NEI recently updated its fact sheet on water consumption at nuclear plants. Below are some highlights (the picture to the right is the cooling tower at the Shearon Harris nuclear plant in North Carolina):Electric power generation is among the smallest users of water, accounting for about 3 percent of freshwater consumption in the United States, according to the U.S. Geological Survey (USGS). This is the same percentage used by industries and the same used to raise livestock. The largest consumption of water is for irrigation, at 80 percent, followed by residential use at 7 percent, the USGS said.
Residential consumption of freshwater is nearly double the consumption of freshwater for electric power generation. According to the latest USGS figures, the residential sector consumes more than 6.6 billion gallons of freshwater per day, compared with the power sector, which consumes 3.8 billion gallons per day.
A typical nuclear plant supplies power for 740,000 homes and consumes the equivalent of six to 16 gallons of water per day per household in a once-through cooling system. The same plant would consume the equivalent of 20 to 26 gallons of water per day per household if it used cooling tower systems. The average U.S. household of three people consumes about 300 gallons of water per day for indoor and outdoor uses, according to the USGS.
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There is nothing unique to nuclear power plants about the possibility of reducing electricity production to moderate water temperatures because of decreased water levels in a drought or a severe heat wave. This preserves safety margins established by the U.S. Nuclear Regulatory Commission for each plant.
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Each reactor design has requirements to decrease power levels if the cooling water source exceeds certain temperature or water-level requirements. The maximum allowed temperature for the heat removal capacity (ocean, river, lake, cooling tower) varies among reactors based on specifications defined in the license.
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Although the southeastern United States recently has suffered from drought conditions, nuclear plants were not affected significantly. In fact, nuclear plants in the region were critical to meeting electricity demand during a two-week heat wave in August 2007.
Comments
http://pubs.usgs.gov/circ/2004/circ1268/
It gives a value of 52% for freshwater withdrawals for thermoelectric power. The USGS value is clearly talking about what is going in prior to evaporation, but I am not sure what the 3% is in your factsheet.
You've pretty much figured it out. Our fact sheet is referring to consumption which is really another word for evaporation.
Here is a link to the 1995 USGS study where it talks in detail about consumption. If you go to the last page of the Summary and Totals (pdf), you can find a diagram on water use where you can find our 3% value. The 2000 study you linked to only discusses withdrawals.
Matthew B.