“Cold” demonstration on a modest scale of the solvent extraction process should be made as soon as possible. The objectives of the demonstration should be to show that the process is adequately robust. In particular, it would need to (i) identify and solve problems such as those mentioned in the previous section and (ii) show that the required DF could be achieved for different feed compositions representative of the range expected for processing of the SRS tank waste. Other important engineering variables should also be investigated. Especially important would be the identification of “show stoppers” which could eliminate solvent extraction from consideration. During this stage, laboratory work should continue on demonstrating thermal, chemical, and radiolytic stabilities of all components of the solvent. Degradation pathways and products should be identified and these products tested for adverse effects. From this work, realistic solvent makeup volume requirements should be established.
Design of a hot laboratory demonstration process—using real tank waste—on a scale sufficient to define the final process should begin immediately. If solvent extraction remains in contention as a possible alternative, implementation of the hot demonstration should begin as soon as a high degree of confidence in the feasibility of the process is achieved from the cold demonstration and solvent-stability tests.
Work should begin immediately on defining the production capability and economics for commercial quantities of the calixarene crown ether. Purity and other specifications relevant to performance of the solvent system should be developed. Suppliers should demonstrate their ability to produce batches of solvent components that conform to specifications.