USA fleet member Xcel Energy’s Prairie Island Nuclear Generating Plant recently ramped up power on its Unit 2 following the completion of a refueling outage which was host to major equipment upgrades and Fukushima compliance projects. Taking center stage were capital projects to replace the main generator and step-up transformer – the lion’s share of the $120 million of capital investments made during the refueling outage.

“Refueling outages are some of the most challenging times for nuclear plants, but they’re also big opportunities,” said Kevin Davison, site vice president. “We installed some major pieces of equipment that are essential to maintaining Prairie Island as part of the reliable backbone of the electric grid. More importantly, we did so safely. Our team deserves a lot of credit for that accomplishment.”

Prairie Island Unit 2’s main electrical generator, which had reached its 40-year operational life, was replaced during the plant’s fall outage. The new generator – weighing approximately 500 tons – was manufactured by Mitsubishi Electric Company in Kobe, Japan. It includes a new digital Automatic Voltage Regulator and is expected to be more efficient.

The new generator step up transformer – which also reached the end of service life since its installation more than 40 years ago – was another major project at Prairie Island this fall. The equipment converts the 22,000 volts put out by the generator into the 345,000 volts needed by the electrical grid’s high-voltage transmission lines. The main step up transformer weighs 734,200 pounds. The transformer was replaced as part of the life cycle management and eliminates a unit reliability vulnerability for the station.

During its recent refueling outage, Prairie Island completed the final projects required in EA-12-049 Mitigation Strategies for Beyond Design Basis External Events (FLEX) and EA-12-051 Spent Fuel Pool Instrumentation (SFPI). The station implemented the NRC’s Orders Nov. 26. The overall project included:

· New FLEX Support Guide (FSG) procedures, a new 11,000 square foot Hardened FLEX Storage Building to house portable equipment

· Plant modifications for fluid and electrical connections

· Extensive training on the equipment and procedures

· Validation of all time sensitive actions to confirm they can be performed in the timeframe necessary

The most significant outcome of all the Fukushima improvements is that Prairie Island Nuclear Generating Plant can now maintain core cooling, preserve containment and ensure the fuel in the spent fuel pool remains covered in water for any external event that impacts its normal power source and normal access to the Mississippi River for cooling.

Prairie Island’s new Main Electric Generator – weighing over a million pounds – is lifted and installed by specially constructed equipment.