ML24213A329

Transmittal of Relief Request (RR) No. 72: Re-Submittal of RR-39

ML24213A329
Person / Time
Site:	Palo Verde
Issue date:	07/31/2024
From:	Horton T Arizona Public Service Co
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
102-08834-TAH/MDD
Download: ML24213A329 (1)

Text

10 CFR 50.55a A member of the STARS Alliance LLC Callaway

• Diablo Canyon

• Palo Verde

• Wolf Creek 102-08834-TAH/MDD July 31, 2024 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Subject:

Palo Verde Nuclear Generating Station Unit 1 Docket No. STN 50-528, Renewed Operating License Nos. NPF-41 Transmittal of Relief Request (RR) No. 72: Re-Submittal of RR-39 Arizona Public Service Company (APS) requests NRC staff approval of the enclosed relief request from the flaw characterization requirements of American Society of Mechanical Engineers (ASME) Code,Section XI, paragraphs IWC-3420 and IWA-3300.

Pursuant to 10 CFR 50.55a(z)(1), licensees may request authorization to implement alternative methodologies that deviate from regulatory requirements provided they achieve an acceptable level of quality and safety.

In addition to addressing the deviation from the Code requirements for flaw evaluation, the enclosure explains that the subject nozzle is not subject to the environmentally assisted fatigue obligations that apply to wetted reactor coolant system pressure boundary components, as part of license extension.

The original RR-39 was approved for Palo Verde Nuclear Generating Station (PVNGS) Unit 1 and relates to the relocation of the pressure boundary weld to the outside surface of the nitrogen gas space of the safety injection tank.

RR-39 was submitted on July 11, 2008 [Agencywide Documents Access and Management System (ADAMS) Accession No. ML082250675] and approved by the NRC staff on July 2, 2009 (ADAMS Accession No. ML091700197). The supporting calculations for RR-39 justified an operating life of 40 years to 2048, which encompasses the period of extended operations (PEO) for PVNGS Unit 1 (expires June 1, 2045). RR-72 renews RR-39 and needs NRC staff approval prior to entering the PEO for PVNGS Unit 1, which is June 1, 2025.

A pre-submittal meeting was held between APS and the NRC staff on July 12, 2024. APS requests authorization of the relief request by May 1, 2025, to facilitate adoption before the PEO.

No commitments are being made to the Nuclear Regulatory Commission by this letter.

Todd A. Horton Sr. Vice President Nuclear Regulatory & Oversight Palo Verde Nuclear Generating Station P.O. Box 52034 Phoenix, AZ 85072 Mail Station 7602 Tel: 623.393.6418

102-08834-TH/MDD ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Relief Request No. 72 Page 2 Should you need further information regarding this submittal, please contact Michael D.

DiLorenzo, Department Leader Nuclear Regulatory Affairs - Licensing at (623) 393-3495.

Sincerely, Todd Horton Senior Vice President Nuclear Regulatory & Oversight MDD/WEH/cr

Enclosure:

PVNGS Unit 1 - Relief Request (RR) No. 72 cc:

J. D. Monninger NRC Region IV Regional Administrator W. T. Orders NRC NRR Project Manager for PVNGS N. Cuevas NRC Acting Senior Resident Inspector for PVNGS Horton, Todd (Z10098)

Digitally signed by Horton, Todd (Z10098)

Date: 2024.07.31 12:29:52

-07'00'

Enclosure PVNGS Unit 1 Relief Request (RR) No. 72

PVNGS Unit 1 - Relief Request (RR) No. 72 1 of 5

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Background===

There are four safety injection tanks (SIT) in each unit which contain borated water and are pressurized with nitrogen. They discharge their contents to the reactor coolant system (RCS) following depressurization as a result of a postulated loss-of-coolant accident (LOCA).

Each tank is piped into a cold leg of the RCS via a safety injection nozzle located on the RCS piping near the reactor vessel inlet. The tank vent nozzle is on the upper head of the SIT in the nitrogen blanket area. Each SIT is approximately 41 ft. high and 9 ft. in diameter. The operating level is maintained at approximately 32 ft. to 34 ft. The upper alarm limit is set at approximately 35 ft. Technical Specifications require the boron concentration be in the range of 2300 ppm to 4400 ppm; and that the nitrogen cover pressure be maintained from 600 pounds per square inch, gauge (psig) to 625 psig. The SIT operates at a temperature range of 60º Fahrenheit (F) to 140º F.

On Thursday, June 5, 2008, Palo Verde Nuclear Generating Station (PVNGS) declared the Unit 1 SIT 1A inoperable when a small leak was identified at the annulus between the tank and the vent line during the performance of a leak test.

Ultrasonic testing (UT) of the carbon steel material of the vessel around the nozzle attachment weld (Alloy 82/182) showed no flaws. It appeared that the leak was due to flaw(s) in the 82/182 weld material. The nozzle repair consisted of making a new J-weld to attach the nozzle at the outer surface of the vessel. The original J-weld on the inner surface was left in place. The design of the new configuration complies with the construction Code.

The weld was completed and examined visually and nondestructively in full compliance with the requirements of ASME Sections III and XI.

Relief Request 39 [Agencywide Documents Access and Management System (ADAMS)

Accession No. ML082250675 and ML091700197] previously authorized the proposed alternative at PVNGS Unit 1 for the remainder of the original operating license which ends at midnight on June 1, 2025.

I.

ASME Code Components Affected ASME Item number: C2.20

==

Description:==

Safety Injection Tank (SIT) Nozzles Code Class:

2 II.

Applicable Code Editions and Addenda The Fourth 10-year inservice inspection interval code for PVNGS Units 1, 2, and 3 is the American Society of Mechanical Engineers (ASME) Code,Section XI, 2013 Edition.

The construction code for PVNGS Units 1, 2, and 3 is ASME Section III, 1971 Edition, and 1973 Winter Addenda.

The installation code for PVNGS Units 1, 2, and 3 is ASME Section III, 1974 Edition, and 1975 Winter Addenda.

PVNGS Unit 1 - Relief Request (RR) No. 72 2 of 5 III.

Applicable Code Requirement

IWC-3420, Characterization, states that each detected flaw or group of flaws shall be characterized by the rules of IWA-3300 to establish the dimensions of the flaw(s). These dimensions shall be used in conjunction with the acceptance standards of IWC-3500.

IWA-3300, Flaw Characterization, states that flaws detected by inservice examinations shall be sized by the bounding rectangle or square for the purpose of description and dimensioning.

IV.

Reason for Request

Unit 1 SIT 1A was indicating a gradual lowering trend in nitrogen pressure. During the investigation of potential leak paths, a leakage source was identified at the 2-inch vent line nozzle annulus (see Figure 1) where leak testing (snoop method) indicated a two bubble per second leak.

Figure 1

PVNGS Unit 1 - Relief Request (RR) No. 72 3 of 5 APS repaired the leak by moving the pressure boundary from the inside of the SIT to the outside by making a partial penetration nozzle attachment weld as shown in Figure 2. This resulted in leaving the flaw in the original weld in place.

Removal of the flaw would require access to the nozzle weld on the interior of the SIT. This would require scaffolding both outside and inside the SIT. The limited size of the manway and the distance from the manway to the repaired nozzle presented significant personnel safety concerns such as, confined space entry due to the small size of the manway and personnel fall protection due to the 40 foot distance from the weld to the tank bottom (see Figure 1).

Additionally, the difficulty in controlling entry of foreign material from grinding and welding into the SIT was considered. The requirements of ASME Section IWC-3420 and IWA-3300 require that a flaw or group of flaws be characterized to establish the dimensions of the flaw(s) and that these dimensions be used in conjunction with the acceptance standards of IWC-3500, Acceptance Standards. Characterization by UT is not possible due to the geometry of the partial penetration weld.

Due to the personnel safety concerns and the inability to characterize the flaw, APS developed an alternative that postulated a worst-case flaw in the original weld, evaluated its acceptance using IWB-3600, Analytical Evaluation of Flaws, and determined that the defective J-weld could be left in place. The postulated flaw is an axial crack in the Alloy 82/182 weld metal. This postulated crack represents the worst-case for the most-likely weld discontinuities such as porosity and slag inclusions that caused the leak. This material, as well as the base material, are not susceptible to stress corrosion cracking at 140º F in a nitrogen environment. In addition, no operating experience concerning incidents of stress corrosion cracking of Alloy 600/182/82 in an air or nitrogen environment at ambient temperature have been identified.

PVNGS Unit 1 - Relief Request (RR) No. 72 4 of 5 V.

Proposed Alternative and Basis For Relief Pursuant to 10 CFR 50.55a(a)(z)(1), APS is proposing an alternative to the required flaw characterization of IWC-3420 and IWA-3300. APS is not proposing any alternative to the required successive examinations (IWB/IWC-2420, Successive Inspections).

This Relief Request seeks approval to continue to allow the analyzed flaw to remain in-place for the remainder of the currently expected plant life for Unit 1.

VI.

Proposed Alternative In lieu of fully characterizing/sizing the existing flaw, APS has assumed a worst-case flaw and Structural Integrity performed the following:

Thermal and Mechanical Stress Analysis of the repair (ADAMS Accession No. ML082250675, Attachment 1, Reference 1), and Flaw Tolerance Evaluation (ADAMS Accession No. ML082250675, Attachment 2, Reference 2) to ensure that the postulated, worst-case flaw, meets the acceptance criteria of the ASME Code.

The flaw tolerance evaluation resulted in a postulated final flaw of 0.352 inch (original depth of the partial penetration weld plus projected growth due to fatigue) in the carbon steel material of the vessel. This postulated flaw was analyzed in accordance with IWB-3600 and shown to be acceptable to the IWB-3612, Acceptance Criteria Based on Applied Stress Intensity Factor. The original flaw evaluation demonstrates that the flaw will remain within acceptable Section XI limits for the expected 40-year plant life (remaining plant operating license plus 20-year life extension).

Subsequent review by Structural Integrity has shown that this external weld was not identified as a bounding location for the environmentally assisted fatigue (EAF) screening analyses as the weld is not wetted and can be managed for fatigue only. Thus, the original analysis remains valid, and the flaw is acceptable for a fatigue life of 40 years (repair occurred in 2008).

VII.

Basis for Relief When moving the pressure boundary of a tank attached nozzle from the inside to the outside of the tank, the flaw must be characterized and shown not to impact the integrity of the tank or new weld. In lieu of fully characterizing/sizing the existing flaw, APS postulated a worst-case flaw and performed the analysis delineated above.

The analysis demonstrates that any flaw in the nozzle or attachment weld will not propagate such that the structural integrity of the new weld or the tank boundary is affected.

Therefore, the proposed alternative provides an acceptable level of quality and safety as required by 10 CFR 50.55a(a)(z)(1).

Relief Request (RR) No. 72: Relief from the flaw characterization requirements of IWC-3420 and IWA-3300 5 of 5 VIII. Duration of Proposed Alternative APS requests that this relief be granted for this repair to PVNGS Unit 1 for the remainder of plant life (through initial license extension).

IX.

Conclusion 10 CFR 50.55a(z) states:

Alternatives to the requirements of paragraphs (b) through (h) of this section or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The applicant or licensee must demonstrate that:

(1) Acceptable level of quality and safety. The proposed alternative would provide an acceptable level of quality and safety; or (2) Hardship without a compensating increase in quality and safety. Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Subsequent review by Structural Integrity has shown that this external weld was not identified as a bounding location for the EAF screening analyses as the weld is not wetted and can be managed for fatigue only. Thus, the original analysis is still valid, and the flaw is acceptable for a fatigue life of 40 years (repair occurred in 2008). The proposed alternative discussed in this evaluation provides an acceptable level of quality and safety.

Therefore, APS requests that the proposed alternative be authorized pursuant to 10 CFR 50.55a(a)(z)(1).

The proposed alternative was originally authorized under Relief Request 39 for the remainder of the original operating license for Unit 1 which expires at midnight June 1, 2025. APS requests NRC approval of the proposed relief by May 1, 2025, to support Unit 1 entering the Period of Extended Operation on June 1, 2025. The proposed alternative authorization would expire at midnight on June 1, 2045 (Unit 1).

X.

References

1. Structural Integrity Associates, Inc. Calculation 0800802.303, Thermal and Mechanical Stress Analysis of Safety Injection Tank Vent Relief Nozzle Repair

2. Structural Integrity Associates, Inc. Calculation 0800802.306, Flaw Tolerance Evaluation of Safety Injection Tank Nozzle Penetration