Seong-Yun Kim

Equilibrium and kinetic studies of selective adsorption and separation for strontium using DtBuCH18C6 loaded resin

A crown ether loaded resin was prepared by successive impregnation and fixing the 4′,4′(5″)-di(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) and its molecule modifier, 1-dodecanol, onto the porous silica/polymer composite support (SiO2-P particles). The characterization of DtBuCH18C6 loaded resin was examined by thermal gravimetry and differential thermal analysis and electron probe microanalysis. The adsorption behavior of Sr(II), Cs(I), Ru(III), Pd(II), La(III), Nd(III), Sm(III), Gd(III), Zr(IV), and Mo(VI) was investigated by the batch method. Furthermore, the column test for Sr (II) was performed. The batch experiments were carried out by varying the shaking times, HNO3 concentration, and initial concentration of metal ions. A relatively large K d value above 182 cm3/g for Sr(II) was obtained in the presence of 3 M HNO3. In contrast, the K d values of Cs(I), Ru(III), Pd(II), La(III), Nd(III), Sm(III), Gd(III), Zr(IV), and Mo(VI) were considerably lower than 10 cm3/g. The adsorption of Sr(II) was found to be controlled by chemisorption mechanism, and followed a Langmuir-type adsorption equation. The breakthrough curve of Sr(II) had S-shaped profile, and the elution percentage was estimated to be 99.9% by using the eluent of H2O.

Development of a simplified separation process of trivalent minor actinides from fission products using novel R-BTP/SiO2-P adsorbents

From a viewpoint of direct separation of trivalent minor actinides (MA: Am, Cm etc.) from fission products (FP) including rare earths (RE) in high level radioactive liquid waste, the authors have developed a simplified separation process using a single column packed with novel extraction adsorbents. Attention was paid to a new type of nitrogen-donor ligand, R-BTP (2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine, R: alkyl group) as an extractant because it has higher extraction selectivity for Am(III) than RE(III). Since the R-BTP ligands show different properties such as adsorbability and stability when they have different alkyl groups, several R-BTP extraction adsorbents were prepared by impregnating the R-BTP ligands with different alkyl groups (isohexyl-, isoheptyl- and cyheptyl-BTP) into a porous silica/polymer composite support (SiO2-P particles). This work investigated: (1) fundamental properties of the synthesized R-BTP/SiO2-P adsorbents, (2) adsorption and desorption properties of Am and FP in nitric acid solution and water using the adsorbents in a batch experiment, (3) radiolytic and chemical stabilities of the adsorbents, and (4) the possibility for developing a simplified separation process of MA using the most promising adsorbent (isohexyl-BTP/SiO2-P) under temperature control between 25 and 50°C.

Challenges to develop single-column MA(III) separation from HLLW using R-BTP type adsorbents

In order to directly separate trivalent minor actinides (MA: Am, Cm) from fission products (FP) containing rare earths (RE) in high level radioactive liquid waste (HLLW), the authors have challenged to develop a simplified MA separation process by extraction chromatography using a single column. Attention has been paid to a new type of nitrogen-donor ligands, R-BTP (2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl) pyridine, R: alkyl group) as an extractant because it shows high extraction selectivity for Am(III) over RE(III). It is known that the R-BTP ligands show different properties such as adsorbability and stability by having different alkyl groups. Therefore, some novel adsorbents were prepared by impregnating different types of R-BTP ligands (isohexyl-, isoheptyl- and cyheptyl-BTP) and a similar ligand to the R-BTP, ATP (2,6-bis(1-aryl-1H-tetrazol-5-yl)pyridines), into the porous silica/polymer support (SiO2-P particles). This work deals with comparison in adsorption and desorption properties of Am and some FP in HNO3 solution onto such R-BTP type adsorbents, as well as chemical and radiolytic stability of the adsorbents. Then the possibility of a single-column separation of MA from main FP was pursued by evaluating the results of column experiments using the most promising adsorbent (isohexyl-BTP/SiO2-P) under temperature control. In addition, elution behaviors of U and Pd were also estimated.

Electrochemical and spectroelectrochemical behaviour of Np(VI) ions in nitric acid solutions

Summary Electrochemical and spectroelectrochemical has been used to investigate the behaviour of neptunium (VI) in 1 ∼ 8 M HNO3 solutions. The electrochemical reactions of Np(VI) ions were found to occur quasi-reversibly. The formal redox potentials (E°) for Np(VI)/Np(V) couples were determined to be +0.906, +0.908, +0.909, +0.902, +0.896, +0.895, +0.888, and +0.884 V (vs . Ag/AgCl) for Np(VI) ions in 1, 2, 3, 4, 5, 6, 7, 8 M HNO3 solutions, respectively. The reduction processes of Np(VI) ions were followed spectroelectrochemically by using an optical transparent thin layer electrode cell. It was found that the absorption spectra measured at the applied potentials from +1.10 to +0.60 V versus Ag/AgCl reference electrode redox couple for Np(VI) in HNO3 solution have clear isosbestic points. These results indicate that the only reduction product of Np(VI) is Np(V), which is of considerable stability in HNO3 solutions.

Adsorption Behaviors of Platinum Group Metals in Simulated High Level Liquid Waste Using Macroporous (MOTDGA-TOA)/SiO2-P Silica-based Absorbent

As fundamental research for separation of platinum group metals (PGMs) from high level liquid waste (HLLW) by macroporous silica-based adsorbent, (MOTDGA-TOA)/SiO2-P adsorbent was prepared by impregnation of N,N′-dimethyl-N,N′-di-n-octyl-thiodiglycolamide (MOTDGA) and Tri-n-octylamine (TOA) into silica/polymer composite support (SiO2-P). The adsorption behavior of Ru(III), Rh(III), and Pd(II) in simulated HLLW onto the adsorbent were investigated by the batch method to obtain their corresponding equilibrium and kinetic data. The adsorbent showed strong adsorption for Pd(II) and the adsorption reached equilibrium within 2 hr. High distribution coefficient (K d) values for Pd(II) were obtained in 0.1–1 M HNO3 concentration. In addition, the use of both MOTDGA and TOA improved adsorption of Ru(III) and Rh(III) better than individual use of them. Especially, the K d value for Ru(III) towards (MOTDGA-TOA)/SiO2-P adsorbent was three times larger than that in the adsorption using only with MOTDGA or TOA as extractant. The adsorptions of Ru(III), Rh(III), and Pd(II) followed the Langmuir adsorption model, and were found to be controlled by the chemisorption mechanism.

MEASURES AGAINST RADIOACTIVE CONTAMINATION DUE TO FUKUSHIMA FIRST NUCLEAR POWER PLANT ACCIDENTS PART III: REMOVING AND DECONTAMINATION OF CONTAMINATED SOIL

We studied the structure of radioactive cesium distribution in soil and found the exponential dependence. This behavior could be explained theoretically. We developed a useful method to decontaminate the soil contaminated with radioactive cesium atoms. We applied our method to the contaminated school yards of elementary schools of Marumori town and decontaminated total area of about 7000 m2.

Electrochemical redox reactions of uranium(VI) complexes with multidentate ligands in dimethyl sulfoxide

Abstract Electrochemical reactions of UO2(β-diketonato)2-dmso, UO2(trop)2dmso, UO2(sap)(dmso)2, and UO2(salen)dmso (dmso = dimethyl sulfoxide, β-diketonate = benzoylacetonate (ba), benzoyltrifluoroacetonate (btfa), and thenoyltrifluoroacetonate (ttfa), trop = tropolonate, sap = 2-salicylidenaminophenolate, and salen = N , N´-disalicylidenethylenediaminate) complexes in dmso solutions containing tetrabutylammonium perchlorate as a supporting electrolyte have been studied with cyclic voltammetry. These uranyl(VI) complexes were found to be reduced quasi -reversibly to U(V) species. The formal redox potentials (E°, vs . ferrocen/ferrocenium) for U(VI)/U(V) couples were determined to be -1.416 V for UO2(ba)2dmso, -1.073 V for UO2(btfa)2dmso, -1.082 V for UO2(ttfa)2dmso, -1.379 V for UO2(trop)2dmso, -1.500 V for UO2(sap)(dmso)2, and -1.602 V for UO2(salen)dmso. Furthermore, the resulting U(V) complexes, [UO2(btfa)2dmso]-, [UO2(ttfa)2dmso]-, and [UO2(salen)dmso]-, were found to be able to exist stably in dmso solutions.

Adsorption Behavior of Platinum Group Metals onto a Silica-based (Crea+Dodec)/SiO2-P Extraction Resin from Simulated High Level Liquid Waste

Basic properties of a silica-based macroporous N’,N’-di-n-hexyl-thiodiglycolamide (Crea) extraction resin, (Crea+Dodec)/SiO2-P were examined. This extraction resin was synthesized by impregnating Crea and its modifier, n-Dodecyl alcohol (Dodec) into the macroporous SiO2-P support with a mean diameter of 50 μm. Adsorption behavior of platinum group metals (PGMs) and some fission product elements from simulated high level liquid waste onto the resin was investigated by batch experiment. It was found that (Crea+Dodec)/SiO2-P extraction resin exhibited good adsorption selectivity for PGMs over other tested elements in 0.1-5.0 M HNO3 solution. This resin showed strong affinity to Pd(II) especially in a short contact time but almost no adsorption for rare earth elements. Adsorption behavior of PGMs in experiment could be expressed by the Langmuir monomolecular layer adsorption mode. Meanwhile, adsorption results were fitted well with the pseudo-second order model and the rate-controlling step of this adsorption process was governed by the chemisorption process. In addition, the adsorption isotherms and thermodynamic parameters of tested elements were calculated by the Langmuir, Freundlich, and van’t Hoff equations, respectively.

Timing Performance of TlBr Detectors

The timing performance of TlBr detectors was evaluated at room temperature (22 °C). 0.5-mm-thick planar TlBr detectors with Tl circular electrodes with a diameter of 3 mm were fabricated from TlBr crystals grown by the traveling molten zone method using a zone-purified material. The pulse rise time of the TlBr detector was measured using a digital oscilloscope as the cathode surface of the device was irradiated with a 22Na gamma-ray source. Coincidence timing spectra were obtained between the TlBr detector and a BaF2 scintillation detector when both detectors were irradiated with 511 keV positron annihilation gamma-rays. The timing resolution of the TlBr detector was found to be inversely proportional to the applied bias voltage. The TlBr detector, in coincidence with the BaF2 detector, exhibited timing resolutions characterized by a 6.5 ns full width at half maximum (FWHM) and an 8.5 ns FWHM with and without an energy window of 350 keV-560 keV, respectively.

TlBr Capacitive Frisch Grid Detectors

Capacitive Frisch grid detectors with the dimensions of 2 mm × 2 mm × 4.4 mm were fabricated from TlBr crystals grown by the travelling molten zone method using zone-purified materials. Spectroscopic performance of the detectors was evaluated at room temperature (24°C), - 5°C and - 20°C. The TlBr detector exhibited an energy resolution of 1.6% FWHM at 662 keV with a peak-to-Compton ratio of 8.7 with the depth correction at room temperature. Improvement of the detector performance was achieved by cooling the detector-preamplifier system. The energy resolutions of 3.4%, 1.5%, 1.0% and 0.9% FWHM at 122 keV, 356 keV, 662 keV and 1332 keV, respectively, were recorded with the TlBr detector without the depth correction at - 5°C. An energy resolution of 0.9% FWHM at 662 keV with a peak-to-Compton ratio of 18.2 was obtained from the TlBr detector with the depth correction at -20°C. An upper limit for the Fano factor of TlBr was estimated to be 0.43 at -20°C.