Masao Aida

A Theoretical Study of Isotope Separation by Displacement Chromatography

Abstract A set of equations is derived to describe mathematically the isotope distribution in the separation process of displacement chromatography. Emphasis is placed on nonsteady-state isotope accumulation in the boundary region of a migration band. The results indicate that the isotope profile in the migration band is expressed by where R, ∊, k, R0, L, and x are local isotope fraction, separation coefficient, slope coefficient, original isotope fraction, migration length, and position in the band, respectively. Mathematical treatment is extended to the determination of HETP of experimental systems. The relation between the frontal isotope ratio r L and the migration length is also obtained. The validity of the derived equations is verified by using the reported experimental data on boron isotope separation by ion-exchange chromatography.

Isothermal release of tritium from neutron-irradiated Li17Pb83

Isothermal release experiments were carried out to study the tritium recovery from lithium-lead alloy Li17Pb83 in which tritium was produced by irradiation with thermal neutrons. The experimental results indicate that the tritium recovery was incomplete within two hours at 200 °C. At temperatures above the melting point, the tritium release rates have been significantly increased and found to be controlled by the diffusion in the alloy. The determined diffusion coefficients of tritium in the alloy are 6.6 × 10−6, 7.8 × 10−6 and 9.5 × 10−6cm2/s at 300, 400 and 500°C, respectively.

Chromatographic Enrichment of 10B by Using Weak-Base Anion-Exchange Resin

Abstract In order to enrich 10B isotope, a boron adsorption band was eluted 620 m in a reverse-breakthrough displacement manner. Thereafter the band was stopped for 10 days and then eluted again up to a total distance of 754 m. The rear boundary of the adsorption band was kept sharp throughout the elution. From monitoring of the isotope abundance during elution, the lighter isotope 10B was confirmed to be accumulated in the band end region. The maximum enrichment of 10B reached 98.43% (10B atomic fraction) at a migration distance of 620 m. The interruption in the operation caused no serious damage in isotope accumulation, but there was a slight broadening of the accumulation curve. The isotopic accumulation was examined based on theoretical equations previously proposed. The results indicate that the HETP of the system is constant, 1.8 mm, up to a migration distance of 620 m and increases slightly at the distance of 754 m. The separation coefficient shows a gradual decrease with an increase of migration d...

Uranium isotope effects in some ion exchange systems involving uranyl–carboxylate complexes

Isotope fractionation between uranyl complexes in aqueous solution and uranyl ions in cation exchange resin was experimentally studied. The isotope separation coefficients e of the uranyl complex systems determined by a chromatographic method were (0.25±0.1)×10−4 (uranyl–chloride system), (0.88±0.1)×10−4 (acetate), (1.03±0.1)×10−4 (glycolate), (1.42±0.15)×10−4 (lactate), and (2.18±0.2)×10−4 (malate) at 25 °C. IR spectroscopic measurements were conducted on the uranyl complexes of which isotope effects were determined. It was found that the separation coefficients are linearly proportional to the shift of the asymmetric stretching vibration ν3 of O=U=O in uranyl complexes. The observed relation is e=4.62×10−6 (960−ν3/cm−1). A theoretical treatment indicated that approximately one third of the observed isotope effects could be attributed to the asymmetric stretching vibration.

Group separation of trivalent actinides and lanthanides by tertiary pyridine-type anion-exchange resin embedded in silica beads

The separation of trivalent actinides and lanthanides was studied by using newly developed tertiary pyridine-type anion-exchange resin embedded in silica beads. Chromatographic elution experiments were carried out by using a packed column of the new resin and methanol-hydrochloric acid solution as an effluent. We confirmed that the actinides were eluted well from the elution bands of lanthanides. Actinides and lanthanides were eluted according to the reverse order of their atomic number.

Ion-Exchange Selectivity of Tertiary Pyridine-Type Anion-Exchange Resin for Treatment of Spent Nuclear Fuels

The tertiary pyridine-type anion-exchange resin has been synthesized for the treatment of spent nuclear fuels and high-level radioactive waste. This resin, with a uniform diameter of 60 {micro}m, is mechanically strong enough and shows no swelling or shrinking regardless of its chemical forms. Systematic analysis was made of the adsorption selectivities of the resin in HCl solutions for a number of cations that exist in spent fuels, such as uranium and fission product elements. The results indicate that the resin is suitable to be used for the treatment of spent fuels and high-level radioactive waste.

Chromatographic Separation of Trivalent Actinides by Using Tertiary Pyridine Resin with Methanolic Nitric Acid Solutions

Chromatographic separation of trivalent actinides (Am, Cm and Cf) was performed by using a tertiary pyridine resin embedded in silica beads with methanolic nitric acid solutions. The trivalent actinides were eluted from the resin column in the reverse order of atomic numbers (Cf-Cm-Am). Higher concentration of methanol in the mixed solution accelerated both the adsorption of these elements on the resin and the separability for these elements. Americium was clearly separated from Cm and Cf by using a 1 cm-ø × 10 cm-height column with a 60vol% of methanol/40 vol% of concentrated nitric acid mixed solution at ambient temperature.

Separation of vanadium isotopes by ion-exchange chromatography

Cation-exchange displacement chromatography of VO2+ was carried out for studying vanadium isotope effects in carboxylate ligand-exchange systems. The heavier isotope 51V was enriched in the carboxylate complex solution. The isotope separation coefficients epsilon(= alpha-1) for 50V/51V were 2.2 x 10(-4) and 2.4 x 10(-4) for citrate and lactate systems at 298 K, respectively. These values are much larger than those obtained in a previous study on the malate system. The existence of binuclear complexes of VO2+ may create the conditions for larger isotope fractionation. From the viewpoint of the process development of isotope separation, the heights equivalent to a theoretical plate of these processes were analyzed and found to be very small in each system due to the homogeneous, small and highly porous resin used. Citrate may be better than the other tested systems for the vanadium isotope separation.

Ion exchange separation for decontamination of centrifuge enrichment plant

Ion exchange separation of uranyl ion (UO2+ 2) from metal cations has been carried out by the columnar operation using ion exchange resins in 0.1 mol/dm3 sulfuric acid medium. Uranyl ion was adsorbed in an anion exchange resin and the rest metal cations, Fe(III), Al(III), Cr(III), Ni(II) and Cu(II) ions, were adsorbed in a cation exchange resin in this system. Desorption of uranyl ion and metal cations adsorbed in the resins were tested by 2 mol/dm3 sulfuric acid solution. Desorbed elements were confirmed to be precipitated by appropriate alkaline solutions. On the basis of the results obtained, a concept was made on a decontamination system for uranium-contaminated waste solution from centrifuge enrichment plant.

Tritium recovery from neutron irradiated li-pb alloys

Tritium release rates were measured for irradiated Li-Pb alloy samples prepared by a rapid cooling of a melt of Li and Pb mixed at the atomic ratio of 17:83, to study the effects of composition change on the tritium release from Li-Pb alloys. The experimental results indicated that the lithium contents varied from sample to sample. However the observed tritium release rates were similar to, previously obtained values for Li17Pb83 and were confirmed to have increased at the temperatures above the melting point.