A technology similar to one used to purify table salt is being investigated as a way to reduce the cost of treating some of Hanford's worst radioactive waste.

Hanford contractor CH2M Hill Hanford Group has awarded a $1.4 million subcontract to Cogema Engineering Corp. to see if a proposal by a CH2M Hill chemist could be adapted for large-scale use.

The Department of Energy is building a $5.8 billion vitrification plant to turn highly radioactive and chemical waste held now in huge underground tanks into a stable glass form for permanent disposal.

But the vitrification plant never was planned to be big enough to meet legal deadlines to treat all 53 million gallons of waste left from processing irradiated fuel for the production of plutonium at Hanford during World War II and the Cold War. The plutonium was made for the nation's nuclear weapons program.

CH2M Hill believes a process called fractional crystallization could reduce costs and remove some of the burden from the first step at the vitrification plant, pretreatment.

The largest complex in the 65-acre vitrification plant will be a pretreatment building the size of four football fields and about 15 stories high to separate waste into low-activity and high-level radioactive streams.

All the waste will be turned into glass, but the low-level waste will remain at Hanford and the high-level waste will be sent to a federal repository, likely Yucca Mountain, Nev., at a far greater cost.

CH2M Hill wants to determine whether 10 percent or more of the waste can skip the pretreatment separation process through its proposed technology.

Chemist Dan Herting of CH2M Hill has spent several years testing ways to use temperature changes and evaporation to selectively precipitate low-activity radiation salts out of the waste.

His tests, most recently using small amounts of radioactive tank waste, have been promising enough to interest DOE.

The technology is not new.

A similar process is used to separate salt and other valuable chemicals from sea water.

But Hanford waste presents some unusual challenges.

Some chemical salts precipitate when heated, others when cooled and all precipitate when the water is evaporated.

"It's up to the Cogema team to come up with the right sequence of heat and evaporation," Herting said.

The process would not work on all tank waste as the pretreatment plant processes must. But the waste in more than half of Hanford's 177 tanks might be candidates for the alternate process, said Richard Raymond, director of supplemental treatment for CH2M Hill.

The fractional crystallization would remove moisture to produce crystals of radioactive sodium nitrates and nitrites. The salts could then be turned into a low-activity glass. Much of it might be turned into glass with another alternate technology, bulk vitrification, which could allow it to bypass the vitrification plant entirely.

That would leave about half the waste remaining as a liquid laced with highly radioactive cesium and technetium. That liquid, which would hold more than 99 percent of the radioactive energy, would still need to be sent to the pretreatment plant. It uses primarily ion exchange and filtration to separate waste into low-activity and high-level waste streams.

Cogema must show not only that the process works on Hanford waste at the engineering scale, but also come up with a way to perform the process at a far lower cost.

"One thing that makes the task challenging is we're asking them to come up with a proposal without a major new capital facility," said Ken Gasper, project manager for supplemental pretreatment for CH2M Hill.

Commercial equipment would be adapted to the project and the process would be done in the field, possibly in temporary facilities.

Cogema has teamed for the project with Framatome ANP, which has expertise in radioactive materials; Georgia Technical Research Corp., which is associated with Georgia Tech University, which has a nationally recognized crystallization expert; and Swenson Technology Inc., which specializes in equipment for the process in nonradioactive environments.

They will produce a design concept for the technology and determine the cost of developing a full scale pre-treatment facility.

In the first phase of the project, engineering work will be done at Hanford, but testing will be done elsewhere. Testing will move back to Hanford when Cogema is ready to try the process with radioactive tank wastes.

"We're hoping the results will be promising enough to warrant a proposal to DOE to go forward," Gasper said.