05000461/LER-2017-009

LER-2017-009, Trip of Emergency Reserve Auxiliary Transformer Static VAR Compensator Causes Positive Secondary Containment Pressure Following Voltage Transient on 138 kV Offsite Source.

Clinton Power Station, Unit 1 .
Event date:	11-05-2017
Report date:	01-04-2018
Reporting criterion:	10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material
4612017009R00 - NRC Website

LER 17-009-00 for Clinton, Unit 1, Regarding Trip of Emergency Reserve Auxiliary Transformer Static VAR Compensator Causes Positive Secondary Containment Pressure Following Voltage Transient on 138 kV Offsite Source

ML18008A062
Person / Time
Site:	Clinton, Clinton Power Station, Unit 1 .
Issue date:	01/04/2018
From:	Stoner T R Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
U-604398 LER 17-009-00
Download: ML18008A062 (5)

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 Int ocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, 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.

3. LER NUMBER

2017 - 00 009

PLANT AND SYSTEM IDENTIFICATION

General Electric -- Boiling Water Reactor, 3473 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in text as [XX].

EVENT IDENTIFICATION

Trip of Emergency Reserve Auxiliary Transformer Static VAR Compensator Causes Positive Secondary Containment Pressure Following Voltage Transient on 138 kV Offsite Source.

A. Plant Operating Conditions before the Event Unit: 1 Event Date: 11/05/17 Mode: 1 Mode Name: Power Operation Event Time: 1240 CDT Reactor Power: 98 percent

B. Description of Event

On November 5, 2017, at approximately 1240 hours0.0144 days <br />0.344 hours <br />0.00205 weeks <br />4.7182e-4 months <br /> CDT the Emergency Reserve Auxiliary Transformer (ERAT)[XFMR] Static VAR Compensator (SVC)[COMP] tripped due to a voltage transient on the 138 kV line owned and maintained by Ameren Illinois. The Main Control Room (MCR) entered Technical Specification (TS) Limiting Condition for Operation (LCO) 3.8.1, AC Sources-Operating, Required Actions A.1 and A.2. As a result of the voltage transient, the Division 1 Fuel Building Ventilation (VF) system isolation dampers closed causing a trip of the VF supply and exhaust fans. Ameren stated that the voltage transient was possibly due to weather. The effect of this condition was that Secondary Containment (SC) vacuum rose to slightly greater than 0 inches water gauge (WG) and exceeded the TS limit of -0.25 inch WG. Operations personnel entered Emergency Operating Procedure (EOP) -8, Secondary Containment Control, and TS LCO 3.6.4.1, Secondary Containment, Required Action A.1. As a result of the momentary loss of power, the following additional system actuations occurred:

• Division 1 MCR Ventilation Chiller tripped,

• Division 1 Diesel Generator Room Exhaust Fan 1VDO2CA tripped,

• Division 1 Shutdown Service Water Pump auto started,

• Fission Product Monitoring (FPM) skid isolation valves shut,

• Division 1 Hydrogen Monitoring system isolation valves shut,

• Containment Service Air System Outboard Isolation valve 1SA029 shut,

• Nuclear Systems Protection System (NSPS) Inverter Trouble alarms (due to loss of synchronization) 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.

3. LER NUMBER

2017 - 00 009 The Standby Gas Treatment System (VG) was manually started and SC vacuum was restored within TS limits at approximately 1242 hours0.0144 days <br />0.345 hours <br />0.00205 weeks <br />4.72581e-4 months <br />. The system actuations were addressed and plant equipment was restored to service in accordance with plant procedures. The momentary loss of power did not adversely affect the safe operation of the plant or the restoration of SC. During the investigation, Ameren reported that the Clinton feeder breaker that supplied the 138 kV line had tripped and reclosed probably due to weather. In addition, during inspection of the offsite power lines, two disconnects were found not fully seated. These disconnects were reseated and the ERAT SVC was returned to service and declared OPERABLE at 1702 hours0.0197 days <br />0.473 hours <br />0.00281 weeks <br />6.47611e-4 months <br />.

C. Cause of the Event

The cause of the SC differential pressure becoming positive is that the circuit design of VF is not adequately robust to withstand the loss of the 138 kV feed.

D. Safety Consequences This event is reportable in accordance with 10CFR50 50.73(a)(2)(v)(C) as a condition that could have prevented fulfillment of a safety function to control the release of radioactive material because the SC was declared inoperable.

The VG system was fully operable at the time of the event and capable of performing its required safety function. Operations entered EOP-8 for SC vacuum less than -0.25 inch WG and entered TS LCO 3.6.4.1 Required Action A.1. The SC vacuum was restored to within TS limits within the completion time requirement. The SC vacuum normally is kept slightly negative relative to atmospheric pressure to prevent leakage to the atmosphere. The VF system is a non-safety ventilation system which is normally in service to maintain SC vacuum. The VG system is the safety-related system which is relied upon to perform this function following an accident. During the event, the VG system was placed in service and restored SC to operability consistent with its safety function. Therefore, the ability of the station to maintain SC vacuum in the event of an accident was never jeopardized or challenged by the VF system trip. Engineering analysis has determined that this event is not considered a safety system functional failure.

E. Corrective Actions

A modification will be installed to prevent tripping VF during a momentary loss of power. Installation of a 138 kV Ring Bus is scheduled that is intended to improve the reliability of the radial feed of the 138 kV line.

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.

3. LER NUMBER

2017 - 00 009 In addition, a License Amendment Request (LAR) was submitted to the NRC on November 8, 2017 to adopt Technical Specifications Task Force (TSTF)-551, Revise Secondary Containment Surveillance Requirements, to adopt a change to the CPS TS that would eliminate the requirement to declare SC inoperable under similar transient conditions. Adoption of this LAR would have prevented this event from being reportable.

F. Previous Similar Occurrences Licensee Event Report 2015-004-00: Trip of Emergency Reserve Auxiliary Transformer Static VAR Compensator Causes Positive Secondary Containment Pressure Following Lightning Strike on 138 kV Offsite Source.

On June 25, 2015 at 0301 CDT, the Main Control Room received numerous annunciators that indicated a trip of the ERAT Static VAR Compensator caused by a voltage transient on the 138 kV offsite source due to thunderstorms in the area. The Division 1 safety bus was manually aligned from the reserve source to its normal source.

As a result of the voltage transient, the Division 1 VF system isolation dampers closed causing a trip of VF supply and exhaust fans. Secondary Containment vacuum increased to greater than 0 inch WG which exceeded the TS requirement. Secondary Containment vacuum was restored within TS requirements by reopening the VF isolation dampers and restarting the VF supply and exhaust fans. The ERAT SVC was returned to service at 0457 CDT.

Licensee Event Report 2016-004-00: Trip of Emergency Reserve Auxiliary Transformer Static VAR Compensator Causes Positive Secondary Containment Pressure Following Lightning Strike on 138 kV Offsite Source On March 30, 2016, at approximately 1545 CDT, the Main Control Room received numerous annunciators that indicated a trip of the Emergency Reserve Auxiliary Transformer Static VAR Compensator caused by a voltage transient on the 138 kV supply. Technical Specification Limiting Condition for Operation 3.8.1, AC Sources-Operating, Required Action A.1 and A.2 were entered. As a result of the voltage transient, the Division 1 Fuel Building ventilation system isolation dampers closed causing a trip of VF supply and exhaust fans. With no operating VF fans, Secondary Containment vacuum rose to slightly greater than 0 inches water gauge which exceeded the TS requirement of greater than 0.25 inches vacuum WG.

Secondary Containment vacuum was restored within TS requirements at 1550 CDT by starting the Standby Gas Treatment System.

G. Component Failure Data

There were no component failures associated with this event.