Xcel Energy on Saturday was continuing to fix a problem with a control valve at its Monticello nuclear power plant that was discovered Wednesday morning, according to a company statement.

The problem on Wednesday led the system to take the reactor offline automatically, shutting it down as it is designed to do, Xcel spokesperson Josiah Mayo said.

No impact on electrical service to customers was expected, he said.

The nuclear team is "taking the necessary steps to bring the plant back to full operations," according to Mayo, and expects to be done soon.

The federal government renewed the Monticello plant's operating license in December, permitting it to continue operating through 2050.

The Monticello plant, located on the Mississippi River, opened in 1971. Xcel has spent billions of dollars maintaining it over the years.

Xcel, Minnesota's largest utility, provides most of the metro area's electricity and has 1.3 million customers. The company also has a nuclear plant in Red Wing.