The 200-foot-tall ventilation stack at the Hanford Site’s Plutonium Finishing Plant crashed to the ground Saturday in an explosive demolition. It was another step toward bringing the plant down to slab on grade by the end of September as required by the Tri-Party Agreement (TPA) covering cleanup at the former plutonium production complex in Washington state.
“Removing the stack is not only historic, but it allows workers in heavy equipment to more easily access and demolish the remaining portions of the facility,” said Tom Teynor, Department of Energy project director for the plant’s demolition. The exhaust stack was used for the entire 68-year history of the plant used to convert plutonium into final form for U.S. nuclear weapons.
The stack, which was about 18 feet in diameter at its base, had fixative blown up its length to help contain any radioactive contamination before the plant’s ventilation system was turned off. A gravel pad was laid on the ground to provide a somewhat cushioned and flat landing area for the stack. A wedge was cut near its concrete base, much like a logger would cut a wedge in a tree trunk, to control where it fell, said Kelly Wooley, Plutonium Finishing Plant deputy project manager for contractor CH2M Plateau Remediation Co.
Controlled Demolition Inc., a subcontractor to CH2M, used only a small amount of explosives to weaken the stack, allowing gravity to bring it to the ground. It pancaked into rubble that will be loaded out and taken to Hanford’s Environmental Restoration Disposal Facility. The same explosive demolition technique has been used at other Hanford stacks, with site officials saying it is safer and more efficient than other methods that would require workers to be high off the ground.
Demolition operations at the Plutonium Finishing Plant had shifted in recent weeks to the ventilation building, which housed powerful exhaust fans, to allow for the scheduled explosive demolition of the stack on Saturday. The mostly underground ventilation building, also called the fan house, was torn down to ground level after removal of equipment with radioactive contamination, including a vacuum line, and any hazardous materials, such as asbestos. It then was backfilled with soil to provide space for demolition of the stack.
Demolition operations had previously been focused on the Plutonium Reclamation Facility, believed to be the most contaminated area of the Plutonium Finishing Plant. Demolition, which began there Nov. 1, stopped June 8 when an alarm sounded, indicating a release of airborne contamination. The portion of the facility being demolished was stabilized to prevent any further spread, but full demolition activities had not resumed before the schedule dictated that workers turn their attention to the fan house.
Rather than return immediately to demolition of the Plutonium Reclamation Facility, workers are expected to next do some tear down of the main portion of the plant, starting before the end of July. Plans call for beginning demolition with a one-story area used for lockers and tasks to prepare workers to enter and exit more contaminated areas of the plant.
Workers also will tear down the section of the main plant closest to the Plutonium Reclamation Facility to provide more working room at the highly contaminated facility. Given the potential for airborne contamination as the central canyon of the Plutonium Reclamation Facility is demolished, only a 2-foot-wide slice of the building from top to bottom will come down each day.
“Even though we have resequenced the facility demolition order, we are still working to meet the TPA milestone basically by the end of September,” Teynor said.
