Radiation Effects in Americium Ceramic Compounds

Along with uranium dioxide, mixed oxides play an essential role as fuels for present or next generation nuclear reactors. Although their production has been studied extensively, the methods applied currently result in materials that are usually not homogeneous at an atomic scale. To improve the quality of the powders (homogeneity and sintering properties), the hydrothermal decomposition of oxalate method was investigated.
Preliminary attempts for the (Th,Pu)O2, (Np,Pu)O2 and (Th,Np,Pu)O2 systems were reported elswhere. The procedure allowed the production of nanometric powders of U1-xPuxO2 solid solution in the full composition range. Partial oxidation of U(IV) to U(V) was observed, while plutonium was assumed to maintain its tetravalent oxidation state. Thanks to the low-temperature of the synthesis, such mixed oxides were used as reagents for the fabrication of more complicated systems. The aliovalent americium, which has a preference for the trivalent oxidation state, can be accommodated in the UO2 fluorite structure by charge compensation with U(V) only in limited amounts. Still, the feasibility of the method has been demonstrated for an Am-content relevant to transmutation fuels. ... mehrThus, U1-xAmxO2 (x = 0.1 and 0.2) and U0.75Pu0.20Am0.05 nanosized powders were produced by hydrothermal decomposition of the corresponding mixed oxalate. Typical oxidation states detected for the cations were U(IV)/U(V) for nanometric and sintered materials, respectively, where both exhibit mixed and Am(III)/Am(IV) oxidation state. Their sintering ability was tested and the volumetric expansion was measured by powder XRD as a function of storage time. A low swelling with no indications of amorphization has been derived over a period of four years.