05000341/FIN-2017004-01
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Finding | |
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| Title | Reactor Recirculation Motor-Generator Set ABrush Gear Failure |
| Description | Inspection ScopeDuring the course of the inspection period, the inspectors performed several observations of licensed operator performance in the plants control room to verify that operator performance was adequate and that plant evolutions were being conducted in accordance with approved plant procedures. Specific activities observed that involved a heighted tempo of activities or period of elevated risk included, but were not limited to:Planned downpower, performance of turbine stop and control valve testing, and main steam isolation valve testing on November 4 and 5, 2017;Subsequent response to a manual trip of reactor recirculation motor-generatorset A and single loop operation on November 26, 2017; andPower suppression testing on December 30, 2017. The inspectors evaluated the following areas during the course of the control room observations: licensed operator performance;crews clarity and formality of communications;ability to take timely actions in the conservative direction;prioritization, interpretation, and verification of annunciator alarms (if applicable); correct use and implementation of procedures;control board (or equipment) manipulations;oversight and direction from supervisors; andability to identify and implement appropriate TS actions and Emergency Plan actions and notifications (if applicable). The performance in these areas was compared to pre-established operator action expectations, procedural compliance and task completion requirements. Documents reviewed are listed in the Attachment to this report.These observation activities by the inspectors of operator performance in the plants control room constituted one quarterly licensed operator heightened activity/risk sample as defined in IP 71111.11.b. Findings Reactor Recirculation Motor-Generator Set A Brush Gear Failure Introduction. The inspectors identified an unresolved item (URI) to further evaluate the events and causes of a failure of the reactor recirculation motor-generator set A brush gear assembly. Specifically, the licensee had not yet completed their root cause evaluation of the event at the end of the inspection period.Description. On November 26, 2017, at approximately 2:38 p.m. while the plant was operating at 100 percent reactor thermal power, the control room unexpectedly received a Recirculation System A Generator Field Ground alarm with no other abnormal indications noted in the control room. A non-licensed operator was dispatched to the reactor recirculation motor-generator room in the reactor building and immediately noted an acrid odor along with significant arcing and sparking on the generator end of reactor recirculation motor-generator set A. Subsequently, at 2:56 p.m., control room operators manually tripped reactor recirculation motor-generator set A and entered abnormal operating procedure 20.138.01, reactor recirculation pump trip. In accordance with the abnormal operating procedure the control room operators promptly inserted control rods and stabilized the plant at approximately 35 percent reactor thermal power in single loop operation. The abnormal operating procedure was exited at 4:37 p.m. following completion of associated operator actions and plant stabilization.The licensee formed an emergent issues team to further investigate the issue. Significant damage was identified on the brush gear assembly mounted on the generator end of the reactor recirculation motor-generator set A including, but not limited to, severely worn slip rings, damaged carbon brushes and holders, and melted insulating materials. Initial evaluation by the licensee indicated the carbon brushes had inadequate spring tension to remain in contact with the slip rings, potentially as a result of a brush gear inspection procedure change that allowed for increased wear on the carbon brushes prior to replacement. Additionally, it was determined that sparks were observed on the brush gear assembly the day before the event, however, no discernable action was taken to address the issue.The brush gear assembly was repaired, however, multiple attempts were made to restart reactor recirculation motor-generator set A unsuccessfully. Further troubleshooting identified that the reactor recirculation motor-generator set A starting circuitry voltage was too low to support a restart during single loop operations. Additionally, a rectifier diode pigtail connection in the automatic voltage regulator was found damaged. The rectifier diode pigtail connection was subsequently repaired. A temporary modification was developed and implemented to increase the reactor recirculation motor-generator set A starting circuitry voltage. The reactor recirculation motor-generator set A was successfully restarted on December 5, 2017. Single loop operations were subsequently exited and the unit returned to 100 percent rated thermal power on December 6, 2017.The licensee entered this issue in the corrective action program as CARD 1729439. Because the licensee had yet to complete their root cause investigation and analysis of the event, the issue is being treated as an unresolved item pending the inspectors review of the licensees completed cause evaluation and proposed corrective actions. (URI 05000341/201700401, Reactor Recirculation Motor-Generator Set A Brush Gear Failure) |
| Site: | Fermi  |
|---|---|
| Report | IR 05000341/2017004 Section 1R11 |
| Date counted | Dec 31, 2017 (2017Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.11 |
| Inspectors (proximate) | T Briley P Smagacz B Bergeon G Hansen V Myers R Walton B Dickson |
| Violation of: | Pending |
| INPO aspect | |
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Finding - Fermi - IR 05000341/2017004 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Fermi) @ 2017Q4
Self-Identified List (Fermi)
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