Endlagerung radioaktiver Abfälle

Mengel, K.; Röhlig, Klaus-Jürgen; Geckeis, Horst

doi:10.1002/ciuz.201200582

Cited by 6 publications

(3 citation statements)

References 2 publications

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“…For the final storage of high-level nuclear waste different types of host rock formations (clays, salt rocks, and crystalline formations) are discussed. 1,[5][6][7][8][9][10][11] Depending on the type of the host rock, different chemical conditions prevail including the presence of organic or inorganic ligands which may affect the geochemical behaviour of the actinides. For example, low molecular weight organic compounds (LMWOC) like formate, acetate, propionate, and lactate as well as macromolecular organic compounds are abundant in clay rocks and different natural systems serving as potential complexation agents.…”

Section: Introductionmentioning

confidence: 99%

Speciation, thermodynamics and structure of Np(v) oxalate complexes in aqueous solution

et al. 2020

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Section: Introductionmentioning

confidence: 99%

Speciation, thermodynamics and structure of Np(v) oxalate complexes in aqueous solution

et al. 2020

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“…The final emplacement of high-level nuclear waste in deep geological formations is the most preferred disposal option. − The intrusion of water into a nuclear waste repository is an important scenario which has to be considered for the safety case. Upon contact of the actinides with dissolved organic or inorganic ligands their (geo)chemical properties and migration behavior can strongly be affected. ,− In terms of nuclear waste disposal, it is a key step to obtain a profound knowledge of the aqueous (geo)chemistry of the actinides including the most relevant interaction mechanisms, which is based on reliable thermodynamic data like standard stability constants log β°(Θ), standard enthalpies Δ r H m ° , and entropies Δ R S m ° of the reaction.…”

Section: Introductionmentioning

confidence: 99%

Complexation of Np(V) with the Dicarboxylates, Malonate, and Succinate: Complex Stoichiometry, Thermodynamic Data, and Structural Information

et al. 2021

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The complexation of Np(V) with malonate and succinate is studied by different spectroscopic techniques, namely, attenuated total reflection Fourier transform infrared (ATR FT-IR) and extended X-ray absorption fine-structure (EXAFS) spectroscopy, as well as by quantum chemistry to determine the speciation, thermodynamic data, and structural information of the formed complexes. For complex stoichiometries and the thermodynamic functions (log β n °(Θ), ΔrH n °, ΔrS n °), near infrared absorption spectroscopy (vis/NIR) is applied. The complexation reactions are investigated as a function of the total concentration of malonate ([Mal2–]total) and succinate ([Succ2–]total), ionic strength [I m = 0.5–4.0 mol kg–1 Na+(Cl–/ClO4 –)], and temperature (Θ = 20–85 °C). Besides the solvated NpO2 + ion, the formation of two Np(V) species with the stoichiometry NpO2(L) n 1–2n (n = 1, 2, L = Mal2–, Succ2–) is observed. With increasing temperature, the molar fractions of both complex species increase and the temperature-dependent conditional stability constants log β n ′(Θ) at given ionic strengths are determined by the law of mass action. The log β n ′(Θ) are extrapolated to IUPAC reference-state conditions (I m = 0) according to the specific ion interaction theory (SIT), revealing thermodynamic log β n °(Θ) values. For all formed complexes, [NpO2(Mal)−: log β1 °(25 °C) = 3.36 ± 0.11, NpO2(Mal)2 3–: log β2 °(25 °C) = 3.95 ± 0.19, NpO2(Succ)−: log β1 °(25 °C) = 2.05 ± 0.45, NpO2(Succ)2 3–: log β2 °(25 °C) = 0.75 ± 1.22], an increase of the stability constants with increasing temperature was observed. This confirmed an endothermic complexation reaction. The temperature dependence of the log β n °(T) values is described by the integrated Van’t Hoff equation, and the standard reaction enthalpies and entropies for the complexation reactions are determined. Furthermore, the sum of the specific binary ion–ion interaction coefficients Δεn °(Θ) for the complexation reactions are obtained as a function of the t from the respective SIT modeling as a function of the temperature. In addition to the thermodynamic data, the structures of the complexes and the coordination modes of malonate and succinate are investigated using EXAFS spectroscopy, ATR-FT-IR spectroscopy, and quantum chemical calculations. The results show that in the case of malonate, six-membered chelate complexes are formed, whereas for succinate, seven-membered rings form. The latter ones are energetically unfavorable due to the limited space in the equatorial plane of the Np(V) ion (as NpO2 + cation).

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“…However, both perspectives consider the uncontrolled leaching of potash seams as highly critical. Whether water contact is enabled by geological fault zones or mining activities: in both cases, the increased solubility of potash salt causes a preferential expansion of leaching zones, jeopardizing the integrity and mechanical stability of mines or technical caverns [2][3][4][5]. In order to assess the hazard potential of leaching zones in potash seams, their evolution has to be described in space and time.…”

Section: Introductionmentioning

confidence: 99%

How Insoluble Inclusions and Intersecting Layers Affect the Leaching Process within Potash Seams

2021

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Potash seams are a valuable resource containing several economically interesting, but also highly soluble minerals. In the presence of water, uncontrolled leaching can occur, endangering subsurface mining operations. In the present study, the influence of insoluble inclusions and intersecting layers on leaching zone evolution was examined by means of a reactive transport model. For that purpose, a scenario analysis was carried out, considering different rock distributions within a carnallite-bearing potash seam. The results show that reaction-dominated systems are not affected by heterogeneities at all, whereas transport-dominated systems exhibit a faster advance in homogeneous rock compositions. In return, the ratio of permeated rock in vertical direction is higher in heterogeneous systems. Literature data indicate that most natural potash systems are transport-dominated. Accordingly, insoluble inclusions and intersecting layers can usually be seen as beneficial with regard to reducing hazard potential as long as the mechanical stability of leaching zones is maintained. Thereby, the distribution of insoluble areas is of minor impact unless an inclined, intersecting layer occurs that accelerates leaching zone growth in one direction. Moreover, it is found that the saturation dependency of dissolution rates increases the growth rate in the long term, and therefore must be considered in risk assessments.

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Endlagerung radioaktiver Abfälle

Cited by 6 publications

References 2 publications

Speciation, thermodynamics and structure of Np(v) oxalate complexes in aqueous solution

Speciation, thermodynamics and structure of Np(v) oxalate complexes in aqueous solution

Complexation of Np(V) with the Dicarboxylates, Malonate, and Succinate: Complex Stoichiometry, Thermodynamic Data, and Structural Information

How Insoluble Inclusions and Intersecting Layers Affect the Leaching Process within Potash Seams

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