High water temperatures in the Tennessee River have forced the Tennessee Valley Authority to shut down the Unit 2 reactor at Browns Ferry Nuclear Plant in Athens.

TVA spokesperson Terry Johnson said Thursday night the utility had to shut down one of the three reactors at the plant about 5:42 a.m. Thursday when the water temperature in the river went over the limit.

“When the water temperature remains at an average of 90 degrees or higher over a 24-hour period, we have to take steps to try and reduce that temperature,” Johnson said. “We had reduced power output from all three units by 15 percent earlier, but that did not bring the temperature down enough.”

The massive cooling towers at the plant usually are sufficient to control the temperature of water released from the plant, Johnson. Due to the historic heat wave currently enveloping much of the Tennessee Valley, however, it now may be necessary to bring cooler water down from tributaries in East Tennessee, Johnson said.

TVA cannot determine when the Unit 2 reactor may go back on line, Johnson said, “it just depends on when we can bring the water temperature down to an acceptable level.”

Units 1 and 3 currently are operating at about 75 percent of capacity, he said, but TVA expects to be able to meet power demand until the plant can return to full capacity. Meanwhile, Johnson said, TVA crews will take advantage of the down time to perform some routine maintenance on Unit 2.