This study investigates the influence of primary variables selection on modeling non-isothermal two-phase flow, using numerical simulation based on the full-scale engineered barrier system (EBS) experiment conducted at the Horonobe Underground Research Laboratory (URL) as part of the DECOVALEX-2023 project. A thermalhydraulic coupled model was validated against analytical solution and experimental data before being applied to simulate the heterogeneous porous media within the EBS. Two different primary variable schemes were compared for discretizing the governing equations, revealing substantial differences in results. Notably, using capillary pressure as a primary variable instead of saturation resulted in closer alignment with analytical solutions and real-world observations. While the modeling work at the Horonobe URL generally exhibited trends consistent with experimental data, discrepancies were attributed to the operational conditions of the heater and the influence of the Excavation Damaged Zone (EDZ) near the borehole.

Introduction Gas migration in low-permeability buffer materials is a crucial aspect of nuclear waste disposal. This study focuses on Gaomiaozi bentonite to investigate its behavior under various conditions.Methods We developed a coupled hydro-mechanical model that incorporates damage mechanisms in bentonite under flexible boundary conditions. Utilizing the elastic theory of porous media, gas pressure was integrated into the soil's constitutive equation. The model accounted for damage effects on the elastic modulus and permeability, with damage variables defined by the Galileo and Coulomb-Mohr criteria. We conducted numerical simulations of the seepage and stress fields using COMSOL and MATLAB. Gas breakthrough tests were also performed on bentonite samples under controlled conditions.Results The permeability obtained from gas breakthrough tests and numerical simulations was within a 10% error margin. The experimentally measured gas breakthrough pressure aligned closely with the predicted values, validating the model's applicability.Discussion Analysis revealed that increased dry density under flexible boundaries reduced the damage area and influenced gas breakthrough pressure. Specifically, at dry densities of 1.4 g/cm3, 1.6 g/cm3, and 1.7 g/cm3, the corresponding gas breakthrough pressures were 5.0 MPa, 6.0 MPa, and 6.5 MPa, respectively. At a dry density of 1.8 g/cm3 and an injection pressure of 10.0 MPa, no continuous seepage channels formed, indicating no gas breakthrough. This phenomenon is attributed to the greater tensile and compressive strengths associated with higher dry densities, which render the material less susceptible to damage from external forces.

Deep geological disposal is the preferred solution for radioactive waste management in many countries, including Belgium, where the Boom Clay is one of the potential candidate host formations. Over the long term, corrosion mechanisms are expected to release large amounts of gas that will rise in pressure and activate different gas transport processes in the system and the surrounding geological formation. Assessing which transfer mode prevails under which range of pressure conditions in the sound rock layers remains a major issue. This paper presents a multi-scale Hydro-Mechanical (HM) model capturing the influence of the microstructure features on the macroscopic gas flow, and especially the emergence of preferential gas-filled pathways. A detailed constitutive model for partially saturated clay materials is developed from experimental data to perform the modelling of a Representative Element Volume (REV), and integrated into a multi-scale scheme using homogenisation and localisation techniques for the transitions to the macroscopic scale. Using this tool, numerical modelling of a gas injection test in the Boom Clay is performed with the aim of improving the mechanistic understanding of gas transport processes in natural clay barriers.

Polymer solutions aid DNAPL (Dense Non Aqueous Phase Liquid)-contaminated soil remediation but are impacted by gravity and viscous forces. This study assesses the interplay between buoyancy and viscous forces in influencing the distribution of DNAPL and the invading phase, by introducing a densified brine (NaI) biopolymer (xanthan) solution as remediation fluid. A matrix of experiments was conducted, encompassing rheological measurements, multiphase flow tests in 1D-columns and 2D-tanks. Numerical modeling was used to assess polymer and DNAPL propagation under different conditions. NaI addition maintains xanthan's shear-thinning yet lowers mid-range shear viscosity 2.6 times. Confined column tests show similar 89 % performance for viscous polymer solutions regardless of density. Unconfined tests mimicking real sites reveal non-densified viscous polymer solution yield mere 0.09 recovery due to density-driven flow. Densified polymer attains radial invasion, boosting recovery to 0.46 with 1.21 aspect ratio. Numerical simulations aligned with experiments, suggesting a near-zero gravity number is necessary to prevent density-driven flow problems. The multiphase flow experiments in confined multilayer system are performed and using the numerical modeling the effects of the permeability contrast and dimensions of the layers on the shape of front are analyzed.

Titan is an ocean world with a dense atmosphere, where photochemistry produces complex organic molecules that fall to the surface. An important astrobiological question is whether this material can mix with water and form molecules of biological interest. Large impacts heat the moon's subsurface and create liquid water melt pools. A recent study investigated impacts into Titan's clathrate-covered ice shell. Methane clathrates are stable at Titan's surface conditions and have low thermal conductivity, making them efficient insulators that can lead to steep thermal gradients and a thin stagnant lid. The authors showed that the clathrate layer thickness primarily influences the melt distribution, while its volume is governed by the impactor size. Here, we investigate the fate of melt formed during an impact into a clathrate-covered ice shell. Our results show two different behaviors: in cases when less melt is produced, the subsurface melt pool remains close to the surface and freezes on timescales less than or similar to 25 kyr; in cases when larger volumes of melt are produced, a downward-oriented transport of the molten material occurs. As it descends, part of the melt freezes but some may reach the ocean within a few kyr under certain conditions; vertical impacts, high surface porosity, low viscosity, and tidal heating all favor this surface-to-ocean exchange. While providing insights on parameters that allow a subsurface melt pool to remain liquid beneath a Selk-sized crater for a few kyr, this study suggests that Dragonfly may be able to sample melt deposits where organics reacted with liquid water to produce biomolecules. Titan, Saturn's largest moon, harbors a subsurface ocean beneath its ice shell. The moon also has an atmosphere, which is rich in large organic molecules that settle onto its surface. When atmospheric methane reacts with surface water ice, it forms methane clathrate. A clathrate layer atop Titan's ice shell affects the formation of Titan's impact craters, as it is both stronger than ice and a better insulator. Here, we study the effect of this clathrate layer on the formation and subsequent fate of melt pools produced by impacts on Titan. We investigate whether the melt descends through the ice shell to reach the ocean or remains near the surface and freezes. Our results show only a limited range of scenarios where impact melt reaches the ocean. In the majority of models, impact melt freezes near the surface within short timescales, ranging from a few thousands to tens of thousands of years. This implies that surface organic molecules may have interacted with subsurface melt pools. These results provide a positive outlook for NASA's Dragonfly mission, which will explore Titan's Selk crater in search of organic materials that have reacted with water to potentially form molecules of biological interest. We studied the evolution of impact melt pools in Titan's ice shell using numerical simulations of two-phase thermal convection While most melt pools never reach the ocean, we observe surface-to-ocean exchange in a small part of the investigated parameter space Our results suggest that Dragonfly may be able to sample melt deposits where organics reacted with liquid water to produce biomolecules

This study develops a dynamic model to better describe the frictional-dilatancy behavior of underwater granular motion. We employ the compressible Navier-Stokes equations as the continuum framework, and introduce mu(J) rheology in treating the constitutive law of the immersed granules. Within the compressible Navier-Stokes framework, the change in granular volume fraction that occurs when the granules undergo shear-induced volumetric dilation (contraction) is considered using the frictional-dilatancy law from soil mechanics. On introducing frictional dilatancy, the constant coefficient of friction at startup in mu(J) rheology, which governs the yielding limit of particles, is replaced by a particle-volume-fraction-dependent evolutionary variable. The proposed model enables an accurate description of the properties of quasi-static deforming granular mass. The validity of the model is verified by classical immersed granular collapse. A comparison with experimental and previous simulation results demonstrated that the introduction of frictional-dilatancy law delays the initiation of submarine granular flow.