Long term response of multi-barrier schemes for underground radioactive waste disposal
The main objective of this thesis is to achieve an improved understanding of the thermo-hydro-mechanical processes and material properties that affect how the gaps and canister) behave during and after installation in the repository. The generated models and methodologies developed in this thesis ha...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2018 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/586172 |
| Acceso en línea: | http://hdl.handle.net/10803/586172 https://dx.doi.org/10.5821/dissertation-2117-119097 |
| Access Level: | acceso abierto |
| Palabra clave: | Àrees temàtiques de la UPC::Enginyeria civil 55 624 |
| Sumario: | The main objective of this thesis is to achieve an improved understanding of the thermo-hydro-mechanical processes and material properties that affect how the gaps and canister) behave during and after installation in the repository. The generated models and methodologies developed in this thesis have provided a deeper understanding of the THM processes taking place in a radioactive spent fuel disposal system and offered strategies for design improvement, material choice and optimization. The Thesis focuses on: - Material characterization (laboratory testing and numerical simulations of these tests), - Thermal dimensioning of repository (fixing canister and tunnel spacing, defining a power decay function for canister, adopting thermal boundary conditions), - 2D THM sensitivity analyses (developing a better understanding of the modelled system, several cases have been studied throughout the thesis), -3 D THM modeling (investigating the effect of variable gas pressure on the thermo-hydro-mechanical results). One of the main contributions of the thesis is to combine comprehensive and complex models to perform the calculations of a single deposition scheme: - BBM (Barcelona Basic Model) to represent clay buffer, BExM (Barcelona Expansive Model) to represent pellet-based components, combined with elasticity to represent rock and canister. - Porosity-dependent permeability and water retention curve (macro-porosity dependent in case of pellets using BExM). - Thermal conductivity depending of degree of saturation. - Gap-specific THM modelling under simplifying assumptions but capturing effects like thermal conductivity that may produce an early peak of temperature, or specific retention curve, which produces extreme, drying near the canister and gap closure that affects swelling pressure development. - Full scale 3D THM modelling with elasto-plastic parameters (BBM) is also an important contribution. The laboratory tests conducted for characterization of materials include: water retention curve tests, thermal conductivity tests, infiltration tests, oedometer tests and tortuosity tests. In general, satisfactory agreement between numerical and measured results is achieved. The majority of 2D sensitivity (fracture position, salinity of the inflow water, rock permeability, filling material between buffer and rock, artificial wetting of pellets etc.) cases show a behavior in safety margins in terms of temperature, density and stresses. A simplified 3D geometry has been adopted for THM calculations to check effect of third dimension. 3D calculations also include a sensitivity analysis. It has been shown that the full saturation of system components is delayed slightly when the air mass balance equation is considered, in other words, a variable gas pressure is taken into account. 3D THM simulations of full scale FISST test (a real scale in situ test will be performed in Onkalo research facility) is considered as a future work to validate, optimize and have better understanding the models and parameters used in the thesis. |
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