05000247/FIN-2016001-06
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Finding | |
|---|---|
| Title | 23 Emergency Diesel Generator Automatic Voltage Regulator Failure |
| Description | Following the initial loss of 480V vital buses and loss of RHR cooling, the operating crew was taking actions to restore normal power to all 480V buses. Before the crew was able to restore off-site power to the 6A bus, the 23 EDG tripped on overcurrent resulting in a loss of bus 6A and the subsequent blackout/unit trip signal that stripped all loads from the remaining 480V buses. The cause of this second trip is still under review by Entergy, and the NRC opened an URI related to this concern to assess whether a performance deficiency exists. On March 7, 2016, approximately one hour after the trip of the 3A normal feed breaker, the 23 EDG tripped on overcurrent while powering the 6A bus. The operators responded by re-entering 2-AOP-480V-1, Loss of Normal Power to Any 480V Bus, and 2-AOP-RHR-1, Loss of RHR. The RHR cooling was restored within five minutes. Throughout the transient, 24 RCP remained in service and available for RCS heat removal as it is powered from 6.9 kV which remained energized from offsite power. Due to ongoing performance of restoration actions from the previous trip, the 21 EDG was not ready to automatically start, so initially only the 2A bus loaded on the 22 EDG. The delay in the starting of 21 EDG combined with the associated loss of 23 vital instrument bus resulted in loss of power to the C pressurizer level channel which then caused both a loss of letdown and loss of pressurizer heaters. These conditions along with the malfunctioning of the 24 loop pressurizer spray valve controller created additional challenges to the operator tasked with controlling pressurizer pressure and level. The delay in the start of the 21 EDG also affected the operator tasked with restoring RHR as the RHR heat exchanger outlet motor operated valves associated with 21 RHR pump were powered from the 5A bus. The crew was able to restore the 3A bus with the 22 EDG, and then start the 21 RHR pump. The 6A bus remained de-energized until the crew restored 6A via off-site power. The 23 EDG was declared inoperable. By 1:49 p.m., all four 480V buses were restored to off-site power; and by 2:07 p.m., 21 and 22 EDGs had been shut down and returned to standby (auto start) condition. Entergys initial review of the second electrical transient determined the most probable cause was a spurious actuation of the A, B, or C phase voltage controlled overcurrent relays. These relays were replaced under WO 00440073 with spare, calibrated relays. Operator observations during the event indicated that the 23 EDG breaker tripped while loads were still being added, including the start of the turbine auxiliary bearing oil pump and various motor control centers, but the 23 EDG load never exceeded the continuous load rating of 1750 kilowatt (kW). Local diesel observations indicated approximately 1650 kW load on the 23 EDG just prior to the trip. Entergy then concluded that all other equipment functioned as per design and that a monthly load test surveillance would be utilized to determine operability after replacing the overcurrent relays. On March 8, 2016, 23 EDG was declared operable following successful completion of the monthly diesel surveillance procedure. The 23 EDG was run, closed onto Bus 6A, and loaded to 2275 kW. Later, as-found bench testing of the overcurrent relays indicated that the relay trip settings were within calibration and should have functioned as designed. Subsequently, on March 10, 2016, during performance of PT-R14, Automatic Safety Injection System Electrical Load and Blackout Test, 23 EDG exhibited anomalous behavior during the train B load sequencing. During the test, the voltage on bus 6A dropped to approximately 200V when the 23 AFW pump was sequenced onto the bus (CR-IP2-2016-01430). 23 EDG was again declared inoperable and the period of inoperability was backdated to March 7, 2016, when it originally tripped. Further troubleshooting and additional failure modes analysis found a degraded resistor associated with the 23 EDG automatic voltage regulator. The 23 EDG voltage regulator was replaced, and the 23 EDG was again tested satisfactorily. The low voltage issue exhibited during PT-R14, Automatic Safety Injection System Electrical Load and Blackout Test, was documented in CR-IP2-2016-01430 and has been closed in CR-IP2-2016-01260 to be included in the ACE associated with the tripping of 23 EDG breaker on March 7, 2016. Entergy was in the process of performing a failure analysis and an ACE at the end of the inspection period. NRC review of Entergys failure analysis and causal evaluation will be performed to evaluate if a performance deficiency exists. The inspectors determined that the issue is an URI. |
| Site: | Indian Point  |
|---|---|
| Report | IR 05000247/2016001 Section 4OA2 |
| Date counted | Mar 31, 2016 (2016Q1) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71152 |
| Inspectors (proximate) | B Haagensen G Dentel G Newman H Gray J Furia J Patel P Ott S Richb Haagensene Dipaolo F Arner G Newman J Amberosini J Furia S Elkhiamy S Rich |
| INPO aspect | |
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Finding - Indian Point - IR 05000247/2016001 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Indian Point) @ 2016Q1
Self-Identified List (Indian Point)
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