Washington Closure Hanford is preparing for one of its largest and most challenging lifts -- hoisting an underground vault weighing an estimated 1,100 tons.
The vault, once used to hold two tanks that collected highly contaminated liquid radioactive waste, must be picked up by a crane and then hauled by a trailer designed for heavy loads to the central Hanford landfill for low-level radioactive waste.
The vault, just north of Richland, is about a quarter-mile from the Columbia River, and workers discovered as they started preparing to move it that radioactive waste had leaked from the vault, probably from a sump at its center.
The vault is large at 40 feet long, 29 feet wide and 25 feet high. But it isn't just its size and weight that make the lift a challenge.
"It's complicated to get under something that sits on soil," said Don McBride, Washington Closure technical services manager for decommissioning and demolition.
The vault is one of just three complex radioactive facilities that still need to be demolished or removed at the Hanford 300 Area.
The 340 Building, also called the Waste Neutralization Facility, next to the vault was torn down in 2011, and in 2012 about 54,000 tons of soil were dug up, leaving the vault in a hole on a pedestal of soil.
To prepare to lift the vault, workers are driving four steel pipes horizontally through the soil platform underneath it. As the 3-foot diameter pipes are pushed through, an auger mines the soil out of the pipe.
The plan is to fill the pipes with concrete to help sustain the weight of the vault, which is made of steel-reinforced, high-density concrete, McBride said.
Washington Closure knew that there was a risk of encountering radioactive material and was carefully checking as the pipes, or casings, were placed. An alarm sounded about halfway through installing the fourth casing.
Further studies, done by pushing radiation detection probes under the vault showed that soil in a four- to six-foot diameter area is contaminated. Initial readings found radiation exposure rates up to 17 rad per hour. Most of it is about two feet beneath the vault, with contamination dramatically decreasing about four feet down.
The vault acted like an umbrella over the contamination, preventing rain or other liquids from driving contamination toward the groundwater, said Mark French, the Department of Energy project director for Hanford work along the Columbia River. The groundwater in high water years can rise to within about 12 feet of the bottom of the vault.
The two 15,000-gallon stainless steel tanks in the vault were used to hold waste piped to the vault from laboratories, fuel fabrication facilities and test reactors in the Hanford 300 Area just north of Richland.
The liquid waste then was taken by rail car to central Hanford to be added to high-level radioactive waste from weapons plutonium production that is held in underground tanks.
The waste that has leaked underneath the vault contains cesium, strontium and americium, McBride said. However, radiation readings are far less than at the leak of cesium and strontium under the 324 Building, also in the 300 Area, which has halted demolition work there. Radiation exposure rates as high as 8,900 rad per hour have been measured there.
Much of the contaminated soil will be augered out by the installation of the fourth casing and taken to the Environmental Restoration Disposal Facility, the central Hanford landfill. To remove most of the rest of the contaminated soil, a fifth casing will be installed under the center of the vault within six inches of adjacent casings.
A low-profile, mini-excavator typically used for mining will be sent under the vault to clear out additional soil to prepare for the lift, said Dan Elkins, decommissioning and demolition deputy director for Washington Closure. Since it will be under the vault, it will be remotely operated.
Then steel beams will be inserted under the vault and attached to a steel lift frame placed around the vault. Once the beams are attached to the lift frame, the vault can be lifted up slightly with a gantry crane to remove the casings and allow the mini-excavator to remove more soil.
A heavy-haul trailer will be driven beneath the vault after it is lifted by the crane. A steel pan, slid under the vault before it is placed on the trailer, is planned to be cemented into place on the trailer, bringing the transport weight to about 1,538 tons.
Washington Closure is expecting to haul the vault to the central Hanford landfill around early November, Elkins said.
DOE expects that the remaining test reactor in the 300 Area will be removed about the same time as the vault. It could come close to weighing as much as the vault, Elkins said.
That will leave the 324 Building, which sits over the extremely high radiation spill of cesium and strontium. A subcontract for work there could be awarded during fiscal 2014, French said.