Areva Federal Services has been awarded a subcontract worth almost $19 million to design and test a system to clean up one of Hanford’s worst radiological spills. Washington Closure Hanford awarded the subcontract for the engineering of a system to dig up soil contaminated by concentrated cesium and strontium beneath the 324 Building in the Hanford 300 Area just north of Richland. The structure will be left standing above the spill to protect workers from contamination as it comes out of the ground within the building. The 324 Building, built in the mid-1960s and operated until 1996, housed shielded rooms called “hot cells,” where workers used remotely operated equipment to perform work with highly radioactive materials. Areva plans to build a mockup of a 30-foot-high hot cell at its Richland campus on Horn Rapids Road to demonstrate the equipment it designs and prove that it works, said Don McBride, Washington Closure manager for the project.
Its team includes four Hanford-area small businesses: Vista Engineering, Remote Systems Engineering, Applied Geotechnical Engineering Construction, and Federal Engineers and Constructors.
Workers were decontaminating the building for demolition in November 2009 when they discovered that the lining of a sump at the bottom of a hot cell had cracked, allowing radioactive material to leak into the soil.
The contamination is suspected of coming from a spill within B Cell in the 1980s. Concentrated cesium and strontium were fabricated into a heat source for Germany to use for tests of a repository for radioactive waste, which emits heat.
“Extensive characterization of the soil indicated radiation levels approaching 10,000 rad per hour,” said Gary Snow, director of Washington Closure’s decontamination and demolition work, in a statement. Direct exposure for a few minutes would be fatal, according to Hanford officials.
Now the 324 Building acts as a shield to protect workers from the radiation from the spill beneath. It also acts as an umbrella above the spill, keeping precipitation from driving the contamination deeper into the soil.
The contamination has not reached groundwater, which is about 42 feet below the bottom of the hot cell. The worst of the contaminated soil is believed to be 5 to 6 feet beneath the hot cell. The spill is about a quarter-mile from the Columbia River and about a mile north of Richland.
B Cell is the largest and most contaminated cell in the building, which also is known as the Chemical and Materials Engineering Laboratory.
Cleanup plans call for several phases of work, starting with the Areva contract to perform assessments, engineering and construction at a full-scale mockup of B Cell and its associated hot cells by September 2015, according to Washington Closure.
The equipment it designs will be installed within the 5-foot-thick walls of B Cell and then remotely operated to chisel out the floor, which measures about 20 by 25 feet. The soil will be excavated to possibly 10 feet deep and transferred to another hot cell in the 324 Building, where it will be prepared for disposal.
The contract for that work has not been awarded.
By leaving the hot cell in place as the floor and soil are removed, workers not only will have radiation shielding but the ventilation system can be used to control airborne radioactive particles, McBride said.
In the second hot cell, the contaminated soil will be immobilized using a form of grout, possibly by mixing it with the material or by putting it in containers surrounded with the material to fill the hot cell. Once that work is done, current plans call for removing the entire B Cell and hauling it to a lined landfill for radioactive waste in central Hanford.
“Remediating this highly hazardous waste site is essential to our mission of protecting the public, the environment and the Columbia River,” Snow said. “It will also allow us to take another step toward completing cleanup of the 300 Area by removing the 324 Building.”
The building is the final one planned to come down in the 300 Area as part of Hanford environmental cleanup, although a few buildings will remain standing for continued use by Pacific Northwest National Laboratory researchers.