Text

Relief Request 70 - Proposed Alternatives for Pressurizer Lower Shell Temperature Nozzle
	ML24197A199
Person / Time
Site:	Palo Verde
Issue date:	09/09/2024
From:	Jennivine Rankin; NRC/NRR/DORL/LPL4
To:	Heflin A; Arizona Public Service Co
	Orders, William
References
	EPID L-2023-LLR-0057 RR 70
	Download: ML24197A199 (1)
	v • d • e

September 9, 2024 Adam C. Heflin Executive Vice President/

Chief Nuclear Officer Mail Station 7605 Arizona Public Service Company P.O. Box 52034 Phoenix, AZ 85072-2034

SUBJECT:

PALO VERDE NUCLEAR GENERATING STATION UNIT 1 RE: RELIEF REQUEST 70 - PROPOSED ALTERNATIVES FOR PRESSURIZER LOWER SHELL TEMPERATURE NOZZLE (EPID L-2023-LLR-0057)

Dear Adam Heflin:

By letter dated October 23, 2023, as supplemented by letter dated October 26, 2023, Arizona Public Service Company (the licensee), requested an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)

Section XI, 2013 Edition, and Code Case N-638-10 Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW [Gas Tungsten Arc Welding] Temper Bead Technique,Section XI, Division 1, dated May 6, 2019, for the Palo Verde Nuclear Generating Station, Unit 1. The licensee submitted Relief Request 70 for U.S. Nuclear Regulatory Commission review and approval to support performing a weld repair on a pressurizer lower shell temperature nozzle weld.

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1), the licensee submitted Relief Request 70 on the basis that the proposed alternative would provide for an acceptable level of quality and safety.

On October 25, 2023, the NRC staff transmitted to the licensee a request for additional information (RAI) to support its review of the requested relief. By letter dated October 26, 2023, the licensee provided the requested response to the NRC staff RAI. The NRC staff provided verbal authorization of Relief Request 70 on October 27, 2023.

In order to support the subsequent NRC review for one fuel cycle of operation, currently Cycle 25, the licensee made a commitment to the NRC in the October 23, 2023, letter that stated:

The final one-cycle flaw analytical evaluation, evaluation of repair, and corrosion evaluation will be submitted within 14 days following the end of the current PVNGS, Unit 1 refueling outage.

The Palo Verde, Unit 1 refueling outage was completed on November 11, 2023. By letter dated November 17, 2023, the licensee provided the supplemental information consistent with the commitment made in the original submittal of RR 70. The supplemental letter reiterated the

discussion in the original relief request that a permanent relief request, with analyses and justification of the remainder of the plant operating life, will be submitted prior to the end of the current operating cycle.

As set forth in the enclosed safety evaluation, the NRC determines that the proposed alternative provides an acceptable level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all regulatory requirements set forth in 10 CFR 50.55a(z)(1).

Therefore, the NRC authorizes the use of Relief Request 70 at Palo Verde, Unit 1 during Refueling Outage 24 (1R24) for the duration of Cycle 25, which concludes in the spring of 2025.

All other requirements in ASME Code,Section XI for which relief was not specifically requested and approved in this relief request remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.

If you have any questions, please contact the Palo Verde Project Manager, William Orders, at 301-415-3329 or by email at William.Orders@nrc.gov.

Sincerely, Jennivine K. Rankin, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-528

Enclosure:

Safety Evaluation cc: Listserv Jennivine K. Rankin Digitally signed by Jennivine K. Rankin Date: 2024.09.09 12:51:12 -04'00'

Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO RELIEF REQUEST 70, PROPOSED ALTERNATIVES FOR PRESSURIZER LOWER SHELL TEMPERATURE NOZZLE REPAIR PALO VERDE NUCLEAR GENERATING STATION, UNIT 1 ARIZONA PUBLIC SERVICE COMPANY DOCKET NO. 50-528

1.0 INTRODUCTION

By letter dated October 23, 2023 (Agencywide Documents Access and Management System (ADAMS) Accession no. ML23296A254), as supplemented by letter dated October 26, 2023 (ML23299A305), Arizona Public Service Company (the licensee), requested an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)Section XI, 2013 Edition, and Code Case N-638-10 Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW [Gas Tungsten Arc Welding]

Temper Bead Technique,Section XI, Division 1, dated May 6, 2019, for the Palo Verde Nuclear Generating Station, Unit 1. The licensee submitted Relief Request 70 for U.S. Nuclear Regulatory Commission (NRC) review and approval to support performing a weld repair on a pressurizer lower shell temperature nozzle weld.

On October 25, 2023 (ML23298A123), the NRC staff transmitted to the licensee a request for additional information (RAI) to support its review of the requested relief. By letter dated October 26, 2023, the licensee provided the requested response to the NRC staff RAI. The NRC staff provided verbal authorization of Relief Request 70 on October 27, 2023 (ML23303A011).

In order to support the subsequent NRC review for one fuel cycle of operation, currently Cycle 25, the licensee made a commitment to the NRC in the October 23, 2023, letter that stated:

The final one-cycle flaw analytical evaluation, evaluation of repair, and corrosion evaluation will be submitted within 14 days following the end of the current PVNGS, Unit 1 refueling outage.

The Palo Verde, Unit 1 refueling outage was completed on November 11, 2023. By letter dated November 17, 2023 (Package ML23325A159), the licensee provided supplemental information consistent with the commitment made in the original submittal of RR 70 dated October 23, 2023.

The supplemental letter reiterated the discussion in the original relief request that a permanent relief request, with analyses and justification of the remainder of the plant operating life, will be submitted prior to the end of the current operating cycle.

2.0 REGULATORY EVALUATION

The regulation in 10 CFR 50.55a(z), Alternatives to codes and standards requirements, states:

Alternatives to the requirements of paragraphs (b) through (h) of [10 CFR 50.55a]

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.

Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request and the Commission to grant the relief and authorize the alternatives requested by the licensee.

3.0 TECHNICAL EVALUATION

3.1 ASME Code Component Affected The affected component is the pressurizer lower shell temperature nozzle, TE101. Specifically, this component falls under ASME Code,Section XI, Table IWB-2500-1 (B-P) Examination Category B-P, Item B15.10. Palo Verde, Unit 1 is currently in its fourth 10-year inservice inspection (ISI) interval, which began June 1, 2019, and ends July 17, 2028.

3.2

Applicable Code Edition and Addenda

The ASME Code,Section XI, 2013 Edition with no addenda is the Code of Record for the fourth 10-year ISI interval. The code of construction for the pressurizer is the ASME Code,Section III, 1971 Edition with Addenda through Winter 1972.

3.3 ASME Code Requirement The ASME Code requirements applicable to this request originate in ASME Code,Section XI are as follows:

Flaw characterization requirements of IWA-3300 and IWB-3420.

Defect removal requirements of IWA-4412 and IWA-4420.

Corrective action requirements of IWA-5250.

Flaw acceptance and evaluation requirements of IWB-3142, IWB-3420, IWB-3500, and IWB-3600.

Successive examination requirements of IWB-2420.

Additional examination requirements of ASME Code Case N-722-1, Additional Examinations for PWR [Pressurized-Water Reactor] Pressure Retaining Welds in Class 1 Components Fabricated with Alloy 600/82/182 Materials,Section XI, Division 1, Item No. B15.180.

Welding requirements of ASME Code Case N-638-10.

3.4 Proposed Alternative During performance of small nozzle inspections in support of a boric acid walkdowns during Refueling Outage 24 (1R24) boric acid leakage was found on the area of the pressurizer lower shell temperature nozzle. Non-destructive examination (NDE) of the weld indicated leakage through the reactor coolant pressure boundary. Due to a preemptive mitigation performed in 1992, the current configuration of the nozzle includes an Alloy 690 nozzle, an Alloy 690 outer sleeve, an Alloy 82 weld pad, and an Alloy 82 nozzle-to-weld pad J-groove weld. The leak may have initiated through the autogenous weld joining the Alloy 690 outer sleeve and the original Alloy 82/182 interior J-groove weld or through the annulus between the Alloy 690 nozzle and the Alloy 690 sleeve. In either case, the leak reached the Alloy 82 weld pad to Alloy 82 J-groove weld and propagated through the exterior J-groove weld until it was through-wall.

In lieu of performing welding to the ASME Code,Section III, NB-4620, the licensee is installing a welded pad using ambient temperature temper bead (ATTB) welding in accordance with ASME Code Case N-638-10. Pursuant to 10 CFR 50.55a(z)(1), the licensee proposes an alternative to ASME Code,Section XI and ASME Code Case N-638-10. As an alternative to the requirement of Code Case N-638-10, paragraph 4(a)(2), which requires a 48-hour hold time prior to performing an NDE, the licensee stated that the weld repairs will be performed with austenitic filler material in accordance with the ambient temperature temper bead welding technique of Code Case N-638-10. The licensee plans to apply the weld pad to the pressurizer shell by using Alloy 52M (ASME Code,Section II, Part C SFA-5.14, Class ERNiCrFe-7A). The licensee stated that as an alternative to performing the required NDE at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> after the three tempering layers have reached ambient temperature, the licensee proposes to perform the NDE methods after completion of the weld repair. The licensee stated that after completion of the weld pad installation, it will perform the required penetrant testing (PT) and ultrasonic testing (UT) in accordance with ASME Code,Section III acceptance criteria after the weld pad has been prepared for NDE and dimensionally inspected.

3.5 Basis For Use To support its repair option, the licensee provided the following technical basis to demonstrate that the structural integrity of the repaired nozzle will be maintained for the duration of one operating cycle:

An evaluation of the pressurizer temperature nozzle repair design loading conditions.

A flaw evaluation based on the linear elastic fracture mechanics methodology.

An evaluation of the pressurizer thermowell to instrument nozzle weld design.

An evaluation of the acceptability of the as-left J-groove weld in the pressurizer.

An evaluation of the potential corrosion mechanisms that may affect the temperature instrument nozzle repair.

An evaluation of the potential for the outer sleeve of the 1992 repair, the original J-groove weld, or fragments of them may become loose and enter the pressurizer.

An evaluation of elimination of the 48-hour hold time for the NDE of the repaired weld.

3.6 Duration of Proposed Alternative The licensees request is applicable for one operating cycle, the duration of Palo Verde, Unit 1 Cycle 25, which is scheduled to conclude in the spring of 2025.

3.7

NRC Staff Evaluation

The licensee is proposing to install a new welded pad using ambient temperature temper bead welding in accordance with ASME Code Case N-638-10. The licensee stated that it will remove the existing Alloy 82 weld pad and etch the ferritic surface to verify all Alloy 82 weld metal has been removed. Upon completion of removing the Alloy 82 weld metal, PT on the outer surface of the pressurizer shell will be performed in preparation for the new weld pad. The new weld pad will be welded to the outer diameter of the pressurizer shell.

The licensee stated that the repair plan will be performed in accordance with the ASME Code Section XI, 2013 Edition. Welding will be performed using the machine GTAW ambient temperature temper bead welding technique, with inert shielding gas using Alloy 52M (ASME Code Section II Part C SFA-5.14, Class ERNiCrFe-7A) filler metal. The weld repair of the new completed weld pad will be a minimum of three layers per the temper bead rules in Code Case N-638-10. The licensee stated that the required Code Case N-638-10 PT and UT examinations of the completed weld pad will be performed in accordance with ASME Code Section III acceptance criteria after the weld pad has been prepared for NDE and dimensionally inspected. These examinations will verify that there are no unacceptable indications (cracking or fabrication defects) in the newly installed weld pad or original base metal material. The UT examinations will be performed in accordance with ASME Code,Section III, NB-5244 and include the weld deposit, fusion zone, and the base metal beneath the weld to assure freedom from lack of fusion and laminar defects.

The licensee stated that, pursuant to 10 CFR 50.55a(z)(1), it proposes an alternative to ASME Code Section XI and ASME Code Case N-638-10. The alternative is proposed to the requirements of N-638-10, paragraph 4(a)(2) that requires a 48-hour hold time prior to performing NDE. The licensee is proposing to perform the final examination using the required PT and UT without waiting the required 48-hours from the completion of the three tempering layers. The licensee stated that the temper bead technique is an effective tool for performing repairs on carbon and low alloy steel materials. The licensee provided white paper based on PVP 2023-107489, Elimination of the 48-hour Hold for Ambient Temperature Temper Bead

Welding with Austenitic Weld Metal, to justify the removal of the 48-hour told time. This white paper was developed for the proposed change to ASME Code Case N-888-1, which is not approved in NRC Regulatory Guide 1.147.

Upon completion of the new weld pad, the licensee stated that a new J-groove weld preparation will be machined into the weld pad. The J-groove weld will be dimensionally inspected and undergo PT. The licensee stated that the new Alloy 690 nozzle to weld pad will be welded with Alloy 52M partial penetration weld and receive progressive PT of the weld in accordance with ASME Code Section III, NB-5245 at half thickness and full thickness after the fillet weld is complete.

The NRC staff finds the licensees proposal to perform the required final examination using PT and UT without waiting for the 48-hour hold time to be acceptable because hydrogen induced or delayed cracking will not be likely to occur. The primary water stress corrosion cracking resistant Alloy 52M weld material is being applied with the machine GTAW process, which produces welds with very low diffusible hydrogen when compared to welding processes that use flux (e.g., SMAW). Therefore, hydrogen induced cracking is not likely to occur, and performing the required final PT and UT examinations prior to the 48-hour hold time provides an acceptable level of quality and safety. All required NDEs per Code Case N-638-10 will be performed by qualified examiners and a procedure qualified in accordance with the ASME Code,Section XI.

In addition, the NRC is unaware of any instances of hydrogen induced cracking out of the numerous weld overlays that have been completed by the nuclear industry using any of the revisions of Code Case N-638-10.

4.0 CONCLUSION

As set forth above, the NRC staff determines that the proposed alternative provides an acceptable level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all regulatory requirements set forth in 10 CFR 50.55a(z)(1).

Therefore, the NRC authorizes the use of Relief Request 70 at Palo Verde, Unit 1 during refueling outage 1R24 for the duration of Cycle 25, which concludes in the spring of 2025.