U.S. Department Of Energy

The disposal facility for mixed and low-level radioactive waste at the Hanford Nuclear Reservation in Washington state is shown in an aerial image.

OLYMPIA, Wash. -- A tank that holds radioactive liquids is leaking at the nation's most contaminated nuclear site, Wash. Gov. Jay Inslee said Friday, raising concerns about the integrity of other storage facilities at the Hanford Nuclear Reservation.

The U.S. Department of Energy said liquid levels are decreasing in one of 177 underground tanks at the nuclear reservation. Monitoring wells near the tank have not detected higher radiation levels, the agency said. Inslee said the leak could be in the range of 150 gallons to 300 gallons over the course of a year.

"I am alarmed about this on many levels," Inslee said at a Friday afternoon news conference. "This raises concerns, not only about the existing leak ... but also concerning the integrity of the other single shell tanks of this age."

The tanks hold millions of gallons of a highly radioactive stew left from decades of plutonium production for nuclear weapons.

Inslee said the state was told such problems had been dealt with years ago and were under control.

Energy Secretary Steven Chu said the federal government must not waiver in its commitment to clean up the highly contaminated site, Inslee told reporters.

The tank in question contains about 447,000 gallons of sludge, a mixture of solids and liquids with a mud-like consistency. The tank, built in the 1940s, is known to have leaked in the past, but was stabilized in 1995 when all liquids that could be pumped out of it were removed.

Inslee said the tank is the first to have been documented to be losing liquids since all Hanford tanks were stabilized in 2005.

At the height of World War II, the federal government created Hanford in the remote sagebrush of eastern Washington as part of a hush-hush project to build the atomic bomb. The site ultimately produced plutonium for the world's first atomic blast and for one of two atomic bombs dropped on Japan, effectively ending the war.

Plutonium production continued there through the Cold War, but today, Hanford is the nation's most contaminated nuclear site. Cleanup will cost billions of dollars and last decades.

Central to that cleanup is the removal of millions of gallons of a highly toxic, radioactive stew — enough to fill dozens of Olympic-size swimming pools — from 177 aging, underground tanks. Over time, many of those tanks have leaked, threatening the groundwater and the neighboring Columbia River, the largest waterway in the Pacific Northwest.

Construction of a $12.3 billion plant to convert the waste to a safe, stable form is years behind schedule and billions of dollars over budget. Technical problems have slowed the project, and several workers have raised lawsuits in recent months, claiming they were retaliated against for raising concerns about the plant's design and safety.

Nuclear Regulatory Commission

Most spent nuclear fuel is stored in pools like this one, with rods typically under 30 feet of water.

In a blow to the nuclear energy industry, a federal appeals court on Friday threw out a rule allowing plants to store spent nuclear fuel onsite for decades after they've closed, and ordered regulators to study the risks involved with that storage -- 65,000 tons now spread across the country, and growing at 2,000 tons a year. 

The Nuclear Regulatory Commission "apparently has no long-term plan other than hoping for a geologic repository," the unanimous ruling stated. "If the government continues to fail in its quest to establish one, then SNF (spent nuclear fuel) will seemingly be stored on site at nuclear plants on a permanent basis. The Commission can and must assess the potential environmental effects of such a failure."

Nuclear plants have been storing spent fuel onsite for decades and the NRC recently said, barring a repository, they may continue to do so even after they shut down.

That regulation was challenged by New York and other Northeast states, as well as environmentalists.

The New York attorney general's office said the ruling means the NRC cannot license or relicense any nuclear power plant until it examines those risks.

That process could take a couple of years, Geoff Fettus, an attorney who argued in court on behalf of the Natural Resources Defense Council, told msnbc.com.

"This is a game changer," he said. "The opinion is quite clear that the agency must comply with the National Environmental Policy Act and do a substantive, searching environmental review of well established legal standards."

The Nuclear Energy Institute, which represents the industry, said it was disappointed with the ruling but urged the NRC to "act expeditiously to undertake the additional environmental analysis."

In recent years, the industry had hoped for a "nuclear renaissance" based on smaller reactors with fewer mechanical parts and less nuclear waste. But Japan's Fukushima nuclear disaster last year was a major setback in building public support.

Nuclear plant operators have been paying $750 million a year to the Energy Department for construction of a central repository. It was being built under Nevada's Yucca Mountain, but engineering issues and a political backlash in Nevada killed the project after $12 billion was spent.

In January, a panel commissioned by President Barack Obama reported that a first step must be to find a site that isn't forced on a particular region by the federal government.

"The need for a new strategy is urgent," the panel wrote in its report, "not just to address these damages and costs but because this generation has a fundamental, ethical obligation to avoid burdening future generations with the entire task of finding a safe, permanent solution for managing hazardous nuclear materials they had no part in creating."

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