UREX+ process could help close the nuclear fuel cycle

Chemical engineer Candido Pereira examines a sample of solvent from an experiment using a centrifugal contactor that is being tested for processing spent nuclear fuel as part of the Advanced Fuel Cycle Initiative. Photo by George Joch.

Spent Nuclear Fuel Generation and Accumulation (poster, .pdf, 4MB) Spent Nuclear Fuel Management Options (poster, .pdf, 1 MB) Under the Department of Energy's Advanced Fuel Cycle Initiative (AFCI), Argonne is leading development of the UREX+ aqueous separations, a multi-step process for separating out the high-risk elements of spent nuclear fuel. Argonne has successfully demonstrated the entire process in hot cells and gloveboxes and is preparing for scale-up demonstration.

Background

Spent nuclear fuel and high-level radioactive waste are materials from nuclear power plants and government defense programs. These materials contain highly radioactive elements, such as cesium, strontium, technetium, plutonium, and neptunium. Some of these elements will remain radioactive for a few years, while others will be radioactive for millions of years. Scientists worldwide agree that the safest way to manage these materials is to dispose of them deep underground in what is called a geologic repository.

Currently, spent nuclear fuel is stored in specially designed pools at individual reactor sites around the country and high-level radioactive waste is stored at government facilities. Before such wastes can be stored in the proposed Yucca Mountain geologic repository, they will require further treatment to reduce overall toxicity, fissile content and volume. In addition, the behavior of waste materials following their disposal in the repository needs to be understood.

Technician Mark Clark (left) remotely handles a radioactive sample using a manipulator in Argonne National Laboratory's shielded-cell facility as chemical engineer Argentina Leyva confers with technician Lohmann Hoffenrichter in preparation for another remote test. Photo by George Joch.

Nearly all the risk from spent fuel comes from about 1-2% of its content — primarily the transuranics plutonium, neptunium, americium, and curium, and the long-lived isotopes of iodine and technetium. With these elements removed, the remaining 98% of the waste needs only about 1,000 years before its toxicity drops below that of natural uranium ore. Removing strontium and cesium with these wastes also reduces decay heat from the final waste form, which means that waste packages can be stored closer together, effectively expanding the repository's capacity. Transuranics will be separated from spent fuel and destroyed in advanced reactors. UREX+ Process for Recovering Key Radionuclides from Commercial Spent Nuclear Fuel Argonne is leading development of the UREX+ aqueous separations, a multi-step process for separating out the high-risk elements of spent nuclear fuel. Argonne has successfully demonstrated the entire process in hot cells and gloveboxes and is preparing for scale-up demonstration. UREX+ was named a 2005 Outstanding Engineering Achievement by the Illinois Engineering Council.

Contactor Is Key

The use of an Argonne-designed multistage contrifugal contactor is an important element in the development of the UREX+ processes.

The device is a cylindrical rotor surrounded by a mixing bowl. The spinning rotor acts as a mixer, a centrifugal settler and a pump. The liquid waste and solvent enter the bowl from opposite directions, and the rotor mixes them, allowing the solvent to extract the material to be removed. The liquids enter the hollow spinning rotor, and centrifugal forces 100 to 400 times gravity separate the liquids, which leave through separate ports at the rotor’s top.

The centrifugal contactors are efficient. They use only about one gallon of solvent per 3,000 gallons of waste.

For More Information

• UREX+
• Pyrochemical Processing (Pyroprocessing)

For more information, contact Candido Pereira (630-252-9832, pereira@cmt.anl.gov).