A regenerable methylamine carbonate (MAC)/diethylenetriamine pentaacetic acid (DTPA) strip solution has been developed, as a collaborative effort between the Khlopin Radium Institute (KRI) and the Idaho National Engineering and Environmental Laboratory (INEEL), for the stripping of actinides, lanthanides, Cs, and Sr from cobalt dicarbollide-based solvent extraction processes. Methodology and experimental results of developing this strip reagent and a distillation method for regeneration of the resulting strip solution are presented. Additionally, countercurrent flowsheet testing of the Universal Solvent Extraction (UNEX) process, using 26 stages of 3.3 cm diameter centrifugal contactors, has been performed at the INEEL using dissolved pilot plant calcine and this regenerable strip solution. Results of stripping Cs, Sr, actinides, and lanthanides from the UNEX solvent with a MAC + DTPA strip solution that was freshly prepared and that has been regenerated are presented. Overall results of the flowsheet test are also presented.