The newest reactor at the Browns Ferry Nuclear Plant in Athens, Ala., shut down over the weekend because of vibration problems in a generator.
The reactor trip is the seventh unplanned outage at a TVA nuclear plant this year and comes just a week after one of the reactors at the Sequoyah Nuclear Plant near Soddy-Daisy shut down because of a fire in the plant's turbine building.
Tennessee Valley Authority spokesman Ray Golden said the federal utility restored power at Sequoyah on Christmas Eve after last week's reactor trip. But two days later, operators had to shut down the Unit 3 reactor at Browns Ferry after detecting excessive vibration in a piece of equipment in the plant's generator, Golden said.
TVA crews still are evaluating the problem at Browns Ferry. Golden said the utility doesn't disclose in advance when it anticipates power production to resume.
"We obviously strive to have no forced outages, but most of these trips were manual outages by our operators and not automatic shutdowns, so it shows that our operators are being vigilant and conservative in their decision making," Golden said.
"These are complex plants with a lot of mechanical and electronic parts, and from time to time we have unplanned outages where something has come up and we have to take the unit off-line to fix it," he said.
During the past year, TVA did have one of its best reactor runs at its Unit 1 at Browns Ferry with 576 days of continuous operation. At Sequoyah Unit 1, TVA also had a continuous run of more than 500 days before the recent outage.
During 2010, Browns Ferry Unit 2 had two unplanned outages, Unit 1 at Watts Bar also had two unplanned outages and each of the two reactors at Sequoyah were idled during the year because of reactor trips.
The Nuclear Regulatory Commission, the federal agency responsible for regulating nuclear reactors, doesn't increase its regulatory oversight of a reactor until it has at least three unplanned outages a year, and NRC rules don't force a nuclear plant to shut down until it has more than 25 such outages in a year, NRC spokesman Joey Ledford said.
But Ed Lyman, a senior scientist for the Union of Concerned Scientists, said TVA and other nuclear utilities should be improving their reliability each year.
"It doesn't look like seven reactor scrams for a utility the size of TVA is that unusual by historical standards," Lyman said. "But I would hope they would be doing better. Just running in place and not getting better is not the way you should go."
Contact staff writer Dave Flessner at dflessner@times freepress.com or at 757-6340.