Hatsuki Onitsuka

Analysis of Enrichment Factor of Uranium Enrichment by Redox Chromatography

Experiments and computer simulation show that the uranium enrichment factor in redox chromatography is determined substantially be electron exchange, isotope adsorption-desorption, and oxidation state adsorption-desorption equilibria. Computer simulation utilizing the theoretical model closely predicts the difference between the value of an enrichment factor derived from the solution equilibrium and that observed in the chromatographic isotope separation, which is attributable to a biased distribution of uranium ions between the solid and liquid phases and a nonequilibrium state in the separation column, thus allowing elucidation of the separation mechanism. A theoretical description of the central role of this enrichment factor in determining plant size and economics is presented.

Isotopic backmixing in a large-scale enrichment column in a chemical enrichment method

The Asahi chemical enrichment pilot plant with four large-scale 1-mm-diam enrichment columns has been operated using the «super» process since June 1987. Uranium with 3.3% enrichment was recovered in April 1988, and higher efficiencies have been observed in the pilot plant than in the bench-scale plant, which has 0.1-mm-diam enrichment columns. A possible reason is that the isotopic backmixing in the pilot plant is much smaller than in the bench-scale plant.Quantitative and statistical studies imply that both the extracolumn volume ratio and wall effect contribute to the smaller backmixing

Process energy of the advanced chemical uranium enrichment process

Process energy of the chemical uranium enrichment process is discussed using the dynamic enrichment factor, avoiding a cluster of commonly used equations that correlate relevant engineering parameters. An advanced process, whose process energy was found to be much smaller than in the original process in both laboratory and bench tests, has been recently developed and applied to a pilot plant. The basic principle underlying the improvement is an inverse redox reaction induced by the increased sorbability of multi-coordinated metal-complex ions onto an ion-exchange resin. The energy requirement for the advanced process will be reduced to <100 kW . h/kg . separative work unit.

The Equilibrium Principle of Displacement Chromatography

Abstract Displacement chromatography, an alternate method to elution chromatography in terms of operation, is described. The principle of displacement is conveniently explained using the concept of an ‘addend’ which is regarded as a species essential to any equilibrium reaction consisting of association of two species and its reverse reaction. Microscopic equilibria in a chromatographic column can be characterized by use of reduction potential strengths (Δμ° and Δμ) and its derived quantities, S and L potentials that we introduced for expression of equilibria. The method for evaluating the separation factor of displacement chromatography is also described. Further, a profile of simulated separation produced by iterative applications of the distribution function to the multistage equilibrium in the column is presented.

Energy Consumption for Product Assay in a Chemical Enrichment Process

The advanced chemical enrichment process, the «super» process, is a new-generation chemical enrichment process. The reducing separation energy consumption is due to the inverse redox reaction, the «Addox» reaction, which takes place in the enrichment columns, resulting in partial in situ self-regeneration of spent redox agents. The process development is now at the pilot plant operation stage. The energy consumption per separative work unit (SWU) for product assay of 235 U by the super process is presented. Analysis and magnitude of energy consumption are studied. The super process has been tested for the best operation method and uranium with enrichment >3% has been recovered in the pilot plant

Recovery of separation energy by inverse redox reactions

Abstract An “inverse redox reaction”, in which ferrous, Fe(II), and titanyl, TiO(IV), ions are converted to ferric, Fe(III), and trivalent titanium, Ti(III), ions, was observed to occur within an anion-exchange resin in adsorption-desorption experiments, even though the standard reduction potential (E 0 ) of the Fe(III) / Fe(II) couple is approximately 0.57 V higher than that of TiO(IV) / Ti(III) in acidic solution. This type of reaction had been predicted by a thermodynamic treatment developed to describe the multiple chemical equilibria of redox chromatography for uranium enrichment, in which the standard reduction chemical potentials of ligand-exchange, redox and ion-exchange reactions can be obtained by theoretical calculations and measurements. Utilization of the inverse reaction in redox chromatography was found to result in 30% to 90% reduction of the separation energy required for uranium enrichment.