SPOKANE, Wash. (AP) — An arm of the U.S. Centers for Disease Control will conduct an evaluation related to the exposure of workers on the Hanford Nuclear Reservation to chemical vapors.

The National Institute for Occupational Safety and Health is expected to focus on four areas: medical, exposure assessment, safety and health program management and exposure control.

Hanford for decades made plutonium for nuclear weapons. Much of the waste from that work is stored in 177 giant underground tanks, which are the focus of cleanup efforts at the site near Richland. Clean up is expected to take decades and cost billions of dollars.

More than 50 workers in recent months have received medical evaluations for possible exposure to chemical vapors, after reporting suspicious odors. Most were cleared to return to work.

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