Pinnacle West Capital (NYSE:PNW) subsidiary Arizona Public Service (APS) took Unit 1 of the Palo Verde nuclear station offline Sept. 7 after experiencing a problem with a stuck valve, according to a report filed with the Nuclear Regulatory Commission (NRC).
Palo Verde Unit 1 was manually tripped due to a stuck open main spray valve while operating at 100% power prior to the event.
“The plant was then manually tripped due to pressurizer pressure continuing to lower,” according to the NRC report.
“The reactor coolant pumps were turned off to terminate main pressurizer spray flow to control pressurizer pressure due to the inability to close the main spray valve,” according to the report.
“All rods inserted and the trip was uncomplicated. Units 2 and 3 were not affected and continue to run at full power,” according to the report filed with the NRC.
APS describes the Palo Verde nuclear station as the nation’s largest producer of emission-free energy. In 2015, the three-unit nuclear complex generated 32.5 million megawatt-hours (MWh) of carbon-free electricity.
When operating fully, the three pressurized water reactors (PWRs) at the Palo Verde station in Maricopa County, Arizona can together generate about 5,000 MW.