Since 1977, more than 6,500-MW of nuclear uprates and been approved and many implemented in the U.S.—equivalent to the construction of six new nuclear power plants, the Energy Information Administration (EIA) said in an update on Wednesday.

The 104 commercial nuclear plants in the U.S. in 2011 provided nearly 20% of the nation’s electricity, or about 786 billion kWh. The Nuclear Regulatory Commission has to date approved 144 uprates, which generally involves physically modifying a nuclear plant to increase its generating capacity.

The EIA notes that there are three types of uprates. The NRC has approved 55 Measurement uncertainty recapture (MUR) uprates (829 MW), generally low-cost uprates that  result in an increase in electrical output of less than 2% and involve implementing enhanced methodologies for calculating reactor power and/or replacing old analog instrument sensors and control systems with modern sensors and digital control systems.. The first MUR uprate was approved for Comanche Peak Unit 2 (near Fort Worth, Texas) in 1999. The smallest MUR uprate, also for Comanche Peak, totaled 4 MWe in 2001.

The NRC has also approved 65 stretch uprates, totaling 2,832 MWe. These increase electrical output by 3% to 7% and generally do not involve major plant modifications. Older components may be replaced with newer designs and modern materials. These are typically moderate-cost uprates. The first stretch uprates were approved for Calvert Cliff Units 1 and 2 (in Lusby, Maryland) in September 1977.

The regulatory body has also approved 26 extended uprates, totaling about 2,883 MWe. These increase electrical output by more than 7% and can be as large as 20%. Extended uprates generally involve significant plant modifications and may take years to fully implement. The first extended uprate was approved for Monticello (near Minneapolis, Minnesota) in March 1998. The largest extended uprate of 193 MWe was approved for the Clinton Unit 1 (near Bloomington, Ill.) in 2001.

According to the EIA, all but six of the 104 U.S. reactors have applied for an uprate, and only one reactor, Vermont Yankee (near Brattleboro, Vermont), applied and was approved for a full 20% extended uprate. Susquehanna Units 1 and 2 (near Berwick, Pennsylvania) and Edwin I. Hatch Units 1 and 2 (near Vidalia, Georgia) are the only reactors to have received NRC approval for all three types of uprates.

Currently, the NRC is reviewing applications for seven extended and nine measurement uncertainty recapture (MUR) uprates. If approved, these uprates would add about 1,140 MWe of nuclear capacity, in addition to the approximately 6,500 MWe already approved by the NRC. The total 7,640 MWe is roughly the equivalent of seven reactors the size of each of the Vogtle Units 3 and 4 reactors, which just received their combined construction and operation licenses in February 2012.

Source: EIA

—Edited by Sonal Patel, Senior Writer (@POWERmagazine)