05000424/LER-2005-003
| Docket Numberisi | |
| Event date: | 04-29-2005 |
|---|---|
| Report date: | 3-0-5000 |
| 4242005003R00 - NRC Website | |
A) REQUIREMENT FOR REPORT 10 CFR 50.73 (a)(2)(iv) requires this report because an unplanned actuation of the reactor protection system occurred.
B) UNIT STATUS AT TIME OF EVENT At the time of this event, Unit 1 was in Mode 1 (Power Operation) at 100% rated thermal power. Other than that described herein, there was no inoperable equipment that contributed to the occurrence of this event.
C) DESCRIPTION OF EVENT On the afternoon of April 29, 2005, with Unit 1 at full power, operators responded to closure of loop I feed water regulating valve 1FV-510, by taking manual control in accordance with abnormal operating procedure 18016-C, "Condensate and Feedwater Malfunction." Steam generator (SG) #1 water level lowered to 42% before being restored to normal at 65%. The SG water level low- low reactor trip nominal setpoint is 37.8%.
Non-intrusive voltage measurements proved controller card IFC-510 had failed low (zero output). This card was part of a circuit in which an additional NTD (tracking-driver) card had been added to the control system by a recent design change in an effort to improve system reliability. This design change was installed on Unit 1 during the refueling outage in the fall of 2003. The design change modified the feed water isolation logic of main feed water regulating valves from 1/2 to 2/2 and also incorporated a dual tracking-driver card arrangement. As a part of the design change process, procedures and training were established that addressed the modification. The procedures and training were developed to address a particular type of card failure (power supply failure).
However, an apparent mis-perception existed that the procedures and training were appropriate for various types of card failures.
The replacement of the failed card was performed in accordance with these procedures and training. Technicians and operators initiated replacement of controller card IFC-510 with a contingency plan for operators to manually re-open 1FV-510 if it were to unexpectedly shut. Further, if the operators were unable to re-open the valve, a manual reactor trip was to be initiated.
Per procedure, technicians placed the circuit in maintenance mode, and valve 1FV-510 unexpectedly shut. There was insufficient time for the operators to manually regain control and re-open valve 1FV-510. Operators took action to manually trip the reactor as SG water level approached the low-low setpoint. However, an automatic reactor trip on low-low steam generator water level occurred 1A second before the manual trip at 2155 EDT.
Operators responded properly to stabilize the plant at normal operating temperature and pressure in Mode 3 (Hot Standby) following the reactor trip. At 2400 EDT, the Control Room notified the NRC Operations Center of this event.
D) CAUSE OF EVENT The failure of controller card 1FC-510 was the direct cause of the first reduction of feed water flow on the afternoon of April 29, 2005. The cause of the card failure has not been determined.
An improper application of a procedure was the direct cause of the second reduction of feed water flow, which led to the reactor trip. The procedure used for replacing the controller card was written for replacement of circuit cards that have power supply failures. This limitation was not specifically stated in the procedure nor was it known by the personnel involved. In addition, this was the first time the procedure had been used since the design change. Therefore, the root causes of this event were:
1)Technical inaccuracies and incomplete information in the procedure used for controller card replacement.
2) Inadequate technician training regarding procedure limitations and the recent design change.
E) ANALYSIS OF EVENT The Main Feedwater system isolated and the Auxiliary Feedwater system actuated as designed following initiation of the reactor trip. Operators responded properly to control feedwater flow and stabilized the unit in Mode 3.
Based on these considerations, there was no adverse effect on plant safety or on the health and safety of the public as a result of this event.
This event does not represent a safety system functional failure.
F) CORRECTIVE ACTIONS 1)The controller card was replaced and the unit was returned to power operations.
2) The procedure for controller card replacement has been revised to clarify title, purpose and pre-requisites.
3) The training material used for replacement of this card has been revised to clarify its intended purpose is for only a power supply failure of the card.
4) I&C Technicians have been briefed on this event and on the limitations of the subject procedure.
5) Guidance for replacement of feed water regulating valve controller cards for analog signal failures will be developed by August 31, 2005.
6) Training will be provided to appropriate personnel on lessons learned from this event by February 28, 2006.
G) ADDITIONAL INFORMATION 1) Failed Components:
Controller card 1FC-510 manufactured by Westinghouse Electric Corporation.
Type/Model 4t NCB1/2038A30G01.
2) Previous Similar Events:
There have been no previous similar events in the past three years.
3) Energy Industry Identification System Code:
Main Feedwater System — SJ Auxiliary Feedwater System — BA