How hot was it?

The Braidwood Nuclear Power Plant in Bracewell, Illinois

It was so hot that a twin-unit nuclear plant in northeastern Illinois had to get special permission to continue operating after the temperature of the water in its cooling pond rose to 102 degrees.

It was the second such request from the plant, Braidwood, which opened 26 years ago.  When it was new, the plant had permission to run as long as the temperature of its cooling water pond, a 2,500-acre lake in a former strip mine, remained below 98 degrees; in 2000 it got permission to raise the limit to 100 degrees.

The problem, said Craig Nesbit, a spokesman for Exelon, which owns the plant, is not only the hot days, but the hot nights. In normal weather, the water in the lake heats up during the day but cools down at night; lately, nighttime temperatures have been in the 90s, so the water does not cool.

Asked whether he viewed Braidwood's difficulties as a byproduct of global warming, Mr. Nesbit said: "I'm not a climatologist. But clearly the calculations when the plant was first operated in 1986 are not what is sufficient today.

Braidwood is not alone in facing a difficult summer; a spokeswoman for the Midwest Independent System Operator, which operates the regional grid, said that another plant had shut down because its water intake pipes were now above the water level of the body from which it draws its cooling water. Another is "partially curtailed."

Braidwood got permission from the Nuclear Regulatory Commission to continue operating last week when its cooling water hit 102 degrees even though the plant is supposed to shut within 6 hours if the lake's temperature exceeds 100.

Mr. Nesbit said that Exelon's Quad Cities plant has sometimes had to shut down when the temperature of the water it discharges is too high to go back into the Mississippi. The reason for the elevated temperature is that the water it takes in is warm, too.

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