Hanford workers are finding huge stainless steel tanks, one with radioactive powder inside, and drums of potentially flammable zircaloy chips as they dig up the final trench at a burial ground just north of Richland.
Contractor Washington Closure Hanford had delayed starting cleanup of the 618-7 Burial Ground until this year, fearing that its contents would be so hazardous that it needed to have a new safety plan required by the Department of Energy in place before work began.
“It’s gone better than we expected,” said John Ludowise, project engineer for Washington Closure. “We prepared for the worst.”
The burial ground was used from about 1960-73 for waste from the Hanford nuclear reservation’s 300 Area along the Columbia River, where fuel was made for Hanford’s reactors and research was conducted.
When the waste was disposed of, it was not expected to be retrieved to meet future environmental standards so records of what it was used for are sketchy. That means there were bound to be some surprises and workers were protected with supplied-air respirators.
Work began shortly after the first of the year to dig up the two largest trenches, each about 650 feet long and 100 feet wide.
Workers found about 800 drums, most with aluminum turnings or vermiculite, a material used for insulation or packing midcentury. About half were open, some with lids that had popped off, and others had to be carefully opened one at a time to make sure their contents were relatively benign.
“We were surprised how tame the contents were in those,” said John Darby, Washington Closure project manager.
Because Washington Closure knew somewhere in the burial grounds there were likely to be drums of zircaloy shavings, which can ignite if fine particles are exposed to air, drums were opened in an enclosure with remotely operated equipment with the capability of adding water or mineral oil to stabilize the contents.
Darby also was surprised by the amount of lead contamination found in the soil.
When fuel was manufactured during the Cold War to produce plutonium for the nation’s nuclear weapons program in Hanford reactors, the fuel was dipped in a lead bath. The bath had to be skimmed every couple of hours and then the slag was disposed of.
“It was just dumped in the dirt,” Ludowise said.
About 66,000 square yards of dirt and debris have been removed from the two large trenches in the burial ground with about 4,800 square yards still to be dug up in one section that appears to be slightly deeper.
Workers also have about 60 percent of the third and final trench dug up, which Washington Closure expected might have different materials. The approximately 500-foot-long trench had been called the thoria trench, a reference to a white, powdery oxide of radioactive thorium that’s sometimes used in gas mantles for lanterns. At Hanford thorium was used in a program to research a new type of nuclear weapon.
In the thoria trench they found the zircaloy shavings, about 100 drums so far. The zircaloy, a metal alloy of zirconium and a small amount of beryllium, has been in pieces large enough so far not to present a fire danger. And the drums have been well marked with a sticker that indicated it contained beryllium.
“So they had a lot of respect for beryllium contamination even back then,” Darby said. Beryllium can cause an incurable lung disease in people who have an allergylike reaction.
The surprise in the thoria trench has been 16 large stainless steel tanks plus piping and processing equipment. The tanks are about 10 feet tall and about 8 feet in diameter.
Not all have been checked, but one had thoria at its bottom.
Ludowise believes the equipment is from a PUREX prototype because historic photos show equipment that look similar. PUREX, a chemical separations plant in central Hanford, was used to process irradiated fuel from the experimental thorium project.
Workers also have unearthed hundreds of 5-gallon buckets left from the thoria project, most marked with a “thorium oxide” label.
The Department of Energy faces a legally binding Tri-Party Agreement deadline to have the burial ground cleaned up and the area replanted in December. More wind than usual this summer has stopped work on several days and Hanford workers are digging and hauling waste on a lengthened work week to meet the deadline.