The proposed program outlines a new strategy for advanced methods for the chemical partitioning of spent nuclear fuel into constituents that can be stored for future disposition (e.g., Cs, Sr and some minor actinides).  This program will be relevant to the Advanced Fuel Cycle R&D Program through the Spent Fuels Separations Technology area.  New waste forms and disposal strategies specific to the steam reforming process for the production of the cesium/strontium storage form will be studied with respect to the incorporation of Sr and Cs  , their decay products Ba, Y and Rb and rare earth fission products.  A combination of the broad synthetic and characterization study of inorganic ceramic waste form phases with the thermochemistry of these phases will provide a comprehensive data set from which to constructively evaluate and select the appropriate waste form. Emphasis will be on perovskite phases as a major constituent of the final waste form.  This proposal is predicated by work at Sandia National Laboratories and UC Davis which shows that thermally treated silicotitanates and niobates for Hanford tank remediation can be tuned to high selectivity for sequestration of cations and high stability (more than borosilicate glass) when converted to a ceramic waste form. 

The proposed work will provide information on the durabilities and stabilities of thermally consolidated Cs, Sr-loaded waste forms so that the potential of these options as viable storage or disposal scenarios can be evaluated.  The technical objective of the proposed work is to (1) fully characterize the phase relationships, structures and thermodynamic and kinetic stabilities of crystalline metal oxide based waste forms (e.g., perovskites) and (2) establish a sound technical basis for understanding key waste form properties, such as melting temperatures and aqueous durability, based on an in-depth understanding of waste form structures and thermochemistry. In addition, since Cs and Sr form new elements by radioactive decay, and this decay occurs almost completely over several hundred years, we will study the behavior and thermodynamics of waste forms containing different proportions of Cs, Sr and their decay products, using non-radioactive analogues.