Unit 2 at the Prairie Island nuclear power plant near Red Wing is undergoing a scheduled refueling outage, Xcel Energy said this morning.

Each reactor is refueled about every 18 months, and outages generally last about four to six weeks. During the outages, Xcel Energy buys power from other utilities or increases electricity production at its other generating plants to ensure an adequate power supply.

This outage began Friday night.

About 900 contractors will help plant employees complete more than 4,500 maintenance tasks to prepare the unit for its next operating cycle and will replace one-third of the unit's fuel.

The outage followed 354 days of continuous operation of Unit 2.

Meanwhile, Xcel's nuclear facility in Monticello remains off-line this morning.

On Wednesday, an employee of an equipment rental company was killed when equipment he was operating contacted a high-voltage power line just outside the plant gates.

The accident occurred as plant operators were working to restore power production after the plant automatically shut down on Sept. 11, when a fault in an underground cable caused a substation breaker to fail. That prompted the plant to switch other power sources. Operators expect to return the plant to full power production within a few days.

In January 2007, the Monticello plant closed for a week after a 35,000-pound control box broke loose from its support beams and fell onto a large pipe carrying radioactive steam. The pipe did not rupture or leak.

In August, Xcel shut down one of its two Prairie Island reactors because of elevated hydrazine levels found in the turbine building. Levels of the anti-corrosive, ammonia-like chemical stayed elevated for about six hours before being corrected. The plant was back to full power the next day.