State Nuclear Profiles, 2010 Edition
"Capacity and generation of electricity from nuclear sources in the United States:

There are 104 nuclear reactors operating at 65 plants around the nation.
Nuclear capacity (100 GW) is 10 percent of the total U.S. generating capacity.
In comparison, nuclear generation (806 TWh) is almost 20 percent of the total U.S. generation.
The reason: nuclear units operate more often and at higher levels than plants using other energy sources.
The capacity factor for nuclear--over 91 percent--is the highest of any energy source. The energy source with the second highest capacity factor is coal which is 74 percent.
Nuclear capacity tends to increase slightly each year, about 0.2% to 0.4%, despite the fact that no new units have been commissioned in over a decade. These increases are due to uprates of the existing plants..."