05000261/FIN-2010009-14
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Finding | |
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| Title | Unexpected Loss of Instrument Bus 3 for Two Minutes |
| Description | The team reviewed the circumstances which resulted in an inadvertent de-energization of Instrument Bus 3. The team reviewed completed procedures, log entries, and system drawings. The team also interviewed personnel and performed a system walkdown. At 18:52 on March 28 the B battery charger de-energized due to loss of power to Bus E-2. Per Path-1, control room operators subsequently dispatched an Auxiliary Operator (AO) to restore the B battery charger. As the AO entered the battery room he made inadvertent contact with the handle for the B Inverter Supply Breaker 72/MCC-B (1K). The contact resulted in breaking the handle off of the breaker. Based on the timeframe when the AO entered the battery room and the time when Instrument Bus 3 was unexpectedly loss, the licensees ERT concluded the contact with the breaker caused the loss of Instrument Bus 3. The Auxiliary Operator recognized the damage to the breaker handle and continued to complete the restoration the B battery charger. The B battery charger was restored at 19:31. Upon exiting the battery room the AO verified the B inverter was operating correctly and reported the damage to the breaker handle. A review of plant data indicated Instrument Bus 3 was de-energized at 19:25 and reenergized at 19:27. The loss of Instrument Bus 3 power deenergized the High Steam Flow bistables in the Engineered Safety Features system. This condition, coincident with an RCS Low Tavg signal due to the RCS cooldown, generated a Main Steam Line Isolation signal, automatically closing all MSIVs and terminating the RCS cooldown. Based on interviews with the AO, no actions were performed to reset or reclose the B Inverter Supply Breaker. The licensee generated Work Order 01735191 to repair the broken breaker handle. The licensee performed troubleshooting activities to determine the cause of the two-minute interruption in instrument bus power, but was unable to detect any problems. The licensee was continuing to perform troubleshooting at the time this report was written. The licensee entered Condition Report 390070 into their corrective action program. Additional review by the NRC will be needed to assess the adequacy of the licensee troubleshooting efforts and evaluate any problems that may be identified. This review will also determine whether any performance deficiencies exist. An Unresolved Item will be opened pending completion of this review. The issue will be identified as URI 05000261/2010009-14, Unexpected Loss of Instrument Bus 3 for Two Minutes. |
| Site: | Robinson  |
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| Report | IR 05000261/2010009 Section 4OA5 |
| Date counted | Jun 30, 2010 (2010Q2) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 93800 |
| Inspectors (proximate) | J Hanna J Hickey L Miller L Wert P Fillion P Pieringer R Monk S Currie F Ehrhardta Nielsen C Kontz D Bollock D Mills G Laska G Skinner J Beavers J Brady J Hickey J Worosilo M Bates P Braxton R Musserr Monk F Ehrhardt J Hanna L Miller J Hickey P Fillion L Wert P Pieringer S Currie |
| INPO aspect | |
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Finding - Robinson - IR 05000261/2010009 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Robinson) @ 2010Q2
Self-Identified List (Robinson)
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