Tachi, Yukio; Ochs, M.*
Progress in Nuclear Science and Technology (Internet), 5, p.229 - 232, 2018/11
Various types of post-accident radioactive waste have been generated from cleanup and decommissioning activities at the Fukushima Daiichi Nuclear Power Plant. For the disposal of these wastes, perturbation effects resulting from co-existing substances (e.g., organic substances, boron, and salts) are needed to be considered. Such co-existing substances may influence on the radionuclide sorption parameters for the safety assessment of the disposal systems. The present study focuses on developing the methodology to quantify sorption parameters by considering such perturbation effects and illustrating example calculations regarding the sorption reduction factors (SRFs) due to the presence of organic ligands (ISA) for cement systems. Three approaches for the derivations of SRFs for cement-Am-ISA case were compared. These options should be applied as a stepwise manner according to the data availability for the perturbation effects resulting from the co-existing substances.
Ochs, M.*; Vriens, B.*; Tachi, Yukio
Progress in Nuclear Science and Technology (Internet), 5, p.208 - 212, 2018/11
The clean-up activities related to the accident at the Fukushima Nuclear Power Plant give rise to several types of wastes containing cementitious materials, such as concrete. Further, the use of cement-based barriers may be considered, due to their favorable and stable chemical properties, including their ability to sorb or incorporate radionuclides. Wastes from Fukushima are expected to contain substances that can have perturbing effects on retention, especially organic complexing substances, boron, and chloride salts. The present study focuses on a methodology for quantifying the retention behaviour of UVI) and U(IV) in cement materials of different degradation and in the presence of organics, boron, and salts on the basis of available literature information. A stepwise approach is proposed and illustrated for Kd setting for U(VI) and U(IV).
Tachi, Yukio; Ochs, M.*; Suyama, Tadahiro
Journal of Nuclear Science and Technology, 51(10), p.1177 - 1190, 2014/10
The integrated sorption and diffusion (ISD) model for bentonite was developed to predict the long-term migration of radionuclides (RNs). The basic premise in the ISD model was to consistently use the same simple model design and parameters for describing RNs sorption as well as the clay surface chemistry. A 1-site non-electrostatic surface complexation model in combinations with 1-site ion exchange model was selected to keep model characteristics relatively robust when applied to compacted systems. Fundamental model parameters were evaluated from titration data for purified montmorillonite. The resulting model was then parameterized on the basis of selected sorption datasets for Np(V), Am(III) and U(VI), which cover key geochemical conditions such as pH, ionic strength and carbonate. The sorption trends for these RNs can be quantitatively described by the model considering a full suite of surface species including carbonate species which are consistent with aqueous RNs speciation.
Tachi, Yukio; Yotsuji, Kenji; Suyama, Tadahiro; Ochs, M.*
Journal of Nuclear Science and Technology, 51(10), p.1191 - 1204, 2014/10
The integrated sorption and diffusion (ISD) model for compacted bentonites was developed based on the consistent combination of (1) the porewater chemistry model, (2) the thermodynamic sorption model (TSM), and (3) the diffusion model based on the electrical double layer (EDL) theory. This ISD model was successfully tested for various actinides with a complex chemistry (Np(V), Am(III), U(VI) under conditions where carbonate complexes are formed), by using published diffusion and sorption data (, , ) as a function of partial montmorillonite density. Quantitative agreements were observed as same as monovalent cations (Cs, Na), anions (Cl, I, TcO) previously reported. The ISD model could be therefore seen to be able to predict sorption and diffusion behavior of various complex radionuclides in compacted bentonites.
Tachi, Yukio; Ochs, M.*; Suyama, Tadahiro; Trudel, D.*
Materials Research Society Symposium Proceedings, Vol.1665, p.149 - 155, 2014/09
Sorption of radionuclides (K) in host rocks depends critically on relevant geochemical conditions, need to correspond to the specific performance assessment (PA) conditions. The integrated approaches for site-specific K setting have been developed focusing two transferring procedures, semi-quantitative estimation procedures and thermodynamic sorption models. The present paper focused on illustrating the derivation of K values and their uncertainties of Cs, Ni, Am and Th for geochemical conditions from the Horonobe URL. These K-setting results were compared with the measured K values, indicating that the magnitude of sorption can be quantitatively evaluated when adequate data and models were available. These comparative discussions between transferring procedures and measured data are effective to enhance the reliability of K setting, and the careful selections from transferred results are needed according to the situation in the existing data and process understanding.
Payne, T. E.*; Brendler, V.*; Ochs, M.*; Baeyens, B.*; Brown, P. L.*; Davis, J. A.*; Ekberg, C.*; Kulik, D.*; Lutzenkirchen, J.*; Missana, T.*; et al.
Environmental Modelling & Software, 42, p.143 - 156, 2013/04
Thermodynamic sorption models (TSMs) can be utilised to provide a scientific basis for Kd setting in the safety case, and for assessing the response of Kd to changes in chemical conditions. The TSM development involves a series of decisions on model features such as surface sites, sorption reactions and electrostatic corrections. There is a lack of consensus on the best ways to develop TSMs, and the NEA has therefore co ordinated an international project to assess the strategies and processes for building a TSM. This paper presents recommendations from the project on a number of aspects of TSM development in the context of radioactive waste disposal. Key recommendations include: definition of modelling objectives, identification of major decision points, a clear decision making rationale with reference to experimental or theoretical evidence, a suitable consultative and iterative model development process, testing to the maximum practicable extent, and documentation of key decisions.
Ochs, M.*; Tachi, Yukio; Trudel, D.*; Suyama, Tadahiro*
JAEA-Research 2012-044, 130 Pages, 2013/03
JAEA has developed the setting approaches of sorption parameter (Kd) for site-specific conditions, to derive reliable parameter for performance assessment (PA) of geological disposal. These approaches include any transferring procedures from experimental conditions to PA conditions through expert judgments, semi-quantitative estimation procedures and thermodynamic sorption models (TSMs). The present report focused on illustrating a range of example calculations regarding the derivation of Kd values and their uncertainties based on semi-quantitative estimation procedures and TSMs. The Kd values of four key radionuclides, Cs, Ni, Am and Th were derived for Horonobe mudstone systems. These Kd-setting exercises allowed to estimate the magnitude of sorption under the site-specific conditions, and to identify some critical gaps in the existing data and process understanding. The possibilities of extending such approaches to further rock types including granitic rocks were also discussed.
Tachi, Yukio; Suyama, Tadahiro; Ochs, M.*; Ganter, C.*
JAEA-Data/Code 2010-031, 168 Pages, 2011/03
JAEA has developed sorption database (SDB) compiling Kd data in buffer material and rock, which is key parameter for performance assessment (PA) of the geological disposal. The present report focuses on developing and updating of the JAEA-SDB as basis of integrated approach for PA-related Kd setting. This includes an overview of database structure, contents and functions including additional data evaluation function focusing on multi-parameter dependence, operating method, PA-related applications of the web-based SDB. Kd data and their QA results are updated by focusing our recent activities on the Kd setting and mechanistic model development. As a result, total Kd values in the SDB are about 28,540, and QA/classified Kd data are about 39 % for all Kd data. The updated JAEA-SDB is expected to make it possible to obtain quick overview of the available data, and to have suitable access to the respective data for PA-related Kd setting in effective, traceable and transparent manner.
Ochs, M.*; Tachi, Yukio; Ganter, C.*; Suyama, Tadahiro; Yui, Mikazu
JAEA-Research 2010-052, 59 Pages, 2011/02
For reliable parameter setting in performance assessment of geological disposal, JAEA has developed the integrated sorption and diffusion (ISD) model/database in bentonite systems. The main goal of the mechanistic model/database development is to provide a tool for a consistent explanation, prediction, and uncertainty assessment. This report focuses on developing the thermodynamic sorption model (TSM) including selection of model design and surface species, and on the quantification and handling of model uncertainties, based on illustrating by example of Ni sorption on montmorillonite/bentonite. Two fundamentally different approaches are presented and compared for representing TSM uncertainties: (1) TSM parameter uncertainties based on optimization routines and statistical procedure, (2) overall error estimated by direct comparison of modeled and experimental Kd values. The overall error in Kd is viewed as the best representation of model uncertainty in ISD model/database development.
Suyama, Tadahiro; Ganter, C.*; Kunze, S.*; Tachi, Yukio; Ochs, M.*
JAEA-Data/Code 2010-026, 72 Pages, 2011/02
Sorption of radionuclides in bentonites and rocks is one of the key processes in the safe geological disposal of radioactive waste. JAEA has developed sorption database (JAEA-SDB) which includes extensive compilation of sorption Kd data. JAEA has been continuing to update the SDB in view of potential future data needs, focusing on assuring the quality level and practical applications to Kd-setting for the geological environment. In this report, the QA/classification of selected entries in the JAEA-SDB, focusing on key radionuclides (Th, Np, Am, Se and Cs) sorption on tuff existing widely in geological environment, was done following the approach/guideline defined in our previous report. As a result, the reliability of 560 Kd values was evaluated and classified. This classification scheme is expected to make it possible to obtain quick overview of the available data from the SDB, and to have suitable access to the respective data for Kd-setting in PA.
Tachi, Yukio; Nakazawa, Toshiyuki*; Ochs, M.*; Yotsuji, Kenji; Suyama, Tadahiro; Seida, Yoshimi; Yamada, Norikazu*; Yui, Mikazu
Radiochimica Acta, 98(9-11), p.711 - 718, 2010/11
Diffusion and sorption of radionuclides in compacted bentonite are the key processes in the safe geological disposal. The effects of carbonate and salinity on Np(V) diffusion and sorption in compacted montmorillonite were investigated by experimental and modeling approaches. Effective diffusion coefficients () and distribution coefficients () of Np in montmorillonite compacted to dry density of 800 kg/m were measured under four conditions with different salinities (0.05/0.5 M NaCl) and carbonate concentrations (0/0.01 M NaHCO). The for carbonate-free conditions decreased as salinity increased, and those for carbonate conditions showed the opposite dependency. The decreased by one order of magnitude under high carbonate condition. Diffusion and sorption behaviors were interpreted by coupling the thermodynamic aqueous speciation, the thermodynamic sorption model based on ion exchange and surface complexation, and the diffusion model based on electrical double layer theory in narrow pores. The mechanistic model could be useful in predicting the sorption and diffusion behavior of complex species in compacted systems.
Tachi, Yukio; Yotsuji, Kenji; Suyama, Tadahiro; Ochs, M.*; Yui, Mikazu
JAEA-Research 2009-069, 83 Pages, 2010/03
This report presents the prototype model/database for integrated sorption and diffusion (ISD2009) in bentonite systems as basis for performance assessment (PA) of geological disposal. The sorption model is based on a relatively simple 1-site surface complexation/diffuse layer model in combination with 1-site ion exchange model. The model parameters for surface chemistry/sorption are evaluated based on existing datasets for Na-montmorillonite, which covers key geochemical conditions, in consistent way. The diffusion model based on homogeneous pore structure and electrical double layer theory was developed and coupled with batch-based sorption model, then was validated by using data in compacted montmorillonite. The sorption and diffusion models were also tested by applying data in bentonite systems. The model and related parameters developed for key radionuclides such as Cs, Np(V), Ni, Am, etc. are integrated to ISD2009 database, which could be useful in future PA exercise.
Ochs, M.*; Suyama, Tadahiro; Kunze, S.*; Tachi, Yukio; Yui, Mikazu
JAEA-Data/Code 2009-021, 144 Pages, 2010/02
Sorption of radionuclides in bentonites and rocks is one of the key processes in the safe geological disposal of radioactive waste. Japan Atomic Energy Agency (JAEA) has developed sorption database (JAEA-SDB) which includes extensive compilation of sorption Kd data by batch experiments, extracted from published literatures. In this report, the QA/classification of selected entries in the JAEA-SDB, focusing granite rocks which are related to reference systems in H12 PA and possible applications in the context of URL activities, and Fe-oxide/hydroxide, Al-oxide/hydroxide existing widely in geological environment, was done following the approach/guideline defined in our previous report. As a result, the reliability of 1,373 Kd values was evaluated and classified. This classification scheme is expected to make it possible to obtain quick overview of the available data from the SDB, and to have suitable access to the respective data for Kd-setting in PA.
Tachi, Yukio; Tochigi, Yoshikatsu; Suyama, Tadahiro; Saito, Yoshihiko; Ochs, M.*; Yui, Mikazu
JAEA-Data/Code 2008-034, 36 Pages, 2009/02
Japan Atomic Energy Agency (JAEA) has been developing databases of sorption and diffusion parameters in buffer material and rock, which are key parameters for safety assessment of the geological disposal. The new web-based sorption and diffusion database system (JAEA-SDB/DDB) has been developed to utilize quality assuring procedure and to allow effective application for parameter setting, based on the existing database. In the present report, practical examples were illustrated regarding the applicability of the database system to the parameter setting by using additional functions such as QA information and parameter estimation. This database system is expected to make it possible to obtain quick overview of the available data from the database, and to have suitable access to the respective data for parameter-setting for performance assessment and parameter-deriving for mechanistic modeling in traceable and transparence manner.
Saito, Yoshihiko; Ochs, M.*; Kunze, S.*; Kitamura, Akira; Tachi, Yukio; Yui, Mikazu
JAEA-Technology 2008-018, 116 Pages, 2008/03
In this report, the QA/classification of selected entries (1,056 Kd values) in the JNC-SDB, especially of Kd values for mudstone system to use in the Kd-derivation exercise for Horonobe rocks, was done following the approach defined in our previous report. This classification scheme made it possible to obtain quick overview of the available data, and to have suitable access to the respective Kd values.
Ochs, M.*; Kunze, S.*; Saito, Yoshihiko; Kitamura, Akira; Tachi, Yukio; Yui, Mikazu
JAEA-Research 2008-017, 89 Pages, 2008/03
In the present report, a first test and illustration was performed regarding the applicability of the JNC-SDB to the derivation of K-values for Th, Np, Cs, and Se valid for Horonobe rocks. The original experimental data selected from the JNC-SDB were converted to the application conditions using the semi-quantitative scaling procedures. To illustrate the effect of the scaling procedures, and of related uncertainties, on the magnitude of the derived K-values, scaling procedures taking into account mineralogy as well as surface and solution speciation were applied sequentially, and all results were discussed in detail. This K-setting exercise allowed to predict the magnitude of K values under the in-situ conditions, however the availability of experimental data that closely match the application conditions is limited for some reasons.
Saito, Yoshihiko; Ochs, M.*; Suyama, Tadahiro*; Kitamura, Akira; Shibata, Masahiro; Sasamoto, Hiroshi
JAEA-Data/Code 2007-014, 24 Pages, 2007/07
Japan Nuclear Cycle Development Institute (JNC) has developed the sorption database (JNC-SDB) for bentonite and rocks in order to estimating a retardation capacity of important radioactive elements on natural barrier and engineered barrier in the H12 report. The database includes distribution coefficient (K) of important radionuclides. And JNC collected the sorption data from 1998 to 2003. In this report, Japan Atomic Energy Agency (JAEA) widely collected the sorption data in order to extend and update the sorption database. The updated database includes the published data which are not registered in the sorption database. In this updated JNC-SDB, 3,205 sorption data for 23 elements, which are important for performance assessment were included. The frequency of K for some elements was clearly shown by addition of the sorption data.
Ochs, M.*; Saito, Yoshihiko; Kitamura, Akira; Shibata, Masahiro; Sasamoto, Hiroshi; Yui, Mikazu
JAEA-Technology 2007-011, 342 Pages, 2007/03
Japan Atomic Energy Agency (JAEA) has developed the sorption database (SDB) for bentonite and rocks in order to assess the retardation property of important radioactive elements in natural and engineered barriers in the H12 report. The database includes distribution coefficient (K) of important radionuclides. The K values in the SDB are about 20,000 data. The SDB includes a great variety of K and additional key information from many different literatures. Accordingly, the following classification guideline and classification system were developed in order to evaluate the reliability of each K value (Th, Pa, U, Np, Pu, Am, Cm, Cs, Ra, Se, Tc on bentonite). The reliability of 3740 K values are evaluated and categorized.
Yoshihiko, Saito,; Ochs, M.*; Jintoku, Takashi*; Suyama, Tadahiro*; Shibata, Masahiro; Sasamoto, Hiroshi; Yui, Mikazu
JNC-TN8410 2005-011, 59 Pages, 2005/08
Japan Nuclear Cycle Development Institute (JNC) has developed the JNC-Sorption Database (JNC-SDB) for bentonite and rocks in order to assess the retardation property of important radioactive elements in natural and engineered barriers in the H12 report. The database includes distribution coefficient (Kd) of important radionuclides. The Kd values in the JNC-SDB are about 20,000 data. And the JNC-SDB includes a great variety of Kd and additional key information from many different experimental conditions. Accordingly, the following classification guideline and classification system were developed in order to evaluate the reliability of each Kd value. (1) Criterion I: Completeness of documentation and type of Kd information (2) Criterion II: Quality of reported data from a technical and scientific point of view (3) Criterion III: Consistency of data with the majority of related reliable studies (4) An overall classification system / The checkpoints in Criterion II evaluate the reliability of each Kd entry in the JNC-SDB ; solid phase, adjustment and control of pH, redox conditions, final solution composition, temperature, solid/water ratio and grain size, sorption value, initial radionuclide concentration, phase separation, reaction time, agitation method, radionuclide loading, reaction vessels, uncertainty estimates, parameter variation
Ochs, M.*; Lothenbach, B.*; Christl, I.*; Yui, Mikazu; Shibata, Masahiro; Jintoku, Takashi
JNC-TN8400 2003-012, 28 Pages, 2003/06
In the original list of ligands to be considered in the JNC-TDB, NH had not been included, but NH, complexes were evaluated for Pd due to their importance for such soft acid metals. Presently, NH- complexes are considered to be important for the Japanese TRU disposal program, because nitrate contained in this type of waste could possibly be reduced to NH under repository conditions. This report presents thermodynamic data that are particularly critical for evaluating the safety functions of the repository near field, but are also of general importance for performance analysis. An extensive data search and initial evaluation for the interaction of NH with Pb, Sn, Bi, Nb, and Sb were carried out, but yielded no useful results. Therefore, no thermodynamic data can be recommended for NH-species of these elements. However, the compiled information allowed a rough comparative evaluation of stability constants in the system NH - HO - Metal, which indicates that NH is not likely to be a critical ligand for Sn(IV), Bi, Nb, and Sb(V) in dilute solutions. For Pb, complexation with NH may become relevant at elevated NH concentrations. Our evaluation further indicated that NH could be a relevant ligand for Ni and Co. Their interaction with NH had been studied to some degree. Subsequently, a first, traceable compilation of original experimental data was carried out for Ni and Co. However, in most case, the possible complex formation of Ni with the anions of the electrolyte and OH has not been considered in the calculations of the different constants. It remains to be studied in detail whether these interactions can be neglected or corrected for in all cases. A brief attempt was made to carry out some calculations for Ni in order to roughly estimate possible effect of the presence of NH on a repository performance. The calculations carried out clearly show that very high NH ...