Water Use and Nuclear Power Plants

May 2010

Key Facts

Comprehensive environmental management programs will yield optimal protection when used in choosing

electric generation facilities and cooling systems.

When considering water resources as part of this holistic approach, power generation accounts for 3.3

percent of freshwater consumption.

Among cooling technologies for coal, natural gas and nuclear power plants, “once-through” systems actually

consume only 1 percent of the water they withdraw. Wet cooling tower systems at these facilities, on

average, consume twice as much water as once-through systems.

Power plant cooling systems do not have an adverse impact on aquatic life, according to scientific studies.

Compared to other energy sources used for electricity production, nuclear power plants use moderate

amounts of water and minimal land per amount of electricity produced.

Holistic Environmental Management

Electricity production and the availability of water are interdependent. While electricity generation requires water

for cooling, usable water production requires substantial amounts of electricity for pumping and purification.

To manage this interdependence responsibly, a range of issues should be taken into account. Within the energy

sector, these issues include the potential environmental impacts of power plant cooling systems, the

environmental footprint of various energy sources, and their reliability and economics when generating electricity.

A holistic approach to environmental stewardship requires balancing the relationships among all aspects of the

environment and making responsible trade-offs appropriate to the unique characteristics of each ecosystem

where an electricity generation facility exists or will be developed.

This integrated approach will yield optimal results for all issues, including water use. Local ecosystem

considerations include water quantity and quality, aquatic life, wildlife, land use (habitat), and air quality. These

issues, in turn, impact the broader environmental issues of sustainable development, climate change mitigation

and drought alleviation.

All low-carbon energy sources—including nuclear energy and renewables—will be required for sustainable

development. These energy sources must be developed in an environmentally responsible manner, taking into

account environmental benefits and potential impacts, economics, and differing electricity generation attributes.

Water Use Definitions

Water use consists of two processes that can occur separately or in sequence: withdrawal and consumption.

Water is withdrawn when it is removed from a water body. Withdrawn water is not necessarily lost water, as it

may be returned to its original source in a manner that complies with environmental law and regulations. Water is

consumed when it either ceases to exist as a liquid through evaporation or is not fit to be returned directly to its

original source.

Water Consumption by Economic Sector

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According to the U.S. Geological Survey, electric generation accounts for 3.3 percent of freshwater consumption,

about the same percentage as the industrial sector (3.4 percent) and raising livestock (3.2 percent). The

residential sector consumes 6.7 percent of freshwater, while the commercial and mining sectors consume the

least, at 1.3 percent and 0.8 percent, respectively. The largest consumption of freshwater is for irrigation, at 81.3

percent.

To put residential and electric power water consumption in perspective, a typical 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, and 23 gallons 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.

The distinction between withdrawal and consumption is important when evaluating potential ecosystem impacts.

According to the U.S. Geological Survey, power plants withdrew the second largest amount of freshwater of all

economic sectors in 1995—131 billion gallons per day. But they returned 98 percent of that water back to its

natural sources.

By contrast, withdrawals for irrigation were 134 billion gallons per day, more than the electric power sector, and

only 20 percent of that water was returned, making irrigation by far the single largest consumer of water

resources. Residential withdrawals were 26 billion gallons per day, but only 74 percent was returned, resulting in

consumption about twice that of power plants.

Electric Power Plant Cooling Systems

Power plants heat water to steam, which turns a turbine to produce electricity. Cooling systems are required to

turn the steam back to water so the cycle can be continued.

Most power plants use one of two types of cooling water systems. Once-through cooling withdraws water from a

water body and circulates it within the plant to condense the steam from the turbine into water through heat

absorption. In a wet cooling tower system, circulating water from the plant moves through the tower and is cooled

by evaporation.

Water Consumption by Energy Source

For energy sources, water consumption is calculated in terms of the amount of water consumed to produce a

standard measure of electricity generated—a megawatt-hour (MWh).

Nuclear energy consumes 400 gallons/MWh with once-through cooling and 720 gallons/MWh with wet cooling

towers. Coal consumes less, ranging from about 300 gallons/MWh for plants with minimal pollution controls and

once-through cooling to 714 gallons/MWh for plants with advanced pollution control systems and wet cooling

towers. Natural gas-fueled power plants consume even less, at 100 gallons/MWh for once-through, 370

gallons/MWh for combined-cycle plants with cooling towers, and none for dry cooling.

Hydropower’s typical water consumption is the most significant at 4,500 gallons/MWh, due in large part to

evaporation from reservoirs. Renewable energy sources such as geothermal and solar thermal consume two to

four times more water than nuclear power plants.

Local Ecosystem Considerations

An examination of the specific environmental and economic issues involved in electricity generation will

demonstrate the value of the holistic environmental management approach for using various types of electricity

production options and cooling systems.

Water Quantity

Considering cooling technologies for coal, natural gas and nuclear power plants, once-through systems consume

1 percent of the water they withdraw. Wet cooling tower systems, on average, consume twice as much water as

once-through systems.

Water Quality

To ensure water quality, the U.S. Environmental Protection Agency or the states regulate discharge water

temperature and impurity concentrations from power plant cooling systems. The higher temperature of water

discharged in a once-through system is reduced by using cooling canals or after-bays before discharge to the

main water body.

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Aquatic Life (Impact Studies)

Energy companies take significant steps to reduce the number of fish trapped in or drawn into cooling water

systems. According to a typical study, once-through cooling systems typically impinge, or trap, 0.2 percent to 1.4

percent of fish on cooling water intake screens. These systems entrain, or draw through, between .01 percent

and 4 percent of the adult fish populations in the water body. Scientific studies demonstrate that these rates do

not have an adverse impact on aquatic life populations in the water body.

Aquatic Life (Mitigation Technologies)

To minimize the impact on aquatic life, power plant operators install and maintain proven fish protection

technologies at cooling water intake structures. The use of a particular technology depends on the species in the

habitat, the geographic location of the plant, the kind of water body, and the design and operating characteristics

of the plant.

Some of these measures include physical barriers that prevent fish from entering the intake structure, such as

stationary screens. These barriers are often equipped with flushing structures to free the fish if necessary and

passageways for fish to return fish to their habitat. Collecting systems, such as traveling screens, gather smaller

aquatic life and mature fish and transfer them to baskets for return transport. Diversion systems direct fish away

from the intake structure, and include angled screens or louver systems that alter flow direction and velocity.

Behavioral deterrents involving light or sound are also used.

Wildlife and Habitat

According to a study commissioned and supervised by the New York State Energy Research and Development

Authority, wind power and nuclear energy have the lowest potential life-cycle impact on wildlife of all energy

sources.

Land use is an indicator of the impairment or loss of habitat for wildlife and plant life, as well as potential impacts

on our communities. Nuclear power plants are the most eco-efficient of any energy source, producing more

electricity per amount of land required for operation.

For example, to generate the electricity equivalent of a 1,000-megawatt nuclear plant, a wind farm would have to

cover about 150,000 to 180,000 acres and a solar photovoltaic park 54,000 acres. Considering actual plants in

operation, the Peach Bottom nuclear plant in Pennsylvania generates twice as much electricity on 400 acres and

the Millstone nuclear plant in Connecticut twice as much on 220 acres. In other words, a nuclear power plant

requires about one-third of a percent of the land required by wind power to produce the same amount of

electricity.

Air Quality

Nuclear power plants produce no air emissions during operations. Several studies have demonstrated that the

life-cycle CO2 emissions of nuclear power plants are comparable to or lower than renewable energy sources.

Broader Environmental Issues

Along with these local considerations, broader environmental issues also are a critical part of the decisionmaking process that constitutes holistic environmental management.

Climate Change Mitigation

Critical for climate change mitigation, nuclear energy generates 72 percent of U.S. emission-free electricity. All

credible domestic and international carbon-reduction proposals call for the expansion of nuclear energy.

Climate Change Adaptation

Clean energy sources, by mitigating climate change, alleviate the water shortages that may be caused by climate

change. Nuclear power plants can contribute to climate change adaptation by providing reliable, emission-free

electricity for desalination and a low-carbon transportation sector.

Sustainable Development

According to the United Nations, sustainable development is simultaneous environmental preservation and

economic progress. Looking at the sustainability from an environmental viewpoint, power plants return 98 percent

of the water they withdraw. They represent half of residential consumption of U.S. freshwater, while irrigation

consumes by far the most freshwater.

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On the economic side of sustainable development, our standard of living depends upon the availability of usable

water and electricity. Fully 90 percent of U.S. electricity is generated by power plants. Conversely, 80 percent of

municipal water processing and distribution costs are for electricity.

Nuclear Energy in a Water-Constrained World

Despite moderate water use, nuclear power plants are a valuable option for water constrained ecosystems

because they can provide large-scale, economical electricity for desalination. The Palo Verde nuclear plant,

located in the Arizona desert, uses reclaimed municipal waste water from Phoenix for cooling. It produces more

electricity than any other U.S. power plant. Two proposed reactors at the Turkey Point site in Florida plan to use

municipal waste water for cooling systems.

Locating nuclear plants on the ocean provides ample water supply for cooling and desalination. For example,

Diablo Canyon and San Onofre nuclear power plants are located on the Pacific coast in water-strapped southern

California.

Industry Sponsoring Cooling System R&D

Extensive cooling system research and development work is being conducted by the Electric Power Research

Institute, often in partnership with the Department of Energy’s national laboratories, and by commercial

enterprises. For instance, for once-through cooling, technology advances are focused on minimizing the

impingement and entrainment of aquatic life. For cooling tower systems, the emphasis is on reducing water

consumption and the adverse effects on equipment when using recycled water for cooling.

Two other cooling systems are the focus of technology development. With dry cooling, circulating water from the

turbine is cooled by heat transfer to the ambient air. For large plants, dry cooling is three times as expensive to

build and 10 times as expensive to operate. It is more viable for smaller plants. R&D is focusing on improving the

air-cooled condenser to reduce cost.

Hybrid cooling uses cooling towers during those seasons of the year when ambient air temperatures are

relatively high, and dry cooling is used during those seasons when temperatures are relatively low. The goal of

R&D for hybrid cooling is to optimize the system’s operating performance. The proposed reactor at the North

Anna nuclear plant in Virginia will use hybrid cooling.

Regulatory Challenges

The Clean Water Act mandates using the best available cooling water system technology for minimizing adverse

environmental impacts. Phase I (new plant) and Phase II (existing plant) of section 316(b) of the regulations

establish national standards that focus only on aquatic life individual mortality at the intake structure. Moreover,

they are based on cooling tower performance, in effect forcing utilities away from once-through systems, which

consume half as much water.

In addition, state initiatives have the potential to compound the effect of Clean Water Act regulations to force

cooling tower retrofits. California, New York and New Jersey are considering such initiatives.

These regulations at the national level, and potentially at the state level, ignore scientific study demonstrating that

individual mortality at the intake structure does not affect population abundance in the water body, and that water

constraints from climate change may be a more significant challenge to aquatic life.

These regulations also make it difficult to take into account unique local ecosystem characteristics—the most

important factor in new power plant and cooling system development.

The most environmentally advantageous policy would be to allow site-specific choices from the full range of

cooling systems and impingement and entrainment mitigation technologies to reach an optimum environmental

solution for each ecosystem.

Over the past decade, DOE and industry have provided EPA with scientific evidence that does not support the

316(b) regulations, that cooling towers will require additional electricity for operation, and that retrofitting projects

will jeopardize grid reliability. In response to a U.S. Supreme Court decision in 2009, the EPA will issue revised

316(b) Phase II regulations governing existing power plants later this year. It is unclear whether the new

regulation will allow cost-benefit analysis and site-specific decisions on cooling systems—policies that have been

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in place for the past 30 years.

For a comprehensive, in-depth treatment of this topic, including references for the information provided above,

please see NEI’s study, Water Use, Electric Power, and Nuclear Energy: A Holistic Approach to Environmental

Stewardship. It is available at www.nei.org, in the Protecting the Environment area under “Water Use and

Environmental Stewardship.”

Nuclear Energy Institute

1776 I Street NW, Suite 400, Washington, D.C. 20006-3708 P: 202.739.8000 F: 202.785.4019 www.nei.org

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