ML23299A305

Response to Request for Additional Information – Relief Request 70 – Proposed Alternatives for Pressurizer Lower Shell Temperature Nozzle

ML23299A305
Person / Time
Site:	Palo Verde
Issue date:	10/26/2023
From:	Harbor C Arizona Public Service Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
102-08695-CDH/MSC
Download: ML23299A305 (1)

Text

10 CFR 50.55a

Cary D. Harbor Vice President Regulatory & Oversight

Palo Verde 102-08695-CDH/MSC Nuclear Generating Station October 26, 2023 P.O. Box 52034 Phoenix, AZ 85072 Mail Station 7605 U.S. Nuclear Regulatory Commission Tel: 623.393.7953

ATTN: Document Control Desk Washington, DC 20555-0001

Subject:

Palo Verde Nuclear Generating Station Unit 1 Docket No. STN 50-528 Renewed Operating License Number NPF-41 Response to Request for Additional Information - Relief Request 70 - Proposed Alternatives for Pressurizer Lower Shell Temperature Nozzle

By letter number 102-08690, dated October 23, 2023 [Agencywide Documents Access and Management System (ADAMS) Accession No. ML23296A254], and pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a, Codes and Standards, paragraph (z)(1), Arizona Public Service Company (APS) requested Nuclear Regulatory Commission (NRC) authorization of Relief Request 70, on the basis that the alternatives provide an acceptable level of quality and safety. APS proposed alternatives to American Society of Mechanical Engineers (ASME) Pressure Vessel Code,Section XI, 2013 Edition, and ASME Code Case N-638-10, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine [Gas Tungsten Arc Welding] GTAW Temper Bead Technique,Section XI, Division 1, dated May 6, 2019, for Palo Verde Nuclear Generating Station (PVNGS), Unit 1.

On October 25, 2023, the NRC staff provided a request for additional information (RAI) to support their review of the requested relief. The Enclosure to this letter provides the APS response to the NRC RAI. A clarification call was held between APS and the NRC staff on October 25, 2023. No commitments are being made to the NRC by this letter.

Should you need further information regarding this letter, please contact Matthew S.

Cox, Licensing Department Leader, at (623) 393-5753.

Sincerely, Harbor, Cary Digitally signed by Harbor, Cary (Z16762)

(Z16762) Date: 2023.10.26 16:07:10 -07'00'

CDH/MSC/cr

Enclosure:

Response to Request for Additional Information - Relief Request 70 -

Proposed Alternatives in Accordance with 10 CFR 50.55a(z)(1) for Pressurizer Lower Shell Temperature Nozzle

cc: J. D. Monninger NRC Region IV Regional Administrator S. P. Lingam NRC NRR Project Manager for PVNGS L. N. Merker NRC Senior Resident Inspector for PVNGS

A member of the STARS Alliance, LLC

Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek Enclosure

Response to Request for Additional Information - Relief Request 70 - Proposed Alternatives in Accordance with 10 CFR 50.55a(z)(1) for Pressurizer Lower Shell Temperature Nozzle Enclosure Relief Request 70 - RAI Response

Introduction

By letter number 102-08690, dated October 23, 2023 [Agencywide Documents Access and Management System (ADAMS) Accession No. ML23296A254], Arizona Public Service Company (APS) requested Nuclear Regulatory Commission (NRC) authorization of Relief Request 70, on the basis that the alternatives provide an acceptable level of quality and safety. APS proposed alternatives to American Society of Mechanical Engineers (ASME)

Pressure Vessel Code,Section XI, 2013 Edition, and ASME Code Case N-638-10, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine [Gas Tungsten Arc Welding]

GTAW Temper Bead Technique,Section XI, Division 1, regarding alternate repair of a pressurizer thermowell nozzle at Palo Verde Nuclear Generating Station (PVNGS), Unit 1.

The NRC staff requested the following additional information to complete its review of the relief request. The NRC request for additional information (RAI) is stated first followed by the APS response.

NRC RAIs and APS Responses

NRC RAI-1

Page 8 of the relief request, section B, Proposed Alternatives, second paragraph states in part that A design analysis is being performed in accordance with the design requirements of ASME Code Section III, 2013 edition. The analysis will confirm that the new nozzle will not eject from the pressurizer under design conditions Provide additional information that supports the conclusion that the preliminary design analysis demonstrates that the proposed new nozzle satisfies the design requirements of ASME Code Section III, 2013 edition, or the construction code for one fuel cycle of operation.

APS Response

The pressurizer lower shell temperature nozzle repair design satisfies the criteria of the 2013 Edition of ASME Section III, Subsection NB, for at least one fuel cycle of operation.

This qualification for one cycle quantitatively demonstrates that all primary stress criteria are satisfied and qualitatively supports that criteria related to secondary stress and fatigue are satisfied for at least one cycle of operation.

NRC RAI-2

Page 9 of the relief request, section C, Basis for Flaw Analytical Evaluation, third paragraph states in part that the existing 2010 J-groove weld flaw analyses for the repaired pressurizer is used for the proposed repair. Discuss whether the 2010 flaw analysis was submitted to the NRC under previous licensing actions? If not, please provide the following information.

(a) Page 10 of the relief request, 5th paragraph states, in part, that Results from the bounding LEFM [linear elastic fracture mechanics] analysis indicated the initial and final flaw sizes on the pressurizer lower shell temperature nozzle ALJGW [As Left J-groove weld] exceeded the LEFM ASME Section XI IWB-3610 criterion for several transients. Describe the initial flaw size in the ALJGW and how the initial flaw propagates to the final flaw sizes in the pressurizer lower shell.

1 Enclosure Relief Request 70 - RAI Response

(b) Page 10 of the relief request, last sentence, states that Therefore, the results from the EPFM [elastic-plastic fracture mechanics] analysis are conservative and bound the current repair OCJ [one cycle justification] in terms of safety factors. Discuss the results of the EPFM analysis performed in 2010 in terms of final flaw sizes.

Discuss the acceptance criteria in the EPFM analysis.

(c) Page 11 of the relief request, second paragraph, states in part that Therefore, the OCJ for PVNGS Unit 1 pressurizer lower shell temperature nozzle further evaluates the primary stress limits of the repaired configuration considering a final flaw depth and width for fatigue plus corrosion flaw growth through the next cycle Provide the final flaw depth and width through the next cycle. If the flaw depth and width through the next cycle is not available, discuss the initial flaw depth and width assumed in the flaw evaluation.

APS Response - General

The flaw analyses performed in 2010 for the side shell temperature element (TE-101) modified in 1992 by Babcock & Wilcox (B&W) was not submitted to the NRC, as it was a pre-emptive replacement. The flaw analyses (LEFM & EPFM) were performed by Structural Integrity in 2010 and were recently provided to the NRC staff for review.

APS Response 2(a)

The initial flaw size in the LEFM analysis, performed in 2010 and recently provided for review, is at the interface of the susceptible Alloy 600 weld butter material with the pressurizer material. The flaw propagates into the low alloy steel (LAS) base metal material through fatigue crack growth only and a crack growth analysis is performed for a maximum operating period of 60 years. The fatigue crack growth is evaluated using fatigue crack growth rate for LAS material from ASME Section XI (2001 Edition with 2003 Addenda).

Loads considered for evaluations are weld residual stresses, transient thermal stresses, and internal pressure (including the crack face).

APS Response 2(b)

For the EPFM evaluation, consistent with the LEFM evaluation, it is determined that the final flaw size used in the 2010 EPFM evaluation for 60 years of fatigue crack growth bounds the projected flaw size applicable to the one-cycle justification (OCJ) considering fatigue crack growth plus corrosion through the next cycle. Using the J-T instability analysis approach described in the ASME Code,Section XI, Nonmandatory Appendix K, K-4330, crack instability is predicted when the applied J-T line intersects the appropriate J-T material curve. For the conditions requiring EPFM evaluation, the applied J, with safety factors of 3.0 on primary pressure loads and 1.5 on secondary loads, for the initial and final flaw size are below the J-T material curve intersection points. Therefore, the potential remnant cracking is acceptable in accordance with the flaw evaluation principles of ASME Code,Section XI, Nonmandatory Appendix K.

APS Response 2(c)

For the OCJ evaluation, the final flaw depth, afinal, is estimated considering fatigue plus corrosion crack growth from the original repair through the next cycle. The final fatigue crack depth from the original repair through the next cycle, afatigue, is estimated based on the plot of flaw depth over number of cycles available at the 2010 LEFM flaw analysis, with the applicable number of cycles prorated from the total number of cycles used in the flaw

2 Enclosure Relief Request 70 - RAI Response

evaluation for 60 years of operation. Additional corrosion crack growth from the original repair through the next cycle of ¨ acorrosion is added for a total final crack depth through the next cycle of afinal = afatigue + ¨ acorrosion. Per design drawing, the initial flaw depth to length ratio, ao/lo, is calculated to be approximately 1.0, therefore, final flaw length, lfinal is estimated to be approximately equal to afinal.

NRC RAI-3

Page 11 of the relief request, section C paragraph, states, in part, that Therefore, the OCJ for PVNGS Unit 1 pressurizer lower shell temperature nozzle further evaluates the primary stress limits of the repaired configuration considering a final flaw depth and width for fatigue plus corrosion flaw growth through the next cycle. To evaluate the requirement, article NB-3228.1 of Section III of the ASME Code is utilized. Discuss whether the proposed repair satisfy NB-3228.1 for one fuel cycle of operation.

APS Response

The criteria from NB-3228.1 is met for the OCJ evaluation. The analysis was run up to a pressure 1.67 times the design pressure, exceeding the requirement of 150% of the design pressure.

NRC RAI-4

Related to page 11 of the relief request, section E, Corrosion Evaluation, provide additional information that supports the conclusion that the preliminary corrosion evaluation demonstrates that corrosion will not affect the operation of the proposed repair for one fuel cycle of operation.

APS Response

The corrosion evaluation considers possible corrosion mechanisms that could affect the implemented repair for one operating cycle. These mechanisms include general corrosion, galvanic corrosion, crevice corrosion, and hydrogen embrittlement of the low alloy steel base metal. In addition, stress corrosion cracking of the low alloy steel, Alloy 690, Alloy 52M and Type 316 materials are considered in addition to low temperature crack propagation of the nickel-based materials. However, in principle, only corrosion of the low alloy steel is expected to be of concern, and a conservative corrosion rate taking into account the time periods of plant start up, plant operating, and plant shutdown is calculated. This corrosion rate is then utilized as an input into other analyses to establish the integrity of the component in the repaired configuration, for one operating cycle [i.e.,

Section III analysis and the Flaw Analytical Evaluation (As Left J-Groove Weld Analysis)].

NRC RAI-5

Related to pages 11 and 12 of the relief request, section F, Loose Parts Evaluation, provide additional information that supports the conclusion that the preliminary loose parts evaluation will not affect the operation of the proposed repair for one fuel cycle of operation.

3 Enclosure Relief Request 70 - RAI Response

APS Response

The pressurizer lower shell temperature nozzle repair has been evaluated for impact from loose parts and it has been determined that there are no anticipated consequences to plant safety or proper operation for at least one cycle of operation as a result of potential loose parts.

NRC RAI-6

Section 5.E of the relief request discusses, in part, that the repair will result in the pressurizer low alloy steel being exposed to the reactor coolant, which implies that the corrosion evaluation will be performed for what can be described as current Leak Path 2 based upon the repair sketch in Figure 2. If the primary water stress corrosion cracking is caused by Potential Leak Path 1 (as defined in Figure 1A on Page 4 of Relief Request 70),

discuss whether roll expanding the alloy 690 outer sleeve in the penetration bore would be sufficient to inhibit continued leakage or will the corrosion evaluation include an analysis of Leak Path 1 along with the potential for corrosion caused by the exposed alloy steel of the pressurizer?

APS Response

The outboard end of the corrosion sleeve is no longer welded to the structure, so discussion of Leak Paths 1 or 2 is no longer relevant. Therefore, both leak paths (Potential Leak Paths 1 and 2 in Figure 1A on Page 4 of Relief Request 70) have been considered in the corrosion evaluation.

The roll expansion is only intended to prevent movement of the corrosion sleeve in the unlikely event that the autogenous weld on the inboard end of the sleeve fails. It is not intended to prevent leakage and the sleeve is no longer credited with prevention of corrosion in the low alloy steel.

With respect to the potential for corrosion, the following comments are applicable. The general corrosion rate for the exposed low alloy steel is determined based on a combined corrosion rate of startup, shutdown, and operating conditions based on historical times spent in these conditions. This corrosion rate applies to anywhere that low alloy steel is exposed, including behind the rolled sleeve (blue line shown in Figure 1B), as the conditions in both this area and the exposed low alloy steel near the new Alloy 690 nozzle (green line shown in Figure 1B) are expected to be very similar.

Figure 1B: Pressurizer Lower Shell Temperature Nozzle and Sleeve

In some situations, crevice corrosion can accelerate the rate of corrosion; as determined in

4 Enclosure Relief Request 70 - RAI Response

the corrosion evaluation, this is not likely for the modified configuration. Additionally, rolling of the sleeve, between the red lines in Figure 1B, makes it unlikely a crevice is formed between the sleeve and the low alloy steel in this area. Therefore, the general corrosion rate is also applicable to the low alloy steel to this area. The general corrosion rate for the exposed low alloy steel behind the rolled sleeve and near the Alloy 690 sleeve is expected to be similar. Therefore, both leak paths (Potential Leak Paths 1 and 2 in Figure 1A on Page 4 of Relief Request 70) have been considered.

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