05000366/LER-2017-002

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LER-2017-002, Emergency Diesel Generator Start Due to Inadvertent Electrical Bus De-Energization
Edwin I. Hatch Nuclear Plant Unit 2
Event date: 02-16-2017
Report date: 4-13-2017
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
3662017002R00 - NRC Website
LER 17-002-00 for Edwin I. Hatch, Unit 2, Regarding Emergency Diesel Generator Start Due to Inadvertent Electrical Bus De-Energization
ML17103A412
Person / Time
Site: Hatch Southern Nuclear icon.png
Issue date: 04/13/2017
From: Vineyard D R
Southern Nuclear Operating Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-17-0624
Download: ML17103A412 (6)


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 Commission, Washington, DC 20555-0001, or by e-mail to Infocollects.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 OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Event Description

On February 16, 2017, at 1320 EST with Unit 2 at 0 percent rated thermal power due to being in a refueling outage, maintenance electricians were sent to the field to perform a protective relay trip test for the 2D start-up transformer (SAT) (EllS Code XMFR). During the test setup, the 2E 4160 VAC Emergency Bus (EIIS Code BU) was inadvertently and momentarily de-energized, causing the 2A Emergency Diesel Generator (EDG) (EIIS Code DG) to autostart, secondary containment to isolate, and start of the standby gas treatment system. Although, the 2A EDG autostarted, it did not tie to the 2E 4160 VAC Emergency Bus as the 2E 4160 VAC Emergency Bus was re-energized from the 2C SAT.

Subsequent investigations revealed that a movement operated contact (MOC) switch adapter had been installed on the 2D normal supply breaker in the 2E 4160 VAC Emergency Bus. The procedure did not call for the MOC switch adapter to be installed and was installed at the direction of supervision. The switch adapter caused the alternate supply breaker that was feeding the 2E 4160 VAC Emergency Bus to momentarily open and then reclose, consequently ending the event.

Event Cause Analysis The cause of the event is due to a MOC switch adapter being incorrectly installed on the 2D normal supply breaker in the 2E 4160 VAC Emergency Bus. Causal analysis determined that the MOC switch adapter was not required to be installed per the procedure. The supervisor made the decision to install the adapter after a review of the electrical prints and assumed he had eliminated the trip potential by opening the appropriate link. The supervisor stepped out of role and did not follow plant standards for procedure use and adherence.

Safety Assessment This event is reportable per 10 CFR 50.73(a)(2)(iv)(A) due to the valid actuation of an emergency ac electrical power system that was not part of a pre-planned sequence.

The electrically powered safety loads are separated into redundant load groups such that loss of any one group will not prevent the minimum safety functions from being performed. Essential loads are divided between the three essential 4160 VAC Emergency Buses: 2E, 2F, and 2G. Availability of any two of these buses is sufficient to meet any accident conditions. The startup transformers are used to supply the 4160 VAC buses during normal operation, maintenance outages, and shutdown. Emergency buses 2E, 2F, and 2G are normally supplied by the 2D startup transformer. On failure of the normal source (2D transformer), the three emergency buses are energized from the 2C startup transformer. This is accomplished by an automatic transfer. In the event that both startup transformer supplies are lost, the power supply for the emergency buses is fed from emergency diesel generators.

Upon a momentary loss of the 2E Emergency Bus supply power, the alternate supply power breaker automatically reclosed, reenergizing the bus. All respective systems operated as designed upon the momentary loss of power and no component failures were identified. Due to Unit 2 being in a scheduled refueling outage, shutdown cooling was being provided by the Decay Heat Removal (DHR) system during this time. Therefore, there was no loss of shutdown cooling and the outage safety assessment was not impacted by this event. This event is considered to have very low safety significance.

Reported lessons learned are incorporated into the licensing process and ted back to industry.

Send comments regarding burden estimate to the FDA, Privacy and Information Collections Branch (1--5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infocollects.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 OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the Information collection.

Corrective Actions

A stand down was held with all maintenance supervisors to cover supervisor roles and responsibilities and the need for all workers to follow plant standards for procedure use and adherence. Also, a stand down was held with craft personnel to reinforce the need to always follow the procedure and to not deviate from written procedures even under the direction of supervision. All breaker procedures and protective relay test procedures were reviewed to determine if a MOC Switch Adapter needs to be installed. Continuing training will also be held to cover this event and its lessons learned.

Previous Similar Events

None.

Edwin I. Hatch Nuclear Plant Unit 2 05000-366