The U.S. Department of Energy's Office of Science and Technology created the efficient separations and processing crosscutting area because new separations technologies and processes have the potential to save billions of dollars in cleanup costs. By removing the most hazardous or most radioactive portions of a waste stream, new separations technologies could reduce the complexity of treatments and the volume of waste slated for expensive high-level waste treatment and disposal. In addition to reducing costs, ESP has also been challenged to design separations processes that minimize risks to plant personnel and the public. Another goal is minimizing secondary wastes, which are additional wastes from the reagents used to carry out the separations. On April 15, 1996, Initiatives talked with Kurt Gerdes, ESP program manager, about some of the issues that confront the efficient separations and processing crosscutting area.
Gerdes said, "The efficient separations program really came into being to support the tanks focus area. And right now roughly 60 percent of our budget is targeted at addressing tank needs. But as we look through fiscal years 1995, 1996, and 1997, we see a trend of decreasing the amount of our budget supporting tanks directly. Although it's still a major portion of our budget, tanks support is slowly giving way to ESP support for the mixed waste, decontamination and decommissioning, and subsurface contaminants focus areas."
The major focus of ESP work is developing technologies for the separation and removal of primarily cesium, strontium, and technetium from the tanks at DOE sites at Richland, Washington; Aiken, South Carolina; Oak Ridge, Tennessee; and the Idaho National Engineering Laboratory in Idaho Falls, Idaho. Gerdes said, "We're trying to separate these elements out of the waste tanks and the question becomes, 'How do we change this or tweak that, modify the chemistry, technology, or system to remove some of these same contaminants from ground water or soil?' That's how we've started our work with mixed waste streams."
Gerdes defined the biggest technical challenge as developing technologies for the selective removal of radionuclides. "The majority of tank waste by volume is not radioactive. By pulling out the radioactive portion, primarily cesium and strontium, the costs of disposal for the remaining volume will be lower by far than having to treat the entire contents as radioactive. If we can develop technologies or methodologies that can hone in on selected ions, then we have a much smaller volume to process into glass logs for disposal at a facility like the Waste Isolation Pilot Plant." Understanding the chemistry that's involved and developing sorbents, ion-exchange resins, or extractants to perform the separations is the technical challenge.
Product Lines
ESP has categorized its inventory of R&D projects into four product lines to address
short-lived radionuclides, long-lived radionuclides, heavy metals, and waste processing
and treatment. Short-lived radionuclides, such as cesium, strontium, and tritium, have
short half-lives. An ESP-funded project is to separate short-lived radionuclides in tank
waste using crystalline silicotitanates, or CST, a new class of inorganic ion exchangers. (See article, page 1.) Gerdes said, "Work with crystalline
silicotitanates began in 1994 with a Cooperative Research and Development Agreement with
UOP Molecular Sieves in New Jersey. The CST existed in a powder form, so it was tough to
use in terms of tank waste. Under this CRADA, the powder was re-engineered for placement
in an ion exchange column for separating out these elements. The technology has proven
itself during pilot-scale studies. In September, a full-scale test of the technology is
planned in Oak Ridge at the Melton Valley Storage Tanks, which is a joint treatment
activity between EM-30 [Office of Waste
Management] and the tanks focus area within EM-50 [Office of Science and Technology]."
The capability of CST to selectively remove particular radionuclides is affected by the physical and chemical composition of tank wastes. Gerdes said tanks at the Idaho National Engineering Laboratory consist predominately of acidic waste; while at the other three sites, alkaline or neutralized waste is the major problem. ESP is funding studies at Sandia National Laboratories and Texas A&M University to further develop and characterize the chemical and physical properties that will determine the conditions under which CST will bond with cesium and strontium.
Another technology project within ESP's short-lived radionuclide product line is developing 3M Empore membranes, a collaborative effort among 3M, Pacific Northwest National Laboratory, IBC Advanced Technologies, and the Idaho National Engineering Laboratory. (See article, page 1.) Gerdes described the membrane as "surface-active particles enmeshed in a web-like matrix of radiation-resistant material. Membranes are formed and packaged into cartridges. The solution is passed through the cartridges, which pull out the selected element." ESP is investigating 3M Empore membranes for their capability to remove volatile organic compounds, cesium, and strontium from acidic ground water at INEL's Test Area North facility.
The long-lived radionuclides product line provides technology to remove radionuclides with long half-lives, such as uranium, plutonium, and technetium. One such technology is a water-soluble chelating polymer. (See article, page 12.) Gerdes said, "This technology was developed to filter out valuable or regulated metal ions from process, or waste, waters. It won an R&D 100 Award for work that was demonstrated at Boeing Aerospace, where nickel and zinc were removed from one of their electroplating processes. We're modifying that technology to address plutonium and americium at Los Alamos and Rocky Flats. It's nothing fancy; it's basically a polymer filtration. You're getting something that will bind to radioactive metal ions, then the radionuclides are removed with an ultrafiltration process. Changing the conditions of the solution elutes [removes] the radionuclides, and the polymers can then be reused. That technology is a real high flyer."
High-temperature vacuum distillation, another technology from the long-lived radionuclide product line, is a method for separating plutonium from waste salts. Rocky Flats residues consist of potassium chloride salts and sodium chloride salts mixed with plutonium. These can be separated by oxidizing the plutonium to form a non-volatile oxide, then heating in a vacuum to distill the alkali metal salts. Gerdes said, "At Rocky Flats some 12 metric tons of these waste salts are stored with less than one metric ton of plutonium within the mixture. This is not advanced chemistry; the process is based on differences in vapor pressure." Gerdes said vacuum distillation technology has been transferred to the Office of Nuclear Material and Facility Stablilization. "In FY97, they are planning to start a pilot study. The field-scale testing could lead to a full-scale operation later in FY97."
Transfers to focus areas
As a crosscutting area, ESP's customers are DOE's focus areas. Success is measured in
transfers of technologies to meet customers' needs. As Gerdes explained, "We try to
bring the investigation up to at least a pilot-scale to prove to the focus area and other
parties that the concept is sound. Then we want to either hand it off to them to fund
fully, or we'll try to find a home for it. We don't really have the budget to do the
full-scale demos."
External collaboration
In developing sorbents, ion-exchange resins, and extractants, ESP has involved private
industry and academic participants. Gerdes estimated that three quarters of ESP's 32
multiyear tasks have some kind of outside collaboration with either university or industry
participation.
The ESP program is also benefiting from the expertise of Russian scientists. Gerdes said three facilities in Russia are providing scientists to participate in cooperative studies of separations technologies. "The Khlopin Radium Institute at St. Petersburg is working with INEL to develop and test a cobalt dicarbollide derivative process for removing cesium and strontium from acidic waste. The Institute for Chemical Technology in Moscow is investigating the use of crown ethers; and the Institute for Physical Chemistry in Moscow is looking at actinide chemistry for removing technetium in alkaline media. I recently met these people at Hanford and received their project updates. The Russian projects are making great progress in solving problems as defined by the focus areas."
Gerdes encouraged people interested in finding out more about ESP to visit its upcoming Internet homepage. For the address, call Julie Gephart at (509) 375-2853, or e-mail her at jm_gephart@PNL.gov. A technology summary document, distributed at ESP's January 1996 technical exchange meeting, is also available. The document is a compilation of each project's technical background, approach, benefits, accomplishments, principal investigators, and other contacts.
