From the article:” The Tennessee Valley Authority shut down one of three units at the Browns Ferry nuclear plant Thursday because water drawn from a river to cool the reactor was too hot, a spokesman said. The nation’s largest public utility shut down Unit 2 about 5:42 p.m. CDT because water drawn from the Tennessee River was exceeding a 90-degree average over 24 hours, amid a blistering heat wave across the Southeast.”
To be clear, there was no safety threat whatsoever. The plant managers simply made the decision to shutdown one of their three reactors because the river water was too hot to properly cool the entire set. Still, this is the first time I can remember hearing about a nuclear plant that had to shut down because it was too hot outside.