are discussed in the paragraphs that follow. For more detail on the environmental impacts of these and other processes, the reader is referred to Annex 8.D.

The primary impact of mining, in which natural uranium is extracted from the earth, and milling, in which natural uranium is chemically converted to a dry and purified uranium concentrate, is the production of slightly radioactive byproducts known as mill tailings, which are disposed of in “tailings piles.” Radon emissions from mill tailings were previously an issue of public concern in the United States. At present, uranium milled in the United States is subject to comprehensive regulation for the control of environmental impacts, including radon emissions, under the Uranium Mill Tailings Radiation Control Act of 1978. The majority of uranium is imported from nations such as Canada and Australia, which have regulations equivalent to those of the United States. However, 17 percent is imported from nations that may not have equivalent regulations, primarily Namibia and Kazakhstan (see; accessed July 2009).

In some locations, a process called in situ leach (ISL) mining has replaced hard-rock mining and milling of uranium. The use of ISL entails smaller amounts of mill tailings to be disposed of; however, there is potential for other environmental impacts, including groundwater contamination and increased water use.

An expanded deployment of nuclear power in the United States (particularly after 2020) may result in increased demand for uranium, with an associated increase in worldwide uranium mining and milling. If more mining is undertaken in the United States to meet increased domestic demand for uranium, domestic environmental impacts may rise.

Water Use

All thermal power plants use significant quantities of water during operation, primarily for cooling. Overall, the committee does not view water use to be a national barrier to an expansion of nuclear power plants in the United States. However, the water use and consumption of new plants may have significant local impacts, as would occur for any thermal power plant.

Nuclear power plants on average require more cooling water per kilowatt-hour of electricity produced than do fossil-fuel plants of comparable age, due to nuclear power plants’ lower average thermal efficiency. Most U.S. power plants use one of two types of cooling processes: once-through cooling or closed-cycle wet cooling. In some instances, these wet cooling systems can

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