Waterford - With the 40-year trend of warming water temperatures in Long Island Sound showing no signs of abating, Millstone owner Dominion is preparing over the next two months to ask the Nuclear Regulatory Commission to allow it to adapt its nuclear power plants to the new normal.

Ken Holt, spokesman for Dominion, said an application will be submitted to the NRC by June 30 to allow it to draw in water from the Sound to cool plant safety systems that is up to 80 degrees, five degrees higher than its current permit allows. Last summer, Millstone 2 was forced to shut down for three weeks when the water in the Sound exceeded 75 degrees. It was the first nuclear plant shutdown in the United States to be caused by rising water temperatures, and it prompted the NRC to ask for a review of climate change impacts on plants nationwide.

The Millstone 3 plant, which draws water from a deeper, cooler part of the estuary, did not have to shut down. But the applications to increase the allowed intake water temperature are being prepared for both plants, Holt said. Temperature data collected by scientists at Millstone and the state Department of Energy and Environmental Protection shows average water temperature in the Sound rising .67 degrees per decade since 1976. Millstone 2 began operating in 1975, and Millstone 3 began producing power 1986. Unit 1 is shut down.

Using warmer water than the plants were originally designed for, Holt said, would require the plants to install more sensitive thermometers, but few other modifications would be required.

"When the equipment was installed, there was extra capacity, and now we will be using that extra capacity," he said.

Intake pipes at the power station draw in between 1 billion and 2 billion gallons of water from the Sound per day, depending on the season. During winter flounder spawning season in April and May, the plant is limited to 1 billion gallons per day. No additional intake water would be needed if the permitted temperature increased to 80 degrees, Holt said.

The engineering analysis required to prepare the application, he added, "was a very extensive process," requiring Dominion to hire outside consultants.

"It is a very expensive effort," he said.

However, shutting down the plant last August was also costly, he said.

"We had to buy replacement power to satisfy our contracts," he said. He declined to give the costs of either the shutdown or the engineering analysis.

Neil Sheehan, spokesman for the NRC, said it will take about a year for the agency to decide on the application. The public will be able to request a hearing, he added.

While Millstone has been the only U.S. plant to shut down due to water temperatures, other plants have made similar requests as water temperatures have approached their permitted maximum. Typically, however, these plants are located on rivers or lakes rather than marine waterways, said David Lochbaum, director of the nuclear safety project for the Union of Concerned Scientists. As long as a thorough analysis verifies that plant systems can handle the warmer temperatures, he said, the change can be made safely.

"As long as you do the homework," he said, "you're fine."

He added, however, that the water temperature issue points to the need for a wide-ranging examination of the effects of climate change on nuclear power plants.

"When the NRC licenses or relicenses plants, they continue to look backward" at weather trends, he said. "It would be better if the NRC would look forward somewhat, since the past is no longer limiting."

While the NRC governs the temperature of the intake water, the state Department of Energy and Environmental Protection oversees the volume and temperature of the water discharged from the plant. The discharge water is not allowed to exceed 105 degrees, but the actual temperature is usually several degrees lower, Holt said, and the analysis shows it would stay within the limit even at 80 degrees.

"But if we did approach (105 degrees), we would take steps to reduce power" so that the discharge water temperature would stay within the limit, Holt said.

DEEP spokesman Dennis Schain said the agency would review and comment on the NRC application once it's submitted. No change in the requirements for the discharge water are anticipated, he said.

"If the NRC allows Millstone to take in warmer water, the plant will still be required to meet these state requirements," he said.

j.benson@theday.com