NEXT GENERATION SOLVENT MATERIALS COMPATIBILITY WITH POLYMER COMPONENTS WITHIN MODULAR CAUSTIC-SIDE SOLVENT EXTRACTION UNIT

Abstract

The Office of Waste Processing, within the Office of Technology Innovation and Development, is funding the development of an enhanced solvent for deployment at the Savannah River Site for removal of cesium from High Level Waste. The technical effort is collaboration between Oak Ridge National Laboratory (ORNL), Savannah River National Laboratory (SRNL), and Argonne National Laboratory. The first deployment target for the technology is within the Modular Caustic-Side Solvent Extraction Unit (MCU). Deployment of a new chemical within an existing facility requires verification that the chemical components are compatible with the installed equipment. In the instance of a new organic solvent, the primary focus is on compatibility of the solvent with organic polymers used in the facility. This report provides the data from exposing these polymers to the Next Generation Solvent (NGS). The test was conducted over six months. An assessment of the dimensional stability of polymers present in MCU (i.e., PEEK, Grafoil{reg_sign}, Tefzel{reg_sign} and Isolast{reg_sign}) in the modified NGS (where the concentration of the guanidine suppressor and MaxCalix was varied systematically) showed that guanidine (LIX{reg_sign}79) selectively affected Tefzel{reg_sign} (by an increase in size and lowering its density). The copolymer structure of Tefzel{reg_sign} and possibly its porosity allows for the easier diffusion of guanidine. Tefzel{reg_sign} is used as the seat material in some of the valves at MCU. Long term exposure to guanidine, may make the valves hard to operate over time due to the seat material (Tefzel{reg_sign}) increasing in size. However, since the physical changes of Tefzel{reg_sign} in the improved solvent are comparable to the changes in the CSSX baseline solvent, no design changes are needed with respect to the Tefzel{reg_sign} seating material. PEEK, Grafoil{reg_sign} and Isolast{reg_sign} were not affected by guanidine and MaxCalix within six months of exposure. The initial rapid weight gain observed in every polymer is assigned to the finite and limited uptake of Isopar{reg_sign} L/Modifier by the polymers probably due to the polymers porosity and rough surfaces. Spectroscopic data on the organic liquid and the polymer surfaces showed no preferential adsorption of any component in the NGS to the polymers and no leachate was observed in the NGS from any of the polymers studied.