ONS-2015-037, Fifth Ten Year Inservice Inspection Interval, Relief Request No. 14-ON-002; Alternative Requirements for Specific Residual Heat Removal System Welds

Fifth Ten Year Inservice Inspection Interval, Relief Request No. 14-ON-002; Alternative Requirements for Specific Residual Heat Removal System Welds

ML15132A278
Person / Time
Site:	Oconee
Issue date:	05/04/2015
From:	Batson S Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ONS-2015-037
Download: ML15132A278 (11)

Text

Scott L.Batson DUKE Vice President 5E N ERGY. Oconee Nuclear Station Duke Energy ONOIVP 17800 Rochester Hwy Seneca, SC 29672 ONS-2015-037 o: 864.873.3274 f 864.873. 4208 May 4, 2015 Scott.Batson@duke-energy.com ATTN: Document Control Desk 10 CFR 50.55a U.S. Nuclear Regulatory Commission Washington, DC 20555 Duke Energy Carolinas, LLC (Duke Energy)

Oconee Nuclear Station, Units 1, 2 and 3 Docket Numbers 50-269, 50-270, 50-287 Renewed License Numbers DPR-38, DPR-47, and DPR-55

Subject:

Fifth Ten Year Inservice Inspection Interval, Relief Request No. 14-ON-002; Alternative Requirements for Specific Residual Heat Removal System Welds

References:

1. Duke Energy Letter, Oconee, Units 1, 2 and 3 - Fifth Interval Inservice Inspection Plan, dated July 15, 2014, (ADAMS Accession No. ML14202AO08)

Pursuant to 10 CFR 50.55a(z)(1), Duke Energy requests the NRC to grant relief regarding specific Residual Heat Removal heat exchanger welds over the duration of the fifth (ten-year) inservice inspection (ISI) interval. Relief Request 14-ON-002 prescribes an examination with an acceptable level of quality and safety as an alternative to the edition of Section'XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) applicable to the fifth ISI Interval.

This relief is needed prior to the Oconee Unit 1, 2016 Fall refueling outage (1 EOC29) projected to start November 5, 2016. Duke Energy requests approval by May 1, 2016 in support of planning for 1 EOC29. The relief request details are provided as an enclosure to this letter.

If there are any questions or further information is needed you may contact David Haile at (864) 873-4742, Sincerely, Scott L. Batson Vice President Oconee Nuclear Station Enclosure Relief Request Serial #14-ON-002:

Request for Alternative in Accordance with 10 CFR 50.55a(z)(1) for Specific Welds on Residual Heat Removal Heat Exchangers, Fifth Inservice Inspection Interval

• ONS-2015-037 May 4, 2015 Page 2 cc (with enclosure):

Mr. Victor McCree, Regional Administrator U.S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, Georgia 30303-1257 Mr. James R. Hall, Project Manager (ONS)

(by electronic mail only)

U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop O-8B1 Rockville, MD 20852 Jeffery Whited (by electronic mail only)

U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop O-8B1A Rockville, MD 20852 Mr. Eddy Crowe NRC Senior Resident Inspector Oconee Nuclear Station

Enclosure to ONS-2015-037 Duke Energy Carolinas, LLC Oconee Nuclear Station, Units 1, 2, and 3 Relief Request Serial #14-ON-002 Request for Alternative in Accordance with 10 CFR 50.55a(z)(1) for Specific Welds on Residual Heat Removal Heat Exchangers Fifth Inservice Inspection Interval

Duke Energy Carolinas, LLC Relief Request Serial No. 14-ON-002 Page 2 of 9

1. ASME Code Component(s) Affected Low Pressure Injection (LPI) Residual Heat Removal Heat Exchangers (Decay Heat Coolers). This request is limited to the following Class 2 tube side inlet and outlet "Nozzle-to-Shell Welds".

These welds are subject to the examination requirements of IWC-2500, Table IWC-2500-1, Category C-B, Item No. C2.32.

Unit I Cooler 1A (Tag No. 1LP-C1A, National Board No. 734) Nozzles Mk. "M"and "N".

Cooler 1B (Tag No. 1LP-CIB, National Board No. 735) Nozzles Mk. "M"and "N".

Summary Numbers: 01.C2.32.001, 002, 003, and 004.

Unit 2 Cooler 2A (Tag No. 2LP-C1A, National Board No. 736) Nozzles Mk. "M"and "N.

Cooler 2B (Tag No. 2LP-C1B, National Board No. 737) Nozzles Mk. "M"and "N".

Summary Numbers: 02.C2.32.001, 002, 003, and 004.

Unit 3 Cooler 3A (Tag No. 3LP-C1A, National Board No. 738) Nozzles Mk. "M"and "N".

Cooler 3B (Tag No. 3LP-C1B, National Board No. 739) Nozzles Mk. "M"and "N".

Summary Numbers: 03.C2.32.001, 002, 003, and 004.

Details of these components can be found on drawings referenced in Section 8 of this request.

Note that Duke Energy Corporation is unable to apply Code Case N-706-1 to these welds as they have not previously been volumetrically examined per Code Case N-706-1, Table 1, Note (2), as detailed in Section 5.2.5(d), below.

2. Applicable Code Edition and Addenda ASME Boiler and Pressure Vessel Code,Section XI, 2007 Edition with the 2008 Addenda.

3. Applicable Code Requirement IWC-2500, Table IWC-2500-1, Examination Category C-B, Item No. C2.32 requires a volumetric examination of the nozzle-to-shell welds when the inside of the vessel is accessible.

4. Reason for Request Duke Energy plans to remove the Channel Cover from each of the Residual Heat Removal (RHR) Heat Exchangers to permit Eddy Current Examination of the heat exchanger tubes during the current inservice inspection interval at each unit. Because these activities will enable access to the interior of the heat exchangers, a volumetric examination of accessible nozzle-to-shell welds would be required in order to satisfy the requirement of IWC-2500, Table IWC-2500-1, Examination Category C-B, Item No. C2.32.

Duke Energy Carolinas, LLC Relief Request Serial No. 14-ON-002 Page 3 of 9 Eddy Current Examinations on the RHR Heat Exchangers are scheduled during plant operation (just prior to refueling outages) in order to minimize radiological dose, which is considerably higher during plant shutdown.

Dose estimates for performing the required volumetric examinations for all three Oconee Units are 600 to 900 mrem (during plant operation) compared to 4.2 to 6.6 rem (during refueling outages).

Duke Energy believes that performing the volumetric examination of these nozzle-to-shell welds is unnecessary because the proposed alternative provides an acceptable level of safety and quality. The proposed alternative will also eliminate all radiation dose associated with performing these volumetric examinations.

5. Proposed Alternative and Basis for Use Pursuant to 10 CFR 50.55a(z)(1), the following alternative is proposed in lieu of the volumetric examinations required by IWC-2500, Table IWC-2500-1, Category C-B, Item C.2.32 for the tube side inlet and outlet nozzles of the Residual Heat Removal Heat Exchangers (Decay Heat Coolers).

5.1. Proposed Alternative:

(a) A VT-2 visual examination shall be performed in accordance with Code Case N-706-1 for Examination Category C-B, Item No. C2.31 welds, and (b) A VT-2 visual examination shall be performed in accordance with IWC-2500, Table IWC-2500-1, Examination Category C-B, Item No. C2.33, and (c) A VT-2 visual examination shall be performed on the RHR Heat Exchangers in accordance with IWC-2500, Table IWC-2500-1, Examination Category C-H, Item No. C7.10 during each inspection period.

5.2. Basis for Use of the Proposed Alternative:

5.2.1. Westinghouse Owner's group (WOG) performed a study (see Reference 8.1.)

as part of the ASME approval process for Code Case N-706. This report provided technical justification for eliminating the volumetric examination of the residual heat removal heat exchangers. The components at Oconee are typical of the heat exchangers described in the WOG report in fabrication, design, inspection requirements and geometric restrictions.

The WOG report also addresses flaw tolerance and risk assessment for these components. Fracture evaluations were performed for the components using finite element models and fracture calculations. It was concluded that the heat exchangers have a large flaw tolerance and that significant leakage would be expected long before any failure occurred. Fatigue crack growth was determined to be extremely slow even in the most highly stressed region.

These heat exchangers do not have a severe duty cycle, and there are no known degradation mechanisms applicable to the tube side nozzle-to-shell welds. Therefore, detailed examinations are not required to ensure their integrity.

Duke Energy Carolinas, LLC Relief Request Serial No. 14-ON-002 Page 4 of 9 A risk evaluation was performed using the accepted methodology applied for Risk Informed ISI piping inspection programs. The following conclusions were made:

" Safety equipment required to respond to a potential event is unaffected.

Potential for loss of pressure boundary integrity is negligible.

• No safety analysis margins are changed.

" Leakage before full break is expected (i.e., there are no core damage consequences associated with leakage).

Thus, elimination of the volumetric examinations required by Table IWC-2500-1, Examination Category C-B, Item C2.32 is expected to result in an insignificant increase in risk. The WOG report indicated that there have been no through-wall leaks on these components or components of similar design reported in the industry. The WOG report indicated that one US plant (San Onofre Unit 3) had experienced a small leak from the letdown line exiting the Regenerative Heat exchanger, but this was caused by excessive vibration on the piping line and is not an indication of a defect in the heat exchanger.

Duke Energy performed a review of industry operating experience reports and did not identify any through-wall leaks in RHR heat exchangers subsequent to the publication date of the WOG report.

5.2.2. Oconee Selected Licensee Commitment (SLC) 16.6.4 currently limits Low Pressure Injection (LPI) system leakage to 2 gph, and LPI system leakage is periodically monitored. Any system leakage through the tube side inlet and outlet nozzle-to-vessel welds would likely be detected by Operations personnel which during plant rounds performed each week include the LPI Cooler (RHR Heat Exchanger) rooms. Any identified leakage from these welds would be noted and entered into the site corrective action program.

5.2.3. The examinations required by IWC-2500, Table IWC-2500-1, Category C-B, Item C.2.32 are conditional (required only if the interior of the heat exchanger is accessible). Therefore, the level of quality and safety afforded by the proposed alternative is equivalent to that provided by other types of RHR heat exchangers where the interior of the heat exchangers are not considered to be accessible.

5.2.4. The proposed alternative and operator rounds will identify defects resulting in through-wall leakage prior to propagation that results in failure of the component structural integrity.

5.2.5. Previous inservice inspections of the RHR Heat Exchangers have not detected any signs of leakage or age-related degradation in the subject RHR Heat Exchanger welds at Oconee Nuclear Station, Units 1, 2, and 3. Specific inspection results are as follows:

a. VT-2 visual examinations performed on the RHR Heat Exchangers at Oconee Nuclear Station, Units 1, 2, and 3 during the 4th Inservice Inspection Interval have not detected any evidence of leakage from these RHR Heat exchangers, including the welds for which relief has been requested.

Duke Energy Carolinas, LLC Relief Request Serial No. 14-ON-002 Page 5 of 9

b. Surface examinations performed on the nozzle Mk. "M"and "N" reinforcing pad-to-shell welds and reinforcing pad-to-nozzle welds on the RHR Heat Exchangers at Oconee Nuclear Station, Units 1, 2, and 3 during the 4th Inservice Inspection Interval have not detected any unacceptable indications.

c. Volumetric examinations performed on the shell-to-head flange welds and shell-to-tubesheet flange welds (adjacent to Nozzles Mk. "M"and "N") on the RHR Heat Exchangers at Oconee Nuclear Station, Units 1, 2, and 3 during the 4th Inservice Inspection Interval have not detected any unacceptable indications. These results provide additional evidence that there has been no service-induced degradation on the IDof the LPI Coolers in the vicinity of the Nozzle Mk. "M"and "N" nozzle-to-shell welds for which relief has been requested.

d. The nozzle-to-shell welds for which relief has been requested have not received any inservice volumetric examinations. However, the inservice volumetric examinations performed on the adjacent shell-to-head flange and shell-to-tubesheet flange welds during the 4th Inservice Inspection Intervals provide reasonable assurance that the service conditions within the RHR Heat Exchangers have not resulted in any age-related degradation in the nozzle-to-shell welds for which relief has been requested.

For the reasons stated above, the proposed alternative provides an acceptable level of quality and safety.

6. Duration of Proposed Alternative The proposed alternative is requested for use during the 5 th inservice inspection intervals for Oconee Units 1, 2 and 3, beginning July 15, 2014, currently scheduled to end July 15, 2024.

7. Related Industry Relief Requests 7.1. Virginia Electric and Power Company (Dominion), North Anna Power Station Unit 1 Relief Request No. NDE-006, submitted October 7, 2008 (ML082880160), approved August 13, 2009 (ML092230647).

7.2. Duke Energy Carolinas, LLC, Oconee Nuclear Station Units 1, 2, and 3, Relief Request No. 10-ON-001 submitted June 9, 2010 (ML101660473) and supplemented March 2,2011 (ML11144A078), approved June 21, 2011.

8. References 8.1. Westinghouse Owner's group (WOG) project MUHP 5093, Working Group Inservice Inspection Optimization Action 97-01 (Boiler Code Item BC03-338), "Technical Basis for Revision of Inspection Requirements for Regenerative and Residual Heat Exchangers,"

August, 2004.

8.2. Duke Energy Drawings (copies provided as Attachments):

a) OM-201.00-0286.001, Decay Heat Coolers (1A and 2A) b) OM-201.00-3131.002, Channels for Decay Heat Coolers (1B and 2B) c) OM-2201.00-0277.001, Decay Heat Coolers (3A and 3B)

Duke Energy Carolinas, LLC Relief Request Serial No. 14-ON-002 Page 6 of 9 Attachments to 14-ON-002 Drawinqs of Decay Heat Exchanger 0 OM-201.00-0286.001, Decay Heat Coolers 0 OM-201.00-3131.002, Channels for Decay Heat Coolers 0 OM-2201.00-0277.001, Decay Heat Coolers