SEATTLE (Reuters) - The collapse of a tunnel used to store radioactive waste at one of the most contaminated U.S. nuclear sites has raised concerns among watchdog groups and others who study the country’s nuclear facilities because many are aging and fraught with problems.

The Savannah River Site (SRS), a 310 square mile (198,046 acres) Department of Energy site, located in the sand-hills region of South Carolina, U.S. shown in this aerial photo made available on July 27, 2012. Courtesy National Nuclear Security Administration/Handout via REUTERS

“They’re fighting a losing battle to keep these plants from falling apart,” said Robert Alvarez, a former policy adviser at the U.S. Department of Energy who was charged with making an inventory of nuclear sites under President Bill Clinton.

“The longer you wait to deal with this problem, the more dangerous it becomes,” said Alvarez, a senior scholar at the Institute for Policy Studies, where he focuses on nuclear energy and disarmament.

The Energy Department did not respond to requests for comment.

No radiation was released during Tuesday’s incident at a plutonium-handling facility in the Hanford Nuclear Reservation in Washington state, but thousands of workers were ordered to take cover and some were evacuated as a precaution.

The state of facilities in the U.S. nuclear network has been detailed by the Department of Energy, Government Accountability Office and Defense Nuclear Facilities Safety Board. They have noted eroding walls, leaking roofs, and risks of electrical fires and groundwater contamination.

In 2016, Frank Klotz, head of the National Nuclear Security Administration, an Energy Department agency overseeing maintenance of nuclear warheads, warned Congress about risks posed by aging facilities.

Decontaminating and demolishing the Energy Department’s shuttered facilities will cost $32 billion, it said in a 2016 report. It also noted a $6 billion maintenance backlog.

In the 1940s the U.S. government built Hanford and other complexes to produce plutonium and uranium for atomic bombs under the Manhattan Project.

“That was an era when the defense mission took priority over everything else,” said Edwin Lyman, a senior scientist at the Union of Concerned Scientists. “We’re dealing with the legacy of that.”

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Many of those sites are now vacant but contaminated.

A 2009 Energy Department survey found nearly 300 shuttered, contaminated and deteriorating sites. Six years later it found that fewer than 60 had been cleaned up.

A 2015 Energy Department audit said delays in cleaning contaminated facilities “expose the Department, its employees and the public to ever-increasing levels of risk.”

Risks identified at the sites included leaking roofs carrying radioactivity into groundwater, roof collapses and electrical fires that could release radioactive particles.

A 2014 Energy Department audit noted a high risk of fire and groundwater contamination at the shuttered Heavy Element Facility at Lawrence Livermore National Laboratory, which is surrounded by homes and businesses near California’s Bay Area.

Problems have also been identified at active facilities including the Savannah River Site, a nuclear reservation in South Carolina. A 2015 report by the Defense Nuclear Facilities Safety Board found “severe” erosion in concrete walls of an exhaust tunnel used to prevent release of radioactive air.

A 2016 Energy Department audit of one of the United States’ main uranium handling facilities, the Y-12 National Security Complex in Oak Ridge, Tennessee, warned that “intense precipitation or snow” could collapse parts its roof, possibly causing an accident involving radioactivity.

“It sounds crazy, but it’s true,” said Don Hancock, who has studied the Tennessee facility in his work at the Southwest Information and Research Center, an Albuquerque nonprofit that monitors nuclear sites.

In Hanford’s case, risk of a tunnel collapse was known in 2015, when the Energy Department noted wooden beams in one tunnel had lost 40 percent of their strength and were being weakened by gamma radiation.

Energy Department spokesman Mark Heeter in nearby Richland said in an email that the agency saw Tuesday’s prompt discovery of the collapse as a success.

“The maintenance and improvement of aging infrastructure across the Hanford site ... remains a top priority,” he said.

Nationwide, part of the risk comes from having to maintain and safeguard so many sites with different types of nuclear waste, said Frank Wolak, head of Stanford University’s Program on Energy and Sustainable Development.

“You’re asking for trouble with the fact that you’ve got it spread all over the country,” he said. “The right answer is to consolidate the stuff that is highly contaminated, and apply the best technology to it.”