Story highlights Leak is in the range of 150 to 300 gallons per year

It poses no immediate risk to public health, says the state governor

Hanford site once played a major part in U.S. plutonium production

A tank storing radioactive waste at the Hanford Nuclear Reservation in southeast Washington is leaking liquids to the tune of 150 to 300 gallons per year, the governor said Friday.

"This is an extremely toxic substance, and we have to have a zero-tolerance policy for leaks of radioactive material into the ground and potentially groundwater of the state of Washington," Gov. Jay Inslee said.

He stressed that the leak poses no immediate public heath risk but said that fact should not be an excuse for complacence.

"At the same time that I am making clear that this is a long-term, very significant concern of the state of Washington; it is not a short-term concern," he said.

"We have been assured by people that I do trust that this poses no immediate threat to ... health. It would be quite some time before these leaks could breach groundwater or the Columbia River."

The governor said he would be traveling next week to Washington to meet with outgoing Energy Secretary Steven Chu, who called Inslee on Friday morning with news of a leaking single-shell tank.

The tank was built in the 1940s and holds roughly 447,000 gallons of sludge, according to the governor's office. The Hanford site houses 177 tanks, 149 of which are single-shell tanks.

The leaking tank is believed to be the first to lose liquids since 2005.

The Hanford site is a 586-square-mile area that once played a major part in U.S. plutonium production. The site is now home to one of the largest nuclear cleanup efforts in the world.