Hanford workers have moved more than a third of the highly radioactive capsules kept underwater in central Hanford after the Fukushima nuclear disaster increased attention on preventive measures.
The capsules haven't had a major rearrangement since the days when they were routinely sent off site to be used by industry and for research, a practice that ended in 1990.
The Waste Encapsulation and Storage Facility, or WESF, holds underwater tubelike capsules that contain about a third of the radioactivity at the Hanford nuclear reservation.
Around 1970, work began to remove cesium and strontium from waste held in Hanford's underground tanks to reduce the heat in the tanks, according to CH2M Hill Plateau Remediation Co.
The radioactive waste is left from the past chemical processing of irradiated fuel to produce plutonium for the nation's nuclear weapons program.
The cesium, which has 74 million curies of radioactivity, was packaged into 1,335 stainless steel capsules. The strontium, which has 32 million curies of radioactivity, was packaged into 601 strontium capsules. Each are about 22 inches long.
They're stored at WESF under about 13 feet of water. Radiation from the capsules casts an eerie blue glow called the Cherenkov Glow as the radioactive material decays and loses radioactivity.
The water helps cool the capsules and protects workers from radiation.
Engineers periodically assess the heat given off by the capsules, but the Fukushima, Japan, nuclear disaster in spring 2011 heightened interest, said Ty Blackford, CH2M Hill vice president.
It made rearranging the capsules to better distribute their heat a higher priority. In the case of a catastrophic event that could caused a loss of water in the WESF pool or a loss of cooling, the capsules could corrode and be breached, Blackford said.
Rearranging the capsules gives workers more time to respond if there were a serious incident at WESF, he said.
It's the first time a major relocation of the capsules has been done in about 20 years. Before that, hundreds of the capsules were rented for research or industrial use. The cesium capsules were used off-site to sterilize medical devices, sterilize sewage sludge and strengthen wood, among other uses.
But the capsules were meant to be stored underwater, and taking them in and out of water to be used for irradiation processes damaged the metal, even though the capsules have two layers of steel.
In 1990, one of them sprang a microscopic leak, forcing closure and cleanup of an irradiation plant in Georgia. The capsules were recalled and returned to Hanford in water-filled shipping casks in an effort that took years because of safety concerns. Several of the capsules were placed in overpacks to ensure their integrity.
In the campaign just completed to rearrange the capsules at WESF, engineers calculated the wattage output of each, said Geoff Tyree, DOE spokesman. Then they determined the best way to rearrange them in order to balance the heat load, he said.
More than 800 of the capsules were moved within the individual underwater cells of WESF.
CH2M Hill workers standing on walkways above the water used long-handled tongs and "pushers" to reach to the bottom of the water and move the capsules.
Underwater lighting and a video camera were used, including to verify that the capsules were correctly placed, Blackford said.
Work began in February and was completed six months earlier than planned, said CH2M Hill spokeswoman Dee Millikin.
Shortly after the project started, workers assigned to the project suggested ways to redesign the tools and collaborated with engineers to optimize the plan of execution for the project, Blackford said.
"They did a fantastic job figuring out how to do it," he said.
Two shifts worked on the project every Thursday, with the same workers assigned each week. Some workers canceled vacations so they could be there with the rest of the crew to move the capsules, Blackford said.
By finishing six months early, risk to workers was reduced, he said.
The capsules are planned to eventually be sent to a national repository for high-level radioactive waste.
-- Annette Cary: 582-1533; acary@tricity herald.com