05000325/LER-2017-002

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LER-2017-002, Foreign Material in Switch Results in Unplanned Automatic Start of Emergency Diesel Generators
Brunswick Steam Electric Plant (Bsep) Unit 1
Event date: 04-17-2017
Report date: 06-12-2017
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
Initial Reporting
ENS 52683 10 CFR 50.72(b)(3)(iv)(A), System Actuation
3252017002R00 - NRC Website

The site's Electrical Power Distribution System sources consist of the offsite power sources (i.e., preferred and alternate power sources), and the onsite standby power sources, EDGs 1, 2, 3, and 4. The AC electrical power system provides independence and redundancy to ensure an available source of power to On April 17, 2017, at 00:04 Eastern Daylight Time (EDT), Unit 1 was in Mode 1 at approximately 100 percent of rated power, and Unit 2 was in Mode 1 at approximately 22 percent of rated power. Unit 2 was restarting following a refueling outage. Personnel were engaged in actions to resolve high bearing vibration on the main turbine [TA].

This event is reportable per 10 CFR 50.73(a)(2)(iv)(A) because the plant experienced a valid start of its four emergency diesel generators (EDGs) [EK].

This event occurred when a contact in a switch associated with a main turbine stop valve did not close correctly in response to a turbine trip. When the switch was disassembled, a small piece of foreign material was found inside, which was a fragment of a plastic tie-wrap. This interfered with proper contact function. The switch was installed with the wire entrance facing upward which allowed foreign material to fall into the switch body. The apparent cause of the event was that vendor guidance does not require any special foreign material consideration for installation of this switch with its wire entrance facing upward.

Energy Industry Identification System (EllS) codes are identified in the text as [XX].

Background

Initial Conditions This event is also reportable per 10 CFR 50.72(b)(3)(iv)(A) via an 8-hour telephone report. The telephone report was completed as Event Number 52683 at 07:40 EDT on April 17, 2017.

On April 17, 2017, at 00:04 EDT, the Unit 2 main turbine experienced high bearing vibration. Control Room personnel tripped the main turbine at a prearranged vibration level. The power circuit breakers (PCBs) [FK] for the main generator [EL] did not immediately open on the turbine trip as expected.

Subsequently, a main generator lockout occurred on reverse power. The generator lockout sends a start signal to the plant's four EDGs. These started as expected but did not tie to their emergency electrical buses because there was no loss of offsite power. The EDGs were then manually shut down.

Reportability Criteria Safety Assessment

Event Description

Event Cause (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)

CONTINUATION SHEET

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to 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.

2017 - 002

3. LER NUMBER

- 000 the Engineered Safety Feature (ESF) systems. Offsite sources for both units are supplied via the 230 kV switchyard either through a startup transformer or the unit auxiliary transformer. The onsite standby power source for 4.16 kV emergency buses E1, E2, E3, and E4 consists of four EDGs. Each EDG is dedicated to its associated emergency bus. The EDGs are designed to start on indications of a loss of coolant accident or inadequate voltage on the emergency busses. The EDGs also have anticipatory starting signals on certain electrical logic conditions such as main generator reverse power, main generator output breaker failure, startup transformer lockout, and others. Receiving one of these signals results in the engine starting, but the EDGs will not tie to their emergency busses while voltage is adequate from offsite sources.

Based on this analysis, it is concluded that this event had no adverse impact on nuclear safety.

Corrective Actions

Any changes to the corrective actions and schedules noted below will be made in accordance with the site's corrective action program.

In this event, the main turbine was manually tripped at a preplanned setpoint to halt an increase in bearing vibration. A reverse power condition resulted in a main generator lockout and a start of all four of the site's EDGs. The EDGs performed as designed given the start signal that was initiated at the time. Since there was no loss of offsite power, all onsite electrical busses remained energized via their normal supplies. Consequently, the EDGs did not tie to their emergency busses and ran unloaded as designed until Operations personnel took action to secure them.

With the exception of the limit switch contact on a main turbine stop valve, all equipment affected by this event performed as expected given the plant condition and logic signals that existed. There was no actual safety consequence that resulted from this event.

No events have been reported in the past three years in which foreign material in a component resulted in an unplanned automatic actuation of a safety-related system or component.

This report contains no new regulatory commitments.

Similarly installed limit switches on the main turbine and bypass valves will be inspected, and seals will be placed at the wire entrance to the switch bodies. This action will be performed during the next scheduled refueling outage on each unit (i.e., Spring 2018 for Unit 1 and Spring 2019 for Unit 2).

Commitments

Previous Similar Events

(See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)

CONTINUATION SHEET

APPROVED BY OMB: NO. 3150-0104 EXPIRES: 03/31/2020 comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to 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.

2017 - 002

3. LER NUMBER

- 000