Xcel Energy's Prairie Island nuclear power plant is back up to full capacity, now that repairs are complete after a false fire alarm in one of its two units sounded more than three weeks earlier.

Unit 2 was back in business shortly before 6 p.m. Saturday, the electricity provider said Monday. The reactor at the plant in Red Wing went down March 5 after the early morning false alarm triggered an "Unusual Event."

The utility said a disk ruptured in a pressure tank, triggering the alarm and affecting the cooling and ventilation systems, leading to the shutdown.

During outages, Xcel Energy buys electricity from other power sources or increases electricity production at its other generating plants to ensure an adequate supply for customers.