05000311/LER-2016-005

LER-2016-005, Automatic Reactor Trip due to Main Generator Protection Trip

Salem Generating Station - Unit 2
Event date:	06-28-2016
Report date:	08-29-2016
3112016005R00 - NRC Website

LER 16-005-00 for Salem Generating Station, Unit 2 Regarding Automatic Reactor Trip due to Main Generator Protection Trip

ML16244A056
Person / Time
Site:	Salem
Issue date:	08/29/2016
From:	Grover F K Public Service Enterprise Group
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LR-N16-0161 LER 16-005-00
Download: ML16244A056 (6)

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.

2016 - 005 - 000

PLANT AND SYSTEM IDENTIFICATION

Westinghouse-Pressurized Water Reactor {PWR/4} Main Generator System/Transformer {EL/XFMR} *Energy Industry Identification System (EIIS) codes and component function identifier codes appear as {SS/CCC}.

IDENTIFICATION OF OCCURRENCE

Event Date: 06/28/2016 Discovery Date: 06/28/2016

CONDITIONS PRIOR TO OCCURRENCE

Salem Unit 2 was in Mode 1 at 100 percent rated thermal power (RTP).

DESCRIPTION OF OCCURRRENCE

On 6/28/16 at 04:22 Salem Unit 2 automatically tripped from 100% power on Generator Protection. The reactor trip was initiated due to a Main Turbine (MT) trip caused by a Main Generator Protection signal.

All emergency core cooling systems and emergency safeguards feature systems functioned as expected. The motor driven and steam driven auxiliary feedwater pumps started as expected on steam generator low level. Operators stabilized the plant in Mode 3 with decay heat removal via the main steam dump valves and auxiliary feedwater system.

Investigation identified that a broken current transformer core ground wire internal to the A Main Power Transformer (MPT) was intermittently touching the X1 and X2 low voltage connections inside the transformer bushing compartment causing a ground fault. This caused the turbine generator trip.

This report is being made in accordance with 10CFR50.73 (a)(2)(iv)(A), "Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B)," for this event actuation of the Reactor Protection System (RPS) and the Auxiliary Feedwater System (AF).

Notification of this event was provided via ENS report 52048.

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.

2016 - 005 - 000

CAUSE OF EVENT

The direct cause for Salem Unit 2 turbine generator trip was an intermittent ground fault caused by a broken Current Transformer (CT) core ground wire that was intermittently touching the low voltage connections inside the transformer bushing compartment.

The exact cause for the broken wire has not yet been determined yet. A Root Cause Evaluation is currently in progress. The preliminary report found that the CT wires were not secured to the transformer tank as expected.

SAFETY CONSEQUENCES AND IMPLICATIONS

There were no safety consequences as a result of this event. Operators appropriately responded to the reactor trip to stabilize the plant. All emergency core cooling systems and emergency safeguards feature systems functioned as expected. The motor driven and steam driven' auxiliary feedwater pumps started as expected on steam generator low level. Operators stabilized .the plant in Mode 3 with decay heat removal via the main steam dump valves and auxiliary feedwater system. Condenser vacuum remained available for the duration of the event.

SAFETY SYSTEM FUNCTIONAL FAILURE

This condition did not result in a safety system functional failure as defined in NEI 99-02, Regulatory Assessment Performance Indicator Guidelines.

PREVIOUS EVENTS

A review of previous events for the past three years identified two similar events. License Event Report (LER) 272/2014-003-00, Reactor Trip Due to Actuation of Generator Protection was issued on June 4, 2014. License Event Report (LER) 272/2014-004-00, Reactor Trip Due to Actuation of Generator Protection was issued on July 3, 2014. Both event were due to a failed wiring termination on the C Phase neutral generator current transformer. The corrective actions taken for those events were specific to them and would not have prevented this event.

CORRECTIVE ACTIONS

1. The broken CT wire on the A MPT was repaired.

2. The B and C MPT's were electrically tested with no anomalies noted.

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.

Salem Generating Station — Unit 2 05000311 CORRECTIVE ACTIONS (cont'd) 3. Additional corrective actions may be taken as appropriate at the conclusion of the root cause investigation.

COMMITMENTS

There are no regulatory commitments contained in this LER.