Prairie Island Nuclear Generating Plant

Location: Red Wing, Minn.

Plant Description: Prairie Island’s two pressurized water reactors generate about 20 percent of the electricity used by Xcel Energy’s customers in the Upper Midwest. The plant is located on a 520-acre site about 40 miles southeast of Minneapolis-St. Paul and about five miles north of Red Wing, Minn. Nearly 800 people are employed full-time at the plant. On June 27, 2011, the NRC renewed for 20 years the plant’s original operating licenses, authorizing the Prairie Island units to continue generating electricity to 2033 and 2034. 

Power Production Capability: Each Prairie Island reactor can generate about 550 megawatts of electricity, for total plant output of about 1,100 megawatts. That’s enough to power about 1 million homes. The Minnesota Public Utilities Commission approved Xcel Energy’s request to increase electricity generating capacity at Prairie Island through an extended power uprate. If approved by the Nuclear Regulatory Commission, the project will increase the plant’s generating capacity by 164 megawatts. Xcel Energy plans to seek NRC approval after the NRC acts on the company’s license renewal application. If approved, it is expected the power uprate project will be completed by 2015.

Fuel Source:  In nuclear power plants, the heat that turns water into steam to turn turbine generators to produce electricity is created by a chain reaction inside a reactor. The reactor uses uranium rods as fuel, and the heat is generated by nuclear fission: neutrons collide with the nucleus of the uranium atoms, which split and release energy in the form of heat. Prairie Island has two pressurized water reactors. In such reactors, water is highly pressurized so it does not boil as it flows through the reactor and picks up heat. From the reactor, the water in the primary system flows through a steam generator where heat is transferred to water in the secondary system, boiling it to steam. The water in the primary system goes back to the reactor and the steam produced in the secondary system is directed to the turbine-generator to produce electricity. Each reactor core holds 121 fuel assemblies. Each assembly is about 13 feet long and is a square array (about 7.75 inches by 7.75 inches in cross-section) of individual fuel rods each about the diameter of a finger. Each unit is shut down for refueling and maintenance about once every 18 months, and approximately 40 percent of the fuel assemblies are replaced. When removed from the reactor, used fuel is stored in a pool inside the plant until it has cooled enough to be safely stored in steel containers called casks and moved to reinforced concrete pads in an on-site dry storage facility.

The Unit 1 reactor began operating in December 1973 and the Unit 2 reactor in December 1974.

Prairie Island is among Xcel Energy’s lowest-cost sources of generation on a per megawatt-hour basis, and it does not produce any greenhouse gas emissions. The plant runs essentially 24 hours a day, seven days per week, except during refueling outages, which occur approximately every 18 months and last about four to six weeks. The plant is very reliable with a five-year average capacity factor of 86.9 percent from 2005-2009. (Capacity factor is the ratio of a power plant’s actual output over a period of time and its output if it had operated at full capacity the entire time.) In 2007, Prairie Island generated nearly 9 million megawatt-hours of electricity, eclipsing its prior record set in 2003. For 2007, the capacity factor was 92.6 percent.

The Prairie Island and Monticello nuclear generating plants help Xcel Energy avoid producing hundreds of millions of tons of greenhouse gases or emissions, compared to fossil-fueled base-load power plants.

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