The separation strategy for the UREX+ type processes is based on an optimization approach for which key objectives of the fuel cycle are pre­determined. Currently the US operates an “open fuel cycle,” in which all of the spent fuel is scheduled for disposal. Recycling of all of the fissile com­ponents, as is currently done in several countries, yields a partially “closed fuel cycle.” Recycling of both the fissionable and fissile components is referred to as a completely closed fuel cycle, although not all components are fully transmuted. Because a fast reactor is required to transmute the fissionable components, the completely closed cycle is often called a “fast reactor fuel cycle.” All fuel cycles generate high-level waste, but the volume and radiotoxicity is a function of the extent to which the spent fuel is sepa­rated and critical components transmuted. Isolation of specific fission prod­ucts, in addition to the actinides, can have a significant bearing on the performance of the wastes and repositories.

For a closed fuel cycle, the first step is to define the specific target prod­ucts that need to be recovered to meet the requirements of the selected recycle and waste options. The second step is to determine the feedstock to the separations process. The feedstock is a selection of SNF from the current inventory that is to be processed to yield the desired products. The third step is to determine the process flowsheet. Given the large variation within the SNF inventory, the process flowsheets are designed to accommodate the wide variation in composition. The flowsheet selection methodology identifies what combination of solvent extraction systems accomplishes the segregation of the specified target products. Processing options need not be limited to solvent extraction; ion exchange, crystallization, electrochemical and other processes can be used in combination. However, the integration requires that the processes be compatible chemically. In summary the UREX+ approach requires:

1. Definition of the specific target products that need to be separated.

2. Determination of the feedstock for the separations process; historically it is SNF, but targets and other forms of nuclear waste may be used.

3. Selection or development of technologies that can accomplish the desired separations so that the final products and waste forms meet either the product specifications or waste acceptance criteria.