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."

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