Oxidation behaviour of uranium in the internally gelated urania–ceria solid solutions – XRD and XPS studies

Hydrothermal conversion of mixed uranium(iv)–cerium(iii) oxalates into U1−xCexO2+δ·nH2O solid solutions

“…Cerium being in the trivalent oxidation state in the initial oxalate, this indicates that cerium is oxidised, at least partly, during the hydrothermal treatment. A few peaks might appear on a random basis, around 2θ = 21°and 28°, and are caused by the presence of small amounts of orthorhombic M 3 O 8 42,43 (M = U and Ce), originating from the partial oxidation of U(IV) during the hydrothermal treatment.…”

“…For holding times longer than 3 h, fluorite is the only structure obtained even though a few peaks can appear on a recurring basis, around 2θ = 21.5 and 26°, caused by the presence of trace amounts of Ce-doped U 3 O 8 . 42,43 Therefore, 3 hours of hydrothermal treatment are required to fully convert oxalate into oxide. Fig.…”

Speciation and Ammonia-Induced Precipitation of Neptunium and Uranium Ions

“…Sol–gel processes can be used to produce actinide oxide microspheres, e.g., UO 2 , PuO 2 , and ThO 2 , as well as mixed-oxide or composite microspheres, such as (U,Th)­O 2 , (U,Pu)­O 2 , and MA-bearing microspheres. − The approach to fabricate such mixed oxides is to mix the uranium feed broth with a solution containing the dopant and to process this “metal blend” solution in the same manner as the conventional feed broth. ,− The hydrolysis behavior of the individual metal ions during the gelation reaction affects the quality of the microspheres. An inhomogeneous mixing of the dopant element into the uranium matrix occurs if the precipitation pH of the individual ions diverges significantly, as is, e.g., the case for Ce 4+ and UO 2 2+ ions, and premature or incomplete gelation can take place.…”

Cation-heterogeneity in internally gelated U1-Ce O2-, 0.15 ≤ z ≤ 0.3 microspheres

“…pelletization, vibro-packing, or TRISO type (pebble) fuel [5]- [8]. Sol-gel processes have been demonstrated extensively on lanthanide (Ln)/actinide(Ac) doped uranium mixed oxide systems, and have been reported to result in homogeneous solid solutions of Uranium (U) with Neodymium (Nd) [9], [10], Cerium (Ce) [11], Gadolinium (Gd) [12], Thorium(Th) [13], Neptunium (Np) [14], Plutonium (Pu) [15], and others [2]. Lanthanides are often used as surrogates for actinides to perform feasibility studies and explore process parameters without the need for shielded facilities.…”