Prairie Island Nuclear Generating Plant

Operator: Xcel Energy/Northern States Power Company - Minnesota
Location: 40 miles southeast of Minneapolis-St. Paul, Minn.
Prairie Island Nuclear Generating Plant
1717 Wakonade Drive East
Welch, MN 55089-9642
Operating License Unit 1: Issued – April 05, 1974, Expires – August 09, 2033
Operating License Unit 2: Issued – October 29, 1974, Expires – October 29, 2034
Reactor Type: Pressurized Water Reactor (PWR)
Electrical Output Unit 1: 551 Megawatts Electrical (MWe)
Electrical Output Unit 2: 545 Megawatts Electrical (MWe)
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. Under
40-year operating licenses granted by the federal Nuclear Regulatory
Commission, Unit 1 began commercial operation in December 1972 and
Unit 2 began commercial operation a year later. 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 until 2033 and 2034.
Each Prairie Island reactor can generate about 550 megawatts of
electricity, for a total plant output of about 1,100 megawatts. That’s
enough to power about 1 million homes.
• In a pressurized water reactor, water is highly pressurized so it does
not boil as it flows through the reactor and picks up heat released by
the fission of uranium atoms. 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
• 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 one-third of the fuel assemblies
are replaced.

Prairie Island is among Xcel Energy’s lowest-cost sources of generation
on a per megawatt-hour basis. It is a carbon-free power source and 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 fouryear
average capacity factor of 88 percent from 2010 – 2013. (Capacity
factor is the ratio of a power plant’s actual output over a period of time
and its output had it operated a full capacity the entire time.)
• In 2013, Prairie Island generated nearly 8 million megawatt-hours
of electricity.
Prairie Island constructed a dry cask storage facility in 1995. The
facility, which is needed to support current plant operations as well
as operations during the 20-year license extension period, is licensed
by the federal Nuclear Regulatory Commission. The Minnesota Public
Utilities Commission also has approved the use of up to 64 casks and
other equipment needed for dry storage.
• Thirty-five casks now are filled and in the dry storage facility.
Others will be loaded as needed.
In Fall 2013, Prairie Island replaced two steam generators in Unit 2 during
the site’s planned refueling outage. These generators had completed
nearly 40 years of operation—an industry-first occurrence. A high
standard of engineering, maintenance of chemistry, effective monitoring
and preventive maintenance allowed for the event-free operation of
these steam generators for the extent of the Unit’s original license.
Prairie Island’s Unit 1 steam generators were replaced in 2004.
• The $280 million project demonstrates Xcel Energy’s commitment
to investing in significant capital and human resources to ensure
continued operations at Prairie Island and exemplifies the company’s
commitment to providing safe, reliable, emission-free energy at a
reasonable cost to customers.
• The steam generator is a key component of a pressurized-water
reactor type nuclear power plant. Steam generators are heat exchangers
used to convert water into steam from heat produced in the nuclear
reactor core.
• AREVA was contracted to fabricate and manufacture the replacement
steam generators. Manufactured in Chalon St. Marcel, France, the
generators are approximately 70 feet tall and weigh 330 tons each.
The generators were transported from France by ocean vessel to
New Orleans, where they were off-loaded onto a barge for their
journey up the Mississippi River to the station.
• With the new steam generators in place, arrangements were made
to remove the old steam generator components from the site. The
upper halves of the two generators were shipped in November 2013
to facilities in Memphis, Tenn., for recycling. The lower halves were
shipped in December 2013 to a licensed disposal facility in Clive, Utah.
• The new steam generators were declared “in-service” on Dec. 16,
2013. Unit 2 was brought back on-line on Dec. 31, 2013, marking the
completion of the refueling outage and the steam generator project.
To request a speaker on nuclear power issues, go to and click on Speakers Bureau in the Company/Community section.
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