05000281/LER-2002-003
| Document Numbersequential Revisionmonth Day Year Year Month Day Year 05000-Number Number | |
| Event date: | 11-23-2002 |
|---|---|
| Report date: | 01-18-2003 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2812002003R00 - NRC Website | |
FACILITY NAME (1) DOCKET � LER NUMBER 16) PAGE (3) 1.0 DESCRIPTION OF THE EVENT At 0303 hours0.00351 days <br />0.0842 hours <br />5.009921e-4 weeks <br />1.152915e-4 months <br /> on 11/23102, a Unit 2 Turbine Control Valve Freedom Test was initiated.
By 0327 hours0.00378 days <br />0.0908 hours <br />5.406746e-4 weeks <br />1.244235e-4 months <br />, testing of the #1 and #2 Turbine Governor and Stop Valves [EIIS-SB- FCV] was completed. Both of these tests were completed with no problems observed. At 0332 while closing the #3 governor valve, the Main Control Room (MCR) [EllS-NA] staff observed several unexpected alarms when the #3 governor valve reached approximately 20% open. The alarms received indicated a loss of turbine load was in progress. The Unit 2 Reactor Operator (RO) observed that the 8 Main Steam Dump Valves [EllS-SB- VTV] had opened in response to the loss of load. The main turbine operator conducting the governor valve testing observed that the turbine valve position limiter [EIIS-SB-ACV] had failed to zero. Multiple alarms annunciated during the transient, and at 03:32:51 hours Unit 2 experienced an automatic reactor trip. The first out annunciator received was "Steam Generator Low Low Level," due to two of three channels of low low level on the Unit 2 "C" Steam Generator (S/G) [EllS-SG]. This is reportable under 10CFR50.73(a)(2)(iv)(A), as an event that resulted in the manual or automatic actuation of any engineered safety feature, including the reactor protection system.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS The shutdown margin for Unit 2 was determined to be satisfactory. Auxiliary feedwater [EIIS-BA] automatically initiated as designed on low low steam generator level. All three Main Steam Trip Valves [EllS-SB-FCV] were manually closed due to inability to verify full closed indication on #1 Turbine Stop Valve. Primary RCS [EllS-AB] temperature decreased to approximately 547 degrees following the reactor trip.
No primary safety or power operated relief valves [EIIS-AB-RV] were actuated during the event. No indication of primary to secondary leakage existed and, therefore, no adverse radiological consequences resulted from this event.
All electrical busses transferred properly following the trip and all emergency diesel generators [EIIS-EK] were operable.
There were no significant safety consequences or implications associated with this event.
3.0 CAUSE The low low S/G level trip was the result of a sudden loss of turbine load. The cause of the loss of turbine load has been attributed to a failure of the turbine valve position limiter.
The failure of the turbine valve position limiter can be attributed to an electrical failure in the Unit 2 EHC control cabinet. A Root Cause Evaluation (RCE) has been initiated to determine the cause of the failure, suspected to be a card failure [EllS-SB-IMOD].
FACILITY NAME (1) DOCKET LER NUMBER (6) 3PAGE (3) 4.0 IMMEDIATE CORRECTIVE ACTION(S) l&C personnel performed initial as-found system checks in the Unit 2 Analog Electro- Hydraulic (AEH) Control Cabinet in accordance with the appropriate procedure. A Work Order was issued to initiate troubleshooting and repairs to the Unit 2 AEH Control Cabinet circuits.
l&C personnel measured the as found voltages for the output of the Digital/Analog (D/A) converter in the valve position limiter circuit. The measured voltage at test point #2 was found to be low. l&C personnel removed and inspected the turbine valve position limit Up/Down Counter circuit card and the D/A Converter card with no abnormalities noted.
l&C personnel then contacted Turbine Control Service Associates personnel and it was recommended that both cards in the circuit, the D/A converter card and the Up/Down counter card, be replaced. Troubleshooting was then completed by monitoring the valve position limiter circuit both prior to and following replacement of the Up/Down Counter and D/A Converter circuit cards.
5.0 ADDITIONAL CORRECTIVE ACTIONS The D/A converter and Up/Down counter cards are being sent to Westinghouse for failure analysis.
6.0 ACTIONS TO PREVENT RECURRENCE Any actions deemed necessary to prevent recurrence as determined by the RCE will be tracked through the Corrective Action System. The RCE will be completed when the results of the failure analysis are available.
7.0 SIMILAR EVENTS None 8.0 MANUFACTURER/MODEL NUMBER ND Converter - Westinghouse Part # 398409 UP/DOWN Counter - Westinghouse Part # 2822A2G01 9.0 ADDITIONAL INFORMATION None