05000414/LER-2018-002, Condition Prohibited by Technical Specifications (TS) Due to Failure of the 2A Diesel Generator (DG)

Condition Prohibited by Technical Specifications (TS) Due to Failure of the 2A Diesel Generator (DG)

ML18226A059
Person / Time
Site:	Catawba
Issue date:	08/13/2018
From:	Simril T Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RA-18-0117 LER 2018-002-00
Download: ML18226A059 (7)

LER-2018-002, Condition Prohibited by Technical Specifications (TS) Due to Failure of the 2A Diesel Generator (DG)

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)
4142018002R00 - NRC Website

text

(_~ DUKE

<{; ENERGY RA-18-0117 August 13, 2018 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555

Subject:

Duke Energy Carolinas, LLC Catawba Nuclear Station, Unit 2 Docket No. 50-414 Licensee Event Report (LER) 414/2018-002-00 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 10 CFR 50.73 Pursuant to 10 CFR 50.73(a)(1) and (d), attached is LER 414/2018-002-00, entitled "Condition Prohibited by Technical Specifications (TS) due to Failure of the 2A Diesel Generator (DG)."

This report is being submitted in accordance with 10 CFR 50.73(a)(2)(i)(B).

There are no regulatory commitments contained in this letter or its attachment.

This event is considered to be of no significance with respect to the health and safety of the public.

Please direct any questions or concerns to Carrie Wilson, Sr. Engineer, at (803) 701 -3014.

Sincerely, Tom Simril Vice President, Catawba Nuclear Station Attachment www.duke-energy.com

U.S. Nuclear Regulatory Commission RA-18-0117 August 13, 2018 Page 2 xc (with attachment):

C. Haney, Region II Administrator U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, GA 30303 M. Mahoney U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mailstop O-8B1A Rockville, MD 20852 J.D. Austin (without enclosure)

NRC Senior Resident Inspector INPO Records Center 700 Galleria Parkway, SE Suite 100 Atlanta, GA 30339-5943

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 03/31/2020 (04-2018)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. Page Catawba Nuclear Station, Unit 2 05000 414 1

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4. Title Condition Prohibited by Technical Specifications (TS) due to Failure of the 2A Diesel Generator (DG).

5. Event Date

6. LER Number

7. Report Date

8. Other Facilities Involved I

Sequential I Rev Facility Name Docket Number Month Day Year Year Number No.

Month Day Year 05000 Facility Name Docket Number 06 11 2018 2018 -

002 -

00 08 13 2018 05000

9. Operating Mode

11. This Report is Submitted Pursuant to the Requirements of 10 CFR §: (Check all that apply) 20.2201(b) 20.2203(a)(3)(i) 50.73(a)(2)(ii)(A) 50.73(a)(2)(viii)(A) 20.2201(d) 20.2203(a)(3)(ii)

50. 73(a)(2)(ii)(B) 50.73(a)(2)(viii)(B) 1 20.2203(a)( 1) 20.2203(a)(4) 50.73(a)(2)(iii)

50. 73(a)(2)(ix)(A) 20.2203(a)(2)(i) 50.36(c)(1 )(i)(A)

50. 73(a)(2)(iv)(A)

50. 73(a)(2)(x)

10. Power Level

• 20.2203(a)(2)(ii)

50. 36( c)( 1 )(ii)(A) 50.73(a)(2)(v)(A) 73.71(a)(4) 20.2203(a)(2)(iii) 50.36(c)(2)

50. 73(a)(2)(v)(B)

73. 71 (a)(5) 20.2203(a)(2)(iv) 50.46(a)(3)(ii) 50.73(a)(2)(v)(C)

73. 77(a)(1) 100 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(D) 73.77(a)(2)(i) 20.2203(a)(2)(vi)

[Z] 50.73(a)(2)(i)(B)

50. 73(a)(2)(vii) 73.77(a)(2)(ii) 50.73(a)(2)(i)(C)

Other (Specify in Abstract below or in must also be operable. If a shared NSWS component becomes inoperable, or normal or emergency power to shared components becomes inoperable, then the required actions of the NSWS LCO must be entered independently for each unit that is in the mode of applicability of the LCO. If both units are in the mode of applicability with the NSWS operating in the normal dual supply and discharge header alignment, one unit may exit the LCO provided that unit's NSWS pump is operable and one unit's flow path to the non-essential header, AFW pumps, and Containment Spray System heat exchangers are isolated (or equivalent flow restrictions). In this case, sufficient flow is available, however, this configuration results in inoperabilities within other required systems on one unit and the associated required actions must be entered.

TS 3.7.8 governs the NSWS. LCO 3.7.8 requires two operable NSWS trains for each unit that is in Modes 1, 2, 3, and 4.

With one NSWS train inoperable, the inoperable NSWS train must be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> per Required Action A.1. If this is not accomplished, the unit must be placed in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> per Required Actions D.1 and D.2. Thus, the LCO for TS 3.7.8 on Unit 1 can be met, while the Unit 2 LCO cannot be met, requiring an extension to the Completion Time.

The NSWS also supports the AFW and Containment Spray Systems since it serves as the assured water source for these systems. TS 3.7.5 governs the AFW System. LCO 3.7.5 requires three AFW trains to be operable in Modes 1, 2, and 3, and one motor-driven AFW train to be operable in Mode 4 when the steam generators are relied upon for heat removal.

With one AFW train inoperable in Mode 1, 2, or 3 for reasons other than an inoperable steam supply to the turbine-driven AFW pump, the inoperable AFW train must be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> per Required Action B.1. If this is not accomplished, the unit must be placed in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 4 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> per Required Actions C.1 and C.2. TS 3.6.6 governs the Containment Spray System. LCO 3.6.6 requires two containment spray trains to be operable in Modes 1, 2, 3, and 4. With one containment spray train inoperable, the inoperable containment spray train must be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> per Required Action A.1. If this is not accomplished, the unit must be placed in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 5 within 84 hours9.722222e-4 days <br />0.0233 hours <br />1.388889e-4 weeks <br />3.1962e-5 months <br /> per Required Actions B.1 and B.2.

At the time of the event, repair and testing of the 2A DG was not anticipated to be completed within the 72-hour completion time mandated by TS 3.8.1, TS 3.7.8, TS 3.7. 5, and TS 3.6.6. Therefore, Duke Energy requested the Completion Time of Required Action be extended from the current 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> by an additional 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />, for a total of 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />, to allow Catawba Unit 2 to remain in Mode 1 (Power Operation) until repairs could be completed and testing to demonstrate operability of 2A DG was completed. The NOED was subsequently granted by the NRC on the same day for an additional 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> of unit operation. The 2A DG was restored to operable status approximately 17 hours1.967593e-4 days <br />0.00472 hours <br />2.810847e-5 weeks <br />6.4685e-6 months <br /> into the 48-hour period allowed by the NOED.

This event is being reported under 10 CFR 50.73(a)(2)(i)(B) as an operation or condition which was prohibited by the plant's Technical Specifications. Throughout the duration of this event, Unit 1 operated in Mode 1 at 100% power. No significant structures, systems or components were out of service at the time of discovery such that they contributed to the event.

EVENT DESCRIPTION

The 2A DG was declared inoperable on June 11, 2018, at 0408 hours0.00472 days <br />0.113 hours <br />6.746032e-4 weeks <br />1.55244e-4 months <br />. This inoperability was planned as part of scheduled maintenance activity. One of the major maintenance activities was Doble testing of the 2A DG Portee Voltage Regulator components. During the post maintenance test, the 2A DG and associated breaker 2ETA-18 tripped on an actuation of Lockout Relay 86D when trying to load in parallel and therefore failed the post maintenance test.

During troubleshooting, two disconnected cables were identified in the Voltage Regulator circuitry. These two cables connect the current transformer to the linear reactor. The two cables were left disconnected from the linear reactor terminal during the current maintenance activities. The cause of the disconnected cables is a failure to properly reassemble the connection after maintenance. As a result of the disconnected cables, damage occurred during the subsequent post-maintenance run that required corrective work for a duration beyond the TS required Completion Time.

During extent of damage visual inspections of the voltage regulator cabinet, evidence of arcing between a heat sink mounting screw and the heat sink for Silicon Controlled Rectifier, SCR1, was discovered. Under normal operation the distance between the heat sink and mounting screw is sufficient to prevent arcing or conduction. However, when the two cables were not terminated, they were allowed to ground against the DG control cabinet and resulted in arcing between the heat sink and mounting screw. This resulted in the need to replace the SCRs and Diodes.

The current transformer was replaced and the associated linear reactor was tested and found to be operating satisfactorily with no damage. The cables were re-landed per design drawings. The SCRs and Diodes were replaced with new components. During the functional run, it was determined that the Voltage Regulator module was not operating correctly.

Two of the three SCRs were not firing as required. These SCRs receive their firing signals from the Voltage Regulator module. Therefore, this indicates that the extent of damage from the two cables that were left disconnected also resulted in damage to the Voltage Regulator module.

On June 14, 2018, at 0234, Catawba requested a NOED for an additional 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> to TS 3.8.1, TS 3.7.8, TS 3.7.5, and TS 3.6.6, to allow for repair of the 2A DG. The NOED was subsequently granted by the NRC for an additional 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> of unit operation. The enforcement discretion period began on June 14 at 0408. On June 14, 2018, at 2106, the 2A DG was declared operable.

CAUSAL FACTORS:

The cause of this event is that two cables in the Voltage Regulator circuitry of the DG were not connected as required.

These two cables connect the current transformer to the linear reactor. The two cables were left disconnected from the linear reactor terminal during the current maintenance activities. The cause of the disconnected cables is a failure to properly reassemble the connection after maintenance.

CORRECTIVE ACTIONS

1. Replaced the Current Transformer, SCRs, Diodes, and Voltage Regulator Module

2. Completed all required post-maintenance testing

3. Communicated lessons learned with maintenance and QC

4. Remediated individuals involved

SAFETY ANALYSIS

An assessment of the safety consequences and implication of the event was performed. The nuclear safety significance of this event was that the site operated for a period of time outside the Technical Specification limits with the 2A DG inoperable. The associated risk, including the Probabilistic Risk Assessment analysis, of this condition was evaluated as part of the NOED and was found to be acceptable. The redundant 2B DG was operable and available and could have performed its intended safety function at all times while the 2A DG was tagged out to support maintenance and testing.

The common mode failure review determined that the 1A, 1 B, and 2B DGs were not susceptible to the same failure mode as 2A DG based on the fact that Doble testing has been successfully completed on the 1A, 1 B, and 2B DGs per scheduled maintenance. Along with successful post maintenance testing and successful monthly surveillance testing, this proves there were no issues reconnecting the respective components.

ADDITIONAL INFORMATION

A three-year search of the Catawba corrective action database revealed that no other DG Voltage Regulators have failed due to cable connection errors following maintenance. Page 5

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