05000364/LER-2010-002
| Joseph M Farley Nuclear Plant - Unit 2 | |
| Event date: | 05-22-2010 |
|---|---|
| Report date: | 07-02-2010 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3642010002R00 - NRC Website | |
Westinghouse -- Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XX]
Description of Event
On May 22, 2010 at 16:34, with Unit 2 at 100% power, the reactor was manually tripped due to 2C Steam Generator (SG) Feedwater Regulating Valve (FRV) [JB] failing closed. At approximately 16:34, the control room crew received multiple alarms associated with 2C SG level and a process cabinet failure. The crew noted no feedwater flow and decreasing level in 2C SG. Manual control of the 2C SG FRV was attempted but there was no power or control capability of the main feedwater regulating valve.
At approximately 40% narrow range level in the 2C SG, the crew manually tripped Unit 2 prior to the automatic trip setpoint of 28% narrow range level. Both the 2A and 2B Motor Driven Auxiliary Feedwater (MDAFW) [BA] pumps automatically started to supply auxiliary feedwater to the 2C S/G. All safety systems functioned as designed without complications.
Investigation revealed that the controller driver (NCD) card in the 2C SG FRV controller circuitry failed causing the 2C SG FRV to close. The failed NCD card impacted no other SG FRV controls.
In accordance with 10 CFR 50.72(b)(2)(iv)(B) for a manual actuation of the reactor protection system on Unit 2, a four hour non-emergency report was issued on May 22, 2010 at 18:10, Event Notification number 45946.
Cause of Event
The NCD card (C8-330) in process control cabinet 8 of the 7300 system failed causing the 2C SG FRV to close. The NCD card malfunction was due to a S1-1 Silicon Controlled Rectifier (SCR) failure. The root cause investigation team, with support of the vendor, found only one other industry occurrence where this component failed.
The NCD card supplies power to the 2C SG FRV controller and controller power was lost when the card failed. Without controller power the 2C SG FRV closed and could not be operated in either manual or automatic mode. A manual Unit 2 reactor trip was initiated at approximately 40% narrow range level in the 2C SG.
Safety Assessment This event had no adverse effect on the safety and health of the public.
The Auxiliary Feedwater (AFW) system automatically supplies feedwater to the steam generators to remove decay heat from the reactor coolant system upon the loss of normal feedwater supply. The AFW system consists of two MDAFW pumps and one steam Turbine Driven Auxiliary Feedwater (TDAFW) pump configured into three trains. The MDAFW pumps both actuated automatically as designed on a low-low water level signal in the 2C SG. The TDAFW pump automatically actuates on low-low level in two of three SGs and did not start since only the 2C SG experienced low-low levels.
Water level in the 2C SG recovered to normal range as expected following the manual reactor trip.
There were no safety system functional failures and all systems functioned as designed.
Corrective Action A root cause was initiated to determine the cause of the failed NCD card. The NCD card malfunction was determined to be a S1-1 Silicon Controlled Rectifier (SCR) failure. The root cause investigation team, with support of the vendor, found only one other industry occurrence where this component failed. The failed NCD card was replaced with a new card. Unit 2 was restarted and returned to Mode 1 on May 23, 2010 at 17:12.
Industry Operating Experience (OE) on the event has been issued.
Additional Information
Previous Similar Events:
� Unit 1 Reactor Trip due to Loss of RCP Breaker Position � Unit 2 Reactor Trip during Unit 1 Main Generator Differential Lockout Relay Test