Studies of the Preparation of Thoria and Thoria-Urania Microspheres Using an Internal Gelation Process

An internal gelation process has been studied for the preparation of thoria microspheres. The gelation behavior of an acid-deficient thorium nitrate solution (NO₃/Th⁴⁺ = 3.0) with hexamethylenetetramine and urea has been investigated to define a gelation field diagram that could be used to select compositions suitable for microsphere preparation. Thoria microspheres have been successfully prepared using many different compositions. The process has also been used to prepare (Th,U)O₂ microspheres containing 5 and 10 mol% uranium.