RA-19-0027, Relief Request (19-ON-002) Alternative to Extend Code Case N-770-2, Inspection Item B Examination Frequency

Relief Request (19-ON-002) Alternative to Extend Code Case N-770-2, Inspection Item B Examination Frequency

ML19087A182
Person / Time
Site:	Oconee
Issue date:	03/28/2019
From:	Burchfield J Duke Energy Corp
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RA-19-0027
Download: ML19087A182 (8)

Text

9,DUKE J. Ed Burchfield, Jr.

Vice President ENERGY* Oconee Nuclear Station Duke Energy ON01VP I 7800 Rochester rtwy Seneca, SC 29672 o 864.873.3478 t 864,873.4208 Ed.Burch/ield@duke-energy.com Serial: RA-19-0027 10 CFR 50.55a March 28, 2019 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 OCONEE NUCLEAR STATION, UNIT NO. 3 DOCKET NO. 50-287 I RENEWED LICENSE NO. DPR-55

SUBJECT:

Relief Request (19-ON-002) Alternative to Extend Code Case N-770-2, Inspection Item B Examination Frequency Pursuant to 10 CFR 50.55a(z)(2), Duke Energy requests the NRC to grant relief from Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) and the augmented inspections of ASME Code Case N-770-2 as prescribed by 10 CFR 50.55a(g)(6)(ii)(F). Relief is being sought due to the hardship, with no compensating increase in quality or safety, caused by performing an augmented inspection required by code case N-770-2 at a frequency of less than 10 years from the previous inspection.

In the absence of this relief being granted, a core barrel removal will be required for the Unit 3 outage currently scheduled in April 2020. Therefore, Duke Energy requests that this Relief Request receive review and approval prior to the April 2020 outage.

Relief Request 19-ON-002 is provided as an enclosure to this letter. If you have questions concerning this request, please contact Art Zaremba, Director - Fleet Licensing, at (980) 373-2062.

Sincerely,

)£/

J. Ed Burchfield, Jr.

Vice President Oconee Nuclear Station

Enclosure:

1. Relief Request 19-ON-002 NRC FORM 366 (04-2017)

U.S. Nuclear Regulatory Commission RA-19-0027 Page 2 cc : (all with Enclosure unless otherwise noted)

C. Haney, Regional Administrator USNRC Region II E. L. Crowe, USNRC Senior Resident Inspector - ONS A. L. Klett, NRR Project Manager - ONS

U.S. Nuclear Regulatory Commission RA-19-0027 Page 3 bcc: (all with Enclosure unless otherwise noted)

Mark Pyne Art Zaremba Austin Keller Kate Nolan David Cummings ELL File: (Corporate)

Ed Burchfield Sheila Dalton Dave Peltola RA-19-0027 Enclosure 1 Relief Request 19-ON-002

Relief Request Serial #19-ON-002 RA-19-0027, Enclosure 1

1. ASME Code Components Affected:

The Code Components included in the scope of this relief request are the nozzle-to-safe end Dissimilar Metal Butt Welds (DMBWs) for the core flood nozzles on Oconee Nuclear Stations Unit 3 (ONS3). This relief request addresses the following welds:

Weld

Description:

ONS3: 3-RPV-WR53 - Reactor Vessel Core Flood Nozzle-to-Safe End, 14 DMBW ONS3: 3-RPV-WR53A - Reactor Vessel Core Flood Nozzle-to-Safe End, 14 DMBW

2. Applicable Code Edition and Addenda

The current edition for the Inservice Inspection (ISI) interval for ONS3 is the ASME Boiler and Pressure Vessel Code,Section XI, 2007 Edition and 2008 Addenda. ONS3 is in the fifth inspection interval with a scheduled end date of July 15, 2024.

10 CFR 50.55a(g)(6)(ii)(F)(1) mandates the use of ASME Code Case N-770-2 for the augmented inspection program.

3. Applicable Code Requirement

Code Case N-770-2, Table 1, Item B requires volumetric examination of unmitigated butt welds at Cold Leg operating temperature 525°F and < 580°F every second inspection period not to exceed 7 years.

Code Case N-770-5, Table 1, Item B-2 requires volumetric examination of unmitigated butt welds at Cold Leg operating temperature 525°F and < 580°F NPS 14 inches or larger once per interval.

Note 11(d) to N-770-5, Table 1, states that Examinations for Inspection Item B-2 may be deferred to the end of the interval and performed coincident with the reactor vessel nozzle examinations required by Examination Category B-D, as provided by IWA-2430. The time between examinations shall not exceed 13 yr.

4. Reason for Request

Relief is being requested to allow the examination frequency of every second inspection period (7 year maximum) to be extended to every 10-year interval (13 year maximum as described in ASME Code Case N-770-5, Table 1, Category B-2). This alternative will allow the N-770 inspections of the requested welds to coincide with the core barrel removal in the 10 Year Reactor Vessel ISI Refueling Outage for Unit 3 (O3R32), currently scheduled in Spring 2024.

Oconees plant design limits access to the outer surface of the core flood nozzle-to-Safe End DMBWs. The core flood DMBWs are obstructed from examination from the outer diameter. Examination from the DMBW inner diameter is required to achieve acceptable examination coverage. The outer surfaces of these welds are obstructed by an approximately 3 ft. wide reactor vessel annulus, and underneath the annulus shield blocks.

The physical interferences and high dose rates associated with the weld location, prevent Page 1 of 4

Relief Request Serial #19-ON-002 RA-19-0027, Enclosure 1 effective ultrasonic examinations from being performed from the outside diameter of the core flood nozzles.

It is possible to access and perform an effective volumetric examination of the weld from the inner diameter, provided the reactor vessel core barrel is removed; however, core barrel removal represents a hardship that produces increased plant risk and elevates the outage dose to workers.

To date, Code Case N-770-5 has not been endorsed by the NRC, but has been reviewed by the NRC and is proposed to replace N-770-2 in 10 CFR 50.55a(g)(6)(ii)(F), with conditions (Reference 8.4). Therefore, Duke Energy is requesting relief under 10 CFR 50.55a(z)(2) from the examination requirements of Code Case N-770-2.

5. Proposed Alternative and Basis for Use:

The proposed alternative is to extend the weld examination frequency required by Code Case N-770-2, Table 1, Item B for the ONS3 Core Flood nozzle DMBWs (listed in Section 1 above) from every second inspection period not to exceed 7 years to every interval not to exceed 13 years from the previous examination.

The ONS3 welds had volumetric examinations performed during their last Reactor Vessel 10 Year ISI in the spring of 2014 with essentially 100% coverage. The inspections were performed in accordance with ASME Section XI, Appendix VIII, Supplement 10 requirements and found no reportable circumferential or axial indications.

ASME Code Case N-770-2 is approved by the NRC for generic use and provides alternative examination requirements and acceptance standards for volumetric examination, and surface examination of DMBW NPS 2 and greater. On November 7, 2016, the ASME approved Revision 5 of ASME BPV Code Case N 770 (N-770-5). The major changes from N-770-2 to N-770-5 include:

1. Table 1 Inspection Item B replaced with B-1 and B-2, separating welds for pipes with NPS less than 14 inches and 14 inches or greater. Examinations for item B-2 (NPS 14 inches or greater) may be deferred to the end of the interval and performed coincident with the reactor vessel nozzle examinations and the time between examinations shall not exceed 13 years.

2. Performance criteria and inspections for peening mitigated welds.

3. Inservice inspection requirements for excavate and weld repair mitigations.

4. Minor editorial and clarification changes.

The basis for the N-770 Code Case change to extend the inspection frequency for cold leg temperature dissimilar metal butt welds for 14 inches is discussed in Reference 8.3, Changing the Frequency of Inspections for PWSCC Susceptible Welds at Cold Leg Temperatures. Applicable excerpts supporting this request are below:

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Relief Request Serial #19-ON-002 RA-19-0027, Enclosure 1 There are a number of technical and practical arguments in favor of making this change, even beyond the excellent service experience, and these arguments are summarized in this paper.

• Pulling the reactor vessel (RV) core barrel is a serious activity which can entail many risks, so additional pulls should be avoided. Inspection at a frequency of less than 10 years involves additional core barrel pulls.

• The flaw tolerance of these large diameter cold leg pipes is very good, and example calculations show that reasonably large flaws are acceptable for ten years.

• The probability of cracks initiating in cold leg piping is significantly lower than that for piping at hotter temperatures, and a detailed model has been developed to demonstrate this.

While there has been a large amount of service experience with primary water stress corrosion cracking of Alloy 82/182 welds, this experience has been limited to those welds operating at hot leg temperatures or higher. There have been no incidents of cracking in welds operating at cold leg temperatures that can be attributed to PWSCC.

Though the MRP-139 and Code Case N-770 requirements for more frequent inspection were taken as a proactive measure, the accumulation of more positive service experience indicates that perhaps this increased inspection frequency for cold legs in particular is not necessary to maintain an acceptable level of safety and quality.

Furthermore, it has been realized that accessing these cold leg weld locations for inspection presents a hardship to utilities and may present an increased risk due to the complications associated with removal of the reactor vessel core barrel.

There have been numerous studies performed to evaluate the likelihood of through-wall cracking and flaw tolerance in cold leg Alloy 82/182 welds. The analyses performed as the original basis for MRP-139 showed that the large diameter cold leg welds had high flaw tolerance and a very low probability of failure. More recent analyses, which considered design specific residual stress distributions, have confirmed the original conclusions that the flaw tolerance is high. Furthermore, the more recent analyses have shown that even large circumferential flaws, with a high likelihood of being detected during inservice inspection, will not grow to the maximum depth allowed by ASME Section XI in 10 years. These analyses have been performed based on the assumption that a flaw has initiated, which as shown by more recent probabilistic analyses based on service data is unlikely at the present time.

Code Case N-770-5 is not yet NRC-approved, but it has been reviewed by the NRC and is proposed to replace N-770-2 in 10 CFR 50.55a(g)(6)(ii)(F), with conditions (Reference 8.4).

The conditions have been reviewed and would not preclude this proposed relief request.

In summary, Duke Energy is seeking approval of the proposed alternative in accordance with 10 CFR 50.55a(z)(2) on the basis that the proposed alternative would result in hardship or unusual difficulty without a compensating increase in the level of quality or safety.

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Relief Request Serial #19-ON-002 RA-19-0027, Enclosure 1

6. Duration of Proposed Alternative:

This request may be implemented for the remainder of the 5th Interval ISI plan and applies to ONS3. This relief will be re-submitted, if needed, for subsequent ISI intervals.

7. Precedents The following relief request includes a requested frequency extension for the same welds for ONS Units 1 and 2; however, the basis for use is different. Due to the subsequent proposed adoption of Code Case N-770-5 by the NRC, the basis of this request is consistent with that of Code Case N-770-5.

7.1 Oconee Units 1 and 2 Docket Numbers 50-269 and 50-270, Relief Request No. 17-ON-001, Alternative to extend the Code Case N-770, Inspection Item B Examination Frequency, including NRC Safety Evaluation dated April 13, 2018 (ADAMS Accession Number ML18100A005).

8. References 8.1 ASME Code Case N-770-2, Alternative Examination Requirements and Acceptance Standards for Class 1 PWR Piping and Vessel Nozzle Butt Welds Fabricated with UNS N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation Activities,Section XI, Division 1, Approval Date: June 9, 2011.

8.2 ASME Code Case N-770-5, Alternative Examination Requirements and Acceptance Standards for Class 1 PWR Piping and Vessel Nozzle Butt Welds Fabricated with UNS N06082 or UNS W86182 Weld Filler Material With or Without Application of Listed Mitigation Activities,Section XI, Division 1, Approval Date: November 7, 2016.

8.3 Proceedings of 2011 ASME Pressure Vessels and Piping Conference PVP2011-57829, Changing the Frequency of Inspections for PWSCC Susceptible Welds at Cold Leg Temperatures, July 17-21, 2011.

8.4 Federal Register 56156-56196, American Society of Mechanical Engineers 2015-2017 Code Editions Incorporation by Reference, Vol. 83, No. 218, dated November 9, 2018.

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