331e Cesium and Strontium Separations for Pyroprocessing of Spent Oxide Nuclear Fuel

Michael F. Simpson and Supathorn Phongikaroon. Pyroprocessing Technology, Idaho National Laboratory, Idaho Falls, ID 83403

Pyroprocessing is a promising method for closing the nuclear fuel cycle, thereby separating fission products into robust waste forms while recycling actinides to fuel fabrication processes. This technology was initially developed for treating metallic spent fuel such as that used in the Experimental Breeder Reactor-II (EBR-II). However, the majority of spent fuel from the world's commercial nuclear reactors is in the form of oxides. Advanced fast reactors are also considering the use of oxide-based fuels. To bridge the gap between oxide spent nuclear fuel and pyroprocessing, it is necessary to have an oxide reduction step. Developed initially at Argonne National Laboratory, Electrolytic Reduction appears to adequately serve this purpose. In this process, spent fuel is placed into a cathode basket that is then immersed in a pool of molten LiCl-Li2O. When a sufficiently high electrical potential is applied, oxygen gas bubbles are evolved at the anode, and actinide oxides are reduced to metals at the cathode. Rare earth fission products appear to remain unreduced in the basket. Alkali and alkaline earth fission products (Cs, Sr, Rb, and Ba) partition into the salt, presumably as chlorides. The accumulation of these alkali and alkaline earth fission products in the salt will require periodic disposal of the salt into a waste form that can be safely stored for approximately 200 years to allow decay of the Cs-137 and Sr-90. Salt can be simply removed from the process once it reaches a contamination limit, blended with zeolite, and formed into a ceramic waste. However, this results in high waste volumes due to the fact that the zeolite loading is based on moles of chloride ions and LiCl is thrown-away along with fission product chlorides. If the fission products could be separated from the LiCl, there is the potential to drastically reduce the volume of waste generated. Options for achieving this separation will be discussed with preliminary experimental results presented.