NMP1L3515, Submittal of Emergency Relief Request I5R-11 Concerning the Installation of a Weld Overlay on Reactor Pressure Vessel Recirculation Inlet Nozzle N2E Safe End-to-Nozzle Dissimilar Metal Weld (32-WD-208)

Submittal of Emergency Relief Request I5R-11 Concerning the Installation of a Weld Overlay on Reactor Pressure Vessel Recirculation Inlet Nozzle N2E Safe End-to-Nozzle Dissimilar Metal Weld (32-WD-208)

ML23086C088
Person / Time
Site:	Nine Mile Point
Issue date:	03/27/2023
From:	David Gudger Constellation Energy Generation
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NMP1L3515
Download: ML23086C088 (1)

Text

200 Exelon Way Kennett Square, PA 19348 www.constellation.com 10 CFR 50.55a NMP1L3515 March 27, 2023 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Nine Mile Point Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-63 NRC Docket No. 50-220

Subject:

Submittal of Emergency Relief Request I5R-11 Concerning the Installation of a Weld Overlay on Reactor Pressure Vessel Recirculation Inlet Nozzle N2E Safe End-to-Nozzle Dissimilar Metal Weld (32-WD-208)

Reference:

1) Letter from D. Gudger (Constellation Energy Generation, LLC) to U.S.

Nuclear Regulatory Commission, Submittal of Emergency Relief Request I5R-11 Concerning the Installation of a Weld Overlay on Reactor Pressure Vessel Recirculation Inlet Nozzle N2E Safe End-to-Nozzle Dissimilar Metal Weld (32-WD-208) dated March 24, 2023 (ML23083B991)

In the Reference 1 letter, Constellation Energy Generation, LLC (CEG) requested emergency approval of the proposed alternative associated with the repair of the recirculation inlet nozzle N2E safe end-to-nozzle dissimilar metal (DM) weld. In a conference call on March 27, 2023, the U.S. Nuclear Regulatory Commission requested additional information regarding the design of the weld overlay. Attached is the requested information.

If you have any questions concerning this letter, please contact Tom Loomis at Thomas.Loomis@constellation.com.

Respectfully, David T. Gudger Senior Manager - Licensing & Regulatory Affairs Constellation Energy Generation, LLC

Attachment:

Evaluation of a Leakage Barrier Weld Overlay cc: Regional Administrator, Region I, NRC NRC Senior Resident Inspector, NMP Project Manager NRC, NMP A. L. Peterson, NYSERDA

ATTACHMENT Evaluation of a Leakage Barrier Weld Overlay

5215 Hellyer Avenue, Suite 210, San Jose, CA 95138 March 25, 2023 REPORT NO. 2300376.401 REVISION: 0 PROJECT NO. 2300376.00 Quality Program: Nuclear Commercial Jennifer Bianculli Nine Mile Point P.O. Box 63 Lycoming NY 13093

Subject:

Evaluation of a Leakage Barrier Weld Overlay

Dear Ms. Bianculli,

Nine Mile Point Nuclear Station, Unit 1 (NMP) identified a flaw in the recirculation discharge N2E nozzle-to-safe end dissimilar metal weld (DMW), 32-WD-208 [1]. Based on the size and location of the flaw, the installation of a fully compliant full structural weld overlay (FSWOL) was initially considered using the rules of ASME Code Case N-740-2 [4].

However, given the protracted welding time that would be required to install a FSWOL, and that the inspection identified the presence of only one axial flaw, NMP is proposing to apply what was historically called a Design weld overlay using guidance from Section XI, Nonmandatory Appendix Q, Weld Overlay Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping Weldments [2].

A Relief Request will be required and will be prepared separately from this document. This document will develop the sizing requirements for a Design weld overlay taking guidance from Appendix Q, Code Case N-740-2 and utilizing other engineering principles.

It is noted that the Relief Request to be submitted is based on the use of ASME Code Case N-740-2 as the weld overlay material will be Alloy 52M (Alloy 690) deposited over an existing Alloy 82/182 weldment. Guidance from Appendix Q will also be invoked in the Relief Request as providing guidance for the design requirements for a Design weld overlay.

© 2023 by Structural Integrity Associates, Inc. All rights reserved. No part of this document or the related files may be reproduced or transmitted in any form, without the prior written permission of Structural Integrity Associates, Inc.

MCG00700 08.21.20

March 25, 2023 Jennifer Bianculli Evaluation of a Leakage Barrier Weld Overlay NONMANDATORY APPENDIX Q / CODE CASE N-740-2 Article Q-3000(a)(5) of Appendix Q states:

For weldments with four or fewer axial flaws, each shorter than 1.5 in. (38 mm), and no circumferential flaws, the weld reinforcement shall satisfy the requirements of Q-2000(d). No additional structural reinforcement is required. The axial length of the overlay shall cover the weldment and the heat-affected zones, and shall extend at least 1/2 in. (13 mm) beyond the ends of the observed flaws. The requirements of (b)(1), (b)(3), and (b)(4) need not be met.

Per Reference [1], the flaw is sized at 1.65 in length, 1.52 in depth (~83% through thickness) and is axially oriented. Thus, there is only one flaw, and it is axially oriented. However, the flaw is slightly longer than that allowed in Q-3000(a)(5), and thus will also require relief. A justification is provided below.

Article Q-2000(d) of Appendix Q states:

The weld reinforcement shall consist of at least two weld layers having asdeposited delta ferrite content of at least 7.5 FN. The first layer of weld metal with delta ferrite content of at least 7.5 FN shall constitute the first layer of the weld reinforcement that may be credited toward the required thickness. Alternatively, first layers of at least 5 FN are acceptable, provided the carbon content of the deposited weld metal is determined by chemical analysis to be less than 0.02%.

The Article Q-2000(d) delta ferrite requirement is specific for a stainless steel weld overlay material. Given that the nozzle-to-safe end weld is Inconel 82, Style A, Class 5 [3], the necessary weld overlay material would be ASME Code,Section II, SFA-5.14, ERNiCrFe-7A (Alloy 52M). Per ASME Code Case N-740-2 [4], Section 1.2(e)(2):

The austenitic nickel alloy weld overlay shall consist of at least two weld layers deposited using a filler material with a Cr content of at least 28%. The first layer of weld metal deposited may not be credited toward the required thickness.

Alternatively, for BWR applications, a diluted layer may be credited toward the required thickness, provided the portion of the layer over the austenitic base material, austenitic filler material weld, and the associated dilution zone from an adjacent ferritic base material contain at least 20% Cr, and the Cr content of the deposited weld metal is determined by chemical analysis of the production weld or of a representative coupon taken from a mockup prepared in accordance with the WPS for the production weld.

Therefore, the weld filler metal requirements of ASME Code Case, N-740-2 are invoked.

Report No. 2300376.401 R0 PAGE l 2

March 25, 2023 Jennifer Bianculli Evaluation of a Leakage Barrier Weld Overlay OVER-SIZED (LENGTH) FLAW JUSTIFCATION As stated, earlier, the measured axial flaw length is 1.65, but Appendix Q, Q-3000(a)(5), limits the axial flaw length to 1.5.

Per ASME Code,Section XI, C-5410 [2], the maximum flaw length for which the stability of a through-wall flaw is maintained is defined as, 1.58 1 (1)

where, f = flow stress, defined in C-8200 as f = (y + u) / 2 h = hoop stress, with structural factor, = SFaxial*pRm/t Rm = mean pipe radius t = pipe wall thickness p = internal pipe pressure for appropriate Service Level condition This equation actually provides the critical flaw length, crit, for a through-wall axial flaw, if the unfactored hoop stress is used. To determine the allowable flaw length, a structural factor must be applied to the hoop stress (h). Per ASME Code,Section XI, Appendix C, C-2622, the Service Level A structural factor for an axial flaw is SFaxial = 2.7.

The material properties of the nozzle (SA-336), the weld (Alloy 82/182. N06600) and the safe end (SA-182, F316) are extracted at the Design Temperature of 570°F along with the Design Pressure of 1200 psig [3].

Reference [3.a] indicates that at the nozzle-to-safe end weld, the safe end side outside diameter is 29.118 and the inside diameter is 25.780, which gives a wall thickness of 1.669.

Reference [3.b] indicates that at the nozzle-to-safe end weld, the nozzle outside diameter is 29-1/16 with a base metal inside diameter of 26.188, which gives a wall thickness of 1.43725.

The nozzle cladding will be conservatively excluded. When evaluating the Alloy 600 weld metal, the safe dimensions are used.

Using Equation 1, and the Service Level A structural factor of 2.7 applied to the hoop stress, the resulting allowable axial flaw length, allow, for a through-wall axial flaw under the Service Level A conditions is calculated for the three materials as follows:

Report No. 2300376.401 R0 PAGE l 3

March 25, 2023 Jennifer Bianculli Evaluation of a Leakage Barrier Weld Overlay Rm t P h f crit allow Material (inches) (inches) (psig) (psi) (psi) (inches) (inches)

SA336 13.813 1.437 1200 11533 61215 36.7 11.9 Alloy 600 13.725 1.669 1200 9868 58430 44.1 14.8 SA182 F316 13.725 1.669 1200 9868 45515 34.0 10.5 As can be seen in the resulting table, the shortest critical flaw length is 34.0 inches, while the shortest allowable flaw length (which includes the structural factor) is 10.5 inches. The measured indication length of 1.65 is only 15.7% of the allowable length and 4.9% of the critical flaw length. Thus, the fact that the flaw is slightly longer than the Article Q-3000(a)(5) length of 1.5 is not adverse.

SIZING - LENGTH As indicated above, Appendix Q states that the length of the Design overlay is:

The axial length of the overlay shall cover the weldment and the heat-affected zones, and shall extend at least 1/2 in. (13 mm) beyond the ends of the observed flaws.

Per Reference [7] the flaw is 1.65 long and is centered on the DMW, and the DMW crown width is 1.88. As weld overlay installations are measured from the toes of the weld, and in this case, the toes of the weld will extend beyond the flaw ends, the 0.5 inch additional length will be applied outside of the weld crown toes. Thus, the minimum weld overlay length is 1.88 + (0.5 x

2) = 2.88. Note that this length will have to be increased beyond this value in order to facilitate ultrasonic (UT) examination of the overlay inspection box, Figure 2 of ASME Code Case N-740-2.

Report No. 2300376.401 R0 PAGE l 4

March 25, 2023 Jennifer Bianculli Evaluation of a Leakage Barrier Weld Overlay SIZING - THICKNESS While Appendix Q (Q-2000(d)) requires two layers minimum be deposited, it does not define the layer thickness required. Per Reference [6], Westinghouse indicates that a layer of weld metal after cleanup is 0.070. Thus, two layers would be approximately 0.14 thick.

However, the Design weld overlay will be applied to the ferritic nozzle material. Thus, ambient temperature temper bead welding will be required to avoid post-weld heat treatment of the nozzle. The temper bead requirements of ASME Code Case N-638-10 [8] will be used for qualification of the welding process. However, Section I-3(c) of ASME Code Case N-740-2 [4]

states:

The area to be welded shall be buttered with a deposit of at least three layers to achieve at least 18 in. (3 mm) overlay thickness with the heat input for each layer controlled to within

+/-10% of that used in the procedure qualification test. The heat input of the first three layers shall not exceed 45 kJ/in. (1.8 kJ/mm) under any conditions. Particular care shall be taken in the placement of the weld layers of the austenitic overlay filler material at the toe of the overlay to ensure that the HAZ and ferritic base metal are tempered. Subsequent layers shall be deposited with a heat input not exceeding that used for layers beyond the third layer in the procedure qualification.

It is Structural Integrity Associates (SI) understanding that NMP intends to complete the rest of the weld overlay at a later date thereby converting the Design weld overlay into a FSWOL. SI Report No. 2300376.401 R0 PAGE l 5

March 25, 2023 Jennifer Bianculli Evaluation of a Leakage Barrier Weld Overlay therefore recommends the entire temper bead process be completed as part of the Design weld overlay implementation and be consistent with the temper bead layer requirements of ASME Code Case N-740-2. Thus, three layers should be applied, resulting in a minimum weld overlay thickness of 0.21 (at on the nozzle side).

Finally, a simplified crack growth evaluation is performed using IGSCC growth only to access the resistance of the Design weld overlay to future Intergranular Stress Corrosion Cracking (IGSCC) for one operating cycle. While, fatigue crack growth is certainly possible, the flaw is located in the recirculation system, which does not see significant pressure cycling, which is the driving load for axial flaw crack growth. Therefore, any fatigue crack growth within a single operating cycle is considered to be insignificant.

For this simplified evaluation, the axial flaw will be conservatively assumed to be 100% through-wall (i.e., it has reached the interface of the base metal and Design weld overlay (the actual flaw is only 83% through-wall)) and will immediately start to grow into the Alloy 52M overlay. The necessary Design overlay thickness must be such that the flaw will not grow through the overlay within one operating cycle (i.e., 2 years).

Per Reference [5], IGSCC growth in Alloy 52M weld material is computed using a constant, K-independent, rate of 4x10E-9 mm/s = 5.67x10E-7 in/hr = 4.97x10E-3 in/yr. This is the highest rate shown in Figure 47 of Reference [5] (see the following figure).

Report No. 2300376.401 R0 PAGE l 6

March 25, 2023 Jennifer Bianculli Evaluation of a Leakage Barrier Weld Overlay The proposed Design overlay requires a thickness of Alloy 52M weld filler metal over the ferritic nozzle of 0.21. Because potential use of stainless steel buffer layers and bridge beads, the Alloy 52M over the safe end/buffer layer can have a thickness as little as 0.10. Using this smaller thickness of Alloy 52M over the safe end (0.10), it would take 0.10 / 4.97x10E-3/yr. =

20.1 years to grow through the safe end weld overlay thickness by IGSCC alone. Note that this conservatively neglects the thickness of the buffer layer and/or bridge beads as additional crack growth margin.

Report No. 2300376.401 R0 PAGE l 7

March 25, 2023 Jennifer Bianculli Evaluation of a Leakage Barrier Weld Overlay RECOMMENDATION In conclusion, it is recommended that the Design weld overlay be at least 2.88 long and 0.21 thick over the ferritic nozzle.

The weld overlay length is conservatively based on the width of the weld crown (1.88),

which is greater than the flaw length (1.65), which is also contained within the weld crown width.

The thickness is based on the ASME Code Case N-740-2, Appendix I requirement that the first three layers of a weld overlay be applied to a ferritic material using ambient temperature temper bead rules. It is acknowledged that the rules of ASME Code Case N-638-10 will be used for qualification of the welding process.

Note that these dimensions do not include any added length or thickness that might be required to facilitate ultrasonic examination.

In addition, the use of these dimensions will require a Relief Request to support the use of Code Case N-740-2 [4], the use of elements of Nonmandatory Appendix Q [2], and the allowance of the slightly larger length of the axial indication.

Report No. 2300376.401 R0 PAGE l 8

March 25, 2023 Jennifer Bianculli Evaluation of a Leakage Barrier Weld Overlay REFERENCES

1. GE/Hitachi Customer Notification Form (CNF), Project: Nine Mile Point, Project No.

N1R27, CNF# CNF-ISI-006, Identification No. 32-WD-208 (N2E), dated 3-18-23, SI File No. 2300376.202.

2. ASME Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 2013 Edition.

3. Constellation Transmittal of Design Information, ID#: TODI-23-001, Revision 1, SI File No. 2300376.201.

a. Ref 4 - CWI-1399K-4-15.pdf

b. Ref 8 - E231-5650000.pdf

4. ASME Boiler and Pressure Vessel Code, Code Case N-740-2, Full Structural Dissimilar Metal Weld Overlay for Repair or Mitigation of Class 1, 2, and 3 Items,Section XI, Division 1.

5. Andresen, Peter L., SCC of High Cr Alloys in BWR Environments, 15th International Conference on Environmental Degradation, TMS (The Minerals, Metals & Materials Society), 2011, SI File No. 2300376.205.

6. Email from Davis Barton (Westinghouse) to Richard Mattson (SI), dated March 22, 2023, at 10:28 AM,

Subject:

RE: Follow up Question on N2E weld, SI File No. 2300376.204.

7. Email from Michael Sally (Constellation) to Dick Mattson (SI),

Subject:

RE: Flaw Orientation and Sizing, dated March 24, 2023, SI File No. 2300376.202.

8. ASME Boiler and Pressure Vessel Code, Code Case N-638-10, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division 1.

Report No. 2300376.401 R0 PAGE l 9

March 25, 2023 Jennifer Bianculli Evaluation of a Leakage Barrier Weld Overlay Prepared by: Verified by:

Richard L. Bax Jr. James W. Axline, P.E.

Associate Associate Approved by:

Richard A. Mattson, P.E.

Senior Associate Report No. 2300376.401 R0 PAGE l 10