Fusion Techniques for the Oxidation of Refractory Actinide Oxides

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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 ... continued below

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Rudisill, T.S. April 15, 1999.

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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 to a large-scale fusion with Na<sub>2</sub>O<sub>2</sub> is needed due to the large amount of heat liberated during oxidation. Two successive fusions using the residue from the calcination and the residue generated from the initial dissolution allowed recovery of 98 percent of the plutonium. The fusion of the residue following the first dissolution was performed at a higher temperature (600 degrees Celsius versus 450 degrees Celsius during the first fusion). The ability to recover most of the remaining plutonium from the residue suggest the oxidation efficiency of the Na<sub>2</sub>O<sub>2</sub> fusion improves with higher temperatures similar to results observed with NpO<sub>2</sub> fusion.

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  • Other: DE00006031
  • Report No.: WSRC-TR-99-00021
  • Grant Number: AC09-96SR18500
  • DOI: 10.2172/6031 | External Link
  • Office of Scientific & Technical Information Report Number: 6031
  • Archival Resource Key: ark:/67531/metadc690829

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  • April 15, 1999

Added to The UNT Digital Library

  • Aug. 14, 2015, 8:43 a.m.

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  • Aug. 2, 2016, 1:13 p.m.

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Rudisill, T.S. Fusion Techniques for the Oxidation of Refractory Actinide Oxides, report, April 15, 1999; South Carolina. (digital.library.unt.edu/ark:/67531/metadc690829/: accessed September 26, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.