Without further treatment, spent nuclear fuel has to be securely stored and isolated from the environment for at least 250,000 years to prevent the spread of contamination in the biosphere. By a progressive deployment of GenIV fast reactors, together with the introduction of Pu multi-recycling into the fuel cycle, the confinement time of nuclear waste can be reduced to 10,000 years. Such a timescale is still too long to ensure the reliability of engineered and geological barriers. If we consider the full removal of plutonium (Pu) and uranium (U) from spent fuel, after a few hundreds of years of cooling, the remaining radiotoxicity and heat load of highly active waste is governed by the long-lived minor actinides americium (Am), curium (Cm) and neptunium (Np).
Np, having multiple stable oxidations states can be separated from spent fuel liquor in a modified PUREX process. The presence of various isotopes of Cm (242Cm - 245Cm) during the fabrication of irradiation targets would require excessive biological shielding (due to neutron emission) and impose rigorous criticality control on the process (due to spontaneous fission). Since the half-life of the most abundant Cm isotopes present in spent fuel is short, it is considered, that an “americium-only” separation from highly active raffinate solution would be the best technical compromise in terms of reduction of waste radiotoxicity, heat load, technical and financial feasibility. Am(III) can be efficiently transmuted into shorter-lived fission products or stable elements via irradiation in a high-flux fast reactor.
In aqueous media Am and Cm, adjacent in the Table of Mendelejev, are only stable in their trivalent oxidation state and show highly similar chemical behaviour. The high chemical similarity between Am(III) and Cm(III) renders their separation challenging.