Precipitation kinetics of a continuous precipitator, with application to the precipitation of ammonium polyuranate
A mathematical model describing the kinetics of continuous precipitation was developed which accounts for crystal nucleation, crystal growth, primary coagulation, and secondary coagulation. Population density distributions, average particle sizes, dominant particle sizes, and suspension density fractions of the crystallites, primary agglomerates, and secondary agglomerates leaving the continuous precipitator can be determined. This kinetic model was applied to the continuous precipitation of ammonium polyuranate, which consists of: (1) elementary crystals, (2) clusters or primary coagulated particles, and (3) agglomerates or secondary coagulated particles. The crystallites are thin, submicron, hexagonal platelets. The clusters had an upper size limit of about 7 ..mu.. in diameter and contained numerous small voids (less than 0.3 ..mu..m) due to the packing of the crystallites. The agglomerates had an upper size limit of about 40 ..mu..m in diameter and contained large voids (approximately 1 ..mu..m). The particle size distribution and particle structure of the ammonium polyuranate precipitate can be controlled through proper regulation of the precipitation conditions. The ratio of clusters to agglomerates can be best controlled through the uranium concentration, and the cohesiveness or internal bonding strength of the particles can be controlled with the ammonium to uranium reacting feed mole ratio. These two conditions, in conjunction with the residence time, will determine the nucleation rates, growth rates, and size distributions of the particles leaving the continuous precipitator. With proper control of these physical particle characteristics, the use of pore formers, ball-milling, and powder blending can probably be eliminated from the nuclear fuel fabrication process, substantially reducing the cost.
- Research Organization:
- Ames Lab., Ames, IA (United States)
- DOE Contract Number:
- W-7405-ENG-82
- OSTI ID:
- 5031496
- Report Number(s):
- IS-T-811; TRN: 78-010559
- Resource Relation:
- Other Information: Thesis
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
AMMONIUM URANATES
PRECIPITATION
CRYSTAL GROWTH
CRYSTAL STRUCTURE
INORGANIC POLYMERS
KINETICS
MATHEMATICAL MODELS
NUCLEATION
PARTICLE SIZE
ACTINIDE COMPOUNDS
AMMONIUM COMPOUNDS
POLYMERS
SEPARATION PROCESSES
SIZE
URANATES
URANIUM COMPOUNDS
050400* - Nuclear Fuels- Feed Processing
400702 - Radiochemistry & Nuclear Chemistry- Properties of Radioactive Materials