SMALL-SCALE TESTING OF PLUTONIUM (IV) OXALATE PRECIPITATION AND CALCINATION TO PLUTONIUM OXIDE TO SUPPORT THE MOX FEED MISSION

Technical Report · Mon Jun 25 00:00:00 EDT 2012

DOI:https://doi.org/10.2172/1044791· OSTI ID:1044791

Crowder, M; Pierce, R; Scogin, J; Daniel, G; King, W

The H-Canyon facility will be used to dissolve Pu metal for subsequent purification and conversion to plutonium dioxide (PuO{sub 2}) using Phase II of HB-Line. To support the new mission, SRNL conducted a series of experiments to produce calcined plutonium (Pu) oxide and measure the physical properties and water adsorption of that material. This data will help define the process operating conditions and material handling steps for HB-Line. An anion exchange column experiment produced 1.4 L of a purified 52.6 g/L Pu solution. Over the next nine weeks, seven Pu(IV) oxalate precipitations were performed using the same stock Pu solution, with precipitator feed acidities ranging from 0.77 M to 3.0 M nitric acid and digestion times ranging from 5 to 30 minutes. Analysis of precipitator filtrate solutions showed Pu losses below 1% for all precipitations. The four larger precipitation batches matched the target oxalic acid addition time of 44 minutes within 4 minutes. The three smaller precipitation batches focused on evaluation of digestion time and the oxalic acid addition step ranged from 25-34 minutes because of pump limitations in the low flow range. Following the precipitations, 22 calcinations were performed in the range of 610-690 C, with the largest number of samples calcined at either 650 or 635 C. Characterization of the resulting PuO{sub 2} batches showed specific surface areas in the range of 5-14 m{sup 2}/g, with 16 of the 22 samples in the range of 5-10 m2/g. For samples analyzed with typical handling (exposed to ambient air for 15-45 minutes with relative humidities of 20-55%), the moisture content as measured by Mass Spectrometry ranged from 0.15 to 0.45 wt % and the total mass loss at 1000 C, as measured by TGA, ranged from 0.21 to 0.58 wt %. For the samples calcined between 635 and 650 C, the moisture content without extended exposure ranged from 0.20 to 0.38 wt %, and the TGA mass loss ranged from 0.26 to 0.46 wt %. Of these latter samples, the samples calcined at 650 C generally had lower specific surface areas and lower moisture contents than the samples calcined at 635 C, which matches expectations from the literature. Taken together, the TGA-MS results for samples handled at nominally 20-50% RH, without extended exposure, indicate that the Pu(IV) oxalate precipitation process followed by calcination at 635-650 C appears capable of producing PuO{sub 2} with moisture content < 0.5 wt% as required by the 3013 Standard. Exposures of PuO{sub 2} samples to ambient air for 3 or more hours generally showed modest mass gains that were primarily gains in moisture content. These results point to the need for a better understanding of the moisture absorption of PuO{sub 2} and serve as a warning that extended exposure times, particularly above the 50% RH level observed in this study will make the production of PuO{sub 2} with less than 0.5 wt % moisture more challenging. Samples analyzed in this study generally contained approximately 2 monolayer equivalents of moisture. In this study, the bulk of the moisture released from samples below 300 C, as did a significant portion of the CO{sub 2}. Samples in this study consistently released a minor amount of NO in the 40-300 C range, but no samples released CO or SO{sub 2}. TGA-MS results also showed that MS moisture content accounted for 80 {+-} 8% of the total mass loss at 1000 C measured by the TGA. The PuO{sub 2} samples produced had particles sizes that typically ranged from 0.2-88 {micro}m, with the mean particle size ranging from 6.4-9.3 {micro}m. The carbon content of ten different calcination batches ranged from 190-480 {micro}g C/g Pu, with an average value of 290 {micro}g C/g Pu. A statistical review of the calcination conditions and resulting SSA values showed that in both cases tested, calcination temperature had a significant effect on SSA, as expected from literature data. The statistical review also showed that batch size had a significant effect on SSA, but the narrow range of batch sizes tested is a compelling reason to set aside that result until tests with larger batch sizes are completed. When feed acidity was not included as a variable, calcination time had a significant effect on SSA. However, including feed acidity as a variable showed that neither feed acidity nor calcination time had a significant effect on SSA in this study. Also, for both cases the statistical review also indicated that digestion time did not have a significant effect on SSA.

• Research Organization: Savannah River Site (SRS), Aiken, SC (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: DE-AC09-08SR22470
• OSTI ID: 1044791
• Report Number(s): SRNL-STI-2012-00338; TRN: US1203565
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
ABSORPTION
ADSORPTION
ANIONS
CALCINATION
CARBON
DIGESTION
MASS SPECTROSCOPY
MOISTURE
NITRIC ACID
OXALATES
OXALIC ACID
OXIDES
PARTICLE SIZE
PH VALUE
PHYSICAL PROPERTIES
PLUTONIUM
PLUTONIUM DIOXIDE
PLUTONIUM OXIDES
PRECIPITATION
PURIFICATION
SPECIFIC SURFACE AREA