Application of a Plasma Mass Separator to Advanced LWR Spent Fuel Reprocessing

The US Department of Energy (DOE) is investigating spent fuel reprocessing for the purposes of increasing the effective capacity of a deep geological repository, reducing the radiotoxicity of waste placed in the repository and conserving nuclear fuel resources. DOE is considering hydro-chemical processing of the spent fuel after cutting the fuel cladding and fuel dissolution in nitric acid. The front end process, known as UREX, is largely based on the PUREX process and extracts U, Tc as well as fission product gases. A number of additional processing steps have become known as UREX+. One of the steps includes a further chemical treatment of remove Cs and Sr to reduce repository heat load. Other steps include successive extraction of the actinides from residual fission products, including the lanthanides. The additional UREX+ processing renders the actinides suitable for burning as reactor fuel in an advanced reactor to convert actinides to shorter-lived fission products and to produce power. New methods for separating groups of elements by their atomic mass have been developed and can be exploited to enhance spent fuel reprocessing. These physical processes dry the waste streams so that they can be vaporized and singly ionized in plasma that is contained in longitudinal magnetic and perpendicular electric fields. Proper configuration of the fields causes the plasma to rapidly rotate and expel heavier mass ions at the center of the machine. Lower mass ions form closed orbits within the cylindrical plasma column and are transported to either end of the machine. This plasma mass separator was originally developed to reduce the mass of material that must be immobilized in borosilicate glass from DOE defense waste at former weapons production facilities. The plasma mass separator appears to be well-suited for processing the UREX raffinate and solids streams by exploiting the large atomic mass gap that exists between lanthanides (< ∼180 amu) and actinides (> ∼220 amu). In one processing step the raffinate and solids would be separated into a group of residual fission products including the lanthanides and another group containing predominately Pu and mixed higher actinides. The plasma mass separator could process the UREX raffinate and solids directly for spent fuel that has cooled for 50 years or more, but there may be some advantage to removing Cs and Sr by hydro-chemical means for relatively short (∼10 years) cooled fuel. This paper will explore the potential cost and environmental impact advantages of combining a hydro-chemical front end with a plasma mass separator back end in an advanced spent fuel reprocessing plant. (authors)