05000311/LER-2016-003

LER-2016-003, Automatic Reactor Trip due to Main Generator Protection Trip

Salem Generating Station - Unit 2
Event date:	02-14-2016
Report date:	04-14-2016
3112016003R00 - NRC Website

LER 16-003-00 for Salem, Unit 2, Regarding Automatic Reactor Trip due to Main Generator Protection Trip

ML16105A264
Person / Time
Site:	Salem
Issue date:	04/14/2016
From:	Perry J F Public Service Enterprise Group
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LR-N16-0075 LER 16-003-00
Download: ML16105A264 (6)

the Desk Officer, Office of information and Regulatory Affairs, NEOB-10202, (3150-0104), Off Ice 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.

PLANT AND SYSTEM IDENTIFICATION

Westinghouse-Pressurized Water Reactor {PWR/4} Main Generator System/Relay {TB/RLY} *Energy Industry Identification System (E IIS) codes and component function identifier codes appear as (SS/CCC).

IDENTIFICATION OF OCCURRENCE

Event Date: 02/14/2016 Discovery Date: 02/14/2016

CONDITIONS PRIOR TO OCCURRENCE

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

DESCRIPTION OF OCCURRRENCE

On 2/14/16 at 20:58 Salem Unit 2 automatically tripped from 100% power on Generator Protection. The trip was initiated due to a Main Turbine 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 feed 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 feed water system.

Condenser vacuum remained available for the duration of the event. Operators also ensured a normal offsite electrical power lineup.

Walk down of the Stator Water Cooling (SWC) Panel identified a SWC valve leak inside a panel that was dripping onto an agastat relay {TB/RLY}, shorting the wiring terminations for contact 1-5.

The leak was noted at the packing associated with an equalizing valve. Water leaked from the valve down the panel, and into one of two Agastat Stator Water trip relays. The relay filled with water and internally shorted closing the normally open trip contact causing the generator to trip.

During the walkdown there were no other water leaks noted within the panel. It should be noted that the developed leak could be related to aging and usage over time which resulted in a loose valve packing nut. All other valves within the panel were verified to be wrench tight without signs of leaking and all tubing appeared to be visually intact without signs of leaking. The adjacent two 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, 02-2014)

CONTINUATION SHEET

Salem Generating Station — Unit 2 05000311 panels did not include electrical trip relays with process tubing, where a similar failure could cause a trip.

The Unit 1 Generator was walked down and it was noted that Stator water trip devices (pressure/flow) were non-panel mounted external units. Outside of the flow and pressure switches themselves, the Salem Unit 1 design differs from the Unit 2 tripping scheme using stand-alone devices. There were no active leaks noted at Salem Unit 1 at this time.

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 and the Auxiliary Feedwater System.

Notification of this event was provided via ENS report 51734.

CAUSE OF EVENT

The direct cause for Salem Unit 2 turbine generator trip was a stator bushing cooling water flow switch equalizing valve leak that caused shorting of an agastat relay contact. Shorting this contact resulted in the turbine generator trip. The apparent cause of the generator trip is that the agastat relay had not been identified as a single point vulnerability. Therefore, the relay did not have a mitigation/elimination strategy.

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 feed 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 feed water system. Condenser vacuum remained available for the duration of the event. Operators also ensured a normal offsite electrical power lineup.

SAFETY SYSTEM FUNCTIONAL FAILURE

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

the Desk Officer, Office of Information and Regulatory Affairs, NEOB-1 0202, (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.

CONTINUATION SHEET

2. DOCKET 6. LER NUMBER

PREVIOUS EVENTS

A review of previous events for the past three years identified no similar events.

CORRECTIVE ACTIONS

• Prior to restarting the unit: the stator bushing cooling water flow switch equilizing valve leak was stopped; and the agastat relay was replaced.

• The agastat relay will be appropriately classified per the component classification process and a mitigation strategy will be developed in accordance with the system vulnerability review process.

COMMITMENTS

There are no regulatory commitments contained in this LER.