The Callaway nuclear power plant has been shut down part of its routine refueling and maintenance.
The refueling process, which will take several weeks, started at 3:01 a.m. Saturday.
"It is difficult to determine just how long an outage will occur because we are doing a lot of inspecting and testing at the same time," said Mike Cleary, an Ameren Missouri spokesman. He said inspections or tests may require some equipment to be replaced, which could lengthen the time of the outage.
"This is the 18th routine scheduled outage we have had since the plant opened. The shortest outage we had for refueling was only 28 days. The longest was 65 days. This outage is fairly routine. We don't anticipate anything out of the ordinary.
"In 2005 we replaced four of our steam generators. Each one is 70 feet tall and they weigh about 400 tons each. They also had to be shipped here from France. That was a big deal but this is more of a routine outage," Cleary said.