Uranium migration through the Swiss Opalinus Clay varies on the metre scale in response to differences of the stability constant of the aqueous, ternary uranyl complex Ca<sub>2</sub>UO<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>
<p>The simulation of uranium migration through the Swiss Opalinus Clay is used as an example to quantify the influence of varying values of a stability constant in the underlying thermodynamic database on the migration lengths for the repository scale. Values for the stability constant of the...
Guardado en:
| Autores principales: | , |
|---|---|
| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
|
| Materias: | |
| Acceso en línea: | https://doaj.org/article/4500645a7c80456282e24aef51089c56 |
| Etiquetas: |
Agregar Etiqueta
Sin Etiquetas, Sea el primero en etiquetar este registro!
|
| Sumario: | <p>The simulation of uranium migration through the Swiss Opalinus Clay is used as an example to quantify the influence of varying values of a stability constant in the underlying thermodynamic database on the migration lengths for the repository scale. Values for the stability constant of the neutral, ternary uranyl complex <span class="inline-formula">Ca<sub>2</sub>UO<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub></span> differ in literature by up to one order of magnitude. Within the studied geochemical system, either the neutral or the anionic complex <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">CaUO</mi><mn mathvariant="normal">2</mn></msub><mo>(</mo><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">3</mn></msub><msubsup><mo>)</mo><mn mathvariant="normal">3</mn><mrow><mn mathvariant="normal">2</mn><mo>-</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="77pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="93f42c0d55d640131c7a956afd34b586"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="adgeo-56-97-2021-ie00001.svg" width="77pt" height="17pt" src="adgeo-56-97-2021-ie00001.png"/></svg:svg></span></span> is the predominant one, depending on the chosen value for the neutral complex. This leads to a changed interaction with the diffuse double layers (DDL) enveloping the clay minerals and thus can potentially influence the diffusive transport of uranium. Hence, two identical scenarios only differing in the value for the stability constant of the <span class="inline-formula">Ca<sub>2</sub>UO<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub></span> complex were applied in order to quantify and compare the migration lengths of uranium on the host rock scale (50 m) after a simulation time of one million years. We ran multi-component diffusion simulations for the shaly and sandy facies in the Opalinus Clay. A difference in the stability constant of 1.33 log units changes the migration lengths by 5 to 7 m for the sandy and shaly facies, respectively. The deviation is caused by the anion exclusion effect. However, with a maximum diffusion distance of 22 m, the influence of the stability constant of the <span class="inline-formula">Ca<sub>2</sub>UO<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub></span> complex on uranium migration in the Opalinus Clay is negligible on the host rock scale.</p> |
|---|