05000338/FIN-2011011-04
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Finding | |
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| Title | 1J EDG Frequency Oscillation |
| Description | Following the seismic event on August 23, 2011, while the 1J EDG was supplying power to the 1J emergency bus, control room operators identified frequency oscillations on the 1J EDG bus as well as 1-III and 1-IV inverter momentary trouble alarms when the pressurizer heaters were cycled. During personnel interviews, bus frequency was reported as oscillating between 59 and 61Hz. The inspectors noted a Technical Specification Limit of 59.5 and 60.5Hz. Engine load cycled between 1600 and 2000KW while the 1J EDG was supplying power to the bus, varying as pressurizer heater loads cycled. The PCS did not have a data point for emergency bus frequency so actual emergency bus frequency was not recorded and could not be conclusively obtained. The licensee entered this issue into the corrective action program as CR 440231. There was a PCS data point that indicated engine speed (rpm), which could have been used to calculate frequency with quality data available; however this PCS point for the 1J EDG was very noisy during the event and could not provide any useful data to determine the magnitude of frequency oscillations. All four EDG speed points on the PCS were trended using engine run data since the seismic event occurred. Each engine was operating parallel to the grid (stable at 900rpm) to observe stability of the data point. There was noise in each data point: 1H, 2H and 2J showed oscillations of 20-30rpm when paralleled and had a nominal speed indication between 895 and 920rpm. The 1J data point showed oscillations of 100rpm in isochronous mode and when paralleled to the grid and could therefore not be used to conclusively determine the 1J emergency bus frequency. This data point was used for indication only and was not related to actual engine stability. On September 5, the licensee conducted a PMT of the 1J EDG in manual mode. During that run, a troubleshooting sheet was prepared in response to CR 440231 and qualified test equipment was used to measure engine frequency/voltage, electronic governor null voltage, and the PCS rpm data point. Frequency responded as expected when control was switched from the mechanical governor to the electric governor actuator and was measured stable at 60.2Hz. The licensee was not able to test the 1J EDG in isochronous mode, which was the configuration during the event due to current plant conditions; however, the licensee was scheduled to recreate the scenario during the upcoming refueling outage. The engine RPM indication is a separate issue that may also be addressed during this evolution. An unresolved item will be opened pending completion and results of licensee testing. This issue will be identified as URI 05000338, 339/2011011-04, 1J EDG Frequency Oscillations. |
| Site: | North Anna  |
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| Report | IR 05000338/2011011 Section 4OA5 |
| Date counted | Dec 31, 2011 (2011Q4) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 93800 |
| Inspectors (proximate) | G Kolcum G Mccoy J Reece J Rivera K Schaaf L Lake M Levine M Meeks R Clagg R Hamilton R Kellner W Pursleyg Kolcuml Suggs M Chakravorty M Franke R Jackson S Park S Walker V Mccree Y Li |
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Finding - North Anna - IR 05000338/2011011 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (North Anna) @ 2011Q4
Self-Identified List (North Anna)
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