05000277/LER-2004-003
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | |
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| Report date: | |
| 2772004003R00 - NRC Website | |
Unit Conditions Prior to the Event Unit 2 was in Mode 1 and operating at 100% rated thermal power. There were no structures, systems or components out of service that contributed to this event.
Description of the Event
On 12/22/04 at approximately 0455 hours0.00527 days <br />0.126 hours <br />7.523148e-4 weeks <br />1.731275e-4 months <br />, a Unit 2 Reactor scram occurred as a result of a Primary Containment Isolation System (PCIS) (EIIS: JM) Group I isolation. The Group I PCIS isolation was a result of low main steam line pressure caused by the opening of Main Turbine Bypass Valves (BPVs) (EIIS: SO) due to an Electro-Hydraulic Control (EHC) (EIIS: TG) circuit malfunction.
The PCIS Group I isolation resulted in the closure of the Main Steam Isolation Valves (MSIVs). As would be expected for a PCIS Group I isolation, Reactor water level decreased to the Level 2 set point resulting in the actuation of the High Pressure Coolant Injection (HPCI), Reactor Core Isolation Cooling (RCIC) and the Alternate Rod Insertion (ARI) / Recirculation Pump Trip systems. PCIS Group II and III isolations also occurred as Reactor water level passed through the Level 3 set point. The PCIS Group II and III isolations resulted in the closure of valves in various systems including the Reactor Building Ventilation system, the Containment Atmospheric Control / Containment Atmospheric Dilution systems, the Reactor Water Cleanup sytems and other containment penetrating process lines. The Standby-Gas Treatment system also actuated as expected on the Group III PCIS isolation. There were no significant anomalies involved with the plant equipment response to the event.
Just prior to the Reactor scram, Shift Operations personnel promptly observed the start of the sequential opening of Main Turbine Bypass Valves resulting from the EHC malfunction. Shift Supervisory personnel promptly directed a manual Reactor scram. However, the plant automatically scrammed prior to being able to take the manual actions.
The PCIS Group II and III isolations were initially reset by approximately 0530 hours0.00613 days <br />0.147 hours <br />8.763227e-4 weeks <br />2.01665e-4 months <br />. The scram and ARI initiation were reset by approximately 0540 hours0.00625 days <br />0.15 hours <br />8.928571e-4 weeks <br />2.0547e-4 months <br />. The PCIS Group I isolation was reset by approximately 0750 hours0.00868 days <br />0.208 hours <br />0.00124 weeks <br />2.85375e-4 months <br />.
As required by 10CFR 50.72, NRC prompt notifications were completed on 12/22/04 at approximately 0808 hours0.00935 days <br />0.224 hours <br />0.00134 weeks <br />3.07444e-4 months <br /> to report the automatic scram, HPCI / RCIC actuations and the PCIS isolations.
This report is being submitted pursuant to 10CFR50.73 (a)(2)(iv)(A) due to valid actuations of the Reactor Protection System, the Primary Containment Isolation System, the HPCI System, and the RCIC System.
Analysis of the Event
There were no actual safety consequences as a result of this event.
All control rods inserted on the reactor scram signal. The Group I / II / III PCIS isolations resulted in the primary containment isolation safety function being met.
The HPCI, RCIC, ARI and Recirculation Pump Trip functions operated as designed with no concerns noted. HPCI, RCIC and Safety Relief Valves were operated for Reactor pressure and level control.
This event is bounded by the design basis event entitled, 'Pressure Regulator Failure'. During this event the plant safety systems responded as necessary. This event did not involve operations that exceeded the design basis.
This event was not considered to be risk significant.
Cause of the Event
The cause of the EHC system malfunction is due to a failed 'A' Pressure Regulator circuit card (ELLS: IT). This circuit card is supplied by Mechanical Dynamics & Analysis (formerly Nova-Tech Corporation), Part No.
99041P1.
Initial troubleshooting was performed on the failed circuit card. The card was found to have low voltage at the 'decrease' input pin. The voltage observed at this pin would cause the control system malfunction symptoms observed and would also adversely affect the 'B' Pressure Regulator from being able to control Reactor pressure.
Detailed failure analyses were performed on the failed circuit card. The card was found to have a manufacturing defect involving excess solder. The excess solder on the circuit card created a short across two traces on the card, causing a voltage drop on the card. Removal of the excess solder resulted in proper card operation.
This card was installed in the EHC system on 9/18/04 during the recent Unit 2 refueling outage. The previously installed card could not be properly calibrated while performing preventive maintenance on the EHC system during the refueling outage. The previous that could not be calibrated had failed in a different manner (i.e. the set point was not able to be raised above 150 psig).
Corrective Actions
The defective card was replaced and the EHC system tested to verify proper operation. The EHC system was placed in service and has been appropriately controlling Reactor pressure since this event.
Similar installed circuit cards on Unit 2 were inspected and no similar solder deficiencies were observed.
Additional evaluations and corrective actions are being performed in accordance with the corrective action program.
Previous Similar Occurrences There was a previous Unit 2 scram on 12/21/02 caused by an EHC circuit card malfunction reported in LER 2-02-01. The failed circuit card was supplied by a different manufacturer and involved failure of a different type of sub-component (i.e. Operational Amplifier). Corrective actions resulting from the event reported in components.