| October 1999 |
A tale of two technologies
Savannah River officials were left with a two-fold problem: Without a successful technology to remove the cesium from the tanks, the waste problem remained, and without the sludge from the process, the vitrification project—involving about 4500 jobs—would stall for lack of the raw material.
Program managers included ORNL in a quest to find an alternative process to remove the cesium from the tanks. The Chemical Technology Division’s Jack Watson was part of a team that came up with 140 ideas at the outset, then narrowed them down to a current two.
The competing solutions involve chemical separations expertise available at only a few places, one of which is ORNL.
“One process is a refined version of in-tank precipitation using a continuously stirred tank reactor,” says Chem Tech’s Phil McGinnis, who is the technical integration manager for pretreatment within the Tanks Focus Area of the Environmental Management program. Savannah River’s Piccolo credits the Tanks Focus Area for “working with us and sending the right processes to the right labs so we can support and cross-check each other.”
McGinnis explains that the tanks contain radioactive waste in an extremely saline liquid called a supernate. In an earlier test of the in-tank precipitation method, officials thought that by adding certain chemicals to the supernate, cesium would replace the sodium in the salt, solidify and sink to the sludge on the bottom. That sludge would be the raw material for the vitrification process. But it wasn’t that simple.
“The original in-tank precipitation process failed because the temperature was not controlled adequately,” McGinnis explains. “The process became too hot, causing trace metals to become catalysts that reacted with the chemicals, degrading them. It also produced benzene, a flammable carcinogen.”
Savannah River and ORNL scientists and engineers have revamped the precipitation process. Temperatures are more adequately controlled and the process’s chemistry is better understood, McGinnis says. Early pilot tests in a hot cell using highly radioactive cesium at ORNL have been very promising.
The competing process, ion exchange with crystalline silicotitanate (CST), is a technology ORNL has experimented with and is currently using. The cesium is removed by pumping the waste through columns filled with ion-exchange beads of CST. The Lab currently uses a version of this technology in the Melton Valley storage tanks project to treat tank wastes.
Chem Tech’s Tim Welch is leading pilot tests with a 16-foot-tall column that is three inches in diameter. In actual use the columns would be five feet in diameter. Recent runs on the pilot version tested the ability to load and unload the column and analyzed the column’s formation of radiolytic gases and other effects of operating the system. That system is also providing promising results.
In addition to the two major processes, ORNL is also helping Savannah River on three other tasks.
Bill Steele, who recently came to ORNL from the BDM research labs in Bartlesville, Okla., is researching with Debbie Bostick the properties of crystal silicotitanate, the ion- exchange process’s active ingredient, to better understand how it will perform on a scale as large as the Savannah River project.
Chem Tech’s Paul Taylor is developing equipment to remix hard cakes of monosodium titanate, which removes strontium-90—another contaminant—from the waste. Taylor is also performing aging tests on crystal silicotitanate to make sure the cesium doesn’t desorb.
Cohn came to Oak Ridge from the University of Chicago in 1943 to perform chemical separations work on the atom bomb project. The Graphite Reactor, or X-10 Pile as it was called then, was a pilot plant to produce gram
quantities of plutonium in preparation for large-scale production at Hanford, Wash.
But it was the reactor’s potential contributions to the life sciences that Cohn recognized early on. He saw that a technique used to identify the chemical species of fission products could also be applied to the nucleic acids DNA and RNA. It was a step toward the discovery of the structures of “life’s building blocks.”
“Cohn was also the first to organize and promote the use of radioactive isotopes produced in nuclear reactors,” says ORNL Director Emeritus Alvin Weinberg. “The widespread use of radioisotopes is perhaps the most important scientific byproduct of the Manhattan Project.”
Cohn helped build Oak Ridge both scientifically and culturally. Not long after arriving, he organized the city’s first symphony orchestra, which is the longest continuously performing orchestra in the state. Cohn, a cellist, also conducted.
He also served as chairman of the early city’s town government and championed school desegregation in the mid-1950s.
McGinnis points out that whichever process is ultimately chosen for the task, ORNL will emerge as a major contributor.
“Oak Ridge has supplied important, unbiased data on both processes and a critical amount of development work,” he says. “Next year we’ll take the selected technology and do more involved pilot-scale support work.”
In August, officials recognized the hard work and dedication of the project team that included Chem Tech, Chemical and Analytical Sciences, Health Physics, Instrumentation and Controls and Plant and Equipment division staff members with a breakfast ceremony. The Savannah River officials, who were stung by a news report’s criticism of the earlier stumbles, have been elated by the progress. Savannah River’s Joe Carter says that ORNL’s facilities were crucial to the proof-of-concept testing of processes developed at Savannah River.
“We were in a position where we had to do radioactive tracer work, and we didn’t have the appropriate hot cell facilities for that. ORNL brought in its facilities, and there aren’t a lot of those around. We also drew from the Lab’s expertise in peroxide chemistry, through Al Mattus, and chemical thermodynamic stability.
“We’ve been very pleased with the interaction and cooperation, and with ORNL making the changes to our processes that have been the right changes,” Carter says.
McGinnis says that the chemical separation science that has helped this project go so well is at the very basis of ORNL’s existence.
“Chemical separation science is at the very core of what ORNL is about. That’s why ORNL was constructed during World War II. And what we’ve accomplished so far with this project has been nothing short of
phenomenal.”—B.C.
ORNL, Savannah River work together on a tough waste remediation challenge
ORNL and Savannah River Site researchers may be seeing the light at the end of the tunnel for one of the South Carolina site’s most challenging waste remediation projects. Expertise in chemical separations, developed at ORNL during the Manhattan Project and Cold War eras, is now playing a major role in the cleanup of radioactive waste at Savannah River.
At the center of the issue are underground storage tanks at Savannah River that contain liquid with radiological contamination, primarily cesium-137. An early version of a process called in-tank precipitation, which captured cesium in a sludge that could then be vitrified into glass, failed.
Chem Tech's Doug Lee leads a pilot project on the in-tank precipitation technology.
Westinghouse’s Steve Piccolo, who manages waste management at Savannah River, has praised the ORNL “Salt Alternatives” team for its ability to solve problems and overcome obstacles and still pay attention to quality of data and research. “I look forward to continuing this relationship,” he says.
Tim Welch, with lead technician Kim Anderson, leads the pilot for the tall-column ion-exchange approach.
“The continuously stirred tank reactor pilot tests, led by Doug Lee and Jack Collins, have performed well in a 230-hour continuous run. We had good mixing and good temperature control. We threw every catalyst waste we could think of into the mix—palladium, copper, mercury, you name it,” says McGinnis. “We had a goal of a 40,000 decontamination factor. Ten thousand would have been acceptable. We got close to a 100,000 factor. It’s working very well.”
Savannah River chemist Mark Barnes is one of several SRS empoyees who have worked on the cesium removal project at ORNL
Waldo Cohn, ORNL chemistry pioneer, dies at 89
It can be argued that ORNL’s Manhattan Project roots are set as deeply in chemistry as in physics. One of those pioneers in chemistry, Waldo Cohn, died August 27 at age 89.
Waldo Cohn (right) in the early days.
