The Purex process was designed to recover plutonium for military applica­tions or for energy production with fast neutron reactors. In the latter case, recovered uranium was also useful. At present, plutonium is recovered for the fabrication of MOx fuels for PWRs and BWRs. The advocates of MOx fuel use insist that it not only is cost effective since it decreases the needs for enriched uranium, but that it can also help reduce the radiotoxicity

of the wastes. However, while plutonium is indeed the main long-term source of radiotoxicity for UOx spent fuels, minor actinide contributions become dominant in spent MOx fuels. Hence the idea to extract also minor actinides in order to transmute them. A number of processes have been proposed lately with that view.

Actinides are extractable by the Purex process when they are in an even state of oxidation. For example uranium is readily extractable in its VI oxi­dation state as the uranyl ion UVIO2+. Plutonium is also easily extracted as PuIV, but not as PunI, which allows separation of plutonium from uranium. Neptunium is present in nitric acid solutions in states NpV and NpVI. This coexistence of odd and even oxidation states of neptunium allows us to consider its extraction by a rather simple modification of the classical Purex process, as shown in reference [145]. The cases of americium and curium are more difficult since they essentially appear in the odd III oxida­tion state in nitric acid solutions. Active research and development in several countries is pursued in order to find efficient processes, compatible with Purex, for their separation [145]. They test different complex organic molecules with high selectivity for americium and curium. One of the main difficulties is that rare earths are also present in the nitric solution in oxida­tion state III, and are co-extracted with americium and curium. Facing this challenge two strategies have been adopted:

1. Use selective stripping with complexants to separate americium and curium from rare earths. Pertaining to this approach are the so-called Talspeak [146], DIDPA [147] and Truex [148] processes.

2. Use a two-cycle separation process with two different solvents where the first step separates americium, curium and lanthanides from the other fission products, and the second step separates americium and curium from the lanthanides. Examples of such processes are TRPO [149] and Diamex [150].

As examples of the two approaches we discuss a little more precisely the Truex and Diamex processes.