ML24295A123

Enclosure 3: Relief Request ANO2-RR-24-001, Revision 0 (Non-Proprietary)

ML24295A123
Person / Time
Site:	Arkansas Nuclear
Issue date:	10/21/2024
From:	Entergy Operations
To:	Office of Nuclear Reactor Regulation
Shared Package
ML24295A119	List: 2CAN102402, Enclosure 2: Framatome Affidavit ML24295A120 ML24295A123
References
2CAN102402 ANO2-RR-24-001, Rev. 0
Download: ML24295A123 (1)

Text

ENCLOSURE 3

2CAN102402

RELIEF REQUEST ANO2-RR-24-001, REVISION 0 (NON-PROPRIETARY) 2CAN102402 Page 1 of 31

RELIEF REQUEST

ANO2-RR-24-001, Revision 0

1. ASME Code Component Affected

Component: Reactor Vessel Closure Head (RVCH) Penetration #71

Code Class: 1

Exam. Cat.: American Society of Mechanical Engineers (ASME) Code Case N-729-6

Item No. B4.20

Unit: Arkansas Nuclear One, Unit 2 (ANO-2)

Interval: Fifth (5th) (March 26, 2020 to March 25, 2030)

2. Applicable Code Edition and Addenda:

ASME Section XI, 2007 Edition through 2008 Addenda

ASME Section XI, Code Case N-729-6, as amended in 10 CFR 50.55a(g)(6)(ii)(D)

ASME Section III, 1968 Edition through Summer 1970 Addenda (Original Construction Code)

ASME Section III, Subsection NB, 1992 Edition

3. Applicable Code Requirements

The applicable requirements of the following ASME Boiler & Pressure Vessel (B&PV) Code and Code Cases from which relief is requested are as follows:

ASME Code,Section XI, 2007 Edition through 2008 Addenda

IWB-3420 states:

Each detected flaw or group of flaws shall be characterized by the rules of IWA-3300 to establish the dimensions of the flaws. These dimensions shall be used in conjunction with the acceptance standards of IWB-3500.

IWB-3132.3 states:

A component whose volumetric or surface examination detects flaws that exceed the acceptance standards of Table IWB-3410-1 is acceptable for continued service without a 2CAN102402 Page 2 of 31

repair/replacement activity if an analytical evaluation, as described in IWB-3600, meets the acceptance criteria of IWB-3600. The area containing the flaw shall be subsequently reexamined in accordance with IWB-2420(b) and (c).

ASME Code,Section III, 1992 Edition

NB-5245, Partial Penetration Welded Joints, specifies progressive surface examination of partial penetration welds.

NB-5330(b) states:

Indications characterized as cracks, lack of fusion, or incomplete penetration are unacceptable regardless of length.

Code Case N-638-11, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique

This Code Case provides requirements for automatic or machine gas tungsten arc welding (GTAW) of Class 1 components without the use of preheat or post-weld heat treatment. Code Case N-638-11 is listed as an acceptable Section XI Code Case in Table 1 of Regulatory Guide (RG) 1.147, Revision 21. The Framatome temper bead welding procedures were established in accordance with Code Case N-638-4. Code Case N-638-11 Section 2, "Welding Qualifications," Paragraph (b) permits use of existing welding procedures qualified in accordance with previous revisions of the Code Case. When the existing welding procedure was qualified in accordance with N-638-4, the test coupon base material was post-weld heat treated to comply with paragraph 2.1(a) of the Code Case (N-638-4) which states:

The base material for the welding procedure qualification shall be of the same P-Number and Group Number as the materials to be welded. The materials shall be post-weld heat treated to at least the time and temperature that was applied to the materials being welded.

4. Reason for Request

ANO-2 is presently in Refueling Outage 2R30. While performing ultrasonic (UT) examinations of RVCH penetration nozzles, in accordance with ASME Code Case N-729-6 (Item No. B4.20) 2, an axial, planar indication was identified in Control Element Drive Mechanism (CEDM)

Nozzle #71. The indication was located along the outside diameter of the nozzle, near the 0° downhill location of the Vessel Head Penetration (VHP) (located at 2°) in the J-groove weld root region (see Figure 11). The UT leak path assessment on CEDM Nozzle #71 did not provide any evidence of base material degradation along the RVCH nozzle bore. Additionally, the bare metal visual examination (Item B4.10) of the RVCH did not identify any evidence of reactor coolant leakage such as boric acid deposits or base material wastage.

2 Code Case N-729-6 as amended in 10 CFR 50.55a(g)(6)(ii)(D) and supplemented by Relief Request ANO2-ISI-022 (Reference 4)

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The UT examination [Reference 8] indicated that the flaw in CEDM Nozzle #71 was 0.195 inch deep from the outer surface of the nozzle and 0.44 inch long. The lower tip of the flaw is approximately 2.58 inch above the bottom of the nozzle. Figure 10 shows the relative location of the nozzles in the RVCH and Figure 11 shows the general location of the axial indication.

The repair technique, sometimes referred to as the half-nozzle repair, will be performed to correct the identified condition on CEDM Nozzle #71. The half-nozzle repair involves machining away the lower section of the nozzle containing the flaws, then welding the remaining portion of the nozzle to the RVCH to form the new pressure boundary. The new weld also attaches a replacement lower nozzle that provides a means for re-attaching the guide cone. This technique requires relief from certain aspects of the ASME B&PV Code as described below.

Because of the risk of damage to the RVCH material properties or dimensions, it is not feasible to apply the post weld heat treatment (PWHT) r equirements of the original Construction Code.

As an alternative to the requirements of the RVCH Code of Construction, Entergy proposes to perform a modification of CEDM Nozzle #71 utilizing Inside Diameter Temper Bead (IDTB) welding to restore the pressure boundary of the degraded nozzle penetration. The IDTB welding is performed with a remotely operated weld tool utilizing the machine GTAW process and ambient temperature temper bead welding with 50° F minimum preheat temperature and no PWHT. The modification described below will be performed in accordance with the 2007 Edition through 2008 Addenda of ASME Section XI, Code Case N-638-11, Code Case N-729-6, and the alternatives discussed in Section 5.

Basic steps for the IDTB repair are:

1. Roll expansion of the nozzle above the area to be modified to stabilize the nozzle and prevent any movement when the nozzle is separated from the nozzle-to-RVCH J-groove weld.

2. Machining to above the J-groove weld to remove the lower portion of the nozzle and eliminate the portions of the nozzle containing the unacceptable indication. This machining operation also establishes the weld preparation area (Refer to Figure 1).

3. Pre-weld Dye Penetrant Test (PT) examination of the machined area (Refer to Figure 1 and Figure 3).

4. Welding the remaining portion of the original nozzle and the new replacement Alloy 690 nozzle using Alloy 52M weld material (Refer to Figure 2).

5. Machining the weld and adjacent original nozzle material to provide a surface suitable for nondestructive examination (NDE).

6. Post-weld PT and UT examination of the weld and adjacent region (Refer to Figure 3).

Note the figures in this request are provided to assist in clarifying the above description. They are not intended to provide design information such as the location of the IDTB weld relative to the inner and outer spherical radii of the RVCH.

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Two fabrication parameters are controlled to ensure the nozzle roll expansion is effective in performing its design function of mechanical support for the nozzle prior to the application of the IDTB weld. The parameters of interest are tool insertion depth and the torque setting on the assembly tool.

Tool insertion depth, based on tooling setup height, will be controlled so that the rolled region is contained within the RVCH penetration bore. The torque applied to the roll expander is controlled so that the desired amount of plastic deformation occurs. The torque limiter assembly will be set and independently verified with a calibrated torque wrench prior to use.

As noted above, the roll expansion process will be completed for CEDM Nozzle #71 and the two parameters of interest (tool insertion depth and applied torque) that could impact the susceptibility to Primary Water Stress Corrosion Cracking (PWSCC) will be validated to be within process specifications. The roll expanded region and at least 1.81 inch above the top of the effective length of the roll expansion will be liquid penetrant examined following the repair to confirm no surface defects are present in that region of the Alloy 600 nozzle. An analysis performed for a similar design determined that after roll expansion steady state operating stresses greater than 20 thousand pounds per square inch (ksi) are limited to the region within 1.81 inch from the top of the effective length of the roll expansion. Framatome determined that this length is a conservative value to use for the ANO-2 repair. As a result, there is high confidence that adequate measures will be applied in the modification of Nozzle #71 with respect to PWSCC for one cycle of operation.

Entergy has determined that modification of CEDM Nozzle #71 utilizing the alternatives specified in this request will provide an acceptable level of quality and safety. Relief is requested in accordance with 10 CFR 50.55a(z)(1).

5. Proposed Alternative and Basis for Use

5.1 Welding Requirements

The half nozzle repair on CEDM Nozzle #71 will be performed using the ambient temperature temper bead process of Code Case N-638-11. Paragraph 2(b) of the Code Case permits use of welding procedures qualified in accordance with previous revisions of Code Case N-638.

Accordingly, the welding procedure to be used on Nozzle #71 was qualified in accordance with N-638-4 (an earlier revision). Code Case N-638-4, paragraph 2.1(a) states:

The base material for the welding procedure qualification shall be of the same P-Number and Group Number as the materials to be welded. The materials shall be post-weld heat treated to at least the time and temperature that was applied to the materials being welded.

PWHT can slightly degrade the fracture (notch) toughness of low alloy steels. Therefore, it is both reasonable and conservative to perform a simulated PWHT of test samples that will be used to evaluate base materials that have received PWHT during fabrication and placed into reactor service. However, it is not conservative to perform a simulated PWHT of welding qualification test plate material that will be compared to the temper bead heat affected zone (HAZ) for acceptance.

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The temper bead weld procedure qualification is required to demonstrate that the Charpy V-notch test results from the weld HAZ are no less than the Charpy V-notch test results for the unaffected base material. EPRI Report 1025169, Section 3.0 (Reference 5) documents that simulated PWHT on procedure qualification test plates degrades the notch toughness of the test plate increasing the contrast between the impact properties of the base material test plate and the temper bead weld HAZ. In other words, the simulated PWHT makes passing the impact testing requirements of the temper bead procedure qualification less difficult. Therefore, simulated PWHT on the temper bead test coupon does not provide conservative results when the simulated PWHT time exceeds the actual PWHT time applied to the component during construction.

The RVCH material at ANO-2 has at least 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br /> of PWHT (Reference 10) but the weld procedure qualification test plate has 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> of simulated PWHT. This condition does not comply with Code Case N-638-4, paragraph 2.1(a) which requires simulated PWHT on the temper bead qualification test plate to be equivalent to or exceed the total aggregate time applied to the component to be welded. There is no maximum limit on the simulated PWHT time.

The simulated PWHT requirement of Code Case N-638 has been recognized by the ASME Code Committee as non-conservative and was changed in Revision 7. Code Case N-638-11, paragraph 2.1(a) now states that simulated PWHT of the "test assembly is neither required nor prohibited. However, if used, the simulated PWHT shall not exceed the time or temperature already applied to the base material to be welded." The welding procedure to be used to implement the half nozzle repair on CEDM Nozzle #71 complies with this requirement.

In conclusion, ambient temperature temper bead welding will be performed on CEDM Nozzle #71 in accordance with Code Case N-638-11 while the welding procedure was qualified in accordance with Code Case N-638-4. The qualified welding procedure does not comply with the simulated PWHT requirements of Revision 4 of the Code Case but does comply with the enhanced and more conservative simulated PWHT requirements in Revision 11 (i.e., N-638-11).

Therefore, Entergy requests approval to apply the simulated PWHT requirements of Code Case N-638-11, paragraph 2.1(a) when using the temper bead welding procedure on CEDM Nozzle #71.

5.2 IDTB Modification Acceptance Examinations

ASME Section Ill, 1992 Edition, NB-5245, specifies progressive surface examination of partial penetration welds. The Construction Code requirement for progressive surface examination, in lieu of volumetric examination, was because volumetric examination is not practical for the conventional partial penetration weld configurations. Therefore, the following combination of UT and PT examinations are proposed.

For a modified VHP, the structural portion of the weld is suitable for UT examination and is accessible from both above and below the weld (Refer to Figure 4 through Figure 8).

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UT volumetric examination of the modified configuration will be performed as specified in ASME Code Case N-638-11, 4(a)(2) and 4(a)(6). The acceptance criteria of NB-5330 of the 1992 Edition of the ASME Section Ill Code apply to all flaws identified within the examined volume.

The UT examination system is capable of scann ing from cylindrical surfaces with inside diameters of approximately 2.82 inch. The scanning is performed using a 0° L-wave transducer, 45° L-wave transducers in two opposed axial directions, and 70° L-wave transducers in two opposed axial directions as well as 45° L-wave transducers in two opposed circumferential directions. Additionally, the low alloy steel extending to a depth approximately 0.25 inch beneath the weld into the low alloy steel base material (see Figure 3) will be examined using the 0° L-wave transducer searching for evidence of under bead cracking and lack of fusion in the HAZ. The examination volume is extended to include 1 inch of the Alloy 600 nozzle material above the structural weld and 1 inch below the structural weld. The structural weld receives essentially 100% UT examination coverage as shown in Figure 4 through Figure 8 of this submittal. The UT examination will be sufficient to verify that defects have not been induced in the ferritic low alloy steel RVCH base material due to welding, to the extent practical.

In addition to the UT examinations, a post-weld PT examination will be performed on the weld as shown in Figure 3. The acceptance criteria of NB-5350 in ASME Section III, 1992 Edition shall apply.

The combination of performing PT and UT examinations depicted in Figure 3 during the IDTB repair provides assurance of structural integrity. Thus, Entergy requests relief from the progressive surface examination requirements specified in NB-5245.

5.3 Triple Point Anomaly

ASME Section Ill, NB-5330(b) states:

Indications characterized as cracks, lack of fusion, or incomplete penetration are unacceptable regardless of length.

An artifact of ambient temperature temper bead welding is an anomaly in the weld at the triple point. There are two triple points in the modification. The upper triple point is the point in the repair weld where the low alloy steel RVCH base material, the Alloy 600 nozzle, and the Alloy 52M weld intersect. The lower triple point is the point in the repair weld where the low alloy steel RVCH base material, the Alloy 690 replacement nozzle, and the Alloy 52M weld intersect. The locations of the upper and lower triple points for the VHP modification are shown in Figure 2.

The anomaly consists of an irregularly shaped very small void. Mock-up testing has verified that the anomalies are common and do not exceed 0.10 inches in through-wall extent and are assumed to exist, for purposes of analysis, around the entire bore circumference at the triple point elevation.

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Detailed "Life of Repair" analyses performed for similar repairs at other plants resulted in a fatigue crack growth life for the triple point anomaly flaw of over 20 years. The typical process for these types of "Life of Repair" analyses is as follows:

1. The outermost penetration is analyzed due to the applied loading conditions being representative and bounding relative to all other locations in the RVCH. The initial flaw size for the triple point anomaly analysis is 0.10 inches. Crack growth analysis determines the future flaw size and concludes that it is acceptable for the stated life. The outermost hillside nozzle is considered, meaning that both extremes of interaction between the IDTB weld and the original J-groove weld are considered (i.e., these welds are very close to each other on the uphill side, and are relatively far away from each other on the downhill side).

2. A fracture mechanics analysis is performed to provide justification, in accordance with ASME Section XI, for operating with the postulated triple point anomaly. The anomaly is modeled as a 0.10-inch-deep crack-like defect, initiating at the triple point locations. Three flaws are postulated to simulate various orientations and propagation paths, as discussed below.

a. Horizontal Flaw (Circumferential and Axially Oriented): Flaw propagation across the nozzle wall thickness from the outside diameter to the inside diameter of the nozzle housing at both the upper and lower triple points. By using a fatigue crack growth rate twice that of the in-air austenitic stainless steel material to bound the Alloy 600/690 nozzle and Alloy 52M weld materials, it is ensured that a potential path through the HAZ between the new repair weld and the Alloy 600 nozzle material is also bounded.

For completeness, two types of flaws are postulated at the outside surface of the nozzle IDTB repair weld. A 360-degree continuous circumferential flaw, lying in a horizontal plane, which is considered to be a conservative representation of crack-like defects that may exist in the weld triple point anomaly. This flaw is subjected to axial stresses in the nozzle. In addition, an axially oriented semi-circular outside surface flaw is also considered since it would lie in a plane normal to the higher circumferential stresses. Both of these flaws would propagate toward the inside surface of the nozzle.

b. Cylindrical Flaw: Flaw propagation extends along the outside surface of the repair weld originating from both the upper and lower triple points. A cylindrically oriented flaw is postulated to lie along this interface, subjected to radial stresses with respect to the nozzle. This flaw may propagate through either the new Alloy 52M weld material or the low alloy steel RVCH base material.

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3. The results of similar prior detailed analysis have demonstrated that a 0.10 inch weld anomaly is acceptable for greater than 20 years of operation following a VHP nozzle inside diameter temper bead weld repair. Acceptable design margins are demonstrated for all flaw propagation paths considered in the analysis. The minimum fracture toughness margin has been shown to be greater than the required margin of 10 (3.16) for normal operating conditions per ASME Section XI, IWB-3612. Fatigue crack growth is minimal. A limit load analysis is also performed for similar prior repai rs considering the ductile Alloy 600/Alloy 690 materials along flaw propagation path lines. This analysis showed a limit load margin greater than the required margin per ASME Section XI, IWB-3644.

4. Since the postulated outside diameter flaw (the weld anomaly) at the upper triple point is not exposed to the primary coolant, and the air environment is benign for the materials at the triple point, the PWSCC time-dependent crack growth rates are not applicable. The crack-like defects due to the weld anomaly at the lower triple point are exposed to primary coolant; however, the materials at the lower triple point are Alloy 52M, Alloy 690, and low alloy steel and, therefore, are only subject to fatigue crack growth.

5. Prior analyses of similar repair configurati ons have demonstrated that fatigue crack growth is acceptable, and the crack-like indications remain stable, satisfying the ASME Section XI criteria.

Given the emergent nature of the ANO-2 CEDM Nozzle #71 repair, there is not sufficient time to perform the detailed "Life of Repair" analysis for the triple point anomaly during the outage.

Instead, a one cycle justification is developed using a comparative analysis approach between a similar nozzle repair with a previously performed triple point anomaly analysis. This comparative analysis is performed based on a prior tr iple point analysis performed for the "Life of Repair" that is most representative and bounding relative to the ANO-2 Nozzle #71 repair considering geometry, materials, transient loading conditions, as well as a conservative crack growth prediction for one fuel cycle of operation. This qualitative justification shows that the weld anomalies postulated in the ANO-2 repair meet the acceptance criteria of IWB-3612 for normal/upset and emergency/faulted operating conditions during one fuel cycle of operation.

This one cycle justification will be submitted to the NRC. If Entergy decides to operate with the current RVCH for more than the next 18-month f uel cycle, a "Life of Repair" analysis would be provided as part of a revision to this request. The revised relief request and supporting analysis will be submitted to the NRC in sufficient time to support the startup from 2R31.

Framatome has reviewed the key parameters at ANO-2 relative to a similar repair (where "Life of Repair" analysis has been performed). These parameters include IDTB weld toughness, IDTB weld wall thickness, and the key transients driving fatigue crack growth (including heat-up/cooldown transients). The ANO-2 repair IDTB weld toughness is equivalent, the IDTB weld wall thickness is equivalent, and the key transients are equivalent. Since the "Life of Repair" analysis for the similar repair resulted in over 20 years of life, Framatome is confident that the one cycle justification for the ANO-2 repair will show acceptance.

Entergy requests relief from the acceptance criteria specified in NB-5330(b) of ASME Section III to permit anomalies, as described herein, at the triple point area to remain in service for a single nominal 18-month fuel cycle of operation.

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5.4 Flaw Characterization and Successive Exams - RVCH Original J-Groove Weld

The assumptions of IWB-3600 of ASME Section XI are that cracks are fully characterized in accordance with IWB-3420 in order to compare the calculated parameters to the acceptable parameters addressed in IWB-3500. There are no qualified UT examination techniques for examining the original nozzle-to-RVCH J-groove weld s. Therefore, since it is impractical to characterize the flaw geometry that may exist ther ein, it is conservatively assumed the "as-left" condition of the remaining J-groove weld includes flaws extending through the entire Alloy 82/Alloy 182 J-groove weld and buttering. It is further postulated that the dominant hoop stresses in the J-groove weld would create a situation where the preferential direction for cracking would be radial. A radial crack in the Alloy 82/Alloy 182 weld would propagate by PWSCC through the weld and buttering to the interface with the low alloy steel RVCH material.

Any growth of the postulated "as-left" flaw into the low alloy steel would be by fatigue crack growth under cyclic loading conditions.

"Life of Repair" analyses performed for similar repairs have resulted in a fatigue crack growth life for the "as-left" J-groove flaw of 14 years or more (linear elastic fracture mechanics (LEFM) only). The typical process for these types of "Life of Repair" analyses is as follows:

1. The outermost penetration is modeled due to the applied loading conditions being the same or worse than all other locations in the RVCH. The initial flaw size for the J-groove weld is conservatively assumed to include all the weld and buttering. This is highly conservative since the buttering sees PWHT, which would tend to reduce welding residual stresses, making it less susceptible to PWSCC. While the analysis considers crack growth on both uphill and downhill sides, the weld on the downhill side of the outermost nozzle has the largest area. Therefor e, the largest possible initial flaw size on the downhill side is considered.

2. The transients applicable for the "as-left" J-groove weld are those due to normal and upset conditions only. The controlling loading condition is identified to be during normal cooldown, for which it was shown, using safety factors of 1.5 on primary loads and 1.0 on secondary loads, that the applied J-integral was less than the J-integral of the low alloy steel head material at a crack extension of 0.1 inch. Flaw stability during ductile flaw growth was easily demonstrated using safety factors of 3.0 for primary stress intensity factors and 1.5 for secondary stress intensity factors. The applied tearing modulus was less than the material tearing modulus of the low allow steel head material.

3. The J-groove flaws are evaluated using worst-case CEDM outermost nozzle penetration configuration with postulated flaw sizes on uphill and downhill sides of the J-groove weld. Fatigue crack growth for cyclic loading conditions using operational stresses from pressure and thermal loads and crack growth rates from ASME Section XI, Non-mandatory Appendix A, Sub-article A-4300 for ferritic material in a primary water environment are calculated. Based on t he results of LEFM analysis only or a combination of LEFM and elastic-plastic fracture mechanics (EPFM) analyses, a postulated flaw remaining in the original Alloy 82/Alloy 182 J-groove weld and buttering for the modified RVCH nozzle is shown to be acceptable.

Given the emergent nature of the ANO-2 CEDM Nozzle #71 repair, there is not sufficient time to perform the detailed "Life of Repair" finite-elem ent based analysis for the "as-left" J-groove flaw 2CAN102402 Page 10 of 31

during the outage. Instead, a one cycle justification will be developed based on a comparative analysis between a previous "as-left" J-groove flaw analysis and the ANO-2 CEDM Nozzle #71 repair. This comparative analysis will be performed using a prior "Life of Repair" "as-left" J-groove flaw analysis that is most representative and bounding relative to the ANO-2 Nozzle #71 repair considering geometry, materials, transient loading conditions, as well as a conservative crack growth prediction for one fuel cycle of operation. This qualitative justification shows that the "as-left" J-groove weld for the ANO-2 repair meets the acceptance criteria of IWB-3612 for normal/upset and emergency/faulted operating conditions during one fuel cycle of operation. In addition, the one cycle justification confirms that the primary stress limits considering reinforcement requirements of NB-3330 are met, considering a local area reduction of the pressure retaining membrane that is equal to the area of the J-groove weld and a conservatively bounding flaw size for one fuel cycle of operation. This one cycle justification will be submitted to the NRC. If Entergy decides to operate with the current RVCH for longer than the next 18-month fuel cycle, the "Life of Repair" analysis will be performed as part of a revision to this request. The revised relief request and analysis will be submitted to the NRC in sufficient time to support the startup from 2R31.

Framatome has reviewed the key parameters at ANO-2 relative to a similar repair (where "Life of Repair" analysis has been performed). These parameters include RVCH toughness, RVCH wall thickness, and the key transients driving fatigue crack growth (including heat-up/cooldown transients). The ANO-2 RVCH toughness is higher, the wall thickness is equivalent, and the key transients are equivalent. Since the "Life of Repair" analysis for the similar repair resulted in 14 years of life, Framatome is confident that the one cycle justification for the ANO-2 repair will show acceptance. Note that the 14-year life was using an LEFM approach and a longer life can be achieved when additionally using EPFM analysis approach.

Relief is requested from flaw characterization specified in IWB-3420 for a single nominal 18-month fuel cycle of operation.

In addition, the potential for debris from a cracked J-groove weld remnant was considered.

Radial cracks (relative to the nozzle) are postulated to occur in the J-groove weld due to the dominance of higher hoop stresses relative to axial stresses. The possibility of transverse cracks occurring that could subsequently intersect the radial cracks is considered remote as there are minimal driving forces for cracks in the transverse direction. The radial cracks would relieve the driving forces for any potential transverse cracks. There are no known service conditions that could drive radial cracks and transverse cracks to intersect to produce a loose part. There is extensive operating experience with remnant J-groove welds for which there are no known cases of debris generation (loose parts) due to PWSCC of the remnant J-groove weld. Therefore, cracking of the J-groove weld resulting in debris (loose parts) is not expected.

5.5 Preservice Inspection (PSI) and lnservice Inspection (ISI) of VHPs

Code Case N-729-6 as approved by the NRC in 10 CFR 50.55a specifies requirements for performing PSI and ISI examinations of RVCHs with nozzles having partial penetration welds.

Code Case N-729-6 Table 1, Item B4.20, permits either volumetric or surface examination. Item B4.20 examination coverage is specified in Figure 2 of Code Case N-729-6.

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The PSI examination of CEDM Nozzle #71 required by Code Case N-729-6, paragraph -2220 will be performed using a volumetric examination method. ISI examination of CEDM Nozzle #71 will also be performed using a volumetric examination method pending submittal of a follow-on relief request (see Section 6.0). In lieu of the volumetric examination region that extends 1.5-inch above and 1.5-inch below the J-groove weld shown in Figure 2 of Case N-729-6, an alternative examination region will be interrogated for the structural and non-structural portion of the repair weld.

The lower extent of the new pressure boundary (structural weld) jurisdiction will be located at the transition point between the inside diameter and taper of the lower replacement nozzle as shown in Figure 2. The portion of the repair weld above the jurisdictional boundary is classified as a pressure-retaining structural weld, and the portion of the repair weld below the jurisdictional boundary is classified as a permanent, nonstructural attachment weld. The structural weld will be subject to PSI and ISI examinations. The PSI and ISI examination volumes will extend up to the outer surface of the head (greater than 1.5-inch above the repair weld), including the roll transition region, and 1-inch below the structural weld as shown in Figure 9. Examination coverage below the structural weld will extend 1-inch below the structural weld and will obtain the maximum volume practical. Examination coverage of 1-inch below the structural weld is considered sufficient due to the following:

The repair weld material (Alloy 52M) is highly resistant to PWSCC The replacement nozzle material (Alloy 690) is highly resistant to PWSCC The replacement nozzle is not pressure retaining

If Entergy operates ANO-2 for more than the next 18-month refueling cycle with the current RVCH, then successive examinations required by Code Case N-729-6 will be performed on CEDM Nozzle #71 during each refueling outage. All other ANO-2 RVCH CEDM and ICI nozzles will continue to be examined in accordance with Code Case N-729-6 as modified by 10 CFR 50.55a(g)(6)(ii)(D) and other NRC approved alternatives. Therefore, future ISI examinations will comply with Code Case N-729-6 as modified by 10 CFR 50.55a(g)(6)(ii)(D) and as depicted in Figure 9.

The re-examination interval of a single fuel cycle for the repaired configuration for CEDM Nozzle #71 will ensure structural integrity and leak tightness of the Alloy 600 remnant material located above the IDTB weld. A PWSCC crack growth analysis will be applied to demonstrate that the crack growth time for a postulated flaw with the remnant Alloy 600 material to grow to the 75% through-wall acceptance limit is greater than the nominal cycle length of 18 months (1.5 years). Entergy will submit this analysis to the NRC within 14 days after return to service from the current refueling outage. Section 7 below discusses the inputs for this forthcoming analysis that show how the analysis will show greater than 1.5 years for the crack growth time.

5.6 General Corrosion Impact on Exposed Low Alloy Steel

The IDTB nozzle modification leaves an annular crevice between the RVCH and the replacement lower nozzle, wherein a small area of low alloy steel in the RVCH will be exposed to primary coolant. An evaluation was performed for similar prior repairs, evaluating corrosion concerns for the RVCH low alloy steel wetted surface. Galvanic corrosion, hydrogen 2CAN102402 Page 12 of 31

embrittlement, SCC, and crevice corrosion are not expected to be a concern for the exposed low alloy steel base metal. General corrosion of the exposed low alloy steel base metal will occur within the crevice between the IDTB weld and the original J-groove weld. As corrosion products pack the crevice, RCS flow will be restricted, resulting in decreased corrosion rate.

However, a conservative, sustained, corrosion rate will be applied and the resultant increase in bore diameter will be considered in the reinforcement calculation (per NB-3330) as part of the ASME Section III analysis one cycle justification. The corrosion evaluation and the ASME Section III analysis one cycle justification will be submitted to the NRC. If Entergy operates ANO-2 for more than the next 18-month refueling cycle with the current RVCH, a "Life of Repair" analysis would be submitted as a part of a revision to this request. The revised relief request and analysis will be submitted to the NRC in sufficient time to support of the startup from 2R31.

Galvanic Corrosion

The results of the NRCs boric acid corrosion program have shown that the galvanic difference between SA-533 Grade B, Class 1, Alloy 600, and Type 308 stainless steel (nominal chemistry of RVCH cladding) is not significant enough to consider galvanic corrosion as a strong contributor to the overall boric acid corrosion process (NUREG-1823). Therefore, it was judged that galvanic corrosion between the exposed RVCH low alloy steel, Alloy 600, Alloy 690, or their weld metals is not a concern for this repair configuration. This is supported by studies documented in EPRI Report 1000975 in which low alloy steel specimens were coupled and uncoupled to stainless steel exposed to a borated water environment at various temperatures.

The corrosion rates for the coupled and uncoupled conditions were similar. Additionally, galvanic corrosion of carbon steel coupled to stainless steel in boric acid solution in the absence of oxygen should be quite low. The results of this study are also applicable to nickel-based alloys as austenitic stainless steels have approximately the same corrosion potential as nickel-based alloys such as Alloy 600 and Alloy 690.

Hydrogen Embrittlement

Hydrogen embrittlement degrades material properties in the presence of hydrogen, usually occurring in combination with an applied stress. High pressure hydrogen environments are not typical of PWRs. Furthermore, lower strength, high toughness carbon and low alloy steels are not particularly susceptible to hydrogen stress cracking at normal operating temperatures.

Therefore, it was determined that hydrogen embrittlement is not a concern for the exposed RVCH low alloy steel in the repaired configuration. This conclusion is supported by many cases of low alloy steels being exposed to primary coolant without any observed cracking due to hydrogen embrittlement.

Stress Corrosion Cracking

There is extensive Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR) operating experience related to low alloy steels being exposed to the reactor coolant environment. This operating experience has not identified any known occurrence of stress corrosion cracking of the low alloy steel of RVCHs. Likewise, there are no existing ASME Section XI Code rules or NRC regulations addressing this issue in RVCH low alloy steels in PWR reactor coolant environment. Therefore, it has been determined that stress corrosion cracking of the low alloy steel of the RVCH is not a concern for this repair configuration.

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Crevice Corrosion

The geometry of the gap between the RVCH and replacement nozzle could create conditions for crevice corrosion. However, operating experience for PWRs shows that crevice corrosion of low alloy steels associated with these half nozzle repairs is not a problem in PWR systems due to expected low oxygen contents. Furthermore, the surface of the low alloy steel material will passivate with time, decreasing the rate of corrosion within the crevice. Therefore, it was determined that crevice corrosion of the low alloy is not a concern.

General Corrosion

Corrosion of the exposed low alloy steel is not expected to be a concern based on existing operating experience. The surface of the low alloy steel material will passivate with time, decreasing the rate of general corrosion. As corrosion products fill this gap, they will isolate the low alloy steel surface from the reactor coolant system, thereby, impeding the transport of oxygen which is necessary to sustain continued corrosion. Due to the reduced amount of oxygen, tight geometry, passivated surface, and restriction of RCS flow at the exposed low alloy steel, general corrosion is expected to decrease over the life of the repair.

5.7 Conclusions

Implementation of an IDTB repair to RVCH CE DM Nozzle #71 will produce an effective repair that will restore and maintain the pressure boundary integrity of the VHP. One IDTB modification at ANO-2 has been in service since 2021 without any known degradation. Other IDTB modifications have been performed successfully (see Section 8) and were in service for several years without any known degradation [e.g., Shearon Harris (2012, 2013, 2015, 2016 and 2018) and Palisades (2004, 2018, and 2020)]. This alternative provides improved structural integrity and reduced likelihood of leakage for the primary system. Detailed finite element based "Life of Repair" analyses performed for similar repairs at other plants resulted in a fatigue crack growth life for the triple point anomaly flaw of over 20 years. Likewise, "Life of Repair analyses performed on the "as-left" J-groove flaw has resulted in a fatigue crack growth life of 14 years or more. Corrosion of the exposed low alloy steel base material is not a concern due to lack of oxygen, tight geometry, and lack of reactor coolant system flow in the exposed region.

A one cycle justification will be developed and submitted to the NRC within 14 days of the end of the refueling outage. If Entergy operates ANO-2 for more than the next 18-month refueling cycle with the current RVCH, then a revision to this relief request will be submitted to justify continued use of the nozzle repair for the remaining service period with the current RVCH.

Accordingly, the use of the alternative provides an acceptable level of quality and safety in accordance with 10 CFR 50.55a(z)(1).

6. Duration of Proposed Alternative

The duration of the proposed alternative is for one cycle of operation. The upcoming operating cycle is currently scheduled to start in in the fourth quarter of 2024, coincident with startup from the current refueling outage. The operating cycle is currently scheduled to be complete in the second quarter of 2026.

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If Entergy operates ANO-2 for more than the next 18-month refueling cycle with the current RVCH, then a revision to this relief request will be submitted to justify continued use of the nozzle repair for the life of the repair. This permanent relief request would contain the appropriate analyses and justification for the remainder of the plant operating life and would be submitted prior to the end of the upcoming operating cycle.

7. Additional information

7.1 PWSCC Initiation and Growth

The re-examination interval of a single fuel cycle for the repaired configuration for CEDM Nozzle #71 will ensure structural integrity and leak tightness of the Alloy 600 remnant material located above the IDTB weld. A PWSCC crack growth analysis will be applied to demonstrate that the crack growth time for a postulated flaw within the remnant Alloy 600 material to grow to the 75% through-wall acceptance limit is greater than the nominal cycle length of 18 months (1.5 years). Entergy will submit this analysis to the NRC within 14 days after return to service from the current refueling outage.

The key inputs to this forthcoming analysis are as follows:

1. The current normal operating temperature of the ANO-2 RVCH is 596.5°F.

2. The effect of stress is conservatively modeled using a bounding weld residual plus operating stress through-wall profile within the remnant Alloy 600 nozzle. As the hoop stress component is calculated to dominate the axial stress, a bounding hoop stress profile will be applied to model growth of an axial PWSCC flaw. Figures 12 and 13 show bounding stress profiles previously calculated for the IDTB weld repair configuration for CEDM Nozzle 46. Note that Figure 12 is obtained from a finite element analysis (FEA) that does not contain any residual stresses caused by the roll expansion process as this process was not directly modeled in FEA; excluding roll expansion stresses is conservative in the weld region for flaw evaluation because they are compressive in this vicinity. Similar stress results are expected for the CEDM Nozzle #71 repair configuration because of the similar geometry for the IDTB structural weld and remnant Alloy 600 nozzle in these two cases. Figure 12 shows the bounding hoop stress profile for the Alloy 600 nozzle material adjacent to the Alloy 52 IDTB weld repair, and Figure 13 shows the corresponding bounding stress profile for the roll expanded transition region of the repaired Alloy 600 nozzle. Note that the maximum hoop residual plus operating stresses in Alloy 600 remnant material occur in the region adjacent to the Alloy 52 IDTB weld repair (Figure 12).

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3. The crack growth rate within the Alloy 600 remnant material is modeled as a function of crack-tip stress intensity factor and temperature using Equation 6-2 in Section 6.1.2 of MRP-420, Revision 1 [Reference 6]. This equation has been incorporated into Appendix Y of the 2023 version of ASME Section XI (within Y-4321). Under the conditions applicable to the ANO-2 RVCH, the MRP-420, Revision 1 equation conservatively predicts somewhat higher crack growth rate than the MRP-55, Revision 1

[Reference 7] PWSCC crack growth rate equation for Alloy 600 incorporated into earlier editions of ASME Section XI. A standard published solution for an idealized cylinder geometry and semi-elliptical flaw shape will be applied to calculate the stress intensity factor as a function of crack depth using the assumed stress profile. A conservatively low dissolved hydrogen concentration of 30 cubic centimeter per kilogram (cc/kg) will be assumed when applying the MRP-420, Revision 1 equation.

4. An initial flaw depth of 10% of the machined thickness of Alloy 600 nozzle material will be assumed (a0 = 0.060 inch). The 10% through-wall depth is a common assumption for initial flaw depth based on the detectability of PWSCC flaws using ultrasonic testing.

The initial flaw length will be based on a total-length-to-depth (2c 0/a0) aspect ratio of 6:1 (2c0 = 0.360 inch). This common assumption reasonably bounds plant experience and is conservative based on the limited axial extent of Alloy 600 material having elevated tensile stresses characterized by the stress profile of Figure 12.

5. The final flaw depth at the end of the evaluation period will be based on the 75%

through-wall acceptance limit for an axial flaw located on the nozzle ID and outboard of the structural weld per IWB-3660 of ASME Section XI. The 75% through-wall limit will be applied to the unmachined original nozzle thickness of 0.666 inch, resulting in an outside diameter (OD) nozzle ligament thickness of 0.167 inch when the flaw reaches the acceptance limit. The final flaw depth at this point is a f = 0.434 inch (0.601 minus 0.167 inch) for the machined Alloy 600 wall. The final flaw length when the flaw reaches the final depth will be calculated based on growth of the crack tips on the nozzle inside diameter (ID) surface according to the calculated stress intensity factor at that location.

These inputs will result with a high degree of confidence in a PWSCC crack growth time of at least 1.5 years for both assumed stress profiles (i.e., per Figures 12 and 13). This result is demonstrated by considering a constant crack growth rate of ((

)). This crack growth rate is conservatively based on characterizations of 103 PWSCC flaws in numerous French PWR RVCH vessel head penetration nozzles and represents the highest crack growth rate observed. Additionally, this crack growth rate bounds the majority of the crack growth rate data in MRP-420, Revision 1 [Reference 6] and MRP-55, Revision 1 [Reference 7]. ((

)) The constant crack growth rate corresponding to 1.5 years is (0.434 - 0.060)/1.5 = 0.249 inch per year. An assumed crack growth rate of 0.249 inch per year at the ANO-2 head temperature of 596.5°F corresponds to a crack growth rate of 0.414 inch per year (3.33x10 -10 m/s) at the reference temperature of 617°F used in MRP-55, Revision 1, applying its thermal activation energy of 31 kcal/mole. A crack growth rate of 3.30x10-10 m/s is higher than that predicted by the MRP-55 crack growth rate equation for stress intensity factors up to about 73 MPam (66 ksiin). Finally, one can readily verify that the calculated stress intensity factor at the deepes t flaw point is substantially less than 73 MPam (66 ksi in) for the applicable ranges of flaw depth and flaw length when applying the stress 2CAN102402 Page 16 of 31

profiles of Figures 12 and 13. This demonstrates the forthcoming PWSCC crack growth analysis will result in a crack growth time of at least 1.5 years with a high degree of confidence.

This conclusion also applies in the event the shallow cut or overbore contingency repair becomes necessary. Both these contingencies would result in a slightly greater extent of machining of the ID of the Alloy 600 remnant nozzle. The machined nozzle wall thickness under these contingencies is 0.591 inch, rather than 0.601 inch. This difference is sufficiently small and not expected to affect the overall conclusion.

The potential effects of cold work in the roll expansion region will also be considered in the crack growth analysis. It was determined that the cold work imparted by roll expansion is approximately 2%. As noted in MRP-420, Revision 1 [Reference 6], the equation used to calculate the crack growth accounts for up to 12% cold work, and therefore adjustment of the crack growth calculated per Equation 6-2 in Section 6.1.2, in order to account for cold work, is not required.

8. Precedents

1. Nuclear Management Company (NMC) letter to the NRC, "Request for Relief from ASME Section XI Code Requirements for Repair of Reactor Pressure Vessel Head Penetrations," ML052870321, dated October 11, 2005.

2. FirstEnergy Nuclear Operating Company (FENOC) letter to the NRC, "10 CFR 50.55a Request for Alternate Repair Methods for Reactor Pressure Vessel Head Penetration Nozzles," ML100960276, dated April 1, 2010.

3. Constellation Energy letter to the NRC, "Re lief Request for Modifications to Pressurizer Heater Sleeves and Lower Level Nozzle Penetrations (RR-PZR-01)," ML110340059, dated January 31, 2011.

4. Progress Energy letter to the NRC, "Relief Request I3R-09 Reactor Vessel Closure Head Nozzles Inservice Inspection Program - Third Interval," ML12131A663, dated May 3, 2012.

5. Progress Energy letter to the NRC, "Relief Request I3R-11 Reactor Vessel Closure Head Nozzles Inservice Inspection Program - Third Interval," ML13143A167, dated May 22, 2013.

6. Progress Energy letter to the NRC, "Relief Request I3R-13 Reactor Vessel Closure Head Nozzle 37, Inservice Inspection Program - Third Ten-Year Interval,"

ML13329A354, dated November 22, 2013.

7. Progress Energy letter to the NRC, "Relief Request I3R-15, Reactor Vessel Closure Head Nozzle Repair Technique, Inservice Inspection Program - Third Ten-Year Interval," ML15092A236, dated April 2, 2015.

8. Progress Energy letter to the NRC, "Relief Request I3R-16, Reactor Vessel Closure Head Nozzle Repair Technique, Inservice Inspection Program - Third Ten-Year Interval," ML16294A218, dated October 19, 2016.

9. Progress Energy letter to the NRC, "Relief Request I3R-18, Reactor Vessel Closure 2CAN102402 Page 17 of 31

Head Nozzle Repair Technique, Inservice Inspection Program - Fourth Ten-Year Interval," ML18108A094, dated April 18, 2018.

10. Entergy letter to the NRC, "Relief Request Number RR 5-7 Proposed Alternative to ASME Section XI Code Requirements for Repair of Reactor Pressure Vessel Head Penetrations," ML18330A142, dated November 26, 2018.

11. Entergy letter to the NRC, "Relief Request Number RR 5-8 Proposed Alternative to ASME Section XI Code Requirements for Repair of Reactor Pressure Vessel Head Penetrations," ML20267A387, dated September 23. 2020.

12. Florida Power & Light Company letter to the NRC, "Unit 1 Relief Request 21 and Unit 2 Relief Request 31 Request for Additional Information Response," ML031060268, dated April 14, 2003.

13. NRC email to Entergy, "Arkansas Nuclear One, Unit 2 - Verbal Authorization of Relief Request ANO-RR-21-002 (EPID L-2021-LLR-0084)," ML21314A121, (2CAN112102),

dated November 9, 2021.

9. References

1. ASME Code Case N-638-11, "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division 1".

2. NRC Regulatory Guide 1.147, Revision 21, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1", ML23291A003.

3. ASME Code Case N-729-6, "Alternative Examination Requirements for PWR Reactor Vessel Upper Heads with Nozzles Having Pressure-Retaining Partial-Penetration Welds,Section XI, Division 1".

4. Entergy letter to the NRC, "Request for Alternative to 10 CFR 50.55a(g)(6)(ii)(D)

Examination Requirements - Relief Request ANO2-ISI-022, ML20329A202,dated November 24, 2020.

5. "Welding and Repair Technology Center: Welding and Repair Technical Issues in ASME Section XI", EPRI, Palo Alto, CA: 2012. 1025169.

6. Material Reliability Program (MRP), "Crack Growth Rates for Evaluating Primary Water Stress Corrosion Cracking (PWSCC) of Thick-Wall Alloy 600 Materials and Alloy 82, 182, and 132 Welds (MRP-420)", Revision 1, EPRI, Palo Alto, CA: 2018, 3002014244

7. Material Reliability Program (MRP) Crack Growth Rates for Evaluating Primary Water Stress Corrosion Cracking (PWSCC) of Thick-Wall Alloy 600 Materials (MRP-55)

Revision 1, EPRI, Palo Alto, CA: 2002, 1006695.

8. WDI-PJF-350990-NDE-001-Penetration 71, Westinghouse UT Inspection Report

9. 2-BOP-PT-24-007, WO-00586509-03 CEDM 71, ANO Supplemental PT Inspection Report October 8, 2024.

10. Entergy Design Input Record EC-54199390 Rev. 2.

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11. U.S. NRC publication NUREG-1823, U.S. Plant Experience with Alloy 600 Cracking and Boric Acid Corrosion of Light-Water Reactor Pressure Vessel Materials, ADAMS Accession Number ML051390139.

12. "Boric Acid Corrosion Guidebook", Revision 2: Managing Boric Acid Corrosion Issues at PWR Power Stations, EPRI, Palo Alto, CA: 2001, 1000975.

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Figure 1

Nozzle Machining

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Figure 2

Nozzle Weld

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Figure 3

Nozzle Examination

Pre - Weld PT k-l-n-o Post - Weld PT m-n-o-p Post - Weld UT a-b-c-d-e-f-g-h-j-a

NOTE: Nozzle #71 Post - Weld PT examination extent above the structural weld extends a minimum of 1.81-inch above the rolled transition.

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Figure 4

Nozzle 0° and 45°L UT Beam Coverage Looking Clockwise and Counter-Clockwise

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Figure 5

Nozzle 45°L UT Beam Coverage Looking Down

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Figure 6

Nozzle 45°L UT Beam Coverage Looking Up

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Figure 7

Nozzle 70°L UT Beam Coverage Looking Down

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Figure 8

Nozzle 70°L UT Beam Coverage Looking Up

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Figure 9

Nozzle PSI / ISI UT Examination

UT a-b-c-d-a UT e-f (leak path)

Note: Extent of examination above the structural weld extends up to the outer surface of the head and extent of examination below the structural weld is 1-inch for Nozzle #71.

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Figure 10

Reactor Vessel Head Penetration Locations

Notes:

3. Figure 10 shows the locations of the RVCH penetrations. There are 81 CEDM penetrations, eight In-core Instrument penetrations, and one Vent line.

4. CEDM Penetration #71 is highlighted.

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Figure 11

Indication Location

Note: The depth of the indication is 0.195 inches into the nozzle wall from the nozzle OD. The azimuth of the indication is located approxim ately 2 degrees clockwise from the downhill side.

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Figure 12

Highest Weld Residual Plus Operating Hoop Stress Through-Wall Profile of Alloy 600 Nozzle Near the Alloy 52 Weld

((

))

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Figure 13

Maximum Hoop Stress Profile in the Roll-Expanded Region

((

))