Sorption behavior of niobium onto clay minerals in the presence of Ca

Ohira, Saki; Iida, Yoshihisa

Proceedings of Waste Management Symposia 2023 (WM2023) (Internet), 10 Pages, 2023/02

The sorption distribution coefficient (d) of niobium-94 (Nb-94) on minerals is one of the important parameters in safety assessment of radioactive waste disposal. In a previous study, the d values of Nb under alkali condition in the presence of Ca, were two orders of magnitude higher than those in the presence of Na. In this study, Nb sorption experiments were performed to reexamine the effect of Ca on Nb sorption on clay minerals, and blank tests were performed to check for precipitation formation. The results showed that the Nb sorption onto montmorillonite and illite, did not depend on the Ca concentration, and d values obtained in the presence of Ca were the same as those in the absence of Ca. A sorption model assuming sorption by complexation on the mineral surface was developed and then calculated using the geochemical calculation code. The model with the surface species X_ONb(OH) and X_ONb(OH) represented trends in the data obtained.

Structural characterization by X-ray analytical techniques of calcium aluminate cement modified with sodium polyphosphate containing cesium chloride

Takahatake, Yoko; Watanabe, So; Irisawa, Keita; Shiwaku, Hideaki; Watanabe, Masayuki

Journal of Nuclear Materials, 556, p.153170_1 - 153170_7, 2021/12

https://doi.org/10.1016/j.jnucmat.2021.153170

Incorporation of U, Pb and rare earth elements in calcite through crystallisation from amorphous calcium carbonate; Simple preparation of reference materials for microanalysis

Miyajima, Yusuke*; Saito, Ayaka*; Kagi, Hiroyuki*; Yokoyama, Tatsunori; Takahashi, Yoshio*; Hirata, Takafumi*

Geostandards and Geoanalytical Research, 45(1), p.189 - 205, 2021/03

https://doi.org/10.1111/ggr.12367

Uncertainty for elemental and isotopic analyses of calcite by LA-ICP-MS is largely controlled by the homogeneity of the reference materials (RMs) used for normalization and validation. In order to produce calcite RMs with homogeneous elemental and isotopic compositions, we incorporated elements including U, Pb, and rare earth elements into calcite through heat- and pressure-induced crystallization from amorphous calcium carbonate that was precipitated from element-doped reagent solution. X-ray absorption spectra showed that U was present as U(VI) in the synthesized calcite, probably with a different local structure from that of aqueous uranyl ions. The uptake rate of U by our calcite was higher in comparison to synthetic calcite of previous studies. Variations of element mass fractions in the calcite were better than 12% 2RSD, mostly within 7%. The Pb/Pb ratio in the calcite showed 1% variations, while the U/Pb ratio showed 3-24% variations depending on element mass fractions. Using the synthetic calcite as primary RMs, we could date a natural calcite RM, WC-1, with analytical uncertainty as low as 3%. The method presented can be useful to produce calcite with controlled and homogeneous element mass fractions, and is a promising alternative to natural calcite RMs for U-Pb geochronology.

Investigation of high-temperature chemical interaction of calcium silicate insulation and cesium hydroxide

Rizaal, M.; Nakajima, Kunihisa; Saito, Takumi*; Osaka, Masahiko; Okamoto, Koji*

Journal of Nuclear Science and Technology, 57(9), p.1062 - 1073, 2020/09

https://doi.org/10.1080/00223131.2020.1755733

The interaction of cesium hydroxide and a calcium silicate insulation material was experimentally investigated at high temperature conditions. A thermogravimetry equipped with differential thermal analysis was used to analyze thermal events in the samples of mixed calcium silicate and cesium hydroxide under Ar-5%H and Ar-4%H-20%H0 with maximum temperature of 1100C. Prior being mixed with cesium hydroxide, a part of calcium silicate was pretreated at high temperature to evaluate the effect of possible structural changes of this material due to a preceding thermal history and also the sake of thermodynamic evaluation to those available ones. Based upon the initial condition (preliminary heat treatment) of calcium silicate, it was found that if the original material consisted of xonotlite (CaSi0(0H)), the endothermic reaction with cesium hydroxide occurred over the temperature range 575-730C meanwhile if the crystal phase of original material was changed to wollastonite (CaSi0), the interaction occurred over temperature range 700-1100C. Furthermore, the X-ray diffraction analyses have indicated on both type of pretreated calsils that regardless of Ar-5%H and Ar-4%H-20%H0 atmosphere, cesium aluminum silicate, CsAlSi0 was formed with aluminum in the samples as an impurity or adduct.

Development of phosphate modified CAC cementitious systems with reduced water content for the immobilization of radioactive wastes

Garcia-Lodeiro, I.*; Irisawa, Keita; Meguro, Yoshihiro; Kinoshita, Hajime*

Proceedings of 15th International Congress on the Chemistry of Cement (ICCC 2019) (Internet), 10 Pages, 2019/09

The immobilization of low or intermediate-level radioactive wastes in cements is a common practise. Grout, a mixture of Portland cement and supplemental cementitious materials, is commonly used to encapsulate the wastes. However, the conventional cementing process based on portland cement has the risk of hydrogen gas generation, due to the radiolysis of the water intrinsically present in the cement matrix both in the pore solution and the hydrated products. The addition of phosphates to calcium aluminate cement (CAC) is interesting because this system sets and hardens via the acid-based reaction, between the acid phosphate solution and the basic CAC cement. Due to this different mechanism of reaction, it would be possible to generate a solid cementitious product with a reduced water content, which can be beneficial to minimize the risk of hydrogen gas generation associated with the radiolysis of water by radioactive wastes. The present study investigates the effect of water reduction on a phosphate modified CAC systems at different temperatures (35C, 60C, 95C, 110C,180C) in the initial 7 days of curing. Experimental results indicate that these phosphate-based cements do not form the conventional CAC crystalline hydration products in the condition tested, but provide a structural integrity despite a significant amount of water loss. The results also suggest the formation of hydroxyapatite in samples cured at 95C.

Reduction of water content in calcium aluminate cement with/out phosphate modification for alternative cementation technique

Garcia-Lodeiro, I.*; Irisawa, Keita; Jin, F.*; Meguro, Yoshihiro; Kinoshita, Hajime*

Cement and Concrete Research, 109, p.243 - 253, 2018/07

https://doi.org/10.1016/j.cemconres.2018.04.019

Radiochemical study of the kinematics of multi-nucleon transfer reactions in Ca + Cm collisions 10% above the Coulomb barrier

Gtz, M.*; Gtz, S.*; Kratz, J. V.*; Dllmann, Ch. E.*; Mokry, Ch.*; Runke, J.*; Thrle-Pospiech, P.*; Wiehl, N.*; Schdel, M.; Ballof, J.*; et al.

Nuclear Physics A, 961, p.1 - 21, 2017/05

https://doi.org/10.1016/j.nuclphysa.2017.02.006

The kinematics of multi-nucleon transfer reactions in the Ca + Cm collisions were investigated using a stacked-foil technique and radiochemical separations. In previous studies, isotopic distributions of the products of below-target isotopes were found to be broader than those of above-target isotopes, which had been interpreted as larger contributions of strongly dumped collisions in the productions of below-target isotopes than above-target ones. However, in the present study, the average total kinetic energy loss (TKEL), and thus, the average excitation energies were determined for both below-target and above-target isotopes, and they were found to be similar. This contradicts the previous interpretation, and thus, a new interpretation has been proposed; highly excited above-target products are lost by fission.

Draft genome sequence of calcium-dependent sp. strain TCA20, isolated from a hot spring containing a high concentration of calcium ions

Fujinami, Shun*; Takeda, Kiyoko*; Onodera, Takefumi*; Sato, Katsuya; Sano, Motohiko*; Takahashi, Yuka*; Narumi, Issey*; Ito, Masahiro*

Genome Announcements (Internet), 2(5), p.e00866-14_1 - e00866-14_2, 2014/09

https://doi.org/10.1128/genomeA.00866-14

Development of frequency stabilized laser system for long-lived isotope analysis, 2; Simultaneous locking system for multiple diode lasers using Zeeman effect and interferometer

Miyabe, Masabumi; Kato, Masaaki; Oba, Masaki; Wakaida, Ikuo; Watanabe, Kazuo

JAERI-Tech 2004-065, 19 Pages, 2004/10

JAERI-Tech-2004-065.pdf:0.99MB

In nuclear waste materials there are various radionuclides to which standard analytical techniques are difficult to be applied. We are developing an analytical technique where such nuclides are ionized and mass-analyzed using diode laser based multi-step RIMS technique. The diode laser, however, has one drawback, i.e. its oscillation wavelength is readily drifted by acoustic, electric and optical noise, and thus the laser without frequency stabilization is not suitable for the analysis. In this study, we have developed (1) the diode laser whose frequency is stabilized to an intense absorption line of Rb by Zeeman effect and (2) the stabilization system where diode lasers for 3-step ionization of Ca are locked to the Rb-stabilized laser using a Fabry-perot interferometer. Additionally, to evaluate overall frequency stability of the stabilization system, fluctuations in the photoion and fluorescence signals arising from 3-step RIMS of Ca were simultaneously observed.

The Factors controlling vertical color variations of North Atlantic Madeira Abyssal Plain sediments

Nagao, Seiya;

Marine Geology, 109, p.83 - 94, 1992/00

https://doi.org/10.1016/0025-3227(92)90222-4

no abstracts in English