SPOKANE, Wash. — While one of the newer double-walled nuclear waste storage tanks at a Washington state complex has leaked, six others have “significant construction flaws” that could lead to additional leaks, according to documents obtained by The Associated Press.

The 28 double-walled tanks at Hanford hold some of the worst radioactive waste at the nation’s most contaminated nuclear weapons site.

One of those giant tanks was found to be leaking in 2012. But subsequent surveys of the other double-walled tanks performed for the U.S. Department of Energy found at least six shared defects with the leaking tank that could lead to future leaks, the documents said. Thirteen additional tanks also might be compromised, according to the documents.

Questions about the storage tanks jeopardize efforts to clean up radioactive waste at the southeastern Washington site. Hanford cleanup already costs taxpayers about $2 billion a year.

“It is time for the Department (of Energy) to stop hiding the ball and pretending that the situation at Hanford is being effectively managed,” Sen. Ron Wyden, D-Ore., wrote Friday in a letter to Energy Secretary Ernest Moniz.

Energy department officials in Richland said the agency continues to make thorough inspections of the tanks, and has increased the frequency of those inspections.

Tom Carpenter of the citizen watchdog group Hanford Challenge said he wasn’t surprised that more of the double-walled tanks are in danger of leaking.

“These tanks have an engineered design life, and we are reaching the end,” Carpenter said. “It’s bad planning that they don’t have new tanks up and running.”

While new tanks are expensive, cleaning up a leak is more expensive, he added. “The price for cleaning up the environment once this stuff gets out there is incalculable.”

Hanford contains some 53 million gallons of high-level radioactive waste from the production of plutonium for nuclear weapons. They are stored in 177 underground storage tanks, many of which date back to World War II and are single-walled models that have leaked. The 28 double-walled tanks were built from the 1960s to the 1980s.

Current plans call for transferring wastes from leaking old tanks to the newer and bigger double-walled tanks, where the waste will be stored while a $13 billion plant for treating the waste is constructed.

But the treatment plant is plagued with design problems and construction has stalled.