05000339/LER-2012-001
| Document Numbersequential Revmonth Day Year Year Month Day Year 05000Number No. | |
| Event date: | 10-24-2012 |
|---|---|
| Report date: | 12-12-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3392012001R00 - NRC Website | |
1.0 DESCRIPTION OF THE EVENT On October 24, 2012, at 0147 hours0.0017 days <br />0.0408 hours <br />2.430556e-4 weeks <br />5.59335e-5 months <br /> with Unit 2 in Model, 100 percent power, an automatic reactor trip occurred due to a low-low level in the "C" steam generator (SG) (EIIS System AB, Component SG) resulting from closure of all four governor valves. Closure of all four governor valves (HIS System TA, Component V) resulted in a loss of load. The governor valves' closure was caused by a spurious speed error signal from the Speed Error Amplifier Card "B" (1A08D) in the Electro-Hydraulic Fluid Control System (EHC) (EllS System TG, Component IMOD).
All systems responded as expected. All control rods (EIIS System AA, Component ROD) inserted into the core at the time of the trip and decay heat was removed via the main condenser steam dumps (HIS System SG, Component RV ). The Auxiliary Feedwater (AFW) pumps (EIIS System BA, Component P) received an automatic start signal due to low-low level in the "C" SG at the time of the trip, SG levels were restored to normal operating level. The AFW System operated as designed with no abnormalities noted.
The Unit 2 Pressurizer Power Operated Relief Valve (PORV), 2-RC-PCV-2455C (EllS System AB, Component RV), opened momentarily during the automatic reactor trip. The valve indicated open for less than 1 second. The PORV reseated and remained available for automatic operation if needed with no ongoing leakage occurring during the transient.
The transient was characterized as uncomplicated.
At 0240 hours0.00278 days <br />0.0667 hours <br />3.968254e-4 weeks <br />9.132e-5 months <br />, a 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> report was made to the NRC as an After-The-Fact Unusual Event due to 2-RC-PCV-2455C opening momentarily exceeding EAL SU6.1. Subsequent review determined that 2-RC-PCV-2455C functioned as designed and therefore did not meet the criteria for an Unusual Event and the notification was retracted.
At 0318 hours0.00368 days <br />0.0883 hours <br />5.257936e-4 weeks <br />1.20999e-4 months <br />, a 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> report was made to the NRC in accordance with (lAW) 10CFR50.72(b)(2)(iv)(B) for Reactor Protection System (RPS) (EllS System JC) actuation and 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> report IAW 10CFR50.72(b)(3)(iv)(A) for AFW system actuation.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS No significant safety consequences resulted from this event since the RPS and the Engineered Safety Feature System (ESF) equipment responded as designed. Steam Generator levels were restored to normal operating level. As such, the event posed no significant safety implications and, the health and safety of the public were not affected by the event.
The event is being reported pursuant to 10CFR50.73(a)(2)(iv) for an event that resulted in automatic actuation of the RPS and AFW System.
3.0 CAUSE The direct cause of this event was a failure of the C4 capacitor (EllS Component CAP) on the Speed Error Amplifier Card B (1A08D). When this capacitor shorted, the -15 VDC power was lost to the Operational Amplifier and this caused the Operational Amplifier to output a spurious high voltage signal to the Governor valves.
The root cause determined the evaluation of capacitor replacement frequency performed in 2002 did not use the most conservative recommendation of the card manufacturer. The evaluation did not consider the sub-component capacitor manufacturer's recommendation.
During the 2002 evaluation the card replacement recommendation from the Electro- Hydraulic Fluid Control System (EHC) Original Equipment Manufacturer (OEM) was thought to be adequate information to establish the replacement frequency of a sub-component on that card. The capacitor replacement recommendation of 10 - 20 years by the OEM was viewed as the governing standard. Benchmarking, Operating Experience (OE) and plant conditions were also used for determining replacement of the component within that band.
The replacement frequency of eight (8) refueling outages (12 years) was at the low end of the OEM specified band and was typical when compared to the industry.
4.0 IMMEDIATE CORRECTIVE ACTION(S) The Control Room crew responded to the reactor trip in accordance with emergency procedure 2-E-0, Reactor Trip or Safety Injection. The post trip response progressed as expected and the Control Room crew transitioned to 2-ES-0.1, Reactor Trip Response. All equipment responded as designed. By 0403 hours0.00466 days <br />0.112 hours <br />6.66336e-4 weeks <br />1.533415e-4 months <br />, Unit 2 exited 2-ES-0.1 and entered 2 OP-1.5, Unit Startup from Mode 3 to Mode 2.
5.0 ADDITIONAL CORRECTIVE ACTIONS The EHC Speed Error Amplifier Card B (1A08D) was replaced and tested satisfactorily.
The problem with 1A08D was able to be duplicated on other Speed Error Amplifier Cards removed from the Unit 2 EHC cabinet. The speed error signal was able to be duplicated to greater than 13 VDC with the 1A08D card installed.
6.0 ACTIONS TO PREVENT RECURRENCE The preventive maintenance (PM) task basis procedure is being revised to ensure that component level replacement recommendations are obtained from component manufacturer guidance. Lessons learned from the root cause and the revision to PM will be added to the Engineering Training Program. The capacitor replacement frequency PM will be revised to align with vendor guidance. Additionally, single point vulnerabilities are being reviewed to ensure that capacitor sub-components have the appropriate replacement frequencies established.
7.0 SIMILAR EVENTS failure in the EHC power supply system. Governor valves closed causing a loss of load and subsequent low-low level in the "A" SG.
8.0 ADDITIONAL INFORMATION Unit 1 was operating in Mode 1, 100 percent power on October 24, 2012 and was not affected by this event.
Description:� Speed Error Amplifier Card Manufacturer: Westinghouse Model No.:� 1A08D Description:� Capacitor Manufacturer: Sprague Model No.:� C4