"It's not acceptable that the hole could have been open for four days", said Alex Smith, nuclear waste manager for the Washington state Department of Ecology, which helps regulate the Hanford site.
The Energy Department says no one was injured in Tuesday's incident and no radioactive material escaped.
Workers have most of the road in place to get heavy equipment to the collapsed tunnels site.
A recent Government Accountability Office (GAO) report on the Hanford site examining risks and costs of operations noted, "The volume and complexity of the tank waste have been a persistent challenge for DOE". The cause of the collapse was not immediately known.
Hanford is one of several active sites undergoing cleanup under the direction of the Department of Energy's Office of Environment Management.
The tunnel is a prime example of the sort of temporary methods to store radioactive waste that abound in the nation's nuclear weapons complex.
Worker safety has always been a concern at Hanford, which is located about 200 miles southeast of Seattle.
The nuclear site, which is twice the size of Singapore, was used to produce plutonium for the bomb that brought an end to World War II.
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The vast majority of the site's 9,000 employees are being asked to stay home Wednesday. "Collapse of the earth covering the tunnels could lead to a considerable radiological release", he said.
After officials confirmed that the contamination had not spread, sheltered employees and non-essential employees of the facility's 9,000 worker labor force were sent home, according to AP.
For instance, at the Savannah River Site in SC, which opened in the 1950s and produced plutonium and tritium, the government is laboring to clean up groundwater contamination along with 40 million gallons of radioactive liquid waste stored in tanks that are decades past their projected lifespan.
Monitoring detected no released radiation, and workers moved into the area to prepare to fill the tunnel breach, said Destry Henderson, a Hanford spokesman, early Wednesday.
The plan is to bury the glass logs at a nuclear waste dump carved inside Nevada's Yucca Mountain, a project that has been on the drawing board for three decades but has run into resistance from Nevada politicians, including former U.S. Sen.
The cause of the partial collapse of the tunnel, which was built in 1956, has not been determined.
Yes. Washington Attorney General Bob Ferguson filed a lawsuit last fall against the Energy Department and its contractor, Washington River Protection Solutions, contending tank vapors pose a serious risk to Hanford workers. There is a massive volume of nuclear waste stored at the Hanford site, about the size of the US state of Rhode Island, and not all of the storage sites are inspected daily, Heeter said.
Worse than a decades-old tunnel leaking radioactive dust into the air? "Upon an additional investigation, crews noticed a portion of that tunnel had fallen, the roof had caved in about a 20-foot section of that tunnel, which is more than 100 feet long".