2. Conditioning minor actinides

The three minor actinides formed during the reactorization of nuclear fuels are neptunium, americium and, to a lesser extent, curium. While americium and curium are almost exclusively stabilized in the trivalent state, neptunium has several stable oxidation states (mainly IV, V and VI). For both minor actinides and long-lived fission products, the methodology considered consisted in testing several materials (families of materials) on the basis of several properties of interest. To this end, simulant elements (mainly rare earth ions, thorium and, to a lesser extent, uranium) were initially used. For actinides, this approach led to the following selection of materials:

• britholite: ${\text{Ca}}_9{\text{An}}_{1-x}^{\text{III}}{\text{An}}_x^{\text{IV}}{\left({\text{PO}}_4\right)}_{5-x}{\left({\text{SiO}}_4\right)}_{1+x}{\text{F}}_{\text{2}}$...