SPOKANE, Wash. -

A large, double-walled tank of waste at the nation's most contaminated nuclear site is leaking into its outer shell, raising new concerns about the long-term storage of the radioactive brew and for the effects on the environment if the waste escapes.

The nation's largest collection of deadly wastes left behind from the production of nuclear weapons sits at south-central Washington's Hanford nuclear reservation.

Late last month, the U.S. Department of Energy, which oversees the site, revealed a slow leak in the oldest of 28 double-shell waste tanks, saying a small amount of waste was leaking into the space between the inner and outer walls.

The agency says no waste is believed to have leaked into the environment on the reservation near Richland.

The state Department of Ecology is working with federal officials to decide how to deal with the leak.