The below-ground portion of a former Hanford experimental reactor building just north of Richland will be blown up Saturday morning, weather permitting.
The Department of Energy and its contractor Washington Closure Hanford have turned to an explosive demolition company to help turn the below-ground concrete structure with walls as thick as 13 feet into rubble.
Some people nearby could hear a dull thud around 7 a.m.
“There may be a bit of dust. From a visual perspective it will be unspectacular,” said Chris Pearson, Washington Closure program manager for the project.
There’s not much to see at the reactor already.
The iconic dome of the Plutonium Recycle Test Reactor stood 80-foot high and was one of the most distinctive features at Hanford just north of Richland until the containment dome was lifted off as part of environmental cleanup in 2011. The concrete exhaust stack, which was 100-feet tall, was destroyed with explosives.
At the start of this year the 100-megawatt reactor was hoisted out of its below-ground housing and hauled to central Hanford for disposal in a lined landfill.
What remains is the below-ground structure that housed the reactor, with a circular deck at ground level with a hole in the center where the reactor was lifted.
None of the concrete is less than 5-feet thick in the three below-ground cells or rooms that remain. The most massive structure is a wall on the south end that was cast to support the rest of the building. The wall is a block of concrete 13-feet thick, 18-feet wide and 28-feet high.
Some of the concrete was poured thick to provide shielding from radiation. But, in addition, when the structure was built in the late ’50s, concrete was relatively inexpensive and readily available, and Hanford officials did not hesitate to use it freely, Pearson said.
Some of the concrete was made not by mixing in rock, but steel kibble, or chunks of steel about the size of charcoal briquettes.
“It’s tough stuff. It’s substantial,” Pearson said.
About 212,000 cubic feet of concrete needs to be demolished.
About 300 holes have been drilled vertically into the ground-level deck of the reactor building and its walls for charges. An international company, Controlled Demolition, which has done other Hanford work, including taking down the reactor’s exhaust stack, will set off the charges in quick succession. The plan is for the concrete rubble to fall to the concrete floor of the structure, which is 32 feet below ground.
While the explosion will be over in two seconds, work to prepare for it has taken months.
After the reactor was hoisted out in January, Hanford workers removed contaminated piping, stored items and equipment from the below-ground structure, including the moderator tank, which held water. A fixative was used on surfaces to glue contamination in place and areas that were difficult to access were filled with grout.
Explosive demolition was picked as the safest method for workers, who would otherwise be down in the structure and exposed to hazards, and also for its substantial cost savings, said Mark French, DOE project director for the work.
Using explosive demolition, rather than breaking up the concrete with an excavator equipped with shears or a jackhammer, is estimated save about $2.5 million.
Cost savings include the greatly reduced time to destroy an estimated 70 percent of the below-ground structure and the savings on wear and tear of heavy equipment.
Conventional demolition on such robust concrete “basically destroys the equipment,” French said. It also would be difficult to break up the below-ground concrete with equipment staged at ground level.
To prepare for the explosion a blast mat has been created to place over the opening where the reactor was lifted out. It was created with double layers of chain link and other material and will be weighed down. It is planned to cut down on dust and as a precaution to prevent any flying debris, which is not expected.
Hanford officials expect the explosion to knock concrete away from rebar and leave it in pieces that are manageable with heavy equipment. The debris will be taken to the central Hanford lined landfill for low-level radioactive waste.
Left will be the shell of the below-ground structure to be removed and the concrete foundation which is up to 14 feet-thick. It will be sampled and, if it meets environmental cleanup standards, it could be buried in place.
But if it does need to come out of the ground, another explosive demolition could be done in December or January.
Demolishing the rest of the reactor building will allow access to areas around it for more cleanup, French said. That includes piping, tanks and soil contaminated by spills.
Most cleanup at Hanford along the Columbia River, including the 300 Area, is expected to be completed next year.
-- Annette Cary: 509-582-1533; firstname.lastname@example.org; Twitter: @HanfordNews