Prairie Island Nuclear Generating Plant

Prairie Island Nuclear Generating Plant

The Prairie Island Nuclear Generating Plant is a two-unit pressurized water reactor (PWR) of Westinghouse design. The plant is located on the Mississippi River about 40 miles southeast of the Twin Cities and about 5 miles north of Red Wing, Minn. The Unit 1 reactor began operating in December 1973, and the Unit 2 reactor in December 1974. About 600 people are employed full time at Prairie Island, which is owned by Minneapolis-based Xcel Energy.

General Background Information

• The Prairie Island plant is located on land acquired by Xcel Energy’s predecessor, Northern States Power Co. (NSP). The site includes former government land either used by the Army Corps of Engineers or under lease to private parties. The site occupies about 520 acres.
• Each reactor unit has a capacity of about 550 megawatts (Mw), for a total plant output of about 1,100 Mw. That’s enough electricity to power about 1 million homes.
• In a PWR, “primary” water is pressurized so that it does not boil as it flows through the reactor and picks up heat released by the splitting of uranium atoms (nuclear fission). From the reactor, the primary water goes to a steam generator where the heat is absorbed by “secondary” water and is boiled to steam. The primary water then returns to the reactor, and the steam is directed to a turbine-generator to produce electricity.
• Each reactor core holds 121 fuel assemblies. Each assembly is about 13 feet long and includes bundles of individual fuel rods—each about the diameter of a finger.
• Every 18 months or so, the plant is shut down for refueling. During a refueling outage, about one-third of the fuel assemblies are removed from the core and replaced with the new ones.

Used Fuel Storage

• When first removed from the reactor, the used (or spent) fuel is stored in a pool inside the plant. Once used fuel has cooled sufficiently, it is transferred to dry storage containers on site—in an Independent Spent Fuel Storage Installation (ISFSI). There it is temporarily stored until the federal government removes it to be reprocessed or stored at a government facility.
• As of summer 2007, Prairie Island’s ISFSI housed 23 dry-storage containers, which hold a total of 920 spent fuel assemblies.

Plant Operational Facts

• U.S. Nuclear Regulatory Commission (NRC) ratings for the Prairie Island plant are at the NRC’s highest ranking (green) for all indicators monitored by the NRC.
• Prairie Island set a generation record in 2003 by producing 8.8 million megawatt hours of electricity, surpassing the prior record in 2000. Prairie Island also set a record in 2003 for longest operational run—a 559-day run that ended in September that year with the Unit 2 refueling outage.

Plant Life

• NRC licenses for Prairie Island’s two units expire in 2013 and 2014 respectively. In fall 2004, the Xcel Energy Board of Directors authorized pursuing license renewal for up to 20 years for both the Monticello and Prairie Island plants. (The NRC renewed Monticello’s operating license in late 2006, allowing that plant to operate for an additional 20 years to 2030.)  Xcel Energy currently plans to submit the application to renew Prairie Islands operating licenses in early 2008.
• Prairie Island’s Unit 2 steam generators will most likely not need replacement before the end of the current license but will need replacement for extended plant operation.
• Unit 1 steam generators were replaced in the fall of 2004.  Reactor heads also have been replaced on both Unit 1 and Unit 2.