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JAEA Reports

Thermodynamic Database for NH$$_{3}$$-Species of Radioactive Elements

Ochs, M.*; Lothenbach, B.*; Christl, I.*; Yui, Mikazu; Shibata, Masahiro; Jintoku, Takashi

JNC TN8400 2003-012, 28 Pages, 2003/06

JNC-TN8400-2003-012.pdf:1.81MB

In the original list of ligands to be considered in the JNC-TDB, NH$$_{3}$$ had not been included, but NH$$_{3}$$, complexes were evaluated for Pd due to their importance for such soft acid metals. Presently, NH$$_{3}$$- 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$$_{3}$$ 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$$_{3}$$ with Pb, Sn, Bi, Nb, and Sb were carried out, but yielded no useful results. Therefore, no thermodynamic data can be recommended for NH$$_{3}$$-species of these elements. However, the compiled information allowed a rough comparative evaluation of stability constants in the system NH$$_{3}$$ - H$$_{2}$$O - Metal, which indicates that NH$$_{3}$$ is not likely to be a critical ligand for Sn(IV), Bi, Nb, and Sb(V) in dilute solutions. For Pb, complexation with NH$$_{3}$$ may become relevant at elevated NH$$_{3}$$ concentrations. Our evaluation further indicated that NH$$_{3}$$ could be a relevant ligand for Ni and Co. Their interaction with NH$$_{3}$$ 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$$_{3}$$ on a repository performance. The calculations carried out clearly show that very high NH$$_{3}$$ ...

JAEA Reports

Bentonite porewater chemistry

Ochs, M.*; Lothenbach, B.*; Shibata, Masahiro; Yui, Mikazu

JNC TN8400 99-075, 153 Pages, 1999/11

JNC-TN8400-99-075.pdf:4.79MB

Porewater composition in a compacted bentonite is dependent on the composition of the surrounding groundwater, and on the characteristics of the bentonite itself. Two mechanisms through which bentonite influences the respective porewater composition are distinguished: sulface chemical reactions (ion exchange, surface complexation) on smectite and dissolution of minerals and soluble impurities included in bentonite. This report provides the results of different activities related to the definition of porewater chemistry through the use of geochemical models: (1) review of thermodynamic model on ion exchange reaction, (2) modeling of bentonite-water interactions under aerobic conditions, (3) performance of sensitivity analyses of key parameters in the bentonite model, (4) model simulation of bentonite porewater chemistry in the engineered barrier system under repository conditions. Experimental information of bentonite-water interaction allowed the determination of soluble impurities in the bentonite, and the knowledge of these impurities is important for predictive modeling. For the impurities of Kunigel-V1, 0.38% of CaSO$$_{4}$$, 0.0011% of NaCl and 0.0044% KCl were determined. The sensitivity analyses resulted in that the presence of calcite, CaSO$$_{4}$$ and pyrite strongly influences the pH in the compacted bentonite, and the pH in compacted bentonite is buffered by the acid/base equilibria at the Na-smectite surface as well. Through the model calculations, some remarks on the expected trends for the long term behavior can be made like that the pH in compacted bentonite is expected to increase with increasing number of water exchange cycles, as long as CaCO$$_{3}$$ contributes to the pH buffering capacity, due to slow depletion of the soluble impurities in the bentonite. The pH of the porewater, however, lies in all cases (but in the presence of CaCO$$_{3}$$) between 5.6 and 9.5. Based on the findings discussed above, a large number of calculations were carried ...

JAEA Reports

Thermodynamic Date for the Speciation and Solubility of Pd, Pb, Sn, Sb, Nb, and Bi in Aqueous Solution

Lothenbach, B.*; Ochs, M.*; Wanner, H.*; Yui, Mikazu

JNC TN8400 99-011, 340 Pages, 1999/01

JNC-TN8400-99-011.pdf:26.06MB

This report provides thermodynamic data for predicting concentrations of palladium Pd, lead Pb, tin Sn, antimony Sb, niobium Nb and bismuth Bi in geologic environments, and contributes to an integration of the JNC chemical thermodynamic database, JNC-TDB (previously PNC-TDB), for the performance analysis of geological isolation system of high-level radioactive wastes. Besides treating hydrolysis in detail, this report focuses on the formation of complexes or compounds with chloride, fluoride, carbonate, nitrate, sulfate and phosphate. Other important inorganic ligands (sulfide for lead and antimony, ammonia for palladium) are also included. In this study, the specific ion interaction theory (SIT) approach is used to extrapolate thermodynamic constants to zero ionic strength at 25$$^{circ}$$C.

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