05000374/LER-2001-001
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3742001001R00 - NRC Website | |
PLANT AND SYSTEM Identification General Electric - Boiling Water Reactor, 3489 Megawatts Thermal Rated Core Power
A. CONDITION PRIOR TO EVENT
Unit(s): 2 � Event Date: 04/06/01 � Event Time: 0909 Hours Reactor Mode(s): 1 � Power Level(s): 100 Mode(s) Name: Run
B. DESCRIPTION OF EVENT
Prior to the event, Maintenance was performing a diagnostic test (flowscan) on 2FW146, Motor Driven Feedwater Pump (MDRFP)[SJ] Low Flow Feed Regulating Valve.
The MDRFP was not in operation, and the valve was manually isolated to allow valve movement without affecting the feedwater system flow paths. In order to perform the flowscan test, leads were lifted locally at the valve to provide signal paths for the flowscan computer. When the valve was cycled, one of the leads came into contact with the cam mechanism inside the valve position unit mounted on the valve. While the lead was taped, it made contact with a screw on the rear of the cam (evidence of an electrical arc was found on the screw). The most probable cause for the lead contacting the screw is inadequate taping of the lead. This caused a short circuit in the feedwater control logic, which caused fuse 2C34A-F7 to blow.
experienced an automatic RPS [JC] actuation (SCRAM) from 100 percent power. The blown fuse caused multiple failures in the feedwater (FW)[JB] control logic, and caused both Reactor Recirculation (RR)[AD] pumps to downshift to slow speed on a false Level 3 signal. The resultant feedwater control failures, and the level swell from the recirculation pump downshifts caused reactor water level to reach the Level 8 setpoint (plus 55 inches). The Main Turbine (TG)[TA] tripped on high reactor water level. When the main turbine tripped, it caused the main turbine stop valves to close. This caused an automatic RPS actuation due to turbine stop valve closure with reactor power above 25 percent power.
Both Turbine Driven Reactor Feedwater (TDRFP)[SJ] pumps tripped due to high reactor water level. As a result of the blown fuse, the feed regulating valve would not open to allow the MDRFP to inject water into the reactor coolant system. The reactor operator (RO) chose to manually start the Reactor Core Isolation Cooling (RCIC)[BN] system to recover water level after the TDRFP trip.
When placed in automatic, the RCIC system instrumentation indicated a slight frequency oscillation. The RO placed the RCIC system back in manual and the system performed normally for the remainder of the time in service. Normal reactor water level was obtained at 0931 hours0.0108 days <br />0.259 hours <br />0.00154 weeks <br />3.542455e-4 months <br />.
This event is reportable pursuant to 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in an automatic actuation of the reactor protection system.
C. C CAUSE OF EVENT The root cause of this event was an inadequate maintenance risk assessment performed for the work. The responsible personnel failed to perform an adequate risk assessment by not identifying that lifting leads created the risk of a short which could lead to a reactor scram. Specifically, the risk assessment for working on energized equipment only focused on the personnel safety risks. The assessment did not address what could happen if one of the leads being manipulated was inadvertently shorted or the impact of a power failure in the FW control system. An additional causal factor in this event was the lack of an independent fuse for the power feeding this valve.
D. C SAFETY ANALYSIS The safety consequences of this event were minimal. A RR pump trip, a TG trip, and a loss of FW flow are analyzed conditions of moderate frequency (Updated Final Safety Analysis Report (UFSAR) Chapter 15). The plant responded as described in the referenced UFSAR chapter. The reactor was safely shut down and recovery performed without incident. There were no safety system functional failures. This event would not be more severe under alternative conditions.
E. C CORRECTIVE ACTIONS 1. The lifted leads were relanded, and fuse 2C34A-F7 was replaced.
2. The immediate corrective action established a policy to strengthen the use of Maintenance Risk Assessments by including a description of potential plant/system effects if a lead to be lifted is shorted. The policy was further explained by stating that every work task performed which requires lifting energized leads will specify in the column "RISK" on the Maintenance Risk Assessment form the lifted lead and its associated impact if it were to short.
Corrective Action to Prevent Recurrence:
3. The Exelon Nuclear Conduct of Maintenance Manual, 0.5, Maintenance Risk Assessment, will be revised to require an evaluation of the risk to the plant for maintenance activities that involve work on an energized circuit with the potential to create a fault in the circuit. (ATM# 49049) F. C PREVIOUS OCCURRENCES A review of Licensee Event Reports over the previous five years found no previous or similar occurrences.
G. C COMPONENT FAILURE DATA Since no component failure occurred, this section is not applicable.