Accommodation of Cerium and Neodymium Oxides into Alumina.

Alumina was studied on its applicability for a host material to incorporate lanthanide and actinide elements present in HLW. Alumina-based waste forms containing about 8 mol% in all of Ce203 and/or Nd203 were prepared by firing at 1,500°C for 25 h in a reducing atmosphere, after drying and denitrating the mixed solutions of aluminum, cerium and/or neodymium nitrates, and then pelletizing the powder mixtures under 36 MPa. The obtained ceramic assemblages were analyzed by X-ray diffraction to determine crystalline phases produced. Tested also was the leachability of the assemblages in a nitric acid solution of pH=1 and deionized water at 150°C. These observations revealed that Ce prefers to be stabilized in magnetoplumbites, while Nd in perovskites. To obtain even denser assemblages, it seems necessary to suppress the formation of magnetoplumbites as much as possible. Leaching study showed that the relatively high dissolution rates of the forms in the solution of pH=1 g/10−6g/cm2·d) were probably due to the innate reactivity of alumina with acid, and perovskites were more prone to leaching than magnetoplumbites. In the deionized water, the elemental release rates from the forms are lower than 10-7g/cm2·d, and not influenced practically by the presence of perovskites.