Hundreds of workers at the Hanford nuclear site have been forced to take cover after a tunnel collapsed at the giant nuclear finishing plant. But this is hardly the first headline to stem from the site, which is located just 200 miles from Seattle, Washington.

Developed in 1943 as a nuclear reactor and processing plant, Hanford was once home to the first large-scale plutonium production reactor in the world. Today, it is the most contaminated nuclear weapons plant in the US.

From 1944 to 1987, the site produced more than 67 metric tons of plutonium for the US defence programme. Reactors at Hanford produced plutonium used in the first nuclear bomb, as well as the bomb detonated over Nagasaki, Japan.

The site, which is about the size of Rhode Island, actually contains five processing plants. These plants processed 110,000 tons of fuel from nine nuclear reactors along the Columbia River. The plant was also used to produce more than 20 million pieces of uranium metal fuel for for those reactors.

All that production also created massive amounts of pollution around the site, located along the Columbia River. Liquid byproducts of plutonium production were also poured into trenches or underground storage tanks.

By the time plutonium production shut down in 1987, the site had produced an estimated 53 million gallons of radioactive waste. Today, the site has leaked more than 1 million gallons of radioactive material into the surrounding earth.

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In 1989, the Department of Energy, Environmental Protection Agency, and Washington State agreed to start what would become one of the biggest nuclear site cleanups in the United States. The project is reported to cost at least $110 billion, and will take more than 50 years.

More than 8,000 people work daily on cleaning up the site. More than 20 studies in the last 25 years have documented safety risks to workers, including toxin levels in the air "far exceeding occupational limits.” Washington Attorney General Bob Ferguson filed a lawsuit last year, alleging hundreds of workers have been exposed to toxins escaping from nuclear waste storage tanks. Lawyers for the Energy Department say there has been no evidence provided showing workers have been harmed by emissions.

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Experts are also concerned with the state of the site’s “double shell” tanks – 1-million-gallon tanks that hold most of the site’s radioactive waste. Some of the tanks are beginning to leak from their inner tanks – and some experts believe the waste has already breached the outer tank.

Even Energy Secretary Rick Perry, who once proposed eliminating the Department of Energy altogether, has acknowledged the severity of the situation at Hanford.