Underground nuclear waste storage tanks on the Hanford Nuclear Reservation continue to deteriorate, raising questions about how their contents will be managed in the future, according to a report released Tuesday by the Government Accountability Office.

Hanford, near Richland in eastern Washington, contains 177 nuclear waste tanks, some of which have leaked. The nation’s largest collection of radioactive waste is left over from the production of plutonium for nuclear weapons.

The GAO report said that both the older single-walled tanks and newer double-walled tanks are deteriorating. Some tanks date to the 1940s and are long past their designed lifespans.

The Energy Department agreed with the report and its recommendations.

But U.S. Sen. Ron Wyden, D-Ore., who requested the report, said the DOE was moving too slowly.

“Agreeing to recommendations is one thing; implementing them is another thing entirely,” Wyden said. “I’m asking for a schedule and a plan of action within 90 days.”

The underground tanks contain about 56 million gallons of deadly nuclear waste, and cost the federal government about $1 billion a year to maintain and monitor.

The 149 older single-walled tanks have been largely pumped of their liquid wastes, which have been transferred into the newer 28 double-walled tanks, the GAO report said.

The Energy Department has found that water is leaking into at least 14 single-walled tanks. One of those tanks has leaked back into the ground since about 2010, at the rate of 640 gallons per year, the report said.

In 2012, the Energy Department also found that a double-walled tank known as AY-102 was leaking from its inner wall into the outer wall. The Energy Department decided that was likely because of construction flaws and corrosion in the bottom of the tank. But the agency has not determined if the other double-walled tanks are subject to the same corrosion problems.

The Energy Department has conducted additional tank inspections and increased the frequency of monitoring single-walled tank waste levels from annually to monthly. The agency has also improved its monitoring methods.

The report said the Energy Department has also changed its monitoring of double-walled tanks.

But “DOE’s current schedule for managing the tank waste does not consider the worsening conditions of the tanks,” the GAO report said.

The current schedule also does not consider the delays in building a $13 billion plant to turn the tank wastes into glass-like logs for eventual burial. Construction of the Waste Treatment Plant at Hanford has been halted by design and safety concerns.

“Future leaks and intrusions, which become more likely as the tanks’ condition worsens, would place additional demands on the already limited DST (double-shell tank) storage space, and it is unclear how DOE would respond,” the GAO report said.

The state of Washington has demanded that the Energy Department build more double-walled tanks, but the agency has not included funding for that in its budget requests.

The Energy Department told the GAO that recent efforts to evaporate some water from the double-walled tanks has freed up about 750,000 gallons of space.

Because of delays in building the Waste Treatment Plant, the Energy Department “cannot estimate how long the waste will remain in the aging tanks,” the GAO report said.

“DOE cannot be sure how long its DSTs can safely store waste,” it said.

The report recommended that the Energy Department assess the corrosion potential of its double-walled tanks; update its schedule for removing waste from the tanks; and assess ways to create additional space in existing double-walled tanks.

The Energy Department said it is already acting on the GAO recommendations.

“DOE has made progress in the management of the tanks at Hanford,” the agency wrote in its response to the report. “The mitigation of risks associated with managing this waste continues to be one of DOE’s highest priorities for Hanford.”