The emergency declared Tuesday at the Hanford Site in Washington state when a breach was discovered in one of the underground waste storage tunnels for the Plutonium Uranium Extraction (PUREX) Plant was formally ended after workers finished filling in the hole late Wednesday night.
“(The work) was accomplished swiftly and safely to prevent any further complications,” said Energy Secretary Rick Perry. “Our next step is to identify and implement longer-term measures to further reduce risks.”
Monitoring by the federal and state governments did not detect any airborne radioactive contamination during the incident.
No workers were injured, though thousands were directed to shelter in place after the hole was discovered early Tuesday. Filling the opening in the top of the tunnel further limited the risk of airborne contamination at the former plutonium production complex that is now the site of a massive DOE cleanup program.
On Thursday, work turned to the next step to protect workers and the public from the possibility of another collapse at the 360-foot-long tunnel. Hanford officials were discussing covering the entire length of the tunnel while longer-term actions are considered. One option considered was layering thick plastic over the dirt berm above the tunnel, but no decision had been announced Thursday. The cover is intended to prevent precipitation from soaking into the 8 feet of soil covering the roof of the tunnel, which would increase the weight on the roof. It also would provide some protection against radioactive contamination spreading into the air if another collapse occurs.
“We’re planning additional protective measures slowly and methodically,” said Destry Henderson, spokesman for central Hanford cleanup contractor CH2M Hill Plateau Remediation Co. “They won’t take place until we’re sure we can do it safely.”
The pace of covering the tunnel will depend on the weather, Henderson said. Breezy and rainy days were in the immediate forecast for the end of this week and early next week.
The cause of the tunnel collapse was not known Thursday. “Our focus remains on near-term protective actions,” Henderson said.
Initial stabilization of the collapsed portion of the tunnel involved dumping 53 truckloads, or about 550 cubic yards, of material in the hole on top of the tunnel using an excavator equipped with a scoop. The fill was primarily sand, selected for its density, with some soil.
Crews worked through the night Tuesday to lay down a gravel road, ending in a pad, to allow heavy machinery to reach the area of the tunnel collapse and stage there. Equipment operators wore air-purifying respirators, according to the Department of Energy.
Washington state, a Hanford regulator, quickly took enforcement action in the incident.
“This alarming emergency compels us to take immediate action to hold the federal government accountable to its obligation to clean up the largest nuclear waste site in the country,” said Maia Bellon, director of the state Department of Ecology.
The state agency on Wednesday evening issued an administrative order with three deadlines for corrective action.
DOE must immediately begin to determine the cause of the breach and assess if the tunnel that collapsed, the older of two waste tunnels at PUREX, and the second tunnel are at immediate risk of further failures. A structural integrity evaluation for both tunnels is due July 1. A month later DOE must submit a draft report detailing corrective actions to ensure the safe storage of waste in both tunnels until the material can be disposed of permanently. On Oct. 1 DOE must deliver a draft permit modification to the dangerous waste section of its Hanford Facility Resource Conservation and Recovery Act permit covering the tunnels. The draft must include a plan to permanently clean up waste in the tunnels.
“The infrastructure built to temporarily store radioactive waste is now more than a half-century old,” Bellon said. “The tunnel collapse is direct evidence that it is failing. It’s the latest in a series of alarms that the safety and health of Hanford workers and our citizens are at risk.”
The PUREX facility began processing irradiated fuel to extract plutonium in 1956. Between 1960 and 1965 eight railcars holding highly contaminated equipment from the plant were pushed into the tunnel built by a remotely controlled engine.
The tunnel was built of creosoted timbers and some concrete. The state said in a legal document that former contractor Westinghouse Hanford Co. had commissioned an evaluation of the tunnel in the early 1990s. The assessment concluded that the rate of loss of structural strength due to gamma radiation was diminishing with time so that by 2001 the timbers would still have 60 percent of their original resilience. It recommended another study be done of the structural integrity of the wood in 2001, but the state document gave no indication whether that was completed.
The second tunnel, which is 1,700 feet long and holds 28 railcars of contaminated equipment, was built in 1964. It was constructed with steel I-beams attached to reinforced concrete arches and a steel liner. The doors to the tunnels were sealed closed in the 1990s.
The incident began Tuesday morning when workers conducting routine monitoring of the area noticed from a distance what appeared to be a depression in the soil over the end of the oldest tunnel. By midmorning, officials had confirmed that the top of the tunnel was actually breached, with a hole measuring about 20 by 20 feet where the tunnel roof had collapsed. The soil covering the tunnel fell into the hole, possibly helping to contain any radioactive materials.
Initially, about 3,000 workers in the 200 East Area, including at the Waste Treatment Plant construction site, were ordered to take cover in buildings with ventilation disabled because of the possibility of airborne contamination. The take-cover order was later expanded to all workers north of the Wye Barricade secure entrance to the site. Early in the afternoon, with no airborne radioactive contamination detected, nonessential workers were sent home.
Most workers returned to the Hanford Site Thursday, with the exception of a couple hundred tank farm workers located nearest the breach who were told to stay home. Thursday is the end of the workweek of 10-hour days for most personnel.
On Tuesday, both Benton and Franklin counties, which have residents living near Hanford, opened emergency operation centers. The state of Oregon set up an emergency operations center in Salem as a precaution. Washington Gov. Jay Inslee said he was notified of the emergency Tuesday morning by both DOE and the White House.
Sen. Ron Wyden (D-Ore.) said the incident should serve as a reminder that “the temporary solutions DOE has used for decades to contain radioactive waste at Hanford have limited lifespans, whether they are underground tunnels for storing contaminated equipment or aging steel tanks filled with high-level radioactive waste. The longer it takes to clean up Hanford, the higher the risk will be to workers, the public and the environment.”
