05000400/LER-2003-003
| Harris Nuclear Plant - Unit 1 | |
| Event date: | 06-14-2003 |
|---|---|
| Report date: | 08-11-2003 |
| Initial Reporting | |
| 4002003003R00 - NRC Website | |
1. � 2 EWeg 1 LQ EVENT' On June 14, 2003 at 1053 EST with the reactor at 100% power, the reactor was manually tripped as directed by plant procedures In response to an automatic trip of one of two operating main feedwater pumps (MFPs) [S.1-12].
The "Er MFP tripped following the failure of a Westinghouse (NAL2) bistable comparator card (ECB D1 associated with MFP feedwater flow control system. This card failure generated a spurious low-flow alarm and low-flow trip signal to the1 3
- MFP. The W MFP remained operable. Both motor-driven auxiliary feedwater (AFW) pumps (BA-P] and the turbine-driven AFW pump [BA-P} auto-started due to lo-lo steam generator level.
Safety systems functioned as required. The operations crew responded to the event in accordance with applicable plant procedures. The plant was stabilized at normal operating no-load reactor coolant system (RCS) [AB] temperature and pressure following the reactor trip The root cause of the unplanned trip of the 13" MFP was due to a random electrical failure of a T30 transistor on a NAL2 bistable comparator card. The transistor failed resulting In an electrical short circuit and the loss of the output voltage to the Operational Amplifiers (Op. Amp.) on the card. The Op. Amps generate the reference signal (setpoint) and perform the comparison between the setpolnt and the Input flow signal. This card has not been found out of calibration during any preventative maintenance calibration.
Energy Industry Identification System (EIIS) codes are Identified in the text within brackets (1.
II. � CAUSE OF EVENT The cause of the unplanned trip of the B" MFP was due to a failed T30 transistor on a NAL2 comparator card.
Ill. � SAFETY SIGNIFICANCE Other than the transient induced by the manual reactor trip, there were no safety significant consequences as a result of this event. The plant was manually tripped from 100% power by control room operators as directed by plant procedures. The plant is designed for a loss of main feedwater, and it responded as expected for this condition. The initial plant conditions were well within the bounding conditions for the plant design. The plant was promptly stabilized at normal operating no-load RCS temperature and pressure, and no unusual conditions were observed for plant equipment following the manual reactor trip. Alt safety equipment functioned as required. No additional or compensatory measures were required for this event. The operating staff performed the required actions for the trip.
The potential safety consequences under other alternate conditions, such as simultaneous random failures leading to toss of both MFPs, may have increased the severity of the transient and caused an automatic reactor trip, but they would not significantly increase the potential safety consequences of this event. The severity of the plant transient generally increases with increasing power, so the same event initiated at a lower power would be expected to result in a less severe transient.
NRC FORM MA (14001)
IV. CORRECTIVE ACTIONS
Immediate corrective action was to replace the failed card. In addition, HNP will modify the system by the end of the next refueling outage (Fail. 2004) such that failure of an NAL2 bistable comparator card in the MFP control system will not cause an unnecessary MFP trip leading to a reactor trip.
V. PREVIOUS BIMMEIDNIaa There have been no previous reactor trips at HNP caused by a failure of this type of transistor on this card type.
There are thousands of this type of transistor and hundreds of cards h service. Failures have occurred on a very small fraction of the Installed components where the cause is either indeterminate or assurned to be age related. Age-based component replacement or refurbishment was considered but not Implemented, consistent with vendor recommendations.
NAC FOAM MA11.2001) z