OAK RIDGE, Tenn. — Update (10:30 a.m.):  Hydrogen fluoride, a potentially deadly chemical, was accidentally released in a small enclosure at the Y-12 National Security Complex in Oak Ridge and required an emergency response Thursday morning.

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Two sensors went off shortly before 8 a.m. indicating the chemical had been released in an area about the size of a walk-in closet within a large room at 9212, a nuclear processing plant that handles uranium, officials said.