This boiling water reactor plant is located on a 215-acre site 40 miles northwest of the Twin Cities. The plant generates approximately 10 percent of the electricity used by Xcel Energy’s customers in the Upper Midwest.
The Monticello facility is among Xcel Energy’s lowest-cost sources of electric generation on a per-megawatt basis and produces virtually no greenhouse gas emissions. As a base load ‘always-on’ plant, it runs essentially 24 hours a day, 7 days a week, except during refueling outages, which occur about every two years.
In a boiling water reactor, the fissioning of uranium atoms in the reactor core generates heat, which boils water to produce steam in the reactor vessel. After the steam is directed to turbine generators to produce electricity, it is cooled in a condenser and returned to the reactor vessel to be boiled again.
The plant’s reactor core holds 484 fuel assemblies. Each assembly is about 14 feet long and is a square array of individual fuel rods about the diameter of a finger. About every 22 months, the plant is shut down and one-third of the used fuel assemblies are removed from the core and replaced with new ones.
The Prairie Island and Monticello nuclear generating plants help Xcel Energy avoid producing hundreds of millions of tons of greenhouse gases or emissions. The plants avoid 13 million tons of carbon dioxide annually compared to fossil fuel plants, the equivalent of removing 2 million cars from the road each year.
The plant received a 40-year operating license from the federal Nuclear Regulatory Commission in 1970, and it began commercial operation in 1971. In 2006, the NRC renewed the Monticello plant’s license for 20 years, which will allow operations until 2030.
We recently completed a project to replace components, re-license the plant for an additional 20 years, and increase its generating capacity from 600 MW to 671 MW – enough energy to power 500,000 homes.
The Minnesota Public Utilities Commission approved the project in 2009, and it was completed over a series of refueling outages.
Major equipment was replaced in 2009, 2011 and 2013, virtually rebuilding the plant to prepare for the re-license period through 2030 and the increased capacity. The final pieces of equipment were replaced in the 2013 outage in which more than 3,000 workers were on site to complete the work.
Life cycle management upgrades included a new main transformer and generator rewind – both original equipment when the plant was commissioned for operation in 1971, a 40-year run.
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