Record heat and drought conditions across the United States this summer have plagued power plants that require cool water to produce electricity.

From Connecticut to California, high water temperatures and diminished access to water caused by drought have forced a number of power plants to ramp down production or acquire waivers to operate with cooling water above regulated temperatures. At least one plant has suspended operations.

Many nuclear plants have struggled this summer with cooling water sources that approached being too warm to generate power at full levels, said David McIntyre, spokesman for the U.S. Nuclear Regulatory Commission (NRC). "If the water gets too warm, you have to dial back production," McIntyre said. "That's for reactor safety, and also to regulate the temperature of discharge water, which affects aquatic life."

Too Hot for Power

On Sunday, one of two reactors at Millstone Power Station near New London, Connecticut, was shut down when temperatures in Long Island Sound, the source of the facility's cooling water, reached their highest sustained levels since the facility began monitoring in 1971. There was no indication when the reactor at Connecticut's only nuclear plant would come back online. Ken Holt, spokesman for the plant operator Dominion, said Millstone's second reactor would also shut down if water temperatures deeper in the sound, where it draws its water, continue to rise.

The outage had no immediate impact on power delivery, as New England was expected to have a buffer of 26 percent more electricity supply than peak demand this summer, according to North America's annual seasonal electricity reliability outlook. But the Connecticut shutdown is a dramatic example of how U.S. power plant operators have had to struggle to keep power generation online through record-breaking weather, including the hottest July on record since 1895 and the most wide-reaching drought since 1956.

In July, Braidwood Generating Station, a nuclear power plant 60 miles southwest of Chicago in Illinois, received permission from NRC to continue operating after temperatures in its cooling pond rose beyond the plant's 100-degree permit limit, according to Krista Lopykinski, spokeswoman for Exelon, which operates the plant. Braidwood's 2,600-acre (1,069-hectare) cooling pond is an old strip mine site that is connected by pipes to the Kankakee River.

During the same heat spell, a second Illinois power plant was forced to request a variance from the U.S. Environmental Protection Agency to pump additional water into its cooling pond, which was evaporating and in danger of heating to levels beyond those allowed by its permit, according to Adam Keech, director of dispatch at PJM, the regional grid operator that coordinates movement of electricity in 13 states and the District of Columbia.

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Keech said drought is potentially a bigger problem for the electrical power industry than high heat, because nuclear and coal power plants rely on water to cool key parts of their systems. "If you don't have a way to refill the cooling pond, then you have to sit there and wait for rain. In summers like this one, you don't know how long it's going to be. Waiting for Mother Nature to fill the reservoir back up, that's not a position you want to be in."

Plants "On the Edge"

But heat and drought work together to overtax the electrical grid, said Michael Webber, associate director of the Center for International Energy and Environmental Policy at the University of Texas at Austin. Water is far more important for energy production than most people understand, Webber said, adding that families use more water to power their homes than they use from their tap.

"In summer you often get a double whammy," Webber said. "People want their air-conditioning and drought gets worse. You have more demand for electricity and less water available to produce it. That is what we are seeing in the Midwest right now, power plants on the edge."

During the 2003 heat wave that killed more than 10,000 people in Europe, Webber said, nuclear power plants were forced to dial back because rivers that supplied their cooling water became too warm. This summer, U.S. power plants have managed through the hot weather and drought, but Webber said the combination is a recipe for future blackouts.

Brandon Wright, a spokesman for the Midwest Independent System Operator, which operates the regional grid, said two power plants in its system have been affected by heat and drought this summer. One of the plants shut down after its cooling water source fell below the plant's intake pipe, Wright said. The second plant ramped back generation when its cooling pond became too hot. Wright declined to name the plants.

The drought has also affected hydroelectric power generation. California hydroelectric power plants were expected to produce 1,137 fewer megawatts this summer than in the past due to drought over the winter, said Stephanie McCorkle, spokeswoman for California Independent System Operator, responsible for operation of most of California's power delivery. Snowpack in the mountains of the Sierra Nevada, which provides water for power generation, was down as much as 50 percent in some areas in spring, McCorkle said.

"That is how we store electricity—in the snowpack," McCorkle said, adding that California relies on hydroelectric power for 16 percent of its peak summer resources and is projected to have a warmer-than-usual fall. "There are many factors that affect grid conditions, but I would say it's of concern," she said.

Industry spokespeople say consumers so far have not been affected by the slowdowns, and that the amount of power lost during the summer months of peak demand has been minimal. Overall, the U.S. nuclear industry's availability has been running above 90 percent, according to Steven Kerekes, spokesman for the Nuclear Energy Institute, an industry trade association. "We are still running at very high levels and powering a whole lot of air conditioners around the country," Kerekes said.

Although the summer months are drawing to a close, and unseasonably warm temperatures have fallen in many parts of the country—including the Midwest—the electric power industry continues to face drought conditions in many areas. Brian Fuchs, a climatologist at the National Drought Mitigation Center at the University of Nebraska, said drought conditions continue to expand and intensify in parts of Missouri, Arkansas, Oklahoma, Kansas, Nebraska, and Illinois. "The drought is heading into the fall and we are not seeing any widespread improvement at all," Fuchs said.