05000461/LER-2012-003
| Docket Number Sequential Revmonth Day Year Year Month Day Year 05000Number No. | |
| Event date: | 11-23-2012 |
|---|---|
| Report date: | 01-17-2013 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 4612012003R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric -- Boiling Water Reactor, 3473 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in test as [XX].
EVENT IDENTIFICATION
Breaker Failure Leads to Loss of Safety Function and System Start
A. Plant Operating Conditions Before the Event
Unit: 1� Event Date: 11/23/2012 Event Time: 2008 hours0.0232 days <br />0.558 hours <br />0.00332 weeks <br />7.64044e-4 months <br /> CDT Mode: 1� Mode Name: Power Operation Reactor Power: 97 percent B. DESCRIPTION OF. EVENT On 11/23/12 at 1951 hours0.0226 days <br />0.542 hours <br />0.00323 weeks <br />7.423555e-4 months <br />, operators completed swapping to the VC B train chiller as part of a routine shifting of the Main Control Room (MCR) Ventilation System (VC) [VI] from the A train to the B train.
At 1956 hours0.0226 days <br />0.543 hours <br />0.00323 weeks <br />7.44258e-4 months <br />, a non-licensed operator (EO) involved in the shifting of the trains reported to the MCR that VC B train chiller [CHU] breaker [BKR] OAPO6E-4D was cycling with no demand signal, although the chiller appeared to be operating normally. The EO attempted numerous times to open the breaker with no success and was directed to shut down the B train chiller. Subsequent to the chiller being shut down, breaker noise increased. Operators in the MCR observed indicator lights [IL] on the MCR VC Chiller alarm panel [PL] 5052 were cycling on and off.
At about 1957 hours0.0227 days <br />0.544 hours <br />0.00324 weeks <br />7.446385e-4 months <br />, operators in the MCR received alarms for Nuclear System Protection System (NSPS) [JG] loss of synchronization and a Division 2 Direct Current ground fault that subsequently cleared.
Operators in the MCR completely shut down the VC B train.
At 2002 hours0.0232 days <br />0.556 hours <br />0.00331 weeks <br />7.61761e-4 months <br />, the EO reported smoke coming from the 480 volts Control Building Unit Sub B Cubicle OAPO6E that contains the VC B chiller breaker; the fire brigade was dispatched to the breaker and determined that no fire existed. Operations shift management investigated the breaker issue and concluded that the VC B chiller breaker was cycling open and closed excessively and should be de-energized immediately due to observing smoke.
At 2005 hours0.0232 days <br />0.557 hours <br />0.00332 weeks <br />7.629025e-4 months <br />, operators de-energized the Unit Sub B Cubicle, racked out the VC B chiller breaker, entered the off-normal procedure actions for loss of AC power, declared VC B train inoperable, and entered the applicable Technical Specification (TS) actions for VC.
De-energizing the Unit Sub B also caused the following conditions: a loss of power to Fuel Building Ventilation System (VF) [VG] Division 2 isolation dampers [DMP] resulting in a trip of the VF system; a loss of Divisions 2 and 4 inverter room coolers and an unplanned inoperability of High Pressure Core Spray System (HPCS) [BG] due to the loss of room cooling to the Division 4 inverter [INVT] and battery charger [BYC] (although HPCS remained available); and a loss of power to the Division 2 Instrument Air System (IA) [LD] containment isolation valve [ISV] 11A006, and Division 2 Service Air System (SA) [LF] containment isolation valve 1SA030 causing the valves to automatically close. Operators entered the off-normal procedure actions for automatic isolation and loss of instrument air, and TS actions for inoperable HPCS.
At 2008 hciurs, the trip of the VF system resulted in Secondary Containment differential pressure becoming positive. Operators entered Emergency Operating Procedure (EOP)-8, "Secondary Containment Control," declared Secondary Containment inoperable, and entered the applicable TS actions for Secondary Containment.
At 2009 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.644245e-4 months <br />, after evaluating plant conditions, operators reenergized the Unit Sub B to support restoration of plant systems, declared VC B train operable, and exited the applicable TS actions for VC ventilation train (chiller remained inoperable). The HPCS system was restored to operable status when the Unit Sub B was restored and operators exited the applicable TS actions for HPCS. Operators re-opened the IA containment isolation valve. Reenergizing the Unit Sub B resulted in an invalid automatic actuation of the Division 2 Shutdown Service Water System (SX) [BI] system pump [P] 1SX01PB as power was restored to the low pressure trip unit [94].
At 2011 hours0.0233 days <br />0.559 hours <br />0.00333 weeks <br />7.651855e-4 months <br /> operators manually initiated the Division 1 Standby Gas Treatment system (VG) [BH] to restore Secondary Containment negative differential pressure, and Secondary Containment differential pressure was restored by 2013 hours0.0233 days <br />0.559 hours <br />0.00333 weeks <br />7.659465e-4 months <br />, and operators exited the applicable TS actions for Secondary Containment. The Division 2 SX pump was shut down by 2222 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.45471e-4 months <br />.
Operators secured the VG A train and restarted the VF system to maintain Secondary Containment differential pressure by 2248 hours0.026 days <br />0.624 hours <br />0.00372 weeks <br />8.55364e-4 months <br /> and exited EOP-8 at 0025 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> on 11/24/12. Following other system restorations ISV 1SA030 was reopened.
This event is reportable under the provisions of 10 CFR 50.73(a)(2)(v)(C) for the loss of Secondary Containment differential pressure as a condition that could have prevented the fulfillment of a safety function needed to control the release of radioactive material, 10 CFR 50.73(a)(2)(v)(D) for the unplanned inoperability of High Pressure Core Spray system as a condition that could have prevented the fulfillment of a safety function needed to mitigate the consequences of an accident, and 10 CFR 50.73(a)(2)(iv)(A) for the invalid actuation of the SX system and isolation of the IA and SA containment isolation valves.
Issue Report 1443700 was initiated to investigate this event.
C. CAUSE OF EVENT
The VC B chiller breaker closing spring charging mechanism failed to operate as designed. Based on breaker testing performed following the event, the latching mechanism for the closing spring of the VC B chiller breaker appears to have failed after the chiller was started, causing the breaker charging motor to run continuously and trying to close the breaker every time it finished charging, thus cycling the breaker open and closed. The reason for the latching mechanism failure is unknown at this time. The breaker has been sent to an offsite laboratory for failure analysis.
D. SAFETY CONSEQUENCES
There were no actual safety consequences of this event. This event resulted in the loss of secondary containment for approximately five minutes, from 2008 to 2013 hours0.0233 days <br />0.559 hours <br />0.00333 weeks <br />7.659465e-4 months <br /> due to the trip of the fuel building ventilation system following loss of power to the VF Division 2 isolation dampers. The Division 1 VG system was operable during this event and was manually started by operators to restore secondary containment negative pressure. The VC B train ventilation system was inoperable for four minutes from 2005 to 2009 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.644245e-4 months <br /> during this event but the VC A train was operable and available for control room ventilation if needed.
Containment isolation valves 1 1A006 and 1SA030 automatically closed at 2005 hours0.0232 days <br />0.557 hours <br />0.00332 weeks <br />7.629025e-4 months <br />; 1 1A006 was restored to open at 2009 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.644245e-4 months <br />, and 1SA030 was restored following the Unit Sub B restoration. The HPCS was inoperable from 2005 hours0.0232 days <br />0.557 hours <br />0.00332 weeks <br />7.629025e-4 months <br /> to 2009 hours0.0233 days <br />0.558 hours <br />0.00332 weeks <br />7.644245e-4 months <br /> due to the loss of room cooling to the Division 4 inverter and charger. Although inoperable, the HPCS continued to be available during this period of inoperability.
Additionally the Reactor Core Isolation Cooling [BN] system and the Low Pressure Core Spray [BM] system were operable and available during this event for accident mitigation if needed. There were no operability concerns with the invalid automatic start of the Division 2 SX pump.
E. CORRECTIVE ACTIONS
The VC B chiller breaker that failed has been replaced with a newly refurbished breaker.
The breaker has been sent to an offsite laboratory for failure analysis.
F. PREVIOUS OCCURRENCES
A review for previous occurrences did not identify similar events at CPS.
G. COMPONENT FAILURE DATA
Manufacturer� Nomenclature� Manufacturer Model Number ABB 480 volts Breaker� Model K600S