05000296/LER-2015-005, Regarding Automatic Actuation of 30 Diesel Generator Due to 4kV Shutdown Board Trip During Testing

Regarding Automatic Actuation of 30 Diesel Generator Due to 4kV Shutdown Board Trip During Testing

ML15292A542
Person / Time
Site:	Browns Ferry
Issue date:	10/19/2015
From:	Bono S Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 15-005-00
Download: ML15292A542 (8)

LER-2015-005, Regarding Automatic Actuation of 30 Diesel Generator Due to 4kV Shutdown Board Trip During Testing

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2962015005R00 - NRC Website

text

Tennessee Valley Authority, Post Office Box 2000, Decatur, Alabama 35609-2000 October 19, 2015 ATTN : Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001

Subject:

Browns Ferry Nuclear Plant, Unit 3 Renewed Facility Operating License No. DPR-68 NRC Docket No. 50-296 Licensee Event Report 50-296/2015-005-00 10 CFR 50.73 The enclosed Licensee Event Report provides details of an unplanned automatic start of 3D Emergency Diesel Generator during pump motor testing. The Tennessee Valley Authority (TVA) is submitting this report in accordance with Title 10 of the Code of Federal Regulations (10 CFR) 50.73(a)(2)(iv)(A), as any event or condition that resulted in manual or automatic actuation of any of the systems listed in 10 CFR 50. 73(a)(2)(iv)(B).

There are no new regulatory commitments contained in this letter. Should you have any questions concerning this submittal, please contact J. L. Paul, Nuclear Site Licensing Manager, at (256) 729-2636.

Enclosure:

Licensee Event Report 50-296/2015-005 Automatic Actuation of 3D Diesel Generator Due To 4kV Shutdown Board Trip During Testing cc (w/ Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant

ENCLOSURE Browns Ferry Nuclear Plant Unit 3 Licensee Event Report 50-296/2015-005-00 Automatic Actuation of 3D Diesel Generator Due To 4kV Shutdown Board Trip During Testing See Enclosed

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED B Y OMB NO. 3150-0104 EXPIRES 01/31/2017 (01-2014)

Estimated burden per response to comply with this mandatory collection request:

80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory LICENSEE EVENT REPORT (LER)

Commission, Washington, DC 20555-0001 '

or by internet e-mail to lnfocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMS control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

, 3. PAGE Browns Ferry Nuclear Plant (BFN), Unit 3 05000296 1 of 6

4. TITLE: Automatic Actuation of 30 Diesel Generator Due To 4kV Shutdown Board Trip During Testing

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED MONTH DAY YEAR YEAR ISEQUENTIALI REV NUMBER NO.

MONT H DAY YEAR N/A N/A 8

20 2015 2015 - 005 - 00 10 19 2015 N/A N/A

9. OPERATING MODE 11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)

D 20.2201(b)

D 20.2203(a)(3)(i)

D 50. 73(a)(2)(i)(C)

D 50.73(a)(2)(vii) 1 D 20.2201 (d)

D 20.2203(a)(3)(ii)

D 50. 73(a)(2)(ii)(A)

D 50. 73(a)(2)(viii)(A)

D 20.2203(a)(1)

D 20.2203(a)(4)

D 50. 73(a)(2)(ii)(B)

D 50. 73(a)(2)(viii)(B)

D 20.2203(a)(2)(i)

D 50.36(c)(1 )(i)(A)

D 50. 73(a)(2)(iii)

D 50.73(a)(2)(ix)(A)

10. POWER LEVEL D 20.2203(a)(2)(ii)

D 50.36(c)(1)(ii)(A) 181 50. 73(a)(2)(iv)(A)

D 50.73(a)(2)(x)

D 20.2203(a)(2)(iii)

D 50.36(c)(2)

D 50. 73(a)(2)(v)(A)

D 73.71(a)(4) 100 D 20.2203(a)(2)(iv)

D 50.46(a)(3)(ii)

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

D 73.71(a)(5)

D 20.2203(a)(2)(v)

D 50.73(a)(2)(i)(A)

D 50. 73(a)(2)(v)(C)

D OTHER D 20.2203(a)(2)(vi)

D 50.73(a)(2)(i)(B)

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

Specify in Abstract below or in

C. Dates and approximate times of occurrences

August 20, 2015, 3ED 4kV SD BO de-energized at 1032 CDT 30 DG fast-started August 20, 2015, Provided eight-hour EN 51333 to the NRC.

at 1851 CDT August 21, 2015, at 0136 CDT 30 DG secured and declared inoperable 3ED 4kV SD BO declared inoperable C SGT declared inoperable August 21, 2015, Offsite power to 3ED 4kV SD BO declared operable at 1945 CDT 3ED 4kV SD BO declared operable C SGT declared operable August 21, 2015, 30 DG declared operable at 2300 CDT D. Manufacturer and model number (or other identification) of each component that failed during the event:

No component failures were identified that occurred during the event.

E. Other systems or secondary functions affected

01 RHR Service Water (RHRSW)[CC] pump tripped.

Control Bay Vent Board B was de-energized.

Loads supplied by 3ED 4kV SD BO were momentarily de-energized.

F. Method of discovery of each component or system failure or procedural error

Degraded voltage for the 3ED 4kV SD BO resulted in multiple Control Room alarms.

G. The failure mode, mechanism, and effect of each failed component, if known:

There were no failed components related to this event.

H. Operator actions

Declared offsite power to 3ED 4kV SD BO inoperable.

Removed 30 DG from service.

Declared 3ED 4kV SD BO, C SGT, and 30 DG inoperable for corrective maintenance.

Declared offsite power to 3ED 4kV SD BO operable following troubleshooting.

Declared 3ED 4kV SD BO, C SGT, and 30 DG operable upon completion of work.

I. Automatically and manually initiated safety system responses

3D DG started automatically upon opening of normal feeder breaker to 4kV SD BD.

Ill.

Cause of the event

A. The cause of each component or system failure or personnel error, if known:

A definitive cause could not be identified for the clearing of the 3ED SD BD metering fuses.

B. The cause(s) and circumstances for each human performance related root cause:

A definitive cause could not be identified for the clearing of the 3ED SD BD metering fuses.

However, a possible failure mode was identified that was related to human performance, shorting between two terminals when attempting to attach the clip.

IV.

Analysis of the event

The Tennessee Valley Authority (TVA) is submitting this report in accordance with 10 CFR 50. 73(a)(2)(iv)(A), as any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of 10 CFR 50. 73 (including DGs), except when:

1. The actuation resulted from, and was part of, a pre-planned sequence during testing or reactor operation

2. The actuation was invalid and occurred while the system was properly removed from service, or was invalid and occurred after the safety function had been already completed.

Because this event resulted in a valid, unplanned actuation of 3D DG, it is reportable under 10 CFR 50. 73(a)(2)(iv)(A).

The safety objective of the Standby Alternating Current Power System is to provide a self-contained, highly reliable source of power, as required for the Engineered Safeguards System, so that no single credible event can disable the core standby cooling functions or their supporting auxiliaries. The DGs are designed to support the electrical load of a 4kV SD BD upon loss of supply from a 4.16-kV shutdown bus. During this event, 3D DG adequately performed its safety function of automatically assuming the load of 3ED 4kV SD BD upon a loss of supply to the board.

Troubleshooting of the DG and SD BD determined that the failure mode for this event was the clearing of one primary and one secondary 3ED SD BD metering fuses. The secondary fuse that cleared supplies the RHR Motor 3D Watt-hour meter. The primary fuse that cleared was one of the 3D SD BD potential transformer fuses that supplies power to the 3D RHR motor watt-hour meter and the 3ED shutdown board under-voltage relays.

An inspection of test equipment by the vendor identified four potential failure mechanisms for this equipment. Two possible failure modes were potentially caused by mechanical failure.

These included a short circuit between two test points or between the first test point and the ground. Potential human error failure modes included shorting between two terminals when attempting to attach the clip. No definitive cause was identified for the clearing of fuses which led to this event. Therefore, corrective actions will be implemented that address the four most probable causes and minimize the likelihood of recurrence.

V.

Assessment of Safety Consequences

This event resulted in an unplanned automatic start of 30 DG. The diesel generators are designed to automatically start upon a loss of offsite power. 30 DG successfully performed its safety function during this event; therefore, TVA has concluded there was no significant increase in risk to the health and safety of the public or plant personnel due to this event.

A. Availability of systems or components that could have performed the same function as the components and systems that failed during the event:

During this event, all four Unit 3 DGs remained available, and all four Unit 3 4kV SD BDs were operable. 02 RHRSW pump was started when 01 RHRSW pump tripped.

B. For events that occurred when the reactor was shut down, availability of systems or components needed to shutdown the reactor and maintain safe shutdown conditions, remove residual heat, control the release of radioactive material, or mitigate the consequences of an accident:

This event did not occur when the reactor was shut down.

C. For failure that rendered a train of a safety system inoperable, an estimate of the elapsed time from discovery of the failure until the train was returned to service:

Offsite power to the 3ED 4kV SD BO was inoperable for approximately thirty-three hours from the time the SD BO de-energized on August 20, 2015, at 1032 CDT, to the time power was restored on August 21, 2015, at 1945 CDT.

VI.

Corrective Actions

Corrective Actions (CA) are being managed by TVA's Corrective Action Program under Condition Report (CR) 1073157. The following CAs are in progress:

1. Perform inspections on circuits used for online dynamic motor testing of motors.

2. Remove potentially faulty test equipment from service.

3. Remove online dynamic motor testing from 4kV motor preventative maintenance. This action will be taken in order to prevent future human performance errors similar to the type of error which may have caused this event.

VII. Additional Information

A. Previous Similar Events at the same plant:

A review of BFN Licensee Event Reports and Corrective Action Program documents for the past three years did not identify any relevant equipment trips caused by the online dynamic motor test equipment.

B. Additional Information

There is no additional information.

C. Safety System Functional Failure Consideration:

This event is not considered to be a Safety System Functional Failure in accordance with NUREG-1022.

D. Scram with Complications Consideration:

This event did not result in a reactor scram.

VIII.

COMMITMENTS

There are no new commitments.