Electricity generation and the production of usable water are interdependent. Water withdrawn from and returned to rivers and lakes is used to cool the equipment at thermoelectric power plants of many types when they are generating electricity. In turn, a substantial amount of electricity is required for pumping and purifying water for use at homes, hospitals, business, and industry.
Water use is one of several interrelated environmental considerations that need to be analyzed together when considering electricity generation and cooling systems. These include water quantity and quality, aquatic life, wildlife, plant life, land use (habitat), and air quality and emissions. Broader considerations include sustainable development, climate change mitigation and adaptation, and electricity supply and reliability.
For instance, because nuclear energy does not emit green- house gases during operations, it can mitigate climate change and, in turn, the water constraints that climate change causes in various regions of the country. Also, nuclear energy requires a fraction of the land necessary to produce the same amount of electricity when compared to such renewables as wind and solar energy, thus preserving habitat.
Sustainable development is also an important consideration, as both water supply and reliable, affordable electricity are essential for economic progress. Nuclear energy has the lowest operating cost for electricity generation among conventional energy sources, such as natural gas and coal, and is competitive with other clean energy sources.
Power Sector Uses Just Three Percent of Water
Water use consists of two distinct processes: withdrawal and consumption. According to the U.S. Geological Survey, thermoelectric power generation is among the smallest consumptive uses of freshwater by any economic sector, at 3.3 percent of total U.S. consumption—about one-half of residential consumption, at 6.7 percent. Thermoelectric power plants withdraw more water than any other economic sector, but they return 98 percent of the water they withdraw back to its natural sources. Thermoelectric power plants—fueled by nuclear energy, natural gas, oil, or coal—generate 90 percent of the electricity in the United States.
To put residential and thermoelectric power water consumption in perspective, a typical U.S. nuclear power plant supplies 740,000 homes with all of the electricity they use while consuming 13 gallons of water per day per household in a once-through cooling system, or 23 gallons of water per day per household in a wet cooling tower system. By comparison, the average U.S. household of three people consumes about 94 gallons of water per day for indoor and outdoor residential uses.
A once-through cooling system returns 99 percent of the water withdrawn back to the water body, at a somewhat higher temperature, as allowed by the plant’s water permit. Wet cooling towers withdraw less water than a once-through system, and discharge water at a temperature only slightly above, or at, that of the water body. But cooling towers consume 70 percent of the water they withdraw. In effect, cooling towers consume twice as much water as a once-through system. However, though cooling towers consume more water than once-through systems, cooling towers can consume as little as one to two percent of the annual flow of the rivers where they are located.
Once-through cooling systems may require plant operators to reduce electricity production to a small degree to observe the discharge water temperature limit during very hot days, while cooling towers do not have to reduce power for this reason. Most proposed new nuclear plants will employ cooling towers, where discharge water temperature will not be a consideration in electricity production.
Responsible Environmental Stewardship
Nuclear plants strive to be responsible stewards of the environment. When they are built, cooling system intake structures are designed to minimize aquatic life mortality, which is usually only one to two percent of the fish population in the water body. As a result, scientific studies demonstrate that these cooling systems do not have any negative impact on the abundance of fish in the water body over time.
State environmental agencies confer with power plant operators to determine the best technology to install at the cooling water intake structure to reduce the impact on aquatic life before an environmental protection license is granted. These deliberations take into account the unique fish populations and ecology at that specific site.
Discharge water temperature limits are also established using scientific research, and compliance is ensured through data taken periodically at the water body. In order to obtain permission to discharge water at a temperature higher than the statewide limit, the plant operator must present to the state environmental agency scientific evidence that the higher temperature will have no adverse impact on aquatic populations or wildlife at the site.
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