Two Tennessee nuclear plants, Sequoyah and Watts Bar, suffered unplanned reactor shutdowns last month.
Both reactors had electrical problems that caused the power plants to scram, said Tennessee Valley Authority (TVA) spokesman Ray Golden.
In the shutdowns, the reactors — Unit 1 at Watts Bar and Unit 2 at Sequoyah — functioned as they should and neither the plants nor the workers or public were at risk.
Sequoyah tripped on Aug. 16 following an electrical short in one of the four reactor coolant pumps. It returned to power Aug. 18.
Watts Bar shutdown Aug. 28 due to human error, Golden said. A worker inadvertently caused a fault one of the unit’s instrumentation systems by plugging in an incorrectly calibrated testing device. The reactor returned to power Aug. 30.
Having two local reactors quit in the same short time period is unusual, and unplanned outages can create difficulties for a utility, Golden said.
While the reactors aren’t generating power, even for just a few hours or days, TVA must increase power generation at other plants and sometimes bring idled plants online.
What’s more, TVA, with a number of unplanned shutdowns at its nuclear and non-nuclear power plants in the past year, is conscious of its image. Sequoyah’s unit 1 had so many that the Nuclear Regulatory Commission last year placed the reactor under its lowest safety concern flag — a white finding. That reactor had more the three unexpected outages in less than 7,000 operating hours or about a year.
“We’re disappointed with having any reactors trips,” Golden said. “But it is a complicated machine with a lot of electrical components.”
NRC spokesman Joey Ledford said NRC inspectors had no initial safety concerns about the reactor scrams. “We will make a complete review,” he said.
Golden said TVA, too, has made a point of looking for the root causes of the shutdowns and for “lessons” to apply for future prevention.
Sequoyah had been operating for 421 days, and Watts Bar had been operating nonstop for 319 days, he said.