05000410/FIN-2014005-04
Finding | |
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| Title | Assessment of UPS3B Failure Which Resulted in a Reactor Scram |
| Description | Introduction. A URI was identified pending Exelons revision and approval of their root cause report associated with the failure of UPS3B that caused a Unit 2 reactor scram on March 4, 2014
Description. Unit 2 is equipped with two 10-kVA UPSs (2VBB-UPS3A and 2VBBUPS3B) that feed RPS logic trip channel loads and main steam line isolation valves control solenoids through their associated distribution panels. 2VBB-UPS3B feeds the RPS trip system B. The loads are normally energized from 600 volts alternating current (VAC) non-safety-related power. In the case of the loss of normal supply power, an inverter allows the loads to receive power from its backup direct current source. In the case of an inverter failure, the UPS can be fed from an alternate non-safety-related 600 VAC source. Each UPS is connected to its associated distribution panel through two redundant electric protective assemblies connected in series. The electric protective assemblies provide redundant protection to the RPS system and other associated essential circuits against overvoltage, undervoltage, and under frequency conditions in the non-safety-related power sources. On March 4, 2014, 2VBB-UPS3B experienced a capacitor failure on an associated circuit card. This failure prevented the UPS from transferring to its alternate source of power causing the electrical protective assemblies to trip, a loss of cooling water to the reactor recirculation pumps, and a subsequent reactor trip. Exelon staff documented the issue in CR-2014-001725 and performed a root cause analysis. Using investigative root cause techniques outlined in procedure CNG-CA-1.01-1004, Root Cause Analysis, Revision 00801, Exelon staff determined the root cause to be a lack of vendor and industry guidance and internal/external operating experience resulting in lack of PM task to preclude backplane failure. The corrective actions to prevent recurrence involved revising the PM strategy in the IQ Review and Maximo database to include replacement of all single-point vulnerable components in 2VBA*UPS2A/2B and 2VBB-UPS3A/3B. During inspection of Unit 2 LER 2014-003-00, Uninterruptible Power Supply Failure and Subsequent Manual Scram, the inspectors reviewed the root cause report associated with this event. The inspectors discovered that, although the root cause postulated that warping/cracking of the backplane contributed to UPS3B failure, when new information regarding the backplane that contradicted this root cause was discovered, Exelo personnel did not properly enter this new information into the CAP or elevate the concern to Exelon plant management. Specifically, the engineering staff and a vendor representative had examined the UPS3B backplane during the Unit 2 refueling outage and found no indication of cracking or warping. This examination occurred following management review committee approval of the root cause. This information, along with other testing performed on the UPS3B during the refueling outage, showed that the theory for potential backplane warping/cracking likely was not the actual root cause and that the corrective actions developed for backplane replacement may not prevent recurrence of the UPS failure. Exelon documented the inspectors observation in IR 2416757 and plans to evaluate the issue further and to reopen and update the root cause report. This issue will be opened as a URI pending Exelon revision of the root cause report; and NRC review of the root cause report to determine whether the issue contains performance deficiency, whether or not that performance deficiency is more than minor, and whether a violation exists. Exelon is tracking this issue through their CAP database with a date to determine root cause revision requirements by December 19, 2014. (URI 05000410/2014005-04, Assessment of UPS3B Failure Which Resulted in a Reactor Scram) |
| Site: | Nine Mile Point  |
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| Report | IR 05000410/2014005 Section 4OA3 |
| Date counted | Dec 31, 2014 (2014Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | A Rosebrook D Schroeder E Miller G Stock H Gray K Kolaczykm Modes T Dunn W Cook A Rosebrook B Sienel C Graves D Schroeder E Andrews E Burket E Miller G Stock J D'Antonio K Kolaczy |
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Finding - Nine Mile Point - IR 05000410/2014005 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Nine Mile Point) @ 2014Q4
Self-Identified List (Nine Mile Point)
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