CNS-17-048, Supplemental Response to Preliminary White Finding, Apparent Violations, and NRC Inspection Report 05000414/2017012; Enforcement Action 17-122

Supplemental Response to Preliminary White Finding, Apparent Violations, and NRC Inspection Report 05000414/2017012; Enforcement Action 17-122

ML17276A345
Person / Time
Site:	Catawba
Issue date:	09/29/2017
From:	Simril T Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CNS-17-048, EA-17-122, IR 2017012
Download: ML17276A345 (6)

Text

~~DUKE

"'e ENERGYr.

Tom Simril Vice President Catawba Nuclear Station Duke Energy CN01VP I 4800 Concord Road York, SC 29745 o: 803. 701.3340 f: 803. 701.3221 tom.simril@duke-energy.com CNS-17-048 September 29, 2017 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001

Subject:

Duke Energy Carolinas, LLC (Duke Energy)

Catawba Nuclear Station, Unit 2 Docket Number 50-414 Supplemental Response to Preliminary White Finding, Apparent Violations, and NRC Inspection Report 05000414/2017012; Enforcement Action 17-122

References:

1. NRC Letter from Joel T. Munday to Tom Simril dated August 22, 2017, Catawba Nuclear Station - NRG Inspection Report 0500041412017012 and Preliminary White Finding (ADAMS Accession No. ML17234A678)

2. Catawba Nuclear Station Letter from Tom Simril to NRC dated August 29, 2017, Response to Catawba Nuclear Station - NRG Inspection Report 0500041412017012 and Preliminary White Finding; EA 17-122 (ADAMS Accession No. ML17243A129)

On August 22, 2017, Duke Energy received NRC Inspection Report 05000414/2017012 (Reference 1) describing a preliminary White finding associated with Catawba Nuclear Station's 2A Emergency Diesel Generator diode failure event on April 11, 2017. The Inspection Report provided Duke Energy the option of either (1) attending and presenting at a regulatory conference or (2) submitting our position in writing within 40 days. Duke Energy's response*

(Reference 2) stated that a written response would be provided within 40 days. This letter provides Duke Energy's written response.

Pursuant to the provisions of 10 CFR 2.201, Duke Energy has prepared the attached statement in response to the subject finding. Duke Energy acknowledges the preliminary White significance determination and does not contest the finding. There are no regulatory commitments contained in this letter or the enclosure.

www.duke-energy.com

United States Nuclear Regulatory Commission Page 2 September 29, 2017 Please address any questions regarding this matter to Cecil A. Fletcher II, Manager Nuclear Regulatory Affairs at 803-701-3622.

Sincerely, Tom Simril Vice President, Catawba Nuclear Station

Enclosure:

Catawba Nuclear Station, Supplemental Response to Preliminary White Finding, Apparent Violations, and NRC Inspection Report 05000414/2017012; Enforcement Action 17-122 xc:

United States Nuclear Regulatory Commission Page 3 September 29, 2017 xc:

C. Haney Region 11 Administrator U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Avenue NE, Suite 1200 Atlanta, GA 30303-1257 J. D. Austin Senior Resident Inspector U.S. Nuclear Regulatory Commission Catawba Nuclear Station M. Mahoney (addressee only)

Project Manager U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mailstop 0-8H4A Rockville, MD 20852 L___

Catawba Nuclear Station Supplemental Response to Preliminary White Finding, Apparent Violations, and NRC Inspection Report 05000414/2017012; Enforcement Action 17-122 Enclosure Significance Determination NRC Inspection Report 05000414/2017012 (Reference 1) states that based on subsequent review, the NRC has preliminarily determined the finding to be White (i.e., low-to-moderate safety significance). In accordance with NRC Inspection Manual Chapter (IMC) 0609, Significance Determination Process, the NRC determined that the issue required a detailed risk evaluation because the finding repres_ents an actual loss of function of a single train for greater than its Technical Specification allowed outage time. Duke Energy has performed its own detailed risk evaluation, and agrees with the NRC significance determination that this represents a finding of low to moderate safety significance.

Restatement of Violation The following violations from the NRC Inspection Report are associated with the preliminary White finding.

"Technical Specification 5.4.1.a, "Procedures," requires, in part, that procedures shall be established, implemented, and maintained covering the applicable procedures recommended in Appendix A of Regulatory Guide 1.33, Revision 2. Section 9.b of Appendix A to Regulatory Guide 1.33, Revision 2, requires, in part, that "preventive maintenance schedules be developed to specify inspection or replacement of parts that have a specific lifetime." The licensee established Procedure AD-EG-ALL-1202 to provide direction for implementing the preventive maintenance program. Section 5.3 of Procedure AD-EG-ALL-1202, requires that maintenance strategies for equipment within the scope of the preventive maintenance program be developed by considering operating experience, corrective maintenance history and SSC performance.

10 CFR 50, Appendix B, Criterion XVI, "Corrective Actions," requires, in part, that conditions adverse to quality be promptly identified and corrected.

Contrary to the above, as of April 11, 2017, the licensee failed to ensure that adequate preventive maintenance activities were developed and adjusted for the EOG excitation system by incorporating operating experience. Specifically, the licensee did not effectively incorporate operating experience documented in Condition Report 1566561 into the preventive maintenance activities for EOG excitation system diodes. As a result, a condition adverse to quality associated with the elevated diode temperatures was uncorrected. This caused the 2A EOG output breaker to trip open during monthly surveillance testing. The licensee entered this condition into its corrective action program as Condition Report 2116069. The 2A EOG was returned to service on April 14, 2017 following replacement of the excitation system diodes. This violation is being treated as an apparent violation pending a final significance determination."

Reason for Violations The violations were attributed to a trip of the 2A Emergency Diesel Generator (EOG) during a scheduled operability periodic test (PT/2/A/4350/002A) on April 11, 2017. Three minutes after reaching full load and 39 minutes after closing the generator output breaker, the 2A EOG output Page 1 of 3

Catawba Nuclear Station Supplemental Response to Preliminary White Finding, Apparent Violations, and NRG Inspection Report 05000414/2017012; Enforcement Action 17-122 breaker 2ETA-18 tripped on overcurrent. This caused Catawba Nuclear Station (Catawba) Unit 2 to enter a Technical Specification (TS) 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> shutdown action statement. Troubleshooting identified the direct cause for the overcurrent trip as a loss of generator excitation resulting from the shorting of the excitation system voltage regulator bridge rectifier diode CR4. Although the NRG inspection report states "the 2A EOG was returned to service on April 14, 2017," after the replacement of all the diodes, the 2A EOG successfully passed its operability periodic test (PT) and was declared operable on April 13, 2017.

Following a similar diode failure diode in 2005, Catawba did not effectively evaluate internal and external operating experience (OE) to recognize the need to take mitigating action. Similarly, Catawba failed to effectively evaluate the 2012 Turkey Point IER L3 12-41. Following the April 11, 2017, 2A EOG diode failure, a Root Cause Evaluation was conducted by Duke Energy to determine the cause of the diode failure.

Corrective Actions Completed i

• On April 12, 2017, the 2A EOG failure investigation process (FIP) identified a shorted 1~' voltage regulator bridge rectifier diode CR4. The failed diode, the remaining five diodes for the 2A EOG, three silicon-controlled rectifiers (SCRs), and the power-driven potentiometer (PDP) were all replaced.

• Complete 4/12/2017 - 2A EOG

• The diodes on all the EDGs were replaced in May 2017 with new diodes that were peak-inverse voltage tested to ensure that there were no latent deficiencies.

• Complete 5/13/2017 - 1A EOG

• Complete 5/08/2017 - 1B EOG

• Complete 5/24/2017 - 2A EDG

• Complete 5/19/2017 - 28 EOG

• An 18-month diode and SCR replacement preventive maintenance activity was established for the current set of diodes.

• Com,plete 9/18/2017 - All EDGs The corre.ctive actions planned and other actions planned do not represent an all-inclusive list that will be implemented as a result of this event; however, the following are deemed noteworthy. These actions will be tracked to completion in accordance with the Corrective Action Program (CAP). Any changes to the actions or schedules noted below will be made in accordance with the Site's CAP.

Corrective Actions Planned Page 2 of 3

Catawba Nuclear Station Supplemental Response to Preliminary White Finding, Apparent Violations, and NRC Inspection Report 05000414/2017012; Enforcement Action 17-122 Corrective Actions Planned

• Interim Action - Implement an engineering change to replace EDG voltage regulator bridge rectifier diodes with a diode model type rated for higher reverse voltage and forward current.

This action is scheduled to be completed by February 28, 2018.

Other Actions Planned

• Modify the EDG voltage regulator for all four EDGs to improve design margin. Modifications will be based on the results of a detailed simulation of the voltage regulator. This action is scheduled to be completed by May 31, 2021.

• Review Cat 1 components that do not have vendor recommended replacement preventive maintenance activity. Determine acceptability based on:

o Industry reliability data from academic, military or other technical sources, o Catawba operating history, and o Industry operating experience.

This action is scheduled to be completed by December 7, 2017.

Full Compliance Although additional actions, as described above, are ongoing, full compliance was achieved on April 13, 2017, when the 2A EDG successfully passed its monthly surveillance testing, PT/2/A/4350/002A, "Diesel Generator 2A Operability Test."

Page 3 of 3