ML24093A102

Alternative Request IR-4-13, Proposed Alternative Request to Support Steam Genera Tor Channel Head Drain Modification

ML24093A102
Person / Time
Site:	Millstone
Issue date:	04/01/2024
From:	James Holloway Dominion Energy Nuclear Connecticut
To:	Office of Nuclear Reactor Regulation, Document Control Desk
Shared Package
ML24093A100	List: ML24093A102
References
24-103
Download: ML24093A102 (1)

Text

PROPRIETARY INFORMATION -WITHHOLD UNDER 10 CFR 2.390 Dominion Energy Nuclear Connecticut, Inc.

5000 Dominion Boulevard, Glen Allen, VA 23060 April 1, 2024 DominionEnergy.com U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 3

a. Dominion

~

Energy:;

Serial No.

NRA/SS Docket No.

License No.24-103 RO 50-423 NPF-49 ALTERNATIVE REQUEST IR-4-13, PROPOSED ALTERNATIVE REQUEST TO SUPPORT STEAM GENERA TOR CHANNEL HEAD DRAIN MODIFICATION Pursuant to 10 CFR 50.55a(z)(2), Dominion Energy Nuclear Connecticut, Inc. (DENC) requests Nuclear Regulatory Commission (NRC) approval of a proposed alternative to certain requirements associated with steam generator (SG) channel head drain weld repairs for Millstone Power Station Unit 3 (MPS3). To alleviate future potential primary water stress corrosion cracking concerns, DENC will be performing proactive modifications on the channel head drain connection on each SG in accordance with American Society of Mechanical Engineers (ASME) Code Case N-839. The proposed alternative requests relief from the Code Case requirements to use a 48-hour hold time and volumetric inspection method for final examination, due to hardship without a compensating increase in quality or safety. The SG channel head drain modifications are scheduled to take place during the spring 2025 MPS3 refueling outage. provides Alternative Request IR-4-13, which concludes that compliance with the specified ASME Code Case examination requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety in accordance with 10 CFR 50.55a(z)(2). Proprietary and non-proprietary versions of Westinghouse's Technical Summary related to the proposed alternative request are provided in Enclosures 2 and 3, respectively. Enclosure 4 provides an Application for Withholding and Affidavit from Westinghouse. contains information proprietary to Westinghouse and is supported by an affidavit (Enclosure 4) signed by Westinghouse, the owner of the information. The affidavit sets forth the basis on which the information may be withheld from public disclosure by the Commission and addresses with specificity the considerations listed in paragraph (b)(4) of Section 2.390 of the Commission's regulations. Accordingly, it is respectfully requested the proprietary information be withheld from public disclosure in accordance with 10 CFR 2.390.

NRC review and approval of the proposed alternative request is requested by April 1, 2025, to support the MPS3 refueling outage scheduled for the spring of 2025. contains information that is being withheld from public disclosure under 10 CFR 2.390. Upon separation from Enclosure 2, this letter is decontrolled.

Serial No.24-103 Docket No. 50-423 Page 2 of2 If you have any questions regarding this submittal, please contact Shayan Sinha at (804) 273-4687.

Sincerely, James E. Holloway Vice President Nuclear Engineering & Fleet Support

Enclosures:

1. Alternative Request IR-4-13, Proposed Alternative Request to Support Steam Generator Channel Head Drain Modification

2. Westinghouse Technical Summary (Proprietary)

3. Westinghouse Technical Summary (Non-Proprietary)

4. Westinghouse Application for Withholding and Affidavit Commitments made in this letter: None cc:

U.S. Nuclear Regulatory Commission Region I 475 Allendale Road, Suite 102 King of Prussia, PA 19406-1415 R. V. Guzman Senior Project Manager - Millstone Power Station U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 9 E3 Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station

Serial No.24-103 Docket No. 50-423 ENCLOSURE 1 ALTERNATIVE REQUEST IR-4-13 PROPOSED ALTERNATIVE REQUEST TO SUPPORT STEAM GENERATOR CHANNEL HEAD DRAIN MODIFICATION MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

Serial No.24-103 Docket No. 50-423, Page 1 of 6 Alternative Request IR-4-13 Proposed Alternative Request to Support Steam Generator Channel Head Drain Modification Pursuant to 10 CFR 50.55a (z)(2)

--Hardship Without a Compensating Increase in Quality and Safety--

1. ASME Code Component(s) Affected ASME Code Class Code Class 1 Reference ASME Code Case N-839 (Reference 2) per Regulatory Guide 1.147, Revision 20, (Reference 3), Table 1 Examination Category Reactor Pressure Vessel Head Penetration Nozzles (RPVHPNs) with Effective Degradation Years (EDY) < 8 years Components ASME Code Class I Steam Generators (SGs) 3RCS*SG1A 3RCS*SG1B 3RCS*SG1C 3RCS*SG1D Description Materials:

SG Bottom Channel Head Bowl - ASME SA-533, Grade B, Class 1 3/8" NPS Drain Pipe - See Enclosure 2/3 Coupling - See Enclosure 2/3 Weld Metal - See Enclosure 2/3

2. Applicable Code Edition and Addenda

Construction: The American Society of Mechanical Engineers (ASME),Section III, 1971 Edition, Summer 1973 Addenda (Reference 8).

In-Service Inspection: ASME Boiler and Pressure Vessel Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 2013 Edition (Reference 1).

Serial No.24-103 Docket No. 50-423, Page 2 of 6

3. Applicable Code Requirement

IWA-4400 details the requirements for welding, metal removal, fabrication, and installation. IWA-4411 specifies that welding preheat and post-weld heat treatment shall be in accordance with the Construction Code for the Item. ASME Code Case (CC) N-839 (Reference 2) states that in lieu of the preheat and post-weld heat treatment requirements of IWA-4411, the materials and welds specified in 1(a) of the CC may be repaired using the manual SMAW temper bead technique without the specified preheat or post-weld heat treatment of the Construction Code. The specific CC N-839 requirements that are the subject of this request are contained in Section 4, paragraph (a)(2), which states:

(2) When ferritic filler materials are used, the weld shall be nondestructively examined after the completed weld has been at ambient temperature for at least 48 hr. When austenitic filler materials are used, the completed weld shall be nondestructively examined after the initial three temper bead layers (i.e., layers 1, 2, and 3) have been in place for at least 48 hr. Examination of the welded region shall include both volumetric and surface examination methods. Demonstration for ultrasonic examination of the repaired volume is required using representative samples which contain construction type flaws.

4. Reason for Request

Dominion Energy Nuclear Connecticut, Inc. (DENC) requests relief from the CC N-839 requirements to 1) hold for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> before examination and 2) perform volumetric examination of the welded region, as these requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

The four SGs for MPS3 include a stainless-steel drain line coupling at the center of the channel head bowl. The drain line was fabricated by filling a machined cavity in the channel head with Alloy 182 weld metal and performing post-weld heat treatment (PWHT) on the weld deposit. A through-the-shell hole was subsequently drilled in the channel head and the build-up was machined to accommodate installation of the coupling. Next, an Alloy 600 pipe was hard rolled into the hole to provide a primary water flow path and seal welded at both ends. Lastly, the coupling was installed with a partial penetration weld joint and reinforcing fillet weld without performing PWHT.

Additional description and illustrations of the original design and fabrication of the MPS3 SG channel head drains are provided in Attachment A of Enclosure 2/3.

Industry operating experience has shown that the Alloy 600 base material and Alloy 82/182 weld filler material are susceptible to Primary Water Stress Corrosion Cracking (PWSCC), as several plants with similar designs have experienced boric

Serial No.24-103 Docket No. 50-423, Page 3 of 6 acid leakage through this connection (Reference 4). DENC is currently planning an ASME Section XI Repair and Replacement activity at MPS3, which will fully remove the Alloy 600 leak path by removing the existing Alloy 182 weld metal. The weld material will be replaced as described in Enclosure 2/3. Completion of this activity is intended to eliminate the concern associated with PWSCC cracking of the MPS3 SG channel head drain.

Welding will be performed with the SMAW ambient temper bead process per CC N-839, except as modified by this alternative. The welding application will include three buttering layers applied to the P-No. 3 surfaces of the channel head bowl and installation of the coupling with a fillet reinforced partial penetration groove weld. In lieu of the volumetric examination required by CC N-839, liquid penetrant examination will be performed at progressive increments. Specifically, examinations will be performed on the three buttering layers, at 3/16 increments thereafter when filling the groove weld, and on the final groove and fillet weld surfaces. Intentional 48-hour holds will not be employed prior to any of the exams.

Additional description and illustration of the planned modification are also provided in Attachment B of Enclosure 2/3.

Performing volumetric examination (UT or RT) of the welds per CC N-839 is an undue hardship. As described in Attachment F of Enclosure 2/3, attempts to develop an ultrasonic examination method have been unsuccessful, largely due to the geometry of the channel head drain, and the partial penetration weld joint design. These attempts resulted in an inability to accurately detect and characterize identified indications. As noted in Attachment D of Enclosure 2/3, the configuration of the channel head also results in an inability to obtain meaningful results with the radiographic examination method. This inability is due to the following:

Optimum source placement would be inside the channel head bowl, which has access limitations.

The thickness of the repair region requiring radiography is significantly thinner than the overall thickness of the shell and requires a source-side plaque Image Quality Indicator (IQI) designation 10 per Table IX-3325-1 of ASME Ill.

Use of this ASME Ill required IQI would result in an unachievable IQI image.

If a larger source-side IQI designation for the entire shell thickness were utilized, indications in the temper bead weld and associated HAZ would likely be missed.

Maintaining the 48-hour hold time requirement of CC N-839 is also considered an undue hardship. The hold time would result in an unnecessary increase in the duration of the repair evolution, which could negatively impact the schedule for the MPS3 refueling outage. Also, since this modification will take place with the

Serial No.24-103 Docket No. 50-423, Page 4 of 6 associated SG drained and the access covers removed, the 48-hour hold time would have the potential to add dose and radiological risk to other outage work being performed in adjacent areas.

5. Proposed Alternative and Basis for Use

Pursuant to 10 CFR 50.55a(z)(2), DENC proposes to perform progressive surface exams with the Liquid Dye Penetrant Examination (PT) process as an alternative to final volumetric inspection. Intentional 48-hour holds will not be employed prior to any of the exams. Three bead layers will be applied. PT examination will be performed on 100% of each layer's surface. The weld area will then be prepared for installation of the coupling. PT will be performed at 3/16 increments when filling the groove weld, and on the final groove and fillet weld surfaces. A detailed weld and non-destructive examination (NDE) sequence is provided in Attachment B of /3. All NDE exams will be performed with examiners and procedure qualified in accordance with ASME Section XI.

The original Owner's Construction Code for the MPS3 SG channel head drain was ASME Section Ill, Division 1, 1971 Edition with Addenda up to and including Summer 1973 (Reference 8). Later editions of this code allow for progressive surface examination for temper bead repairs to partial penetration welds, in lieu of volumetric examination if meaningful results cannot be obtained (Example provided in Reference 5, NB-4622.11(d)(3)) and Reference 6, NB-4622.9(d)(5)). This provides a precedent for the suitability of progressive surface exams in lieu of volumetric exams for partial penetration joints, when meaningful results cannot be obtained with volumetric methods.

Also, the precedents listed in Section 7 of this enclosure document the NRC staff's approval of progressive PT in lieu of volumetric inspection of temper bead welds on other component repairs.

DENC also proposes that the final PT examination be performed without the 48-hour hold time based on Attachment E of Enclosure 2/3. Elimination of the 48-hour hold time was supported by PVP2023-107489, "Elimination of the 48-hour Hold for Ambient Temperature Temper Bead Welding with Austenitic Weld Metal (Reference 7). A white paper based on PVP2023-107489 was provided in Attachment 2 of Request 2-TYP-4-RV-06 for Beaver Valley Power Station, Unit No. 2, which was submitted on April 28, 2023 (Reference 9). DENC concludes that PVP2023-107489 and the white paper apply to the MPS3 channel head drain modification project, since an ambient temper bead process using austenitic filler material will be used.

Serial No.24-103 Docket No. 50-423, Page 5 of 6 Conclusion The geometry of the modified MPS3 SG channel head drain results in an inability to obtain meaningful results with either the ultrasonic or radiographic examination methods. Precedence in the ASME Section Ill code for partial penetration groove welds, as well as NRC-approval of precedents provide a basis for concluding that the use of progressive PT examination for the MPS3 SG channel head drain modification provides reasonable assurance of structural integrity, because sound welds are deposited. Attachment E of Enclosure 2/3 and Reference 7 provide a technical basis for eliminating the 48-hour hold time requirement when using austenitic filler materials in temper bead welding, which is consistent with the planned welding process for the MPS3 SG channel head drain modification.

Therefore, DENC concludes that the subject CC N-839 requirements present a hardship with no compensating increase in quality or safety, and removal of the 48-hour hold time requirement and use of progressive PT examination of the subject welds provide an acceptable alternative.

6. Duration of Proposed Alternative

The proposed one-time alternative is applicable to MPS3s fourth 10-year Inservice Inspection (ISI) interval, which began on February 23, 2019, and ends on February 22, 2029. Specifically, the proposed alternative only applies through completion of the SG channel head drain modification project, which is scheduled for the spring 2025 MPS3 refueling outage.

7. Precedents

1. Entergy Relief Request PWR-R&R-001, Entergy Operations Inc, Arkansas Nuclear One, Units 1 and 2 (ANO-1 and ANO-2) and Waterford Steam Electric Station Unit 3 (Waterford 3), ADAMS Accession No. ML031060501.

2. Seabrook Station, Unit No. 1 - Relief Request 4RA-22-01, Relief from the Requirements of the ASME Code, ADAMS Accession No. ML23073A156.

3. Verbal Authorization for NMP1 [Nine Mile Point Nuclear Station, Unit 1] Proposed Alternative Weld Overlay N2E Safe-end to nozzle DM [dissimilar metal] Weld, ADAMS Accession No. ML23090A130.

4. Beaver Valley Power Station, Unit No. 2, Alternative Request No. 2-TYP-4-RV-06, ADAMS Accession No. ML23249A184.

Serial No.24-103 Docket No. 50-423, Page 6 of 6

8. References

1. ASME Boiler and Pressure Vessel Code,Section XI, "Rules for lnservice Inspection of Nuclear Power Plant Components," 2013 Edition.

2. ASME Code Case N-839, "Similar and Dissimilar Metal Welding Using Ambient Temperature SMAW Temper Bead Technique,Section XI, Division 1," approved September 4, 2014.

3. Regulatory Guide 1.147, Inservice Inspection Code Acceptability, ASME Section XI, Division 1, Revision 20.

4. Westinghouse Technical Bulletin TB-04-19, "Steam Generator Channel Head Bowl Drain Line Leakage," October 18, 2004.

5. ASME Section Ill, Rules for Construction of Nuclear Facility Components Division 1, Article NB-4622.11(d)(3), 1998 Edition, No Addenda.

6. ASME Section Ill, Rules for Construction of Nuclear Facility Components Division 1, Article NB-4622.9(d)(5), 2017 Edition

7. PVP2023-107489, "Elimination of the 48-hour Hold for Ambient Temperature Temper Bead Welding with Austenitic Weld Metal," McCracken and Patel.

8. ASME Section III, 1971 Edition, Summer 1973 Addenda.

9. Beaver Valley Power Station, Unit No. 2, Alternative Request No. 2-TYP-4-RV-06, 10 CFR 50.55a Request 2-TYP-4-RV-06 for Alternative Repair Methods for Reactor Pressure Vessel Head Penetrations, dated April 28, 2023 (ADAMS Accession No. ML23118A381)

Serial No.24-103 Docket No. 50-423 ENCLOSURE 3 WESTINGHOUSE TECHNICAL

SUMMARY

ATTACHMENTS OF LTR-CECO-24-001-NP (NON-PROPRIETARY)

MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 3 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 Attachment A Original Design and Fabrication of Millstone Unit 3 Steam Generator Channel Head Drain To drain reactor coolant (i.e., primary side water) from the channel heads of the Millstone Unit 3 steam generators after plant shutdown but prior to primary side maintenance operations, a through-the-shell drain configuration was provided at the bottom center of the Model F steam generator channel heads. The drain configuration consists of an Alloy 600 pipe that provides a flow path for reactor coolant through the channel heads wall thickness. The entry end of the drain (within the channel head bowl) is located directly under the divider (partition) plate which separates the hot leg chamber from the cold leg chamber. A semi-circular opening in the divider plate (commonly referred to as a mouse hole) allows for drainage from both the hot leg and cold leg chambers simultaneously. A stainless-steel coupling is welded at the lower (i.e., outlet) end of the drain pipe external to the channel head. Drain line piping and valves are then welded to this coupling to provide any residual reactor coolant with a flow path out of the steam generator. Figure 1A shows the original drain configuration in the Millstone Unit 3 steam generators.

Figure 1A Original Configuration of Millstone Unit 3 Steam Generator Channel Head Drain In order to install the channel head drain during steam generator manufacture, channel head base metal was removed from the outer diameter surface of the channel head in the bottom center location to create a cavity with a [ ]a,c,e-inch nominal depth. The cavity was then completely filled in using [

]a,c,e filler metal. For a,c,e

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 4 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 the first layer of weld material, a preheat temperature was maintained in the range of [ ]a,c,e°F to [ ]a,c,e°F.

For the remaining layers of weld material, preheat was not required unless the temperature was below

[ ]a,c,e°F, which then required preheat to raise the temperature to within the range of [ ]a,c,e°F to [ ]a,c,e°F.

Following completion, the weld build-up was post-weld heat treated (PWHT) for a minimum of [ ]a,c,e hour at [ ]a,c,e°F.

After completion of welding, a nominal [ ]a,c,e -inch diameter through-wall hole was then machined in the channel head and the [ ]a,c,e weld build-up was machined for fit-up of the drain coupling, including preparations for a partial penetration weld to attach the drain coupling. Following machining, the final machined surfaces of the preparations for the partial penetration weld were liquid penetrant examined. Figure 2A shows the drain cavity after welding and preparatory machining.

Figure 2A Channel Head Drain Cavity after Welding and Preparatory Machining Next, an [ ]a,c,e pipe was inserted into the channel heads through-wall hole and hard-rolled into position. The top (i.e., inlet) end of the drain pipe was then seal welded around its perimeter to the stainless-steel cladding on the inner diameter surface of the channel head using [ ]a,c,e filler metal and the final surface of the weld was liquid penetrant examined. Likewise, the lower (i.e., outlet) end of the drain pipe was welded around its perimeter to the [ ]a,c,e weld build-up in the previously machined cavity using [ ]a,c,e filler metal and the weld was subsequently liquid penetrant examined. Both the welds at the upper and lower ends of the drain pipe had a minimum preheat temperature of [ ]a,c,e°F with no PWHT required. The installed drain pipe, which is shown in Figure 3A, provides a barrier between the reactor coolant and the base metal of the channel head.

a,c,e

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 5 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 Figure 3A Insertion of [ ] a,c,e Drain Pipe Finally, an [ ]a,c,e stainless steel drain coupling was welded to the

[ ]a,c,e weld build-up on the channel heads outer diameter using a partial penetration weld that was capped by a fillet weld, as shown in Figure 4A. Both the partial penetration weld and fillet weld were made using [

]a,c,e filler metal with a minimum [ ]a,c,e°F preheat temperature. The welding of the drain coupling occurred after all major PWHTs affecting the channel head were completed. Liquid penetrant examination was performed on the partial penetration J-groove surface prior to the start of welding, on the root pass of the partial penetration weld, on the completed partial penetration weld prior to installation of the fillet weld, and on the final fillet weld.

a,c,e

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 6 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 Figure 4A Installation of Drain Coupling a,c,e

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 7 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 Attachment B Design of Modified Millstone Unit 3 Steam Generator Channel Head Drain In order to mitigate the potential of primary water stress corrosion cracking (PWSCC) in the Millstone Unit 3 steam generator channel head drains, the drains will be modified to replace the existing drain coupling and

[ ]a,c,e weld build-up with a new drain coupling and partial thickness weld build-up. The drain modification has been designed and qualified in accordance with the design requirements of Section III of the 1971 Edition through Summer 1973 Addenda of the ASME Boiler and Pressure Vessel (B&PV) Code, which is the original code of construction for the Millstone Unit 3 steam generators. The drain modification shall be performed in accordance with Westinghouse Drawing 10184D01.

The channel head drain modification process will begin with removal of the existing (i.e., original) drain coupling and [ ]a,c,e weld build-up. During the removal of the weld build-up, a short length of the lower (i.e., outlet) end of the existing drain pipe will be trimmed such that it is flush with the base metal of the channel head. Note that this process will also remove the existing seal weld between the lower end of the drain pipe and the [

]a,c,e weld build-up. Following machining, the surfaces of the channel head base metal will be acid etched to verify that the existing weld build-up material has been removed. Figure 1B shows the drain configuration following completion of machining operations.

Figure 1B Drain Configuration Following Removal of Original Drain Coupling and Weld Build-up Following the removal of the weld build-up, the area where the initial temper bead layer will be deposited shall be VT-1 visually examined in accordance with ASME B&PV Code Case N-839. Following VT-1 visual examination, the first weld bead of the initial temper bead layer shall seal the existing drain pipe around its a,c,e

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 8 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 perimeter to completely cover the annulus between the drain pipe and channel head base material using [

]a,c,e weld material. After the annulus is sealed, the first weld bead of the initial temper bead layer and machined channel head surfaces shall be liquid penetrant examined in accordance with the requirements of Section III, Subsection NB-5350 of the 1971 Edition through Summer 1973 Addenda of the ASME B&PV Code and ASME B&PV Code Case N-839. (Note: Sealing of the drain pipe-to-channel head annulus is to be completed prior to the liquid penetrant examination of the channel head base metal surfaces in order to prevent the reporting of false indications at the annular gap between the outer diameter of the drain pipe and the inner diameter of the machined bore in the channel head base metal.) Figure 2B shows the drain configuration following completion of sealing of the drain pipe annulus.

Figure 2B Drain Configuration Following Sealing of Drain Pipe Annulus Continuing from the first bead of weld that seals the annulus between the drain pipe and channel head base material, 3 layers of buttering will be applied to the surfaces of the newly machined channel head cavity using

[ ]a,c,e weld material. The buttering will be applied using an ambient temperature shielded metal arc welding (SMAW) temper bead technique in accordance with ASME B&PV Code Case N-839. Thus, field-implemented post-weld heat treatment (PWHT) of the buttering is not required. Each layer of buttering applied will be liquid penetrant examined in accordance with the requirements of Section III, Subsection NB-5350 of the 1971 Edition through Summer 1973 Addenda of the ASME B&PV Code (pending approval of a relief request by the United States Nuclear Regulatory Commission). Figure 3B shows the drain configuration following completion of the temper bead buttering layers.

a,c,e

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 9 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 Figure 3B Drain Configuration Following Installation of Temper Bead Buttering Following the application of the temper bead buttering layers, the buttering will be manually prepared for the installation of the replacement drain coupling. Then, the replacement drain coupling will be installed via a partial penetration weld designed in accordance with Paragraph NB-3352.4(d) of Section III of the 1971 Edition through Summer 1973 Addenda of the ASME B&PV Code. The partial penetration weld will be installed using [ ]a,c,e or [

]a,c,e weld material. (Note: The partial penetration weld will not require PWHT as the weld will attach the replacement drain coupling to the previously installed

[ ]a,c,e buttering and will not directly contact the channel head base metal.) In accordance with Paragraph NB-3352.4(d) of Section III of the ASME B&PV Code, the partial penetration weld will be liquid penetrant examined progressively at an interval of every 3/16 inch of weld thickness in accordance with the requirements of Section III, Subsection NB-5350 of the 1971 Edition through Summer 1973 Addenda of the ASME B&PV Code. Upon completion of the partial penetration weld, the final surface of the weld will be liquid penetrant examined in accordance with the requirements of Section III, Subsection NB-5350 of the 1971 Edition through Summer 1973 Addenda of the ASME B&PV Code.

Finally, the partial penetration weld will be capped with a fillet weld using [

]a,c,e or [

]a,c,e weld material. (Note: The fillet weld will not require PWHT as the weld will attach the replacement drain coupling to the previously installed [

a,c,e

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 10 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024

]a,c,e or [ ]a,c,e partial penetration weld and will not directly contact the channel head base metal.) Upon completion, the final surface of the fillet weld will be liquid penetrant examined in accordance with the requirements of Section III, Subsection NB-5350 of the 1971 Edition through Summer 1973 Addenda of the ASME B&PV Code. Figure 4B shows the final modified drain configuration.

Figure 4B Final Modified Drain Configuration a,c,e

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 11 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 Attachment C Original Drain Coupling and Weld Build-up Removal and Replacement Drain Coupling Installation Sequence The sequence for the removal of the original channel head drain coupling and weld build-up and installation of the replacement drain coupling is below:

1. Machine out the existing coupling and existing Alloy 600 material

2. Verify Alloy 600 material has been removed using an acid etch test.

3. Perform initial measurement of bowl drain excavation to establish baseline depth.

4. Perform VT-1 visual examination on newly machined excavation (site to supply personnel to perform VT-1 exam).

5. Perform first temper bead pass to seal gap between drain pipe and channel head. This will prevent liquid penetrant from entering the annulus between the drain pipe and channel head.

6. Perform Liquid Penetrant (PT) examination of excavation.

7. Complete first layer of temper bead welding.

8. Mechanically prepare the surface for next temper bead layer.

9. Perform PT examination.

10. Weld second layer of temper bead.

11. Mechanically prepare the surface for next temper bead layer.

12. Perform PT examination.

13. Weld third layer of temper bead.

14. Mechanically prepare the surface of the last temper bead layer for PT examination.

15. Perform PT examination.

16. Manually prepare temper bead layers (pocket) for replacement drain coupling fit-up.

17. Measure the depth and verify there is [ ] a,c,e inch of [ ] a,c,e weld deposit at the bottom of the excavation.

18. Fit-up drain line coupling and perform first layer of Partial Joint Penetration (PJP) weld.

19. Prepare surface of first PJP weld layer for PT examination.

20. Perform PT examination on first PJP weld layer.

21. Measure depth of excavation to determine when next PT examination is required.

22. Continue making PJP weld until [ ] a,c,e inch of weld metal is deposited.

23. Prepare surface of PJP weld for PT examination.

24. Perform PT examination on PJP weld layer.

25. Continue making PJP weld until [ ] a,c,e inch of weld metal is deposited.

26. Prepare surface of PJP weld for PT examination.

27. Perform PT examination on PJP weld layer.

28. Repeat Steps 25, 26, and 27 until the thickness of the PJP weld has a min thickness of [ ] a,c,e inch and the PJP weld is even with the end of the temper bead weld.

29. Perform final PT examination on PJP weld.

30. Install fillet weld on coupling.

31. Prepare surface of fillet weld for PT examination and visual examination.

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 12 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 Attachment D Impracticality of Radiographic Examination of Modified Steam Generator Channel Head Drain The geometry of the channel head and the new channel head drain coupling weld joint does not lend itself to optimum film and source placement. Radiographic examination (RT) relies on a sufficiently large change in density, along the path taken by the radiation, to show up in the film. Just as with an x-ray of a broken bone, one takes images at multiple angles and only certain views show the break. The geometry of the modified channel head drain weld joint makes obtaining the necessary multiple angles virtually impossible. The geometry will also complicate the sizing of any given indication. Any indication in the film will be a projection, based on the angle that the radiation passes it. Foreshortening will occur and calculating what the actual length is from the projected view will very likely yield errant results. These errant results could result in an acceptable indication being perceived as unacceptable and leading to the unnecessary removal and re-application of weld material, which will subsequently increase radiological dose received by the field crew.

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 13 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 Attachment E Elimination of 48-Hour Hold Prior to Non-Destructive Examination of Temper Bead Weld per ASME B&PV Code Case N-839 Removal of the 48-hour hold after the temper bead weldment has cooled prior to performing the final non-destructive examination (NDE) is consistent with the requirements of ASME B&PV Code Case N-888-1 and is supported by the white paper, PVP2023-107489, that was developed for the proposed change. Code Case N-888-1 is the combination of Code Cases N-638 and N-839. Although ASME B&PV Code Case 888-1 is not approved in Regulatory Guide 1.147, it has been approved by the ASME B&PV Code Section XI Standards Committee. The white paper, PVP2023-107489, which was accepted for publication in the 2023 Pressure Vessels & Piping (PVP) Conference Proceedings in July 2023, provides a technical basis for eliminating the 48-hour hold requirement and includes operating experience that demonstrates the 48-hour hold is inconsequential.

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 14 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 Attachment F Limitations of Ultrasonic Examination of Channel Head Drain Modification A project was initiated to develop an ultrasonic (UT) examination method to perform a volumetric examination of the proposed modification of the steam generator channel head drains at Millstone Unit 3.

1. Sample Development A review of the ASME B&PV Code was performed to identify the applicable flaw type and dimensions applicable for this modification. These were located in the samples to provide the basis for demonstrating that the UT technique was suitable for the application.

In addition, volumetric type of reflectors, which would be acceptable in the field modification, were included.

Three different samples were made with varying depth of fill: 0.75 inch, 1.0 inch, and a full fill.

2. Probe Development Work with multiple vendors was initiated to design and develop applicable probes for this application. Since the partial fill designs would preclude scanning a probe in the traditional sense, a phased array technique was selected to allow for the steering of the beam to insonify the weld volume.

CIVA modeling was performed to assist in the probe design and the flaws present in the samples were placed in the CIVA model to assist in finalizing the probe design.

3. Technique Development The probes and phased array UT instrument were used to scan the samples and develop a procedure for the scanning and the interpreting of the data obtained.

4. Demonstration A demonstration was given to Dominion Energy representatives during the week of August 15th, 2022 and limitations to the technique were identified. Those limitations, and proposed additional efforts that could address them, are summarized below:

1. Coverage Examination must be 100% of the weld volume. At present, there is a volume close to the examination surface, at the radial minimum and extremes, where there does not appear to have coverage.

2. Low Angle Usage Per the Electric Power Research Institute (EPRI) Performance Demonstration Initiative (PDI) Weld Overlay (WOL) Procedure (ERPI-WOL-PA-1 Rev. 5) Table 8.9-1, for components with less than 4.0 inch diameters, angle ranges for axial scans are 45° to 80°. For components greater than or equal to 4.0 inch diameter, angle ranges for axial scans are 25° to 80°.

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 15 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 Thus, to comply with these requirements, sector sweep angles less than 25 cannot be used. Multiple flaws were only detected with angles less than 10.

3. Relevant vs Non-relevant Indications It is difficult to distinguish relevant (planar flaws) from non-relevant (volumetric) reflectors in coupons. Per the ASME B&PV Code, a crack or lack of fusion, of any size, is rejectable. Volumetric flaws are only rejectable if they exceed a specific length. The fact that the technique cannot clearly distinguish between the two types of reflectors could lead to false positives.

4. Volumetric Length Measurement As stated previously, volumetric indications below a specified length are acceptable. At present, the technique overestimates the length of volumetric indications. This could result in false positives.

5. Flaw Sample Set in Coupons One Dominion Energy representative stated that there may be flaws that are harder to find in the field compared to the flaws in the coupons.

6. Transverse Flaws The ability of the technique to detect flaws in this orientation is marginal. In addition, length sizing is limited. It was even more difficult to detect these types of flaws in the full fill sample.

7. Field Ergonomics During the demonstration, the samples were laying on the ground and it was relatively easy for the operator to scan them. Work in the field will be overhead in a high dose zone. It is not clear how this will affect the inspectors performance.

5. Challenges Associated with the Full Fill

1. UT Issues It was noted during the development that the attenuation of the modifications weld joint was sufficient that the full fill sample posed unique challenges over and above the partial fill samples. Based on this experience, and based on other EPRI WOL applications, the use of a lower frequency probe is the solution to this attenuation issue. Thus, for the full fill weld joint, a lower frequency probe (1 MHz) would need to be investigated.

Initial evaluations could be performed using the CIVA model; however, a 1 MHz probe would need to be procured and the full fill sample scanned to benchmark the CIVA model results and demonstrate the ability to find, characterize, and length size the flaws in the full fill sample.

2. Welding Issues Full Fill One approach to the modification to the channel head drain is to replace the drain coupling weld joint in a like-for-like, full fill configuration. The welding in the field will require a temper bead welding approach due to the channel head material. There are two temper bead approaches which can be utilized; ASME Section XI, IWA-4630, which requires preheat and post hydrogen soak or ASME

• • • This record was final approved on 03/15/2024 09:49:57. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 Page 16 of 16 Our ref: LTR-CECO-24-001-NP, Rev. 0 March 14, 2024 B&PV Code Case N-839, which is ambient temper bead. Both approaches require the application of 3 layers of weld metal to the excavation in a controlled manner. With a full fill approach, to accomplish proper tempering at the corner junction of the channel head surface and the excavation, the temper bead layers will have to be installed up to the corner and then extended out onto the surface of the channel head. The width of the band of weld metal has to be wide enough to support the required 3 layers for proper tempering. After the 3 layers of temper bead have been applied to the surface of the excavation including the material applied to the surface of the channel head, and post temper bead welding requirements fulfilled, the coupling will be installed using a J-groove approach using normal welding practice followed by the installation of the fillet weld.

To support UT examination with a full fill approach, the temper bead material applied to the channel head surface will have to be ground off to facilitate a smooth transition for the UT probe. Additionally, the material between the coupling and the temper bead will have to be ground to meet the radial dimensions of the channel head using templates as guidance to assure proper UT coverage and smooth probe traverse. UT and surface examinations will be performed after surface contouring has been complete.

After successful UT examination of the weld, the fillet weld between the coupling and ground surface will be installed.

Partial Fill The approach that has been successfully used on P1 channel head drain modifications/repairs is to partially fill the excavation to a [ ] a,c,e inch depth followed by the installation of the fillet weld. The P3 G3 channel head material for the Millstone Unit 3 SGs will require a temper bead welding technique. Using a temper bead technique, the layers will be contained within the excavation and limited to the depth required to meet the mechanical requirement of the modification design. After the 3 layers of temper bead are installed and post-temper bead requirements fulfilled, the coupling will be installed via a partial penetration weld using normal welding practice. The surface of the completed weld will require very careful surface preparation to meet the smoothness and contour required for the UT probe.

Following the successful UT examination, the surface will be liquid penetrant (PT) examined. The fillet weld will then be installed and examined with visual examination (VT) and PT.

False positives with either path, Full Fill or Partial Fill, will create modifications which may require the removal of the material within the temper bead portion of the modification weld. This will require observance of the original temper bead methodology used for the modification. Excavation to support temper bead repair will result in additional material removal to form a suitable excavation to support proper tempering. Once completed, the surface will require additional blending to achieve a suitable surface to support the UT probe. Given the extent of the reported indication, full removal may be required due to the limited access within the modification excavation.

Serial No.24-103 Docket No. 50-423 ENCLOSURE 4 WESTINGHOUSE APPLICATION FOR WITTHOLDING AND AFFIDAVIT MILLSTONE POWER STATION UNIT 3 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

• • • This record was final approved on 03/15/2024 15:38:58. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 AFFIDAVIT CAW-24-012 Page 1 of 3 Commonwealth of Pennsylvania:

County of Butler:

(1)

I, Zachary Harper, Senior Manager, Licensing, have been specifically delegated and authorized to apply for withholding and execute this Affidavit on behalf of Westinghouse Electric Company LLC (Westinghouse).

(2)

I am requesting the proprietary portions of LTR-CECO-24-001-P be withheld from public disclosure under 10 CFR 2.390.

(3)

I have personal knowledge of the criteria and procedures utilized by Westinghouse in designating information as a trade secret, privileged, or as confidential commercial or financial information.

(4)

Pursuant to 10 CFR 2.390, the following is furnished for consideration by the Commission in determining whether the information sought to be withheld from public disclosure should be withheld.

(i)

The information sought to be withheld from public disclosure is owned and has been held in confidence by Westinghouse and is not customarily disclosed to the public.

(ii)

The information sought to be withheld is being transmitted to the Commission in confidence and, to Westinghouses knowledge, is not available in public sources.

(iii)

Westinghouse notes that a showing of substantial harm is no longer an applicable criterion for analyzing whether a document should be withheld from public disclosure. Nevertheless, public disclosure of this proprietary information is likely to cause substantial harm to the competitive position of Westinghouse because it would enhance the ability of competitors to provide similar technical evaluation justifications and licensing defense services for commercial power reactors without commensurate expenses. Also, public disclosure of the information would enable others to use the information to meet NRC requirements for licensing documentation without purchasing the right to use the information.

• • • This record was final approved on 03/15/2024 15:38:58. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 AFFIDAVIT CAW-24-012 Page 2 of 3 (5)

Westinghouse has policies in place to identify proprietary information. Under that system, information is held in confidence if it falls in one or more of several types, the release of which might result in the loss of an existing or potential competitive advantage, as follows:

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The information reveals the distinguishing aspects of a process (or component, structure, tool, method, etc.) where prevention of its use by any of Westinghouse's competitors without license from Westinghouse constitutes a competitive economic advantage over other companies.

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Its use by a competitor would reduce his expenditure of resources or improve his competitive position in the design, manufacture, shipment, installation, assurance of quality, or licensing a similar product.

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It reveals cost or price information, production capacities, budget levels, or commercial strategies of Westinghouse, its customers or suppliers.

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It reveals aspects of past, present, or future Westinghouse or customer funded development plans and programs of potential commercial value to Westinghouse.

(f)

It contains patentable ideas, for which patent protection may be desirable.

(6)

The attached documents are bracketed and marked to indicate the bases for withholding. The justification for withholding is indicated in both versions by means of lower-case letters (a) through (f) located as a superscript immediately following the brackets enclosing each item of information being identified as proprietary or in the margin opposite such information. These lower-case letters refer to the types of information Westinghouse customarily holds in confidence identified in Sections (5)(a) through (f) of this Affidavit.

• • • This record was final approved on 03/15/2024 15:38:58. (This statement was added by the PRIME system upon its validation)

Westinghouse Non-Proprietary Class 3 AFFIDAVIT CAW-24-012 Page 3 of 3 I declare that the averments of fact set forth in this Affidavit are true and correct to the best of my knowledge, information, and belief. I declare under penalty of perjury that the foregoing is true and correct.

Executed on: 3/15/2024 Signed electronically by Zachary Harper