The Nuclear Regulatory Commission defines two emergency planning zones around nuclear power plants: a plume exposure pathway zone with a radius of, concerned primarily with exposure to, and inhalation of, airborne radioactive contamination, and an ingestion pathway zone of about, concerned primarily with ingestion of food and liquid contaminated by radioactivity. According to the 2010 U.S. Census, the population was 62,976 within of Monticello, an increase of 36.5 percent in a decade; and 2,977,934 within, an increase of 8.6 percent. Cities within 50 miles include the Twin Cities of Minneapolis and St. Paul. To the delight of local residents and tourists, the Monticello section of the Mississippi River remains unfrozen during winter and attracts hundreds of trumpeter swans, largely due to warm water discharged by the nuclear plant.
Incidents and updates
Roughly 1,300 gallons of radioactive water which accidentally leaked from the plant into the Mississippi River in an incident on 5 May 1982, was determined to be "no threat" to the public. In January 2007 a 13-ton control box fell eight to twelve inches and caused an unexpected shutdown. This control box was located in the condenser room of the turbine building and contained valves which controlled steam pressure. Emergency response teams at the station deemed that the event was likely caused by inadequate welds at the time of installation and fatigue due to vibrations over the life of the plant. Construction of the on-site independent spent fuel storage installation pad began in June 2007. The target date for the completion of the pads is December 2007 with insertion of the first ten dry storage containers into horizontal storage modules in mid-2008. Initially, 12 HSMs will be placed on the storage pad. Each HSM—a thick, reinforced, pre-cast concrete structure about the size of a single car garage—has the capacity to hold 61 fuel bundles. On September 11, 2008, a cable fault tripped the transformer which supplied power to the site. This resulted in a loss of off-site power and the plant automatically shut down. On September 18, 2008, an employee for a rental equipment company was electrocuted by one phase of the 115-kV power line outside of the plant due to a lack of situational awareness. The individual was raising a bucket lift without watching overhead and contacted one phase of the 115-kV line. The plant was offline at the time due to the forced outage described above. In February 2011, the site's plant officials determined that four control rod blades could be affected by a potentially substantial safety hazard. Vice PresidentTim O'Connor indicated that the blades would be replaced in March. Monticello has struggled with safety culture issues of significant concern, leading to a yellow finding by the NRC based on Monticello being unable to mitigate a maximum probable flood which, if it occurred, would have likely led to core damage and significant risk to the health and safety of the public. The NRC has cleared Monticello of the concerns to flooding. In 2006, Xcel Energy proposed a series of upgrades to the plant in order to increase its output and extend its life for an additional 20 years. In December 2013, the Nuclear Regulatory Commission approved the license amendment allowing the unit to increase output from 600 MWe to 671 MWe However, final project implementation costs significantly outstripped initial estimates by more than $400 million. In 2015, the Minnesota Public Utilities Commission denied full cost recovery and determined that, while Xcel Energy could include the additional cost in customer rates, it could not earn a return on those costs. Xcel Energy would record a greater than $100 million loss in 1Q 2015 as a result and recouped $27 million less than expected from the project. In March 2013, the plant was shut down for a routine refueling. During this time, workers replaced several original plant components. This increased the plant's electrical output from the original 600 MWe to 671 MWe. In early August, the plant was brought back online with the new equipment. Refueling outages as such increase the population of the plant's workforce by the thousands.
Seismic risk
The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at Monticello was 1 in 52,632, according to an NRC study published in August 2010.
