The Nuclear Regulatory Commission said they have sent a special team of investigators to the Palo Verde Nuclear Generating Station 50 miles west of Phoenix, Az, to study why a back up diesel generator failed in December during a routine monthly equipment test.
The NRC said a piston failed in one of two backup diesel generators and that operators put the plant on alert for two hours on Dec. 15, 2016, despite the backup systems in place – additional gas powered generators – in case the diesel generators fail.
The diesel generators are part of the second line of defense after the primary cooling system fails and that backup system has a backup system – the natural gas generators.
The diesel generators are tested monthly. The plant, when the piston failed, was put on the second lowest alert status out of four possible status categories.
The backup generator that failed is part of Unit 3 and the three-reactor plant that generates more electricity than any other plant in the country. It also has the highest capacity factor – 92 percent – of any of the world's 10 largest nuclear power plants, out of which Palo Verde is ranked as the ninth largest – although it is substantially smaller than the Bruce Power Station in Canada that has eight reactors and is the world's largest in terms of electricity generated.
The NRC team will spend a week at the plant and issue a report available to the public within 45 days following the end of the investigation. The NRC also said no personnel was injured during the event,,which “had no effect on plant operations.”