Ameren Missouri respectfully requests approval of relief request 14R-05 by April 5, 2019.

This letter does not contain new commitments.

If there are any questions, please contact Jim Kovar at 314-225-1478.

Sincerely, Pt4 Roer C. Wink.

Manager, Regulatory Affairs JPK/

Enclosure:

10 CFR 50.55a Request Number 14R-05

U LN RC-0 642 0 April 9,201$

Page 3 of 4 cc: Mr. Kriss M. Kennedy Regional Administrator U. S. Nuclear Regulatory Commission Region IV 1 600 East Lamar Boulevard Arlington. TX 76011-4511 Senior Resident Inspector Caltaway Resident Office U.S. Nuclear Regulatory Commission

$201 NRC Road Steedman. MO 65077 Mr. I. John KIos Proj ect Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop O$F14 Washington. DC 20555-0001

U LN RC-06420 April 9,2018 Page 4 of 4 Index and send hardcopy to QA File A 160.0761 II ard copy:

Ceilrec Corporation 6100 Western Place. Suite 1050 Fort Worth. TX 76107 (Certrec receives ALL attachments as long as they are non-safeguards and may be publicly disclosed.)

Electronic distribution for the following can be made via Other Situations ULNRC Distribution:

F. M. Diya T. F. Herrinann S. P. Banker S. L. Abel B. L. Cox R. C. Wink T. B. Elwood A. W. Alley W. P. Muskopf Corporate Communications NSRB Secretary STARS Regulatory Affairs Mr. Jay Silberg (Pillsbury Winthrop Shaw Pittman LLP)

Missouri Public Service Commission

10 CFR 50.55a Request Number 14R-05 Proposed Alternative In Accordance with 10 CFR 50.55a(z)(1)

--Alternative Provides Acceptable Level of Quality and Safety-

1. ASME Code Component(s) Affected The components coveted under relief request 14R-05 include four dissimilar metal (DM) Hot Leg butt welds and four DM Cold Leg butt welds on the reactor vessel tRy). The dissimilar metal welds (DMWs) are detailed in Table 1 Table 1: Large Bore RV Nozzle Dissimilar Metal (DM) Butt Welds Nominal Weld Code Inner

. . Weld Description . .

Diameter Wall Designation Class . Thickness (inches)

(inches) 2RV301J21A* 1 Loop 1 outlet nozzle to safe-end 28.97** 2.925**

2RV301121B* 1 Loop 2 outlet nozzle to safe-end 28.97** 2.925**

2RV301121C* 1 Loop 3 outlet nozzle to safe-end 28.97** 2.925**

2RV301121D* 1 Loop 4 outlet nozzle to safe-end 28.97** 2.925**

2RV3O2121A* 1 Loop 1 inlet safe-end to nozzle 27.47** 279**

2RV302121B* 1 Loop 2 inlet safe-end to nozzle 2747** 2.79**

2RV302121C* J Loop 3 inlet safe-end to nozzle 27.47** 279**

2RV302121D*

Reference 8.27 1

J Loop 4 inlet sate-end to nozzle 27.47** 2.79**

Reference 8.28

2. Applicable Code Edition and Addenda

The current inservice inspection program at the Callaway Plant, Unit 1 (Callaway) is based on the ASME Code, Section Xl, 2007 Edition with 2008 Addenda. Examination of the Table 1 welds is performed in accordance with 10 CFR 50.55a(g)(6)(ii)(F) which specifies the use otASME Code Case N-770-2 with conditions.

The code of construction for the Reactor Pressure Vessel is ASME Section III, 1971 Edition through Winter 1972 Addenda.

3. Applicable Code Requirement

The dissimilar metal welds of Table 1 are fabricated from Alloys 82 and 182 and thus fall under the requirements of ASME Code Case N-770-2 as stated in Section 2 above. The Hot Legs as described in the code case are Inspection Item A-2, Unmitigated butt weld at Hot Leg operating temperature 625°F (329°C), and the Cold Legs are Inspection Item B, Unmitigated butt weld at Cold Leg operating temperature. inspection item A-2 requires an examination frequency of every 5 years, and Inspection Item B requires an examination frequency of every second inspection period not to exceed 7 years.

As an alternative to the inspection frequency requirements above, Union Electric Company (Ameren Missouri) proposes the inspections to be conducted in accordance with the inspection requirements for Alloy 82/1 82DM welds mitigated by water jet peening, based on Item L of Table 4-1 in MRP-335, Page 1 of 14

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Revision 3A, Materials Reliability Program: Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement, November2016 (Reference 8.3).

4. Reason for Request Ameren Missouri has implemented the Water Jet Peening (WJP) process on the Callaway Hot and Cold leg butt welds identified above in Table 1, and are requesting a change to the reexamination interval of the follow-up inspections for the peened welds in accordance with MRP-335 Item L Table 4-1.

As discussed in Section 3 above, N-770-2 requires examination of the Hot Legs every 5 years and the Cold Legs every 7 years at a maximum. The examination schedule of N-770-2 does not address the effects of Surface Stress Improvement (SSI) by WJP or the associated inspection frequency for DM butt welds in this mitigated state. The Electric Power Research Institute (EPRI) developed, using analytical tools, an appropriate re-examination frequency for Alloy 600/82/182 DM welds that have had WJP performed. (See Section 5.1.1 for Proposed Alternative details.) The MRP-335 technical basis demonstrates that for any uncracked DM butt welds mitigated by a peening process meeting the performance criteria in Section 4.2.8 of MRP-335, the re-examination interval can be changed to the Table 4-1 inspection schedule found in MRP-335. Probabilistic analyses have shown that the application of peening coupled with the required post-peening inspection schedules results in reduced safety risk as compared to that associated with unpeened components inspected at the currently required schedule.

As described in detail in Section 5.4 below, the WJP process implemented at Callaway meets the performance requirements specified in MRP-335.

5. Proposed Alternative and Basis for Use 5.1. Introduction The WJP process implemented at Callaway was developed by vendor Mitsubishi Heavy Industries (MHI) for use in Japan and has been successfully implemented on the Reactor Vessel nozzles in the Japanese PWR fleet (Reference 8.4). It was brought to the United States (US) by MHI subsidiary MNES (Mitsubishi Nuclear Energy Systems); where MHI and MNES are referred to hereafter as Mitsubishi. Mitsubishi has classified WJP as a Special Process in accordance with 10 CFR 50 Appendix B. Qualification of the Mitsubishi WJP process on primary DM butt welds such as the welds identified in Section 1 above is documented in DUS-1 50319 and the Technical Report (References 8.5 and 8.4 respectively).

Peening Mechanism for PWSCC Mitigation When the applicable MRP-335 performance criteria are met, peening mitigation prevents initiation of PWSCC (Reference 8.3). The possibility of pre-existing flaws that are not detected in pre-peening NDE is identified through the required follow-up inspections. Peening also has the benefit of arresting PWSCC growth of shallow surface flaws that are located in regions at the surface where residual plus normal operating stress is now compressive (References 8.3 and 8.4).

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 (Reference 8.3) is a conservative lower bound of the stress level below which PWSCC initiation will not occur. This threshold stress of Page 2 of 14

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+20 ksi 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 a more compressive value (0 ksi) for the case of DM butt welds.

For their safety evaluation (Reference 8.3) the NRC reviewed the MRPs deterministic analysis and performed independent calculations to determine if any missed PWSCC or fabrication flaws in the DM butt welds could threaten the structural integrity or leak tightness of the DM butt weld. The NRC staff determined that the use of eddy current examinations in combination with volumetric examinations at the time of peening and in subsequent inspections provide reasonable assurance that a flaw would be detected. It would be detected either at the time of peening or, if not, it would be detected during subsequent inspections prior to affecting plant safety.

Stress Effect to Prevent Future PWSCC Initiations The compressive residual stress depth requited by the performance criteria ensures that the stress improvement effect extends an effective distance into the material. As documented in Reference 8.7 Section 20.1.3, the WJP process implemented at Callaway met the MRP-335 depth-of-compression requirements. As stated above, the NRC determined that preexisting flaws are effectively identified by the pre-peening and follow-up inspections that are required per the NRCs safety evaluation. In the case of a shallow pre-existing flaw located within the region of compressive residual plus operating stress, PWSCC growth of the pre-existing flaw would be arrested by peening (References 8.3 and 8.4).

Effect of Pie-Existing Residual Stresses High residual tensile stresses do not interfere with the ability of peening to develop the stress effect needed to be effective (Reference 8.3). The peening effect is self-normalizing with regard to the level of pre-peening residual stresses (Reference 8.3). 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.

5.1.1. Proposed Alternative Ameren Missouri, owner and operator of Callaway, is requesting relief from the examination frequency requirements of 10 CFR 50.55a(g)(6)(ii)(F) which requires in-service volumetric inspection of DMWs in accordance with ASME Code Case N-770-2 (Reference 8.2) with conditions. Specifically, relief is requested to allow the inspections to be conducted in accordance with the inspection frequency requirements for Alloy 82/182 DM welds mitigated by WJP, based on Item L of Table 4-1 in MRP-335, Revision 3A (Reference 8.3).

The alternative inspection frequency requires a pre-peening inspection, follow-up inspection, and subsequent in-service inspection, as summarized below:

Pre-Peening Baseline Inspection Prior to implementation of peening but during the same outage, examinations are to be performed in accordance with the requirements in MRP-335 Table 4-1, Note 19 (Reference 8.3). Examinations include an ultrasonic examination of the weld and an eddy current inspection of the weld inner surface.

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Follow-Up Inspection During the follow up inspection(s), volumetric examination of the required volume and surface examination of the required area are performed in accordance with the requirements in Table 4-1 (Reference 8.3). The follow-up inspection schedule depends on the operating temperature of the welds (as applicable to the Callaway design basis):

• For hot leg piping DMWs with normal operating temperature equal to or below 625°F, the follow-up inspections are to be performed within 5 years following the application of peening and a second examination within JO years following the application of peening.

• For cold leg DMWs, a follow-up inspection is to be performed within 10 years but no sooner than the third refueling outage following the application of peening.

Subsequent SI Program The in-service inspection requirements for peened DMW5 after completion of the follow-up inspection(s) are shown in Table 4-1 (Reference 8.3). Examinations include surface and volumetric examinations of 100% of the peened DMWs once each Section Xl inspection interval (nominally 10 years).

5.2. Description of Application Specific Process The Mitsubishi WJP process was used at Callaway for its mitigating effect on PWSCC by its creation of a thin layer of residual stresses on the wetted surface of the susceptible Alloy 82/182. This leaves the surface in a residual stress state of biaxial compression which does not allow cracks to initiate and therefore prevents PWSCC. The WJP process is controlled within key critical parameters and ranges which not only ensure the mitigation effect is attained (improved residual stress) but also prevents the potential of excessive cavitation-induced erosion by the peening process, which could harm the component material and its integrity. Qualification testing (Reference 8.5) and analyses (References 8.4 and 8.14) have confirmed the levels and depths for which a residual stress state of compression required to mitigate and prevent PWSCC can be achieved with the WJP process.

5.2.1. Description of Peened Components and Peened Area Alloy 82/182 DM butt welds were used on the reactor vessel nozzles (RVN5) [Hot and Cold Legs] listed above in Section 1 to attach a stainless steel safe-end to the low alloy steel nozzle of the RV. The area peened was the entire wetted surface of the susceptible material in this region of the RVN. The extent of the Alloy 82/1 82 buttering and weidment (at the safe end and nozzle ends) was first determined by ECT using the WJP RVN tool prior to initiation of WJP. The tooling is fixed in place inside the nozzle before the ECT process and does not move until the WJP operation has been completed.

The ECT technique used to find the boundaries of the PWSCC susceptible material in the RVNs is based on changes in background impedance between the different components of the nozzle to safe-end weld. The process is empirical based on observations from WJP performed on many plants in Japan and was validated by mockup testing for application in the US at Callaway. It is observed on an eddy current scan of the location of interest that the background impedance is highest when the ECT probe is on the stainless steel cladding of the forged nozzle, at an intermediate level on the Alloy 182 weld metal (buttering and weld), and at the lowest level on the stainless-steel safe-end.

Once the extent of susceptible material was determined, then supplemental coverage area was added to address the tolerance/uncertainty stack up of the WJP tooling. In addition to this equipment-imposed Page 4 ofl4

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stack up, additional coverage areas were considered/evaluated and added as necessary, to address industry/regulatory guidance on additional margin. Details of this effort are provided in DUS-150354 (Reference 8.6).

For WJP of RVNs, the WJP nozzle path is a simple internal circumferential pass with no axial motion other than repositioning of the WJP nozzle from one pass to the next. In order to ensure that the path followed by the WJP nozzle achieves the desired peening effect, the coverage areas must be mapped onto the WJP nozzle path. The WJP nozzle paths are controlled by the operators, tooling, and WJP software, and are actively monitored and recorded to demonstrate that effective peening and coverage are achieved.

5.12. Process Description Performance demonstration is the method used to ensure that peening fully covers all the areas being mitigated, 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 the peened areas (References 8.5 and 8.7). Reference 8.5 is the qualification report that demonstrates desired results are achieved per MRP-335 with a bounded set of parameters. The implementation travelers, work instructions, and Special Process Plan ensure the entire process is implemented per the requirements in the qualification plan and that it meets special process requirements. During the implementation process, critical parameters are recorded for each RVN. As part of implementation efforts, the tooling software and recorded data are validated by pre and post functional implementation checks. Data output files and plots are provided in the Final Report (Reference 8.7) to document and log the performance results of the as-implemented WJP process.

Reviews performed on the critical parameters are documented in the Final Report and confirm performance demonstration of peening at each nozzle (Section 17 and Appendix F of Reference 8.7).

Surface Condition Considerations As described in Reference 8.12, the WJP process is intended for application to bate metal surfaces and is suitable for the normal range of fabricated surface finishes (as-fabricated base metal, machined surfaces, weld metal as deposited or after surface grinding), It is also suitable for surfaces covered by the normal, thin oxide layer that forms under operating conditions in primary coolant. Therefore, no preparations of the surfaces to be peened are required before peening is performed.

Pre-Peening NDE The pre-peening DM butt weld NDE inspection was performed in accordance with MRP-335 Table 4-1 Note 19. The inspection report stated No indications for both the UT exam and ECT for each of the RV Hot Leg and Cold Leg DM welds. In addition, 100% coverage of the Code-required volume (UT requited exam volume) was obtained for all the Hot Leg and Cold Leg DM welds.

Contingencies If critical parameters go outside of the specified range during the peening process, the operators are notified via software alarms and the process is shutdown. If peening is stopped for any reason, the process is restarted in accordance with the approved peening process procedures to ensure achievement of critical parameters and adequate peening coverage. A non-conformance report (NCR) is issued if any action is required that is outside of the approved peening process procedures and appropriately evaluated by MNES and Ameren Missouri, Copies of the implementation NCRs are included in Appendix D of the Final Report (Reference 8.7).

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5.3. Performance Criteria The following is an overview of MRP-335 (Reference 8.3) performance criteria requirements for WJP.

The Callaway implementation demonstrated meeting these requirements, as addressed below in Section 5.4.

Peeninq Coverage The required coverage is the full area of the susceptible material along the entire wetted surface under steady-state operation. Susceptible material includes the weld, butter, and base material, as applicable. The coverage shall be extended at least 0.25 in (0.64 cm) beyond the susceptible material.

Stress Magnitude The residual stress plus normal operating stress is compressive on all peened surfaces.

Depth of Effect The compressive residual stress field extends to a minimum nominal depth of 0.04 in (1.0 mm) on the susceptible material along the wetted surface.

Sustainability of Effect The mitigation process is effective for at least the remaining service life of the component, i.e., the residual plus normal operating surface stress state after considering the effects of thermal relaxation and load cycling (i.e., shakedown) must remain compressive.

Inspectability The capability to perform ultrasonic examinations of the relevant volume of the component is not adversely affected, and the relevant volume is inspectable using a qualified process. The capability to perform eddy current examinations of the relevant surface of the component is not adversely affected.

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 HotlCoId Leg Nozzles Implementation Results 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 it is a special process, it is required to be controlled in a manner consistent with Appendix B Criterion IX, Control of Special Processes.

Per 10CFR5O Appendix B, Criterion IX, the following Special Process categories are considered relevant and form the basis for the special process implementation of Water Jet Peening at Callaway:

• Qualification of Process

• Qualification of Equipment

• Qualification of Procedures

• Qualification of Personnel Below is a brief summary of each category; for more detailed information, see the Special Process Plan for Water Jet Peening (Reference 8.8).

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Qualification of Process The WJP process has undergone a significant testing effort to effectively validate the WJP process attributes. The WJP process attributes validated in DUS-1 50319 (Reference 8.5) provide evidence that when applied and controlled, effective peening can be achieved.

Qualification of Equipment All equipment associated with the WJP project underwent a documented factory acceptance testing (FAT) program to verify all functionality is within defined acceptance criteria. All WJP and support equipment FATs have been successfully completed.

An Integration Testing program has also been completed and has proven that the W]P tools and support equipment are satisfactory qualified for use as an integrated WJP process delivery system.

Accordingly, this means that the equipment has been suitably qualified and demonstrated to be able to deliver the WJP treatment within the established critical parameter acceptance criteria. More detailed information on the equipment qualification is provided in the Special Process Plan for WJP (Reference 8.8) and/or the Final Report (Reference 87).

Qualification of Procedures and Personnel This project utilized implementation Travelers, supported by Work Instructions and Procedures, to implement the WJP process in accordance with an approved Appendix B QA program. These documents controlled the overall implementation of WJP, including equipment operation. Appropriate Quality Control inspection criteria were integrated into the procedures to provide assurance that the safety-related aspects of the Special Process were documented and found acceptable. Inclusion of calibration verification related to the critical parameters provided reasonable assurance of the validation of equipment and software operation when combined with training, qualification and procedures implemented through an approved Appendix B QA program.

The program for qualifying Travelers, Work Instructions, and Procedures for personnel who utilized them ensured that implementation personnel exhibited operational understanding and proficiency as it relates to the equipment and processes. Prior to deployment, a comprehensive process demonstration was also performed as part of the qualification program in order to effectively demonstrate control of the equipment and process through Travelers, Work Instructions, and Procedures, as applicable. This entire program provided QA controls for the process.

The use of qualified personnel and procedures ensured that the critical parameters were controlled and monitored within acceptable limits of the qualified ranges and acceptance criteria established by the process qualification documented in DUS-1 50319 (Reference 8.5). The Final Report (Reference 8.7) contains the Special Process related personnel qualifications and certifications (Appendix E) and the implementation Travelers and Work Instructions (Appendix B).

Critical Process Parameters and Acceptable Values MRP-335 Performance Criterion 4.2.8.1 requires testing to 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. Testing was performed and has been documented in DUS-150319 (Reference 8.5).

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Demonstration that the stress improvement parameters are met is provided, in part, by verification that all of the critical parameters were maintained within the specified ranges during the application of WJP.

The peenihg process parameters were maintained and verified within abceptable ranges (Final Report Section 17 and Appendix F) with one evaluated exception (see NCR SP-17-052 overview below). As described in the Special Process Plan (Reference 8.8), the computer performs a data acquisition function to save a record of equipment actions and process parameters in one second intervals. The data was reviewed by MNES to confirm acceptability. The critical parameters and acceptable ranges for WJP at Callaway are provided in PMP-TSP-13 (Reference 8.11), which is based upon the process qualification and testing program found in DUS-1 50319 (Reference 8.5).

NCR SP-17-052 Post Flow Calibration The post-WJP flow calibration check for the A high pressure pump system (HPPS) was found to be out of tolerance. Review of the issue showed the adjusted actual lowest recorded flow rate was 4484 liters/minute (Llmin) (occurring for no more than three seconds during the entire WJP implementation) which equates to an approximate 0.36% deviation from the minimum allowed of 45 L/min. This deviation is considered insignificant since at the recorded location on the associated previous scanning steps, the adjusted flowrate was greater than the 45 L/min minimum. Additionally, since there is a relationship with the implementation time and scanning step speed (application time), there is additional margin relative to time of peening.

Specifically, the recorded application time was consistently 98 mm/mm which is 2% longer than used during the qualification test (DUS-1 50319 Reference 8.5). The non-conformance report (NCR) concluded, based on known quantifiable margins available from the process qualification, that the deviation was insignificant and the WJP was acceptably performed.

Further details on the evaluation are provided in NCR SP-17-052 (Reference 8.7 Appendix D) 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 meets the required stress magnitude and depth and that the required stress effect will be sustained for at least the service life of the peened components. The testing and analysis are documented in DUS-150319 (Reference 8.5) and 1001077.305 and 1001077.323 (References 8.13 and 8.14), as discussed below.

Residual Stress Measurements Using Representative Test Coupons Qualification testing (Reference 8.5) was performed that met the requirements of MRP-335 Performance Criterion 4.2.8.1. The testing was performed on coupons manufactured from a plate of Alloy 600 weld metal. The test coupons were thinner than the actual components on the reactor vessel, but are thick enough to be representative and have similar behavior to the RVN locations that were peened at Callaway. Additional details on the test program and configuration are presented in DUS 150319 (Reference 8.5).

Following the WJP treatment of the specimens, residual stress measurements were performed using the X-ray diffraction method. The X-ray diffraction method was used to measure the residual stress at various depths after electro-chemical etching of the coupons. At each location, residual stress measurements were performed in two directions: along the weld (equivalent to hoop stress) and perpendicular to the weld direction (equivalent to axial stress). Surfacemnspections to verify integrity of the material were also performed using visual methods.

As a result of this testing; critical parameters were developed that identified the minimum and maximum application ranges for effective WJP treatment. The tests demonstrate that under all test conditions Page 8 of 14

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applied, the WJP process creates a surface layer of compressive residual stresses to a minimum depth of 1.0 mm (0.04 in) (MRP-335 Performance criterion 4.2.8.1.2). The tests have verified that as long as the WJP process is applied using process parameters within the ranges identified in the testing, the required surface stress mitigation will be achieved with no adverse effect to material integrity.

It is important to note that the testing performed prior to implementation at Callaway was a re performance of legacy testing (Reference 8.26) performed as part of the Japanese PWR fleet WJP efforts nearly 20 years prior. All testing performed to support Callaway (Reference 8.5) by comparison did not result in any changes in critical parameters which were effectively implemented on the Japanese PWR fleet.

Post Peening Residual plus Operating Stress MRP-335 Performance Criterion 4.2.8.2 requires that analysis or testing shall be performed to verify that the peening process maintains the compressive surface stress condition for at least the remaining service life of the component.

Stress analysis used finite element models (FEM5) to show that the WJP process adequately mitigates potential PWSCC of the RV Hot and Cold Leg nozzle to safe-end DM butt welds. The residual stress state prior to peening is calculated by simulating the key steps during plant construction and applying five operating cycles. Full details of the evaluations performed to obtain the pre-peening stress state are discussed in Section 5 of Reference 8.14.

The peening effect is then created in a FEM using a two-step pressure application process (Reference 8.13). Before the pressure application is imposed on the model, a selection of nodes around the region to be peened is fixed. After the nodes are fixed, a static pressure load is applied to the surface of the peening area. The pressure values are selected to provide the level of compression that has previously measured in the test data. The model results, when compared to test results, were conservative but the general slope of the compressive stresses and the depth is in agreement with the testing data.

Following the WJP effect, the thermal transients and piping loads are applied to determine the residual stress washout potential (shakedown). Full details of the shakedown analysis are provided in Reference 8.14. The key results of the WJP and the subsequent loss of residual stress due to shakedown are summarized in the table below.

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Tensile Axial Stress -49,545 -45,033 4,511 (Pull)

Shakedown Load Hoop Stress -34,559 -30,045 4,514 Compressive Axial Stress -63351 -46,942 16,409 (Push)

Shakedown Load Hoop Stress -36,364 -26,427 9,937 Notes: 1) The reported stress is the averaged stress over the DMW region.

2) Negative stress denotes compression.

3) Operating conditions are operating temperatures and pressure and operating nozzle loading (pressure, deadweight, and operating thermal).

Despite the residual stress loss due to shakedown, in all load cases, for both axial and hoop stresses, it is shown that the majority of the compressive residual stress generated by WJP is maintained following the operating conditions and that these compressive stresses are sufficient to mitigate PWSCC.

Therefore, the effectiveness of peening is shown to be permanent, thus meeting Performance Criterion 4.2.8.2 of MRP 335.

As a part of developing the technical basis and verifying the sustainability of WJP, Mitsubishi performed testing to demonstrate stability of the WJP effect under plant operating conditions. This testing was done to show how WJP-mitigated components behave over time as the plant is operated. Thermal aging tests were carried out at three different temperatures. In addition to temperature testing, the cyclic stresses associated with plant startup and shutdown were simulated and tested. Details of this testing effort are provided in DUS-140030 (Reference 8.12). Results of the testing concluded that the compressive stresses generated by WJP are stable and will be maintained for plant life.

X-Ray Diffraction As required by MRP-335, the uncertainty in residual stress measurements shall be considered when assessing the measured surface stress after peening. Mitsubishi performed an assessment of the x-ray diffraction technique that was used to determine residual stresses in the Appendix B qualification testing. DUS-160056 (Reference 8.23) describes the verification of Mitsubishis measurement instrumentation using the x-ray diffraction technique, and how the results are evaluated to develop actual residual stress measurement values. As stated in the Mitsubishi document, ASTM Standards F915 and E2860 are utilized as references for the assessment of measurement uncertainty. In general, the acceptance criteria for results uncertainty are that the averaged measured values out of five measurements should be within 14 MPa (2.0 ksi), and the standard deviation of the five measurements should be within 6.9 MPa (1.0 ksi). The Mitsubishi document indicates that the material microstructure does have an impact on the measurement and that adjustments in technique are required to address different grain or texture components, and it also describes adjustments made to produce measured results.

The measured results demonstrate compressive stresses (<0) to the specified depths (Reference 8.5),

and that the threshold for crack initiation is at least 20 ksi (Reference 8.3), thus providing margin for acceptance of the measured uncertainties listed above.

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5.4.3. Peening Coverage MRP-335 Performance Criterion 4.2.8.1 requires the susceptible material along the entire wetted surface under steady-state operation to be mitigated, including the weld, butter, and base material as applicable. In addition, to provide high assurance that the susceptible areas are covered, the area to be peened shall extend at least 0.25 in (0.64 cm) beyond the susceptible area.

WJP Coverage of the susceptible areas as applicable to RVNs are defined in Document DUS-J 50319 (Reference 8.5) and DUS-1 50354 (Reference 8.6), as described in the Technical Report (Reference 8.4).

First, the dissimilar weld boundaries were identified using qualified ECT techniques. Then, prior to peening the RVNs, a predetermined coverage scheme (Reference 8.6) was defined which accounted for the spray width from the WJP nozzle, spray overlap between passes, and spray coverage relative to edge of DMWs. As found in this reference document, a value of 13.4 mm is used to establish the extent of coverage beyond the edge of susceptible Alloy 600 material for the RVNs. These numbers were inputs into the RV nozzle dissimilar metal weld evaluations (References 8.15 thru 8.22) which were used to determine the software inputs to define the peening area and number of required peening passes. As a part of the evaluation the required coverage beyond the edge of susceptible material is verified to be acceptable.

The control software for the WJP tooling guides the WJP nozzle along a predefined path that assures coverage of the defined surface areas at an appropriate speed to ensure effective peening. The WJP software is non-safety related (Reference 8.29), so it was implemented as a commercial software in accordance with ISO standards. Its accuracy was confirmed by pre- and post- functional tests, and measurements were made by transducers that were calibrated and verified by M&TE procedures. This provided assurance that the software and equipment performed as designed during implementation and that it created a data base record of the implementation process for historical documentation. As a result, the position of peening (coverage) performed can be confirmed by the .csv files (data base records) (Appendix F of Reference 8.7).

Based on a detailed review of the completed dissimilar weld evaluations (Appendix B of Reference 8.7) and data files (.csv files) (Appendix F of Reference 8.7), coverage of the RVNs has been confirmed. As concluded from the weld evaluations and .csv files analysis, the MRP-335 (Reference 8.3) requirement to have at least 0.25 in (0.64 cm) beyond edge of the DMW has been achieved.

5.4.4. Depth of Compression Effect MRP-335 Performance Criteria 4.2.8.1.2 states that testing shall demonstrate that the nominal depth of the compressive surface residual stress field produced by the peening technique is at least 0.04 in (1.0 mm).

Per Reference 8.5, as a result of testing, critical parameters were developed that identified the minimum and maximum application ranges for effective WJP treatment. The tests demonstrate that under all test conditions applied, the WJP process creates a surface layer of compressive residual stresses to a minimum depth of 0.04 in (1.0 mm). Based on the review of the RVN .csv files (Section 17.0 of Reference 8.7), critical parameter application ranges were achieved during peening at Callaway such that the experimentally achieved depth of compressive residual stress, i.e., 0.04 in (1.0 mm) has been achieved.

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10 CFR 50.55a Request Number 14R-05 Proposed Alternative In Accordance with 10 CER 50.55a(z)(1)

--Alternative Provides Acceptable Level of Quality and Safety-5.4.5. Technical Rigor Additional technical rigor was applied to the peening process, beynd the requirements of MRP-335, through additional testing to ensure peening does not adversely affect the RV nozzles DMWs.

Lack of Adverse Effects Qualification testing (Reference 8.5) identified critical parameters and their acceptable ranges of application. Qualification Test #5 used parameters that would maximize the peening effect when at the upper limit application time of 240 minutes/meter (mm/rn). Also included in the testing was WJP application without moving for two minutes (stuck nozzle). The results of the testing were that there were no defects or abnormal structures, thus confirming there is no adverse effect of WJP application within these application conditions.

As a contingency, Mitsubishi performed additional testing (Reference 8.24) that increased the existing qualified upper application limit from 240 min/m to 480 mm/rn. Again, testing confirmed no adverse effect of WJP application with this increased application time.

Review of the RVN .csv files confirms that critical parameter ranges during peening stayed within the values identified in the initial qualification testing, thus confirming no adverse effects during peening at Callaway.

In addition, after WJP was complete at Callaway, to ensure there were no resultant adverse effects to the plant components, a formal VT3 was conducted on each of the RVNs. The exams found no indications or abnormalities (Reference 8.25).

lnspectability As found in Section 5.0 of Reference 8.4, it has been documented that peening will result in no adverse impact on the surface, using VT and PT, and that no adverse surface profile change occurs.

Additionally, in References 8.4 and 8.9, the documented success for re-exams of Japanese plants for which WJP was applied, is discussed therein. There is no geometry change, no significant increase in surface roughness, and no measurable change in surface contour from peening.

EPRI concluded in Reference 8.10 that the capability to perform ECT and UT on a Mitsubishi WJP process peened surface was not adversely affected by the peening application.

5.4.6. Corrosion Testing to Confirm PWSCC Mitigation Effectiveness Mitsubishi performed corrosion testing for crack initiation and growth for the peening process (Reference 8.12). For these tests, the treated and untreated mock-ups were immersed in a MgCI2 solution for a total of 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />. The untreated sample experienced significant SCC in the test. The treated sample showed no SSC. The test clearly demonstrates that the mock-up contained tensile stresses in the un-treated condition since significant SCC developed from the test exposure. The WJP treated mock-up contained no SSC indications, demonstrating effective mitigation.

5.5. Conclusions On the basis of the above, the applicable peening Performance Criteria of MRP-335 Section 4.2.8 are satisfied, considering coverage area and post-peened residual plus operating stresses. The testing, analysis and implementation documentation show that the surface stress improvement was achieved Page 12 of 14

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and that the required operating stress effect and depth of compression is sustained with sufficient margin for the remaining service life of the reactor vessel nozzles.

On the basis that the MRP-335 Section 4.2.8 Performance Criteria were met, the inspection of the peened DM bull welds at the alternate schedule requested will provide an acceptable level of quality and safety. Pending follow-up examinations confirming no previous PWSCC is present, the life of the peened RVN DM butt welds is acceptable for a 60-year plant license. Thus, in accordance with 10CFR5O.55a(z)(1), it is requested that the NRC authorize the proposed alternative.

6. Duration of Proposed Alternative The duration of the proposed alternative is requested for the remainder of the fourth 10-year ISI interval at Callaway, which is currently scheduled to end on December 18, 2024.

7. Precedents (Optional)

Byron request (l4R-14) (NRC Docket No. 50-455) for Ultra High Pressure Cavitation Peening (UHPCP) based on MRP-335 was approved on September 19, 2017 (CAC No, MF9018).

8. References 8.1. ASME Boiler and Pressure Vessel Code, Section Xl, Rules for lnservice Inspection of Nuclear Power Plant Components, 2007 Edition including 2008 Addenda 8.2. ASME Code Case N-770-2, Alternate Examination Requirements and Acceptance Standards for Class I PWR Piping and Vessel Nozzle Butt Welds Fabricated with UNS N06082 or UNS W86182 Weld Filler Material with or Without Application of Listed Mitigation Activities, Section Xl, Division 1, Approved June 9, 2011.

8.3. 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.coml 8.4. Structural Integrity Document 1001077.401, Revision 0, Mitigation of Reactor Vessel Hot and Cold Leg Nozzle DMWs and Reactor Vessel Bottom Mounted Nozzles and Associated DMWs by Water Jet Peening [Callaway] (Referred to as Technical Report) 8.5. Mitsubishi Document DUS-150319, Revision 8, Water Jet Peening Process Qualification Test 8.6. Mitsubishi Document DUS-150354, Revision 8, Coverage of WJP Implementation 8.7. Mitsubishi Document NS-RPT-100004, Revision 0, WJP Implementation Final Report for Callaway 8.8. Mitsubishi Document PMP-TSP-09, Revision 3, Special Process Plan for Water Jet Peening 8.9. Mitsubishi Document TSP-WSI-000105, Summary of Review of Pre- and Post-Peening Examination Data Reports from Kansai OHI Unit 1, dated 31 October 2014.

8.10. EPRI Technical Report Document 3002008359, dated April 2016, Pressurized Water Reactor Materials Reliability Program: Effects of Surface Peening on the Inspectability of Nondestructive Evaluation 8.11. Mitsubishi Document PMP-TSP-13, Revision 6, WJP Controlled Parameter Listing For Implementation 8.12. Mitsubishi Document DUS-140030, Revision 1, MHI Input for Technical Basis Document Technical Summary of Water Jet Peening Page 13 ofl4

10 CFR 50.55a Request Number l4R-05 Proposed Alternative In Accordance with 10 CFR 50.55a(z)(1)

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8.13. Structural Integrity Document 1001077.305, Rev. 0, Development of Water Jet Peening Simulation using Finite Element Methods.

8.14. Structural Integrity Document 1001077.323, Rev. 0, Water Jet Peening Stress Analysis of Reactor Pressure Vessel Nozzle.

8.15. Mitsubishi Document NS-RVNDMW-100011, Revision 3, Reactor Vessel Nozzle Dissimilar Metal Weld Evaluation RVN ID A Hot Leg 8.16. Mitsubishi Document NS-RVNDMW-1 00012, Revision 3, Reactor Vessel Nozzle Dissimilar Metal Weld Evaluation RVN ID A Cold Leg 8.17. Mitsubishi Document NS-RVNDMW-1 00013, Revision 3, Reactor Vessel Nozzle Dissimilar Metal Weld Evaluation RVN ID B Hot Leg 8.18. Mitsubishi Document NS-RVNDMW-100014, Revision 4, Reactor Vessel Nozzle Dissimilar Metal Weld Evaluation RVN ID B Cold Leg 8.19. Mitsubishi Document NS-RVNDMW-1 0001 5, Revision 2, Reactor Vessel Nozzle Dissimilar Metal Weld Evaluation RVN ID C Hot Leg 8.20. Mitsubishi Document NS-RVNDMW-100016, Revision 2, Reactor Vessel Nozzle Dissimilar Metal Weld Evaluation RVN ID C Cold Leg 8.21. Mitsubishi Document NS-RVNDMW-100017, Revision 3, Reactor Vessel Nozzle Dissimilar Metal Weld Evaluation RVN ID D Hot Leg 8.22. Mitsubishi Document NS-RVNDMW-100018, Revision 3, Reactor Vessel Nozzle Dissimilar Metal Weld Evaluation RVN ID 0 Cold Leg 8.23. Mitsubishi Document DUS-160056, Revision 0, Calculation Method and Uncertainties of Residual Stress by the X-rays Stress Measurement 8.24. Mitsubishi Document DUS-160119, Revision 1, Test Report for Confirmation Test of No Adverse Effect by Ultra-Long-Time Application 8.25. Callaway RVN VT-3 Examination Reports filed with Callaway Job 16003266-900 and Callaway Job 16003267-900 dated 10/3112017 thru 11/0312017.

8.26. Mitsubishi Document DUS-140030, Revision 0, MHI Input for Technical Basis Document Technical Summary of Water Jet Peening 8.27. Callaway drawing ISI-REBOI Sheet 4, Reactor Vessel RBBOI ISI Equipment Welds Sheet 4 8.28. Callaway N-I Code Data Report for Nuclear Vessels Roll 02850 Frame 2586 8.29. Mitsubishi Document PMP-TSP-14, Revision 1, MNES Safety Classification Report for Water Jet Peening Page 14 of 14