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Journal Articles

Activity report of the Task Group on Parameters Used in Biospheric Dose Assessment Models for Radioactive Waste Disposal

Takahashi, Tomoyuki*; Fukaya, Yukiko*; Iimoto, Takeshi*; Uni, Yasuo*; Kato, Tomoko; Sun, S.*; Takeda, Seiji; Nakai, Kunihiro*; Nakabayashi, Ryo*; Uchida, Shigeo*; et al.

Hoken Butsuri (Internet), 56(4), p.288 - 305, 2021/12

We report the results of activities related to the Task Group of Parameters Used in Biospheric Dose Assessment Models for Radioactive Waste Disposal at the Japan Health Physics Society.

Journal Articles

Stochastic estimation of radionuclide composition in wastes generated at Fukushima Daiichi Nuclear Power Station using Bayesian inference

Sugiyama, Daisuke*; Nakabayashi, Ryo*; Tanaka, Shingo*; Koma, Yoshikazu; Takahatake, Yoko

Journal of Nuclear Science and Technology, 58(4), p.493 - 506, 2021/04

 Times Cited Count:2 Percentile:24.93(Nuclear Science & Technology)

Journal Articles

Development of calculation methodology for estimation of radionuclide composition in wastes generated at Fukushima Daiichi Nuclear Power Station

Sugiyama, Daisuke*; Nakabayashi, Ryo*; Koma, Yoshikazu; Takahatake, Yoko; Tsukamoto, Masaki*

Journal of Nuclear Science and Technology, 56(9-10), p.881 - 890, 2019/09

 Times Cited Count:4 Percentile:37.41(Nuclear Science & Technology)

Oral presentation

Observation of the interaction between bentonite and hyperalkaline fluid by X-ray computed tomography and geochamical modeling of the interaction

Nakabayashi, Ryo*; Elakneswaran, Y.*; Chino, Daisuke*; Sato, Tsutomu*; Yoneda, Tetsuro*; Oda, Chie; Kaneko, Katsuhiko*

no journal, , 

Flow-through dissolution experiment was carried out using compacted bentonite with hyperalkaline solutions. In-situ observation of bentonite during the experiment was concocted by using X-CT analysis. Time-dependence of secondary minerals formation inside the compacted bentonite during the experiment was analysed and quantified based on the observation. Geochemical modeling using a 1D reactive transport code was able to reproduct time-dependence of space-distribution of minerals in the bentonite and Si, Al concentrations in the output solutions.

Oral presentation

X-ray CT observations and geochemical modeling of bentonite alteration by hyperalkaline fluids

Nakabayashi, Ryo*; Elakneswaran, Y.*; Sato, Tsutomu*; Oda, Chie; Yoneda, Tetsuro*; Kaneko, Katsuhiko*

no journal, , 

The objective of this study is to develop a microstructural analysis method by X-ray CT to track the alteration process arising from bentonite and hyperalkaline fluid interactions as a function of time and to use these data to underpin a geochemical model of the alteration process. Advective alteration experiment of bentonite was performed at 80 $$^{circ}$$C (pH = 13.5 at 25 $$^{circ}$$C) for 180 days and in-situ analysis by X-ray CT during the experiment was conducted. The geochemical reactive transport code PHREEQC was used to simulate the results of the experiments. Consequently, the formation of secondary minerals (analcime) in the bentonite could be confirmed by X-ray CT at different times and quantified by X-ray CT images analysis. The predicted time-dependency of volume of analcime by a geochemical reactive transport model became consistent with the results obtained by X-ray CT analysis, and the concentration of dissolved Si and Al in the output solution could be replicated.

Oral presentation

Dissolution kinetics of montmorillonite in Ca(OH)$$_{2}$$ solution; The Effect of pH and C-S-H precipitation

Kijima, Tatsuya*; Nakabayashi, Ryo*; Elakneswaran, Y.*; Oda, Chie; Otake, Tsubasa*; Sato, Tsutomu*; Yoneda, Tetsuro*

no journal, , 

pH dependency of Montmorillonite dissolution rate in Ca-Cl-OH aqueous solution system was confirmed by conducting a flow-through type dissolution experiment. C-S-H formed depending on the experimental pH and concentration of Ca. The dissolution rate determined in the condition where C-S-H formed differed from the rates obtained in NaOH solutions.

Oral presentation

An Evaluation study on the interaction of bentonite with highly alkaline porewater by using X-ray CT method; Dissolution rate of montmorillonite in compacted bentonite

Nakabayashi, Ryo*; Elakneswaran, Y.*; Chino, Daisuke*; Sato, Tsutomu*; Yoneda, Tetsuro*; Oda, Chie; Kaneko, Katsuhiko*

no journal, , 

Flow-through dissolution experiment of compacted purified bentonite with highly alkaline solution was carried out in order to quantitatively understand the bentonite-cement interaction. A combined analysis with XRD and in situ-observation by using X-ray CT method were applied. A geochemical model simulation of the experiment considering kinetics of montmorillonite (the main component of bentonite) dissolution was carried out. From output of the simulation, it was found that (1) dissolution rate of montmorillonite in compacted system were slower than that in suspension system, (2) slowering rate resulted in invisible change in dry density of montmorillonite in the simulation, which was consistent with the experimental result, and (3) the reason for slowring rate could likely to be attributed to the constraint of reactive surface area of montmorillonite and the effect of saturation degree of powewater.

Oral presentation

Effect of compaction on dissolution rate of smectite under hyperalkaline condition

Sato, Tsutomu*; Takayama, Hideki*; Chino, Daisuke*; Nakabayashi, Ryo*; Oda, Chie; Yoneda, Tetsuro*

no journal, , 

The dissolution experiments for the compacted smectite with different dry densities were performed to understand the effect of compaction on dissolution rate of smectite. From the experimental results, it is clearly showed that the more compacted smectite has the less dissolution rate. According to the results of caesium adsorption test, variable charge density was decreased with increasing of dry density. This decreasing indicates that active edge surface area was decreased. According to the previous studies such as Yokoyama, et al. (2005), smectite particles are predominantly dissolved from the edge of the particle. However, the difference in dissolution rate between lower and higher compacted smectites can not be fully explained by considering of the decreasing in the reactive surface area. According to the results of reactive transport modeling, delta-Gr effect obtained by Sato, et al. (2007) should be took into account for filling the gap in dissolution rate.

Oral presentation

Effect of aqueous aluminium and silica concentrations on smectite dissolution kinetics at hyperalkaline conditions

Chino, Daisuke*; Sato, Tsutomu*; Otani, Yusuke*; Nakabayashi, Ryo*; Oda, Chie; Yoneda, Tetsuro*

no journal, , 

Steady-state dissolution rates of smectite were determined as function of aqueous Al and Si concentrations using a stirred-flow-through reactor at 70 degrees in 0.3M-NaOH solution to obtain the reliable dissolution rates of smectite at hyperalkaline condition and to formulate the effect of deviation from equilibrium on smectite dissolution rate. The dissolution rates were calculated based from the dissolved Si or Al concentrations of the output solutions or from ex situ AFM observations. Results of the flow-through dissolution experiments and ex situ AFM observations suggest that the dissolved Si and Al concentrations in the solutions appear to be retarding the dissolution rate of smectite. If we assume the decrease is attributed by the effect of deviation from equilibrium on dissolution rate, the dissolution rate of smectite can be expressed in a non-linear function of the Gibbs free energy. This non-liner relationship is nearly same as that obtained by Cama, et al. (2000).

Oral presentation

X-ray CT observations of altered bentonite by hyperalkaline-fluids; Dissolution kinetics of montmorillonite in compacted bentonite

Nakabayashi, Ryo*; Elakneswaran, Y.*; Sato, Tsutomu*; Otake, Tsubasa*; Oda, Chie; Yoneda, Tetsuro*; Kaneko, Katsuhiko*

no journal, , 

The current study developed developed an in situ microstructural analysis method using X-ray CT to track bentonite/hyperalkaline fluid interactions. An advective alteration experiment was conducted by reacting a compacted bentonite (0.3 Mg/m$$^{3}$$) with a 0.3M NaOH solution at 80$$^{circ}$$C for 180 days. No significant dissolution of montmorillonite in the bentonite was observed using X-ray CT, although the formation of secondary minerals could be quantified by X-ray CT. A geochemical modeling using the dissolution rate of montmorillonite obtained in a dispersed system did not fit the experimental data, but could provide a satisfactory match to that by changes to the reactive surface area and the inclusion of an empirical term to account for the saturation state of montmorillonite. This implies that there is difference in effective reactive surface area and effect of the saturation state on the dissolution rate between dispersed and compacted systems.

Oral presentation

Development of inventory evaluation methods for the radioactive wastes of Fukushima Daiichi Nuclear Power Station, 7; Comparison of inventory estimation methods for secondary wastes from contaminated water treatment system

Meguro, Yoshihiro; Kato, Jun; Oi, Takao; Koma, Yoshikazu; Ashida, Takashi; Sugiyama, Daisuke*; Nakabayashi, Ryo*; Fujita, Tomonari*; Tsukamoto, Masaki*; Uchiyama, Hideaki*; et al.

no journal, , 

Inventory evaluation results obtained by analytical results of contaminated water was compared with that obtained on the basis of an analytically-calculated method for the secondary wastes generated from the water treatment system such as the cesium adsorption device, the second cesium adsorption device and the coagulating sedimentation device in the Fukushima Daiichi Nuclear Power Station.

Oral presentation

Development of inventory evaluation methods for the radioactive wastes of Fukushima Daiichi Nuclear Power Station, 13; Introduction of stochastic approach to the modelling estimation method

Sugiyama, Daisuke*; Koma, Yoshikazu; Takahatake, Yoko; Aoki, Yoshio*; Nakabayashi, Ryo*; Fujita, Tomonari*

no journal, , 

The introduction of a stochastic approach to the calibration of the radionuclide transport parameters, which processes the frequency distribution of the analytical measured data accumulated progressively on the wastes and contaminated water, into the modelling estimation method of the radioactive waste inventory generated at the Fukushima Daiichi Nuclear Power Station is investigated. It is expected that the accuracy of the modelling estimation of radionuclide composition in wastes will be improved by describing the radionuclide transport parameters as a lognormal distribution.

Oral presentation

Oral presentation

Alteration of montmorillonite by KOH solutions

Ueda, Mai*; Nakabayashi, Ryo*; Kijima, Tatsuya*; Sato, Tsutomu*; Yoneda, Tetsuro*; Otake, Tsubasa*; Oda, Chie

no journal, , 

In the current study, the promoted illitization of montmorillonite in KOH solutions was investigated. Montmorillonite was added to 0, 0.1, 0.5, 1.0, and 3.0 M KOH solutions, which were then sealed and kept at 35 or 60 $$^{circ}$$C for up to 270 days. Reaction products were analyzed by XRD to check the expandability, an empirical determination of layer charge and observation by AFM. 10 and 35% of illite layer in randomly interstratified illite/smectite minerals were estimated by XRD for 0.1 M and 3.0 M solutions, respectively. Changes in the peak intensities obtained from the XRD patterns could be assigned to the dissolution of montmorillonite, but with some uncertainty affected the reliability of the quantification of illite. No significant illitization was observed based on the results of layer charge and AFM observation. Consequently, there is no direct evidence for significant illitization of montmorillonite in KOH solutions under the experimental conditions of the current study.

Oral presentation

Montmorillonite alteration in KOH solutions at 35$$^{circ}$$C and 60$$^{circ}$$C

Ueda, Mai*; Nakabayashi, Ryo*; Kijima, Tatsuya*; Sato, Tsutomu*; Yoneda, Tetsuro*; Otake, Tsubasa*; Oda, Chie

no journal, , 

Montmorillonite-rich bentonite is expected to be used as a buffer material in the geological disposal of radioactive wastes. Cement used for the construction of the disposal facility will generate highly alkaline leachates dominated by KOH and NaOH, which may act to cause the alteration of montmorillonite and the loss of the properties of bentonite suitable for the buffer material. In the current study, the illitization of montmorillonite in KOH solutions, which is considered as one of possible alteration processes, was investigated by conducting batch-type reaction experiments at 35 and 60$$^{circ}$$C for up to 270 days. Based on XRD analyses and AFM observations for the reaction products, the formation of illite/smectite interstratified minerals, the increase in the layer charge, and the increase in hight and the decrease in basal area of the dispersed flat particles were recognised. These results indicate that illitization proceeded simultaneously with dissolution of montmorillonite.

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