Unit 2 at Nine Mile Point in upstate New York is back online after the failure of an uninterruptible power supply prompted operators to shut it down last week.The Valley News reported that the reactor returned to full power on Sunday afternoon following repairs and testing. It had been offline since March 4.According to a report filed with the Nuclear Regulatory Commission, the reactor reduced its power output automatically when the UPS failed. Operators shut the unit down completely six minutes later when systems indicated a loss of cooling water to reactor recirculation pumps. During the event, a reactor building ventilation radiation monitor also stopped working when the building isolated in response to the failed UPS, according to the NRC, and a standby gas treatment system restored the reactor building differential pressure.Constellation Energy, majority-owned by Exelon, runs two General Electric boiling water reactors that generate 1,990 megawatts at the plant near Syracuse, N.Y. On Feb. 16, an off-site event caused the loss of a 115 kilovolt line to the plant and resulted in the startup of emergency diesel generators at unit 2. The event preceded a feedwater level control lockup and affected gas and water monitoring systems, but the unit did not need to shut down while they were restored.
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UPDATE: The reactor has tripped offline again. From the NRC:
"Event Date: 03/10/2014
Event Time: 16:28 [EDT]
REACTOR SCRAM DUE TO ACTUATION OF THE ALTERNATE ROD INSERTION SYSTEM
"At 1628 EDT Nine Mile Point (NMP) Unit 2 experienced an actuation of the Alternate Rod Insertion (ARI) system which resulted in a reactor scram. Coincident with the scram, the Reactor Core Isolation Cooling (RCIC) system initiated.
"Prior to the event, maintenance personnel were working in the vicinity of a reactor vessel level instrumentation rack and may have agitated the common drain line of the transmitters. A prompt investigation is underway to investigate the incident.
"The actuation signal for the RCIC system was invalid because reactor vessel level did not reach level two and the actuation was not in response to actual plant conditions or parameters.
"The reactor scram is reportable in accordance with 10 CFR 50.72(b)(2)(iv)(B) as, 'Any event or condition that results in actuation of the reactor protection system (RPS) when the reactor is critical.'
"The event has been entered into the NMP corrective action program as CR-2014-001963.
"The NRC Resident Inspector has been notified."
The licensee has notified the State of New York.
The reactor is shutdown with all rods inserted. Decay heat is being rejected to the condenser and reactor water level is being maintained by condensate, feedwater, reactor water clean up, and control rod drive systems."
Nuclear Street News Team