ENS 46045
ENS Event | |
|---|---|
18:34 Jun 24, 2010 | |
| Title | Instrument Buses 3 and 8 Failed Causing Closure of Rhr Valves |
| Event Description | At 14:34 hours on June 24, 2010, with the unit in MODE 5, Cold Shutdown, with approximately 50% pressurizer level, during Refueling Outage 26, Instrument Buses 3 and 8 unexpectedly de-energized during performance of testing in accordance with procedure OST-163, 'Safety Injection Test and Emergency Diesel Generator Auto Start on Loss of Power and Safety Injection.' The loss of Instrument Buses 3 and 8 occurred during the loss of power and Safety Injection testing of the 'A' Train.
Instrument Buses 3 and 8 are normally powered from Inverter 'B' which is normally supplied by the Train 'B' DC Bus. During the test, it was noted that the power supply to Instrument Buses 3 and 8 had tripped. The cause of the failure of Inverter 'B' is not currently known. The failure of inverter 'B' caused the closure of the Residual Heat Removal (RHR) Heat Exchanger discharge valve (HCV-758) and the RHR Heat Exchanger bypass valve (FCV-605). Both trains of RHR continued to operate and reactor coolant system temperature remained in the range of approximately 93 to 96 degrees Fahrenheit. Abnormal Operating Procedure AOP-020, 'Loss of Residual Heat Removal (Shutdown Cooling)' was entered. Power was restored to Instrument Buses 3 and 8 by use of the alternate power supply at 14:49 hours. Normal configuration of the RHR system was restored and AOP-020 was exited at 14:51 hours. Currently Instrument Buses 3 and 8 are being powered from the alternate power supply which causes the associated 'B' EDG to be inoperable due to the inoperability of the automatic load sequencer that starts the associated Service Water and Component Cooling Water pumps. The 'A' EDG is inoperable due to the need to complete required post-maintenance testing. Therefore, both EDGs are currently inoperable. Both EDGs are currently considered available and are aligned for automatic starting. Both EDGs would be expected to automatically supply their respective buses if a loss of offsite power were to occur. Manual action would be required to start the required loads on the 'B' Train due to the current alignment of the Instrument Buses 3 and 8 on the alternate power supply. It is expected that the 'B' EDG will be restored to operable status when Inverter 'B' is restored to operable status and realigned to supply Instrument Buses 3 and 8. The Technical Specifications (TS) Action Statement currently in effect for loss of Inverter 'B' (TS 3.8.8 Condition A) requires initiation of action to restore AC instrument bus sources to OPERABLE status immediately. The actions to restore Inverter 'B' were initiated immediately and are continuing. This report is being made in accordance with 10 CFR 50.72(b)(3)(v)(D), for any event or condition that at the time of discovery could have prevented the fulfillment of structures or systems that are needed to mitigate the consequences of an accident. The licensee has notified the NRC Resident Inspector.
This is a follow-up notification to Event Notification EN#46045 regarding Instrument Buses 3 and 8 that unexpectedly de-energized during performance of testing in accordance with procedure OST-163, 'Safety Injection Test and Emergency Diesel Generator Auto Start on Loss of Power and Safety Injection.' Power was restored to Instrument Buses 3 and 8 by use of the normal power supply at 08:03 hours on June 27, 2010. Inverter 'B' has been realigned to supply Instrument Buses 3 and 8. The restoration of inverter 'B' has returned the associated 'B' EDG to operable status at 11:09 hours with the return of the automatic load sequencer that starts the associated Service Water and Component Cooling Water pumps. The 'A' EDG continues to be inoperable due to the need to complete required post-maintenance testing. Currently 'A' EDG is considered available and aligned for automatic starting. The Technical Specifications (TS) Action Statement for loss of Inverter 'B' (TS 3.8.8 Condition A) that requires initiation of action to restore AC instrument bus sources to OPERABLE status immediately was exited at 11:09 hours on June 27, 2010. TS Action Statement for loss of 'B' EDG (TS 3.8.2 Condition B) that requires initiation of action to restore required DG to OPERABLE status immediately was also exited at 11:09 hours on June 27, 2010. The licensee is still investigating the cause of the failure. The licensee notified the NRC Resident Inspector. Notified the R2DO (Shaeffer). |
| Where | |
|---|---|
Robinson  South Carolina (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| LER: | 05000261/LER-2010-005 |
| Time - Person (Reporting Time:+3 h0.125 days <br />0.0179 weeks <br />0.00411 months <br />) | |
| Opened: | Curtis Castell 21:34 Jun 24, 2010 |
| NRC Officer: | John Knoke |
| Last Updated: | Jun 27, 2010 |
| 46045 - NRC Website
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Unit 2 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Cold Shutdown (0 %) |
| After | Cold Shutdown (0 %) |
Robinson with 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
WEEKMONTHYEARENS 507782015-01-29T00:57:00029 January 2015 00:57:00
[Table view]Other Unspec Reqmnt, 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Safety System Will Not Function as Required ENS 477482012-03-16T08:00:00016 March 2012 08:00:00 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident Refueling Water Storage Tank Connected to an Unqualified System ENS 480112011-05-04T17:25:0004 May 2011 17:25:00 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident Refueling Water Storage Tank Connected to Non-Seismically Qualified System ENS 463172010-10-07T17:15:0007 October 2010 17:15:00 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident Feedwater Isolation Inadvertently Disabled ENS 460452010-06-24T18:34:00024 June 2010 18:34:00 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident Instrument Buses 3 and 8 Failed Causing Closure of Rhr Valves ENS 406172004-03-28T15:26:00028 March 2004 15:26:00 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Both Trains of High Pressure Safety Injection Inoperable for 25 Minutes 2015-01-29T00:57:00 | |