ENS 41252
ENS Event | |
|---|---|
19:17 Dec 10, 2004 | |
| Title | Reactor Scram Due to Loss of Vital Instrument Bus |
| Event Description | At 1317 [hrs CST] on December 10, 2004, an automatic actuation of the reactor protection system (RPS) occurred resulting in a reactor scram. The apparent cause of the event was loss of a vital instrument bus due to a fault in a nonsafety related vital inverter. This inverter provides power to selected control room instrumentation and controls. This resulted in the loss of feed water level control.
Reactor level is being maintained by the High Pressure Core Spray System. The feed water system is not available. Reactor pressure is being controlled through the main turbine steam bypass system to the condenser. The condenser is available and being used as the heat sink. The residual heat removal system was operated in suppression pool cooling mode to provide a means of rejecting water from the suppression pool [water input from High Pressure Core Spray System minimum flow line]. The plant is currently stable, and being maintained in hot shutdown. Systems responded as expected based on the initiating event. Reactor Core Isolation Cooling is not being used pending evaluation of a system alarm that is currently being investigated. Investigation of the initiating fault is being pursued in order to recover the vital bus and feed water level control. It has been preliminarily determined that the loss of instrument power resulted in the Main Feedwater regulating valve failing as-is and the "B" Reactor Recirculation Pump shifting down in speed. The reduction in reactor power with constant feed flow resulted in a high reactor vessel water level, producing a direct reactor scram signal at the High Level 8 setpoint. The licensee has notified the NRC Resident Inspector.
At 1657 CST [on 12/10/04], reactor level control was restored to the normal Feedwater and Condensate Systems. The High Pressure Core Spray System was restored to the normal standby lineup. Investigation into the cause of the reported RPS actuation continues. Investigation into the Reactor Core Isolation Cooling System alarms has resulted in declaring this system inoperable. The licensee will notify the NRC Resident Inspector. Notified R4 DO (L. Smith), NRR EO (M. Tschiltz) and IRD Manager (S. Frant)
The final determination of the cause of the scram was determined to be due to the B recirc pump downshift and subsequent power to flow scram on APRM flux. The licensee will notify the NRC Resident Inspector. Notified R4DO (L Smith)
The Reactor Core Cooling System was returned to available status at 0343 on 12/11/2004 and was restored to operable status at 2200 on 12/11/2004." The licensee notified the NRC Resident Inspector. Notified R4DO (Kriss Kennedy). |
| Where | |
|---|---|
River Bend  Louisiana (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(2)(iv)(B), RPS Actuation | |
| Time - Person (Reporting Time:+-1.72 h-0.0717 days <br />-0.0102 weeks <br />-0.00236 months <br />) | |
| Opened: | Gary Huston 17:34 Dec 10, 2004 |
| NRC Officer: | Mike Ripley |
| Last Updated: | Dec 16, 2004 |
| 41252 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | A/R |
| Before | Power Operation (100 %) |
| After | Hot Shutdown (0 %) |
WEEKMONTHYEARENS 568872023-12-13T07:02:00013 December 2023 07:02:00
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ECCS Discharge Reactor Scram as a Result of Loss of Normal Power 13.8 Kv Bus ENS 436682007-09-27T03:44:00027 September 2007 03:44:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation Automatic Reactor Scram During the Performance of Aprm Surveillance Testing ENS 433452007-05-04T17:56:0004 May 2007 17:56:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation Manual Reactor Scram Due to Loss of Cooling to Number 2 Main Transformer ENS 429212006-10-19T22:56:00019 October 2006 22:56:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(iv)(A), System Actuation, 10 CFR 50.72(b)(2)(iv)(A), System Actuation - ECCS Discharge Automatic Scram Following Spontaneous Feedwater Valve Closure ENS 425052006-04-15T21:15:00015 April 2006 21:15:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation Reactor Scram from 100% Power ENS 413392005-01-15T08:12:00015 January 2005 08:12:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation Manual Reactor Scram Due to Receiving a Main Generator Alarm ENS 412522004-12-10T19:17:00010 December 2004 19:17:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation Reactor Scram Due to Loss of Vital Instrument Bus ENS 410822004-10-01T12:30:0001 October 2004 12:30:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(2)(iv)(A), System Actuation - ECCS Discharge Reactor Trip Due to Main Generator Load Rejection ENS 409572004-08-15T09:05:00015 August 2004 09:05:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation Automatic Reactor Scram Following Partial Loss of Offsite Power ENS 401912003-09-23T03:43:00023 September 2003 03:43:00 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation Automatic Reactor Scram Received During Main Turbine Control Valve Testing 2023-12-13T07:02:00 | |