Description: Small-scale experiments were performed to demonstrate the feasibility of fusing refractory actinide oxides with a series of materials commonly used to decompose minerals, glasses, and other refractories as a pretreatment to dissolution and subsequent recovery operations. In these experiments, 1-2 g of plutonium or neptunium oxide (PuO<sub>2</sub> or NpO<sub>2</sub>) were calcined at 900 degrees Celsius, mixed and heated with the fusing reagent(s), and dissolved. For refractory PuO<sub>2</sub>, the most effective material tested was a lithium carbonate (Li<sub>2</sub>CO<sub>3</sub>)/sodium tetraborate (Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub>) mixture which aided in the recovery of 90 percent of the plutonium. The fused product was identified as a lithium plutonate (Li<sub>3</sub>PuO<sub>4</sub>) by x-ray diffraction. The use of a Li<sub>2</sub>CO<sub>3</sub>/Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub> mixture to solubilize high-fired NpO<sub>2</sub> was not as effective as demonstrated for refractory PuO<sub>2</sub>. In a small-scale experiment, 25 percent of the NpO<sub>2</sub> was oxidized to a neptunium (VI) species that dissolved in nitric acid. The remaining neptunium was then easily recovered from the residue by fusing with sodium peroxide (Na<sub>2</sub>O<sub>2</sub>). Approximately 70 percent of the neptunium dissolved in water to yield a basic solution of neptunium (VII). The remainder was recovered as a neptunium (VI) solution by dissolving the residue in 8M nitric acid. In subsequent experiments with Na<sub>2</sub>O<sub>2</sub>, the ratio of neptunium (VII) to (VI) was shown to be a function of the fusion temperature, with higher temperatures (greater than approximately 400 degrees C) favoring the formation of neptunium (VII). The fusion of an actual plutonium-containing residue with Na<sub>2</sub>O<sub>2</sub> and subsequent dissolution was performed to demonstrate the feasibility of a pretreatment process on a larger scale. Sodium peroxide was chosen due to the potential of achieving higher actinide recoveries from refractory materials. In this experiment, nominally 10 g of a graphite-containing residue generated during plutonium casting operations was initially calcined to remove the graphite. Removal of combustible material prior ...
Date: April 15, 1999
Creator: Rudisill, T.S.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department