Sorption of Sn and Nb on montmorillonite at neutral to alkaline pH

Ishidera, Takamitsu; Okazaki, Mitsuhiro*; Yamada, Yoshihide*; Tomura, Tsutomu*; Shibutani, Sanae*

Journal of Nuclear Science and Technology, 60(5), p.536 - 546, 2023/05

https://doi.org//10.1080/00223131.2022.2125453

The distribution coefficient () value of radionuclides is an important parameter in the radionuclide migration analysis in the safety assessment of the geological disposal of high-level radioactive waste. The values must be extensively evaluated especially under conditions where they might be decreased to improve the reliability of safety assessment. In this study, the pH dependence of the values for Sn and Nb on montmorillonite was evaluated using batch sorption experiments at neutral to alkaline pH, which might be caused by the leaching of cementitious materials and the corrosion of carbon steel. The values were determined in the range 8 pH 12 by the experiments and were found to decrease with increasing pH. A model calculation using a thermodynamic sorption model was conducted on the measured pH dependence of the values. Two different sorption sites were required to describe the pH dependence of the values of Sn in the model calculation, whereas one sorption site was considered predominant in the sorption of Nb.

Selenide [Se(-II)] immobilization in anoxic, Fe(II)-rich environments; Coprecipitation and behavior during phase transformations

Francisco, P. C. M.; Matsumura, Daiju; Kikuchi, Ryosuke*; Ishidera, Takamitsu; Tachi, Yukio

Environmental Science & Technology, 56(5), p.3011 - 3020, 2022/03

https://doi.org/10.1021/acs.est.1c04216

Development of evaluation method for diffusion and filtration behavior of colloid in compacted bentonites using dendrimers

Endo, Takashi*; Tachi, Yukio; Ishidera, Takamitsu; Terashima, Motoki

Nihon Genshiryoku Gakkai Wabun Rombunshi, 20(1), p.9 - 22, 2021/03

https://doi.org/10.3327/taesj.J20.001

Evaluation method of colloid diffusion and filtration in compacted bentonites was developed using dendrimers. Diffusion and filtration behavior of PAMAM dendrimers with the size of 5.77.2nm was investigated by the through-diffusion experiment in bentonite compacted to 0.8 Mg/m and saturated with 0.0050.5mol/L NaCl. Effective diffusivities (De) and filtration ratios (Rf) of dendrimers were determined from the breakthrough curves and the depth profiles in compacted bentonite, respectively. The De values of negatively charged dendrimer increased when porewater salinity increased and dendrimer size decreased as influenced by anion exclusion effect in negatively charged clay surfaces. The Rf values increased when porewater salinity decreased and dendrimer size increased, demonstrating significant fractions of dendrimer were filtered by narrow pores in complex pore networks. These trends consistent with the previous studies emphasize the validity of the evaluation method using dendrimer.

Key factors controlling radiocesium sorption and fixation in river sediments around the Fukushima Daiichi Nuclear Power Plant, 2; Sorption and fixation behaviors and their relationship to sediment properties

Tachi, Yukio; Sato, Tomofumi*; Takeda, Chizuko*; Ishidera, Takamitsu; Fujiwara, Kenso; Iijima, Kazuki

Science of the Total Environment, 724, p.138097_1 - 138097_10, 2020/07

https://doi.org/10.1016/j.scitotenv.2020.138097

To understand and predict radiocesium transport behaviors in the environment, sorption and fixation behaviors of radiocesium on river sediments from Ukedo and Odaka rivers around the Fukushima Daiichi Nuclear Power Plant were investigated systematically focusing on Cs sorption and fixation mechanisms and their relationship with Cs concentrations and sediment properties including clay mineralogy and organic matter.

Interaction of Fe and Si under anoxic and reducing conditions; Structural characteristics of ferrous silicate co-precipitates

Francisco, P. C. M.; Mitsui, Seiichiro; Ishidera, Takamitsu; Tachi, Yukio; Doi, Reisuke; Shiwaku, Hideaki

Geochimica et Cosmochimica Acta, 270, p.1 - 20, 2020/02

https://doi.org/10.1016/j.gca.2019.11.009

Brief introduction of repository design and engineering technology, and safety assessment on the geological disposal of radioactive waste

Ishidera, Takamitsu

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 23(1), p.99 - 101, 2016/06

http://nuce.aesj.or.jp/jnuce/vol23/Jnuce-Vol23-1-p99-102.pdf

In this presentation, the author introduced an overview of the research and development on repository design and engineering technology and safety assessment on the geological disposal of radioactive waste as well as the examples of evaluation methods used in these R&Ds and recent studies.

Enhancement of the methodology of repository design and post-closure performance assessment for preliminary investigation stage, 3; Progress report on NUMO-JAEA collaborative research in FY2013 (Joint research)

Shibata, Masahiro; Sawada, Atsushi; Tachi, Yukio; Makino, Hitoshi; Wakasugi, Keiichiro; Mitsui, Seiichiro; Kitamura, Akira; Yoshikawa, Hideki; Oda, Chie; Ishidera, Takamitsu; et al.

JAEA-Research 2014-030, 457 Pages, 2015/03

JAEA-Research-2014-030.pdf:199.23MB

JAEA and NUMO have conducted a collaborative research work which is designed to enhance the methodology of repository design and post-closure performance assessment in preliminary investigation stage. With regard to (1) study on rock suitability in terms of hydrology, based on some examples of developing method of hydro-geological structure model, acquired knowledge are arranged using the tree diagram, and model uncertainty and its influence on the evaluation items were discussed. With regard to (2) study on scenario development, the developed approach for "defining conditions" has been reevaluated and improved from practical viewpoints. In addition, the uncertainty evaluation for the effect of use of cementitious material, as well as glass dissolution model, was conducted with analytical evaluation. With regard to (3) study on setting radionuclide migration parameters, based on survey of precedent procedures, multiple-approach for distribution coefficient of rocks was established, and the adequacy of the approach was confirmed though its application to sedimentary rock and granitic rock. Besides, an approach for solubility setting was developed including the procedure of selection of solubility limiting solid phase. The adequacy of the approach was confirmed though its application to key radionuclides.

Effect of sodium nitrate on the diffusion of Cl and I in compacted bentonite

Ishidera, Takamitsu; Miyamoto, Shinya*; Sato, Haruo

Journal of Nuclear Science and Technology, 45(7), p.610 - 616, 2008/07

https://doi.org/10.3327/jnst.45.610

For safety assessment of TRU waste disposal, the effective diffusion coefficients () for CO, Cl and I ions in compacted bentonite (Kunigel V1) were determined as a function of NaNO concentrations from 0.01 to 5 mol/dm. The values increased from 10 to 10 m/s with increasing NaNO concentration. The rock capacity factor , indicative of the effective porosity, were also increased with increasing NaNO concentration. The maximum values of 0.21 for Cl ion and of 0.25 for I ion at 5 mol/dm NaNO concentration were lower than the net porosity of compacted bentonite (0.40). Therefore, the increases in the values were interpreted by the decrease of anion exclusion effect. The values for Cl and I ions normalized by the diffusivities for diffusants in the bulk water were found to increase in proportion to the values on the log-log diagram. The maximum value for CO ion was higher than the net porosity. The high concentration of CO ion was also found in the concentration profile in compacted bentonite. This retention of CO ion was possibly accounted for by isotopic exchange of C with inactive carbon of calcite in Kunigel V1.

The Effect of NaNOon Diffusion of CO, Cland I Ions in Tuff

Ishidera, Takamitsu; Sato, Haruo

JNC TN8400 2005-018, 49 Pages, 2005/09

JNC-TN8400-2005-018.pdf:1.6MB

The migration data ofC,Cl andI nuclides are required for safety assessment of TRU waste disposal. The specific phenomena for TRU waste disposal such as the influence of NaNOconcentration and the hyper alkaline groundwater due to degradation of cementitious materials should be considered for reliable safety assessment. In this study, the effective diffusion coefficient (De) for CO, Cland Iions in tuff were determined with various NaNO concentrations under hyper alkaline condition. The obtained De values for CO, Cland Iions were on the order of 10-10m/s and decreased with increasing NaNO3 concentration. The De values for HDO and HTO were also decreased with increasing NaNO concentration. Because the degradation of tuff samples was not observed by X-Ray diffractometry, SEM and EPMA, the decreases in the De values were considered to be due to the decreases in the diffusivities in free water. The apparent diffusion coefficient (Da) values for Clion with 5mol/dm NaNOconcentration and for COion were lower than those of the other conditions. These low Da values suggested retardation in tuff samples.

Diffusion of Iron and Neptunium in Buffer Material

Arima, Tatsumi*; Idemitsu, Kazuya*; Xia, X.; Ishidera, Takamitsu; Iijima, Kazuki

JNC TY8400 2004-005, 59 Pages, 2004/05

JNC-TY8400-2004-005.pdf:1.3MB

For the safety assessment of high level waste disposal, it is necessary to investigate the radionuclide migration in the presence of corrosion products of carbon steel under reducing condition. In this study, the reliable apparent diffusion coefficients of neptunium (Np) in bentonite were obtained by in-diffusion method and migration of the corrosion products was investigated. Furthermore, effects of the corrosion of carbon steel on Np diffusion were discussed. The corrosion of carbon steel under reducing condition provided Feions, which were considered to migrate in the interlayer spaces of montmorillonite sheets of bentonite exchanging with two Naions. The corrosion rate of carbon steel was controlled by the diffusivity of Feions into bentonite when they were accumulated at the surface of carbon steel. The corrosion rate increased with increasing dry density of bentonite because of the increase of the diffusivity of Feions. The corrosion rate was estimated to be ~0.1 micro m/y, which was remarkable lower than the setting value, 20 micro m/y, in the second progress report. The Np profiles in the bentonite consisted of two overlapping slopes, a fast and a slow fractions, for both the experiments with and without carbon steel. The apparent diffusion coefficients of the fast and the slow fraction of Np were 10~10m/s and 10~10m/s, which were considered to be the diffusion of Np(V) and Np(IV), respectively. The corrosion of carbon steel provided strong reducing condition to keep most Np in the low oxidation state, Np(IV), which has lower solubility and mobility than Np(V). Therefore, it could be expected that the corrosion of carbon steel will restrain effectively migration of Np into the bentonite.