05000333/LER-2012-008
| James A. Fitzpatrick Nuclear Power Plant | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 48501 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(a)(1)(i), Emergency Class Declaration |
| 3332012008R00 - NRC Website | |
EVENT DESCRIPTION & ANALYSIS On November 11, 2012 at 03:56, an electrical fault occurred on James A. FitzPatrick Nuclear Power Plant (JAF) Main Transformer [EIIS System Identifier: EL], 71T-1A, which resulted in a main turbine trip and an automatic reactor scram. At the time of the event, the unit was operating at 100% power in Mode 1. The failure of 71T-1A caused a generator load reject and a Turbine Stop Valve closure, which in turn resulted in the reactor scram. All Reactor Protection Systems (RPS) actuated with no complications and the reactor was shutdown. The Reactor scram caused reactor water level to shrink causing High Pressure Coolant Injection (HPCI) [BJ] and Reactor Core Isolation Cooling (RCIC) [BN] to start. RCIC did inject and HPCI did not inject. The HPCI system did not inject due to the prompt recovery of reactor water level.
Combustible gasses, ignited by the electrical fault, ruptured the main tank of 71T-1A. This resulted in an oil leak from the transformer to the surrounding oil containment moat. The electrical fault ignited a oil fire in the transformer and damaged the Isophase Bus duct. The transformer's fire suppression system mitigated the spread of the fire. An Unusual Event was declared under Emergency Action Level (EAL) HU6.1 based on a conservative decision by the shift manager. This event was reported to the NRC by ENS 48501 along with the actuation of the RPS. The fire was extinguished by the onsite fire brigade, assisted by the local fire department and the Unusual Event was terminated at 0801. This report is being made in accordance with 10 CFR 50.73(a)(2)(iv)(A) for an event which resulted in automatic actuation of RPS.
Potential causes for transformer failures were analyzed. Thermography, corona inspections, oil sampling are performed on a periodic basis. No significant degradation in the transformer was detected by these tests.
CAUSE OF EVENT
This event was caused by an arcing fault, possibly caused by either a connection or coil failure internal to the transformer; by internal insulation breakdown; or both. Arcing produces heat which in turn produces combustible gas that could then ignite. The precise cause will not be known until an extensive forensic investigation is completed.
EXTENT OF CONDITION
Other high-voltage transformers include Main Transformer 71T-1B, Reserve Station Service Transformers [FK] 71T-2, 71T-3, or Normal Station Service Transformer 71T-4.
71T-2 and 71T-3 were replaced in R20. These transformers are isolated from 71T-1A and were unaffected by this event. They are monitored per the existing system monitoring plan, predictive maintenance, and preventive maintenance programs.
71T-1B and 71T-4 are electrically connected to the 71T-1A transformer. An external examination and electrical testing of these transformers indicate no impact from this event. In addition, the fire walls on the north and south side of transformer 71T-1A prevented the spread of fire and its potential impact on adjacent transformers.
Manual oil samples were taken for both 71T-1B and 71T-4. The Dissolved Gas in Oil Analysis (DGA) for both of these units indicates that total combustible gas rates are within limits.
Completed Actions
- Isophase Bus was repaired.
- 71T-1A was replaced and tested.
- Performed inspection and testing of 71T-1B, 711-4, and the Main Generator to verify components were not impacted by the event and ready for service.
Future Actions
- Perform failure analysis of Transformer 71T-1A.
ASSESSMENT OF SAFETY CONSEQUENCES
Nuclear Safety This event was an automatic reactor trip. Automatic reactor trips do present a challenge to nuclear safety systems; however, all safety systems functioned properly.
During the event, an electrical transient caused a loss of the Spent Fuel Pool Cooling (FPC) System [DA]. There was minimal challenge to nuclear safety due to the loss of FPC because operators restored it to service promptly.
Radiological Safety There is no impact on radiological safety because this event occurred in the transformer yard, which is not a radiologically controlled area. This event did not cause any radiation exposure to workers or the public.
Environmental Safety No oil escaped the contained switchyard area. Contaminated stone was removed from the switch yard as remediation. A New York State Department of Environmental Conservation individual inspected the area around the 71T-1A transformer and expressed no issues or concerns.
Industrial Safety There were no personnel injuries or accidents associated with this event. The industrial safety significance was the failure of the transformer that resulted in a fire in the transformer yard. There were no personal present in the yard at the time of the fire.
SIMILAR EVENTS
Catastrophic Transformer failures are a known industry issue but JAF has no previous failures of this type.
REFERENCES
- JAF Condition Reports: CR-JAF-2012-08084 - Root Cause Evaluation; CR-JAF-2012-08090 — Notification of Unusual Event Declaration