International benchmark on radionuclide solubility and speciation for the Long-term In-situ Test (LIT) at Grimsel Test Site (GTS, Switzerland)

Noseck, U.*; Schfer, T.*; Alonso, U.*; Hamamoto, Takafumi*; Havlova, V.*; Hibberd, R.*; Ishidera, Takamitsu; Kitamura, Akira; Klajmon, M.*; Missana, T.*; et al.

Applied Geochemistry, 201, p.106762_1 - 106762_23, 2026/04

https://doi.org/10.1016/j.apgeochem.2026.106762

Thermodynamic benchmark calculations have been performed to better understand the behavior of Se(VI), Tc(VII), U(VI), Np(V), Am(III), Th(IV) and Pu(IV)) in the evolving geochemical conditions of the Long-term In-situ Test (LIT) at the Grimsel Test Site (GTS) and corresponding mock-up experiment. It also aims to identify the status of the geochemical speciation models and databases for these elements. The experiments are simulating the near-field conditions in some radioactive waste repository concept including a bentonite engineered barrier emplaced in crystalline rock and the findings are contributing to the long-term safety assessment of these facilities.

Thermodynamic properties and revised Helgeson-Kirkham-Flowers equations of state parameters of the hydrated and dehydrated monomeric silica species at = 0.01-600C, = 1-3000 bars, = 0.35-1.1 g cm, and = 0

Walker, C. S.*; Arthur, R. C.*; Anraku, Sohtaro; Sasamoto, Hiroshi; Mihara, Morihiro

Applied Geochemistry, 175, p.106086_1 - 106086_17, 2024/11

https://doi.org/10.1016/j.apgeochem.2024.106086

The thermodynamic properties and revised Helgeson-Kirkham-Flowers equation of state (r-H-K-F EoS) parameters of the hydrated (Si(OH)(aq), SiO(OH) and SiO(OH)) and fictive dehydrated (SiO(aq), HSiO and SiO) monomeric silicon species are used extensively to describe the pH, composition, temperature, and pressure dependence of formation/breakdown reactions of all silicon-bearing compounds globally. Experimental log10 equilbrium constant, K values describing the formation reactions of the hydrated and dehydrated monomeric silicon species were therefore compiled from the literature, extrapolated to zero ionic strength by specific ion interaction theory as required and used to derive their thermodynamic properties and r-H-K-F EoS parameters. Consideration of all formation reactions in the same study provides a collective, internally consistent update to the thermodynamic properties and r-H-K-F EoS parameters of the monomeric silicon species that can provide a satisfactory match to the experimental log10 K values at = 0.01-600C, = 1-3000 bars, = 0.35-1.1 g cm, and zero ionic strength. These temperature and pressure limits comfortably bracket t=0.01-100C and P =1-270 bars relecant to the geological disposal of radioactive wastes at depths of up to 1 km.

Quantitative analysis of microstructure evolution, stress partitioning and thermodynamics in the dynamic transformation of Fe-14Ni alloy

Li, L.*; Miyamoto, Goro*; Zhang, Y.*; Li, M.*; Morooka, Satoshi; Oikawa, Katsunari*; Tomota, Yo*; Furuhara, Tadashi*

Journal of Materials Science & Technology, 184, p.221 - 234, 2024/06

https://doi.org/10.1016/j.jmst.2023.10.037

Decrease of radionuclide sorption in hydrated cement systems by organic ligands; Comparative evaluation using experimental data and thermodynamic calculations for ISA/EDTA-actinide-cement systems

Ochs, M.*; Dolder, F.*; Tachi, Yukio

Applied Geochemistry, 136, p.105161_1 - 105161_11, 2022/01

https://doi.org/10.1016/j.apgeochem.2021.105161

Various types of radioactive wastes and environments contain organic substances that can stabilize the aqueous complexes with radionuclides and therefore lead to a decrease of sorption. The present study focuses on testing a methodology to quantify sorption reduction factors (SRFs) in the presence of organic ligands for cement systems. Three approaches for the estimation of SRFs; (1) analogy with solubility enhancement factors, (2) radionuclide speciation based on the thermodynamic calculations, and (3) experimental sorption data in ternary systems, were coupled and tested for the representative organic ligands (ISA and EDTA) and selected key radionuclides (actinides). Our approach allows to critically evaluate the dependence of SRFs for various systems on the chosen method of quantification, in accordance with the data availability for a given systems. The reliable SRFs can only be derived from the sorption measurements in ternary systems. SRF often need to be derived in the absence of such direct evidence, and estimations need to be made based on analogies and speciation information. However, such estimates may be subject to substantial uncertainties.

JAEA-TDB-RN in 2020; Update of JAEA's thermodynamic database for solubility and speciation of radionuclides for performance assessment of geological disposal of high-level and TRU wastes

Kitamura, Akira

JAEA-Data/Code 2020-020, 164 Pages, 2021/03

JAEA-Data-Code-2020-020.pdf:3.11MB
JAEA-Data-Code-2020-020-appendix(DVD-ROM).zip:0.56MB

Part of JAEA's Thermodynamic Database (JAEA-TDB) for solubility and speciation of radionuclides (JAEA-TDB-RN) for performance assessment of geological disposal of high-level radioactive and TRU wastes has been updated with subsuming the database for geochemical calculations (JAEA-TDB-GC). This report has focused to update JAEA-TDB-RN after selecting change in standard Gibbs free energy of formation (), change in standard enthalpy change of formation (), standard molar entropy () and, heat capacity (), change in standard Gibbs free energy of reaction (), change in standard enthalpy change of reaction () and standard entropy change of reaction () as well as logarithm of equilibrium constant (log) at standard state. The extent of selection of these thermodynamic data enables to evaluate solubility and speciation of radionuclides at temperatures other than 298.15 K. Furthermore, the latest thermodynamic data for iron which have been critically reviewed, selected and compiled by the Nuclear Energy Agency within Organisation for Economic Co-operation and Development (OECD/NEA) have been accepted. Most of previously selected log have been refined to confirm internal consistency with JAEA-TDB-GC. Text files of the updated JAEA-TDB have been provided for geochemical calculation programs of PHREEQC and Geochemist's Workbench.

Methodology development and determination of solubility-limiting solid phases for a performance assessment of geological disposal of high-level radioactive and TRU wastes

Kitamura, Akira; Yoshida, Yasushi*; Goto, Takahiro*; Shibutani, Sanae*

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 27(2), p.58 - 71, 2020/12

https://doi.org/10.3327/jnuce.27.2_58

Evaluation and estimation of solubility values are required for a performance assessment of geological disposal of high-level radioactive and TRU wastes. Selection of solubility-limiting solid phases (SSPs) that control the solubility of radionuclides is necessary for the evaluation and estimation of solubility values. The authors have developed a methodology for selection of the SSP through a calculation of saturation indices (SIs) using thermodynamic database to show a transparent procedure for the selection. Literature survey should be performed to confirm decision of the SSP from candidate SSPs which generally have larger SIs from realistic point of view for precipitation and solubility control. The authors have selected the SSPs for the elements of interest for the latest Japanese performance assessment in bentonite and cement porewaters after grouping various water compositions.

Chemical forms of uranium evaluated by thermodynamic calculation associated with distribution of core materials in the damaged reactor pressure vessel

Ikeuchi, Hirotomo; Yano, Kimihiko; Washiya, Tadahiro

Journal of Nuclear Science and Technology, 57(6), p.704 - 718, 2020/06

https://doi.org/10.1080/00223131.2020.1720844

To suggest efficient process of the fuel debris treatment after the retrieval from the Fukushima Daiichi Nuclear Power Plant (1F), thorough investigation is indispensable on potential source of U in the fuel debris. Estimation on the fuel debris accumulated in the reactor pressure vessel is specifically important due to its limited accessibility. The present study aims to estimate the chemical forms of U in the in-vessel fuel debris, especially in the minor phases such as metallic phases, by performing the thermodynamic calculation considering the material relocation and changing environment during the accident progression in the 1F Unit 2. Input conditions for the thermodynamic calculation such as composition, temperature, and oxygen amount were assumed mainly based on the results of severe accident analysis. The chemical form of U varied depending on the local amount of Fe and O. In regions of low steel content, the U-containing metallic phase was dominated by -(Zr,U)(O), while regions of high steel content were dominated by Fe(Zr,U) (Laves phase). A few percent of U was transferred to the metallic phases under reducing conditions, raising challenging issues on the chemical removal of nuclear material from fuel debris.

Cesium chemisorbed species onto stainless steel surfaces; An Atomistic scale study

Miradji, F.; Suzuki, Chikashi; Nakajima, Kunihisa; Osaka, Masahiko

Journal of Physics and Chemistry of Solids, 136, p.109168_1 - 109168_9, 2020/01

https://doi.org/10.1016/j.jpcs.2019.109168

Update of JAEA-TDB; Update of thermodynamic data for zirconium and those for isosaccahrinate, tentative selection of thermodynamic data for ternary M-UO-CO system and integration with JAEA's thermodynamic database for geochemical calculations

Kitamura, Akira

JAEA-Data/Code 2018-018, 103 Pages, 2019/03

JAEA-Data-Code-2018-018.pdf:5.66MB
JAEA-Data-Code-2018-018-appendix1(DVD-ROM).zip:0.14MB
JAEA-Data-Code-2018-018-appendix2(DVD-ROM).zip:0.15MB
JAEA-Data-Code-2018-018-appendix3(DVD-ROM).zip:0.19MB

The latest available thermodynamic data were critically reviewed and the selected values were included into the JAEA-TDB for performance assessment of geological disposal of high-level radioactive and TRU wastes. This critical review specifically addressed thermodynamic data for (1) a zirconium-hydroxide system through comparison of thermodynamic data selected by the Nuclear Energy Agency within the Organisation for Economic Co-operation and Development (OECD/NEA), (2) complexation of metal ions with isosaccharinic acid based on the latest review papers. Furthermore, the author performed (3) tentative selection of thermodynamic data on ternary complexes among alkaline-earth metal, uranyl and carbonate ions, and (4) integration with the latest version of JAEA's thermodynamic database for geochemical calculations. The internal consistency of the selected data was checked by the author. Text files of the updated and integrated thermodynamic database have been prepared for geochemical calculation programs of PHREEQC and Geochemist's Workbench.

Thermodynamic data development; Solubility method and future research needs (PLENARY)

Rai, D.*; Yui, Mikazu; Kitamura, Akira

Progress in Nuclear Science and Technology (Internet), 5, p.19 - 26, 2018/11

https://doi.org/10.15669/pnst.5.19

The objectives of this presentation are (1) to describe the solubility method, (2) to list desirable criteria of the solubility method so that the reader can recognize which studies have been done in a way that yields quality information, (3) to present an example of how to use the evaluation criteria, and (4) to provide a few examples of future research needs where the solubility method is ideally suited and the other methods are unsuitable for these investigations.