Nonstoichiometry of Pyrochlore Ca(U,Pu)Ti2O7 and Problem of Brannerite (U,Pu)Ti2O6 in Ceramic for Actinide Immobilization Available to Purchase

Pyrochlore with stoichiometry (Ca,Gd,Zr,Hf,U,Pu)₂^VIII Ti₂^VI O_7−x is considered as host for actinide in the waste form designed at LLNL. Amount of the phase in ceramics ranges from 80 to 95 vol.%. Other actinide-containing phases — brannerite, zirconolite, and perovskite were also observed. Perovskite and brannerite have low durability relatively to the pyrochlore. Hence, appearance of the phases will affect confinement properties of the ceramic. This paper has addressed to problem of brannerite formation in the actinide waste forms. Data on properties of synthetic and natural brannerites, as well as chemical and radiation stability of the phase are analyzed. Reasons for brannerite appearance in the crystalline actinide waste forms and ways to prevent its formation are discussed.