As an alternative to the traditional PUREX process for recycling spent nuclear fuel (SNF), a new process is being developed that utilizes hydrogen peroxide to dissolve SNF in aqueous carbonate solutions. Some of the primary benefits of the new peroxide promoted carbonate process include a smaller footprint, fewer separations steps, elimination of hazardous organic waste, and enhanced proliferation resistance by elimination of the pure plutonium stream produced in the PUREX process.
The dissolution rate of several uranium oxides into carbonate has been studied, and H2O2 has proven to be the most effective oxidant in promoting the dissolution. Hydrogen peroxide shows high affinity for complexing with U, Np, and Pu, forming surprisingly strong mixed carbonate-peroxo complexes. Several of these species, including K4[UO2(O2)(CO3)2]•nH2O and Na8Pu2(O2)2(CO3)6•12H2O, have been isolated and characterized by single crystal x-ray diffraction studies. Uranium shows extremely complex behavior by forming multiple mono- and poly-nuclear solution species. Thermodynamic studies indicate that selective removal of lanthanide (Ln(III)), Np, and Pu from U can be achieved by controlling the concentration of carbonate and H2O2 in solution. This gives great flexibility in the design of the separations flowsheet and allows for significant non-proliferation advantage by controlling the partitioning of the trans-uranium elements. We will discuss the dissolution rates for several uranium oxides, spectroscopic characterization and thermodynamic parameters for solution species formed in aqueous carbonate-peroxide media, as well as solution speciation and solubility behavior of mixed solutions of U with Pu and U with Ln(III) fission products.