NEWPORT, Mich. - DTE Energy hopes to have its Fermi 2 nuclear plant in northern Monroe County back at full power soon.
Restart began Saturday night after the utility fixed a fault in a protective circuit, Guy Cerullo, utility spokesman, said.
That problem was diagnosed as the cause of Thursday's unexpected shutdown, which began when automatic safety systems shut off the power plant's main turbine at 4:27 p.m. that day.
The turbine shutdown automatically activated other safety systems to engage in a rapid shutdown, or "scram," of the nuclear reactor.
The utility's attempt to bring the reactor back to full power has been hampered by an issue that emerged shortly after restart with the plant's main condenser vacuum, which is used to convert steam back into water in the plant's closed-loop system.
Operators are keeping the reactor at 4 percent power until that issue is resolved, Mr. Cerullo said.
Nuclear reactors usually have to be operating at 20 percent power or greater before plants can produce enough power to synchronize to the region's electrical grid.
Ascending to full power can take a couple of days even if no issues arise.
Safety systems are designed so that shutdowns occur automatically when certain components of the plant are involved. Reactors also can be shut down manually if safety systems aren't activated.
The Fermi 2 reactor was operating at 67 percent power at the time of Thursday's shutdown. The two-day outage ended 135 days of continuous operation for the plant.
It was the plant's first shutdown since Sept. 30, when generator repairs were made.
The reactor's power was reduced from 100 to 50 percent early last week so that repairs and adjustments could be made to a water recirculation pump. The utility was bringing the reactor back to full power when the turbine shut off Thursday.
Fermi 2 is along Lake Erie, about 30 miles north of Toledo.
The plant's next extended outage is scheduled for this fall, when the reactor is to be refueled. Refueling occurs once every 18 to 24 months and typically takes four to six weeks.
The plant went online in 1988. It provides enough energy for about a million DTE customers.
- Tom Henry