“This makes it clear that the second tunnel may also pose a risk to human health and the environment,” said Alex Smith, nuclear-waste program manager for the state Department of Ecology.

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A second tunnel storing radioactive waste at the Hanford nuclear reservation has structural problems and is at risk of failing, according to a U.S. Energy Department investigation released Friday.

This tunnel is more than four times longer than the smaller Hanford tunnel that suffered a partial roof collapse May 9, triggering an order for more than 4,800 employees to stay indoors.

Officials say the May 9 event did not trigger any radioactive releases. But it did escalate safety concerns about the storage of high-hazard materials left from the legacy of Hanford’s plutonium production.

State Department of Ecology officials ordered an engineering evaluation as part of a series of corrective actions. The findings were jointly released Friday in Richland by state and federal officials.

“This makes it clear that the second tunnel may also pose a risk to human health and the environment,” said Alex Smith, nuclear-waste program manager for the Ecology Department.

The two tunnels are in the 200 East Area, where plutonium was recovered from irradiated uranium-fuel rods.

Doug Shoop, a manager at the Energy Department’s Richland office, said a plastic covering has been placed over the tunnel that had the partial collapse in May.

It is not clear what caused the collapse of the wood-and-concrete tunnel that contains eight flatbed railcars holding radioactive waste. Possible factors included heavy rainfall in early May and deteriorating wood, according to the Energy Department.

The stabilization plan for the smaller tunnel involves filling it with grout, with work scheduled to be done by year’s end.

The Energy Department has until Aug. 1 to submit a plan to state officials for shoring up the second tunnel, which stretches for some 1,700 feet.

Made of metal and concrete, it was built in the 1960s and, like the other tunnel, holds railcars containing radioactive waste.

Investigators found it does not meet codes for structural integrity, and may not be able to bear the weight of soil above it.

“We took quick action in response to the Tunnel No. 1 collapse because of the potential for additional structural failures,” said Smith, of the state Department of Ecology.

“We’re closely monitoring the situation to make sure Energy finds an effective solution.”

Shoop said the Energy Department is examining options to shore up the larger tunnel. The task is complicated by the fact that, because of radiation, no one can enter the tunnel to assess its conditions.

Beginning in the 1940s and lasting for more than 40 years, Hanford made plutonium for nuclear weapons, including for the bomb that was dropped on Nagasaki, Japan.

About 8,000 people are working on a complex cleanup expected to cost more than $100 billion and last for decades.