Disposal Of High-level Nuclear Waste Research Articles

Anisotropic swelling behaviour of unsaturated compacted GMZ bentonite hydrated under vertical stresses

Bentonite has been considered as a potential buffer/backfill material for construction of engineering barriers in deep geological repository for disposal of high-level nuclear waste. Anisotropy will be inevitably generated during static compaction during preparation of bentonite blocks, leading to induce possible influences on buffering function formation of the engineering barrier system and even the safety of the whole repository. In the present work, swelling deformation tests along the directions both perpendicular and parallel to the compaction plane were conducted on unsaturated compacted GMZ bentonite specimens using a self-developed lateral confined swelling test setup. Influences of initial dry density and vertical pressure on the final swelling strain and its anisotropy, as well as the mechanism of evolution of anisotropy coefficient on hydration, were analysed. Results demonstrate that the swelling time, average strain rate and final swelling strain increase with increasing initial dry density and decrease with increasing vertical pressure. Meanwhile, the swelling strain along the perpendicular direction is much higher than that along the parallel direction, exhibiting an obvious anisotropic swelling characteristic. The anisotropy coefficient is relatively large at the initial swelling stage, and then gradually decreases to be stabilised. The final anisotropy coefficient increases with initial dry density and decreases with vertical pressure.

Natural and Anthropogenic Analogues for High-Level Nuclear Waste Disposal Repositories: A Review

ABSTRACTProjects involving deep geological disposal of nuclear waste are unique in that predictive models of long-term safety often involve geological timeframes. This manuscript provides a review of natural and anthropogenic analogues for high-level nuclear waste disposal in a deep geological repository. We also occasionally highlight analogues that have been used for low- and intermediate-level waste. Most studies define natural analogues as either naturally occurring or anthropogenic systems. In this paper, we distinguish between natural analogues and anthropogenic analogues because the latter generally provide non-technical (anecdotal) illustrations of concepts and processes for the safety case, whereas the former can provide technical and quantitative information. In addition, natural analogues can provide information over geological time scales (millions of years) and spatial scales (kilometers), whereas anthropogenic analogues provide information over a much more limited time scale (hundreds or thousands of years). Regardless of the definition, analogue studies provide one of the multiple lines of evidence intended to increase confidence in the safe geological disposal of high-level nuclear waste. They are deemed necessary because they complement the experiments that are carried out over a period of months or years. They also provide a way to validate numerical long-term safety assessment models with information and data covering geological time scales and spatial scales.The first part of this review describes the analogue concept. The second and third parts provide examples of natural and anthropogenic analogues for engineered barrier systems and natural barriers. Part four describes analogues for complex coupled transport processes. Finally, we discuss general and specific areas of future research.A concerted effort should be made to ensure that there is a transfer of data from the complex, natural analogue field studies to simplistic models which, by necessity, are used to evaluate the long-term safety of deep geological repositories. Field analogue studies should be planned to interface with laboratory experiments and, ultimately, with in situ field experiments, when the final repository site is selected. This will involve using natural analogue data in a quantitative way to support the deep geological repository safety case.

Experimental Investigation on Drying and Wetting of GMZ Bentonite Using X-Ray Tomography and Volumetric Digital Image Correlation Technique

To investigate the shrinking and swelling properties of Gao-Miao-Zi (GMZ) bentonite, which has been considered as engineering barriers for high-level radioactive nuclear waste disposal in China, drying and wetting tests were carried out. The microstructure of the material at each hydric state was recorded using X-ray tomography (X-CT). The 3D images of the material were analyzed using digital volume correlation (DVC) technique, and the full-field strains at mesoscale (i.e., in the order of clay aggregate) during drying and wetting were quantified. The results show that the GMZ bentonite exhibits notable swelling characteristics during wetting and the swelling strain of the material is up to 8% at mesoscale. The full-field strain in 3D of the material is heterogeneous, anisotropic, and irreversible during drying and wetting. The corresponding deformation mechanisms are discussed. Two different swelling mechanisms were also identified: traction occurs in the interface between the matrix and inclusions during swelling; pre-existing fissure closes during swelling.

(Invited) Surface Analysis of Corrosion Products Built up at Interfaces of Different Nuclear Waste Forms in Near-Field Environment

In this study, we applied a series of surface analysis techniques to explore the structure and chemistry of the corrosion products built up at the interface of different materials, which is relevant to the permanent disposal of world-wide high-level nuclear waste. Metallic alloys, amorphous glass, and crystalline ceramics are typical candidate nuclear waste forms planned for immobilizing and isolating the dangerous radionuclides enriched in the waste. The near-field corrosion interactions between these dissimilar materials are the focus of this study. The experiments were performed by corroding metallic alloys in intimate proximity to glass or ceramics in Cl--containing solutions at 90 oC. The exposed materials were subsequently subjected to comprehensive surface characterization using X-ray photoelectron spectroscopy, scanning transmission electron microscopy, energy dispersive spectroscopy, time-of-flight secondary ion mass spectrometry, and Raman/infrared spectroscopy analysis. The systematic study revealed localized damage on the alloy surface due to crevice corrosion. Interestingly, localized corrosion was also identified on the surface of some glasses and ceramics that were present nearby, while an inhibition effect was observed in other systems. These interactions were found to strongly depend on the type of materials and environment, which led to different corrosion phenomena.

Permeability evolution and crack characteristics in granite under treatment at high temperature

The evolution of permeability and microcrack characteristics of granite at high temperature has significant effect on the safe and stable operation of high-level nuclear waste disposal repositories. We measure the permeability, porosity and formation factors of granite specimens following thermal treatment including the use of NMR to certify observed response. The results indicate that the initial and residual permeability and porosity change little when T ≤ 300 °C, but increase rapidly when 300 °C ≤ T ≤ 600 °C before entering a stable phase when 600 °C ≤ T ≤ 750 °C. At T = 150 °C microcrack apertures and radius only slight increase while microcrack density and fraction of connectedness all slight decrease, but net causing porosity, the peak strength and elastic modulus to increase. The strength and elastic modulus decrease exponentially with fractional connectivity of microcrack while the initial compressibility of microcracks scale linearly with initial aperture. The formation factor for the granite increases near-linearly with effective stress with the rate of increase generally decreasing with increasing temperature. Thermal conductivity first increases rapidly before remaining constant with increasing effective stress. With increasing temperature, the thermal conductivity decreases and becomes more sensitive to the effective stress.

Chemical forms of rhodium ion in pure water and nitric acid solution studied using ultraviolet-visible spectroscopy and first-principles calculations

We have investigated chemical forms of rhodium (Rh) ion in nitric acid solution by using spectroscopic and first-principles methods, in order to develop the disposal of high-level radioactive nuclear liquid wastes (HLLW). The electronic structure of Rh complexes in both pure water and nitric acid solutions was investigated using ultraviolet-visible (UV-vis) absorption spectroscopy. Comparison with many-electron calculations indicates that Rh ion forms an octahedral bidentate complex coordinated with three nitrate ions, [Rh(NO3)3], in both pure water and nitric acid solutions. This is consistent with thermodynamic prediction. Since the overall feature of UV-vis spectra of the Rh complex remained unchanged in a range of 0-3 M nitric acid solutions, the structure of the Rh complex was found to be stable in the range. In addition, since no significant changes in UV-vis spectra of Rh complex were observed under γ-ray radiation, the Rh complex, [Rh(NO3)3], can be expected to be stable in actual HLLW.

Short-term elemental release from Portland cement concrete in hypersaline leaching conditions

In the context of the long-term safety assessment of high-level nuclear waste (HLW) disposal, the initial release of metal ions from cementitious materials used as technical barriers is of great interest due to their possible interactions with HLW radionuclides (e.g. influencing the retention behaviour of radionuclides in engineered and natural barriers) due to water ingress. In the geochemical conditions in northern Germany, the porewater is of very high salinity, with salt contents of up to 2·5 M. In this work, the elemental composition of leaching water (with different types and amounts of salt) after 24 to 72 h contact with concrete was studied in order to simulate different water intrusion scenarios. It was found that in, addition to the main concrete elements (calcium, silicon, aluminium and iron), many trace elements were quantified in the concrete leachate. The influence of the concrete grain size in the leaching experiment showed that the use of particles <100 μm is necessary to obtain reproducible results. The influences of different solution salinities and the addition of calcium chloride and sodium sulfate on the leaching process were examined. For most elements, an increase in sodium chloride concentration enhanced the leaching process.

Effects of contact time, pH, and temperature on Eu(III) sorption onto MX-80 bentonite

MX-80 bentonite is considered a popular buffer/backfill material for the construction of artificial barriers. In particular, it plays an important role in the disposal of high-level nuclear waste in deep geological repositories. In the present study, the sorption of Eu(III) on MX-80 bentonite was investigated using a batch technique; furthermore, a comprehensive analysis was performed on the influence of contact time, pH, temperature, and concentration on sorption. The results showed that the sorption regime leveled off within 30 min and the Eu(III) sorption capacity of MX-80 bentonite was approximately 46.06 mg/g under certain conditions. A second-order kinetic equation was used to fit the equilibrium sorption data. Additionally, the variation in the sorption capacity of MX-80 bentonite increased as the pH increased from 1 to 9. The optimum pH value was determined to be 7.0 at a temperature of 293.15 K. The negative value of enthalpy change (ΔH°) indicates that the temperature had a negative effect on the sorption. The sorption process was most accurately described by the Langmuir isotherm model. These results will definitely be benefit to the artificial barriers in the disposal of high-level nuclear waste.

A model for hydraulic conductivity of compacted bentonite – inclusion of microstructure effects under confined wetting

Hydraulic behaviour of compacted smectite-rich clays is of practical interest in geological disposal of high-level nuclear waste, as the buffer component of the engineered barrier system. Despite several decades of research, a sound theoretical description of the unsaturated hydraulic conductivity of clay buffer (compacted bentonite) and its performance remains challenging. This is evidenced by experimental data on unsaturated hydraulic conductivity, which, albeit limited, show that the hydraulic behaviour of compacted bentonite during confined wetting is considerably different from that typically observed in non-expansive clays. This work addresses the challenge by proposing a predictive model for the saturated and unsaturated hydraulic conductivity of compacted smectite under confined wetting. By considering the microstructure evolution of compacted smectite, a theoretical description of its pore system variations with relative humidity is presented based on a geochemical modelling approach. The Kozeny–Carman (KC) relationship for hydraulic conductivity of compacted smectites is revisited as a basis to derive a new model, which also incorporates more accurately the effects of key properties, such as porosity, specific surface area and tortuosity. The model predictions for saturated hydraulic conductivity for four types of bentonite clays (GMZ, Kunigel-V1, MX-80 and FEBEX) show close correlations with the experimental data. The results of model prediction for unsaturated hydraulic conductivity of compacted bentonite are in close agreement with the experimental data over a large range of suction values.

Monte-Carlo Simulation of Pitting Corrosion with a Deterministic Model for Repassivation

A theory is developed for calculating the delayed repassivation (“stifling”) rate constant for stable pits on a metal surface with attention being paid to pitting of the carbon steel overpack in the Belgian supercontainer concept of the disposal of high-level nuclear waste. It is shown that, under the conditions that are expected to exist at the overpack surface, substantial concentration and potential drops cannot exist between the pit internal surface and the external surface far away from the pit mouth. This conclusion is valid for both open and semi-closed pits, if there is no porous, high resistance, corrosion product layer (salt film and/or remnants of the ruptured passive film) between the active metal surface inside the pit and the external surface, as supported by recent artificial pit experiments. It is shown that the existence of a low conductivity, corrosion product layer between the active pit base and the external surface can protect pits from the repassivation. The condition of repassivation is based upon the concept of the existence a critical pit propagation rate, Vcr, corresponding to a critical coupling current. If the rate of pit propagation becomes less than Vcr the pit passivates, because the coupling current is too low to maintain the necessary aggressive conditions within the pit cavity. A model and computer code have been developed for estimating the probability of failure in the Belgian high-level nuclear waste (HLNW) disposal repository.

Impact of dry density, saturation, and confinement on gas permeability of clay-barrier materials

The safe isolation of high-level radioactive waste from the human environment is a key requisite in the nuclear fuel cycle. Deep geological repositories (i.e. >500m) in a suitable rock mass, involving both engineered and natural barriers is currently the most favoured option for the disposal of high-level nuclear waste. Complex Thermal-Hydro-Mechanical and Chemical (THMC) phenomena are anticipated during the repository lifetime. The formation of gasses (e.g., as a result of oxidation processes) and their possible migration through the engineered barrier system (EBS) could jeopardise the main barrier functions. This paper focuses on the experimental study of the gas flow process through clay-barrier materials, particularly on the effect of degree of saturation, clay initial dry density, and confinement stress on gas permeability. It is shown that the initial dry density of the clay has a significant impact on gas flow, especially at low saturations. As expected, lower gas permeability values were obtained near saturation. Confinement has a minor impact on gas flow, at least for the range of stresses investigated in this paper.

Fracture analysis of Beishan granite after high-temperature treatment using digital image correlation

A systematical knowledge of the fracture characteristics and thermal damage mechanism of granite at elevated temperature is an important issue in the high-level nuclear waste disposal and geothermal energy exploration field. To investigate the influence of high temperature on the fracture behaviors and characteristics of Beishan granite, three-point bending tests were conducted on specimens subjected to different high temperatures, i.e. 200 °C, 300 °C, 400 °C, 500 °C, 600 °C and 800 °C, and specimens at room temperature (25 °C) were also tested for comparison. An innovative technique called digital image correlation (DIC) was used in this study to trace the fracture process, and important fracture parameters, such as the fracture process zone (FPZ) size and critical opening displacement, were measured by full-field displacement and strain measurement. The experimental result illustrates that thermal treatment has a significant influence on the fracture behavior of the Beishan granite. Comparisons reveal that the enhanced ductile feature, a linear decline in the peak load and a rapid increase in critical crack mouth opening displacement is observed with the increase of temperature from 200 °C to 600 °C. Moreover, the increasing temperatures also reduce the applied load for fracture initiation. The FPZ length and critical opening displacement are significantly affected by the thermal treatment, while the FPZ width almost does not change with the increasing temperatures. The fracture toughness for Beishan granite shows a decreasing trend with the increase of temperature from 25 °C to 300 °C, while a valid fracture toughness value cannot be obtained for granite specimens subjected to temperature over 300 °C due to the existing of a large FPZ above the notch tip. Finally, the thermal-induced damage mechanism is also revealed by optical microscopic observation, and the thermal-induced microcracks are considered as the essential cause for the change of the fracture behavior of Beishan granite.

Investigation on anisotropic thermal conductivity of compacted GMZ bentonite

Gaomiaozi (GMZ) bentonite has been considered as a potential material for construction of engineering barrier in Chinese deep geological repository for disposal of high-level nuclear wastes. In the present work, thermal conductivity tests were conducted on statically compacted GMZ bentonite specimens using the needle probe method. Cubic specimens with different initial saturation degrees and dry densities were prepared and the thermal conductivity tests were conducted along the directions both parallel and perpendicular to the bedding plane of the specimen. Results show that the thermal conductivity nonlinearly increases with increasing saturation degree with a transition point that proximately corresponding to the air entry value. Meanwhile, the thermal conductivity along the parallel direction is much higher than that along the perpendicular direction. The anisotropy coefficient decreases with increasing saturation. However, the anisotropy coefficient increases with increasing dry density and the influence depends on saturation degree.

Adsorption of caesium on raw Ca-bentonite in high saline solutions: Influence of concentration, mineral composition, other radionuclides and modelling

Concentration depended retention of Cs+ was analysed in alkaline and very high saline solutions (0.1–5 M), mainly NaCl but also in an artificial cement pore water (ACW), representing conditions in a potential high level nuclear waste disposal in northern Germany. Adsorbent agent was Calcigel, a raw Ca-bentonite proposed as a clay based buffer material, which was used as supplied. Batch experiments were carried out in a wide concentration range (5–250,000 nmol L−1) and subsequently, the aqueous phase was analysed via mass spectrometry with inductively coupled plasma (ICP-MS). The adsorption still depended on the Cs+ concentration in every medium and decreased with increasing electrolyte concentration, in general. In nanomolar concentration range, the retention was above 50% but dropped rapidly to only approximately 10% when ionic strength exceeded 1 M. The amount of Cs+ leached out of the clay appeared to be commensurate with electrolyte concentration. Ion exchange modelling was done using specific ion interaction theory to calculate activity coefficients. Two surface complexations were chosen to describe different adsorption sites on Calcigel. One with high selectivity for Cs+ (logKCs = 8.14) and very low capacity, such as frayed edges sites in micaceous minerals, the other one based on cationic exchange capacity of Calcigel and rather unselective for Cs+ (logKCs = 1.96). With refined selectivity constants, it was possible to describe experimental data quite perfect. However, determined values for constants differ from those found to be best for lower ionic strength. In addition, adsorption on raw Ca-bentonite was compared with that on Na-montmorillonite as a single mineral. Lower dependence on concentration was determined on single mineral in 0.1 M NaCl (79% to 53% adsorption on Na-montmorillonite, 89% to 36% on Ca-bentonite), but at higher ionic strengths the differences between the investigated clays diminished. The Cs+ adsorption on Calcigel was also analysed in presence of Eu3+, UO22+ and I−, representing potential competing ions attendant in high level nuclear waste. Here, almost no relevant influence could be detected, except at highest investigated concentration and ionic strength >1 M. At an initial concentration [Cs+]i = 250 μmol L−1, the adsorption declined remarkably in presence of other ions from approximately 10% adsorption to at least 0–5%.

Penentuan Parameter Rangkak pada Bentonit sebagai Bahan Penyangga (Buffer Material) dengan Uji Geser Langsung

A preliminary research to investigate the creep behavior of bentonite as buffer material in a high-level nuclear or radioactive waste disposal hole as bentonite needs to maintain the stability of the waste canister for a long time, to avoid the displacement caused by the weight of the canister itself and the thermal, hydrological, mechanical and chemical (THM-C) processes of the near filed. The increase of bentonite time-dependent strain or creep needs to be taken into account for the safety of the disposal hole. The creep parameters obtained from the angular strain rate equation, through stress-controlled direct shear test using compacted SPV200 bentonite samples. The test results show an increase in angular strain rate with increasing of the applied stress.

Effects of NaCl solution on the swelling and shrinkage behavior of compacted bentonite under one-dimensional conditions

Because of its low hydraulic conductivity, high swelling capacity, and good adsorption properties, Gaomiaozi (GMZ) bentonite has been proposed as a suitable buffer/backfill material for construction of artificial barriers in deep geological repositories for high-level nuclear waste (HLW) disposal in China. By varying the concentration of NaCl solution and total suction, the swelling and shrinkage characteristics of compacted GMZ bentonite were studied under one-dimensional conditions. Results show that the swelling strain of compacted GMZ bentonite decreases as the concentration of NaCl solution increases under one-dimensional conditions. During drying with suction control by vapor phase technique, the density increases with suction. Simultaneously, the sample saturated with salt solution has a larger void ratio than that of the sample saturated with distilled water under the same suction. The void ratio and water content of the samples decrease with increasing suction. For a given suction, the sample saturated with salt solution has a higher degree of saturation than the sample saturated with distilled water. With the obtained water content (w), void ratio (e), and the degree of saturation (Sr), soil-water retention curves (SWRCs) were calculated for samples initially hydrated with different concentrations of NaCl solution. The SWRCs reveal that the sample with salt solution has higher water retention capacity than the sample with distilled water. A modified SWRC equation was proposed to account for the effect of NaCl solutions on the drying process of compacted GMZ bentonite under one-dimensional conditions. The results confirm that the modified SWRC equation can effectively describe the SWRCs of compacted GMZ bentonite considering the effects of NaCl solutions.

A continuum-scale two-parameter model for non-Darcian flow in low-permeability porous media

Numerous studies have demonstrated that Darcy velocity exhibits nonlinear dependence on the pressure gradient in lower-permeability porous media such as clays and shales when the pressure gradient is low. Non-Darcian flow has important implications to geologic disposal of high-level nuclear waste, because shale has been proposed as a disposal medium, with compacted bentonite clay as a buffer material. Consideration of the impact of temperature on non-Darcian flow in an engineered clay barrier is necessary, because the clay barrier is subjected to significant temperature changes resulting from the heat-releasing nuclear waste package. In this study, a continuum-scale, two-parameter predictive model is developed to facilitate experimental data interpretation and to provide mechanistic insights into the role of temperature on non-Darcian flow in saturated low-permeability porous media. This model has several advantages when it is applied at the continuum scale. First, this model is consistent with the current theory about the role of temperature and provides more flexibility in fitting experimental data associated with varying temperatures. Second, the values of the two independent parameters in the model can be easily determined and the solution is unique. This leads to practical convenience when the model is used to interpret continuum-scale laboratory data. Third, although the two-parameter model is simple, its performance in fitting existing experimental data is satisfactory. This suggests that the model achieves a balance between simplicity and effectiveness.

Experimental and Modeling Study of Soil Water Retention Curves of Compacted Bentonite considering Salt Solution Effects

Due to its low hydraulic conductivity, high swelling capacity, and good adsorption properties, the Gaomiaozi (GMZ) bentonite has been selected as potential buffer/backfill materials for construction of engineered barriers in the deep geological repository for disposal of high-level nuclear waste (HLW) in China. Investigation of salt solution effects on the water retention properties of compacted bentonite is of great importance in the context of geological disposal of HLW based on the multibarrier concept. In this study, amended specimens were obtained through a spray of different concentrations of salt solutions to reach target salt contents, respectively. With employment of the vapor phase technique for suction control, water retention tests were conducted on densely compacted GMZ bentonite (1.7 Mg/m3) with different salt contents under confined conditions. Corresponding soil water retention curves (SWRCs) were obtained. Analysis indicates that, for a given suction, the measured water content of GMZ bentonite specimen increases as the salt content (or pore fluid concentration) increases. The influencing rate depends on suction. For lower suctions (lower than 38 MPa), the water retention capacity increases as the salt content increases, while for higher suctions (higher than 38 MPa), the influence can be negligible. Based on the Fredlund and Xing (1994) equation, a soil water retention model was proposed for simulation of the SWRCs of compacted GMZ bentonite with consideration of pore fluid chemistry. Parameters were analyzed and determined with consideration of influences of the pore fluid concentration. Verification indicates that the SWRCs simulated by the proposed model are well agreed with the measured ones.

Effects of deep geological environments for nuclear waste disposal on the hydrogen entry into titanium

Abstract The surface of nuclear waste container will be completely wetted by the groundwater infiltrating through the bentonite or concrete buffer after the closure of its deep geological disposal. Because of its excellent corrosion resistance, titanium is one of the candidates for the container materials for high-level nuclear waste (HLNW) disposal. However, once oxygen depleted in the large time scale deep geological disposal, titanium container will suffer from hydrogen embrittlement (HE). Therefore, in order to predict the potential danger of the HLNW container caused by HE, the hydrogen entry into titanium was studied at different temperatures in simulated deep geological environment of Beishan, which is the preselected HLNW disposal area in China. Devanathan-Stachurski cell methods were firstly implemented in measuring apparent hydrogen diffusivity in titanium with hydrides being formed during hydrogen charging at low temperature ranges (298–373 K). Given the characteristic of the Devanathan-Stachurski cell method's capable of getting apparent diffusivity with combined influencing factors easily, the technique provides a simple way to measure the parameter that is necessary for the estimation of hydrogen penetration depth, facilitating the design of HLNW containers.

Investigation on gas migration in saturated bentonite using the residual capillary pressure technique with consideration of temperature

Determination of parameters for description of gas migration in saturated bentonite is of great importance for the design and construction of artificial barriers in the geological repository for the disposal of high-level radioactive nuclear waste. In this paper, temperature-controlled gas injection tests were conducted on initially water-saturated bentonite specimens using the residual capillary pressure (RCP) technique. Effective gas permeabilities in low injection pressures and the gas breakthrough pressures at temperatures 20, 40 and 60°C were obtained. Results show that: (i) for all the temperatures tested, the intrinsic water permeabilities (kin) range between 3.2 × 10−20 and 5.72 × 10−20 m2, furthermore, those values increase with rising temperature. Meanwhile, the intrinsic water permeabilities derived from the steady state tests are lower than those obtained from the non-steady state tests; (ii) for all the temperatures tested, the effective gas permeabilities (keff) corresponding to the viscous gas flow before gas breakthrough range between 4.81×10-24 and 2.74×10-22 m2, with slight fluctuations with time. The maximum effective gas permeabilities measured at the occurrence of gas breakthrough on the initially water-saturated bentonite specimens extend from 2.27×10-18 up to 3.32×10-17 m2 and increase as temperature increases, while the time required for gas breakthrough decreases as temperature increases; (iii) for all the temperatures tested, the gas breakthrough pressures measured on the initially water-saturated bentonite specimens vary from 2.74 to 4.08 MPa, while the residual capillary pressure differences, also denoted as snap-off pressures (Psnap-off), range from 0.2 to 0.38 MPa. Additionally, the gas breakthrough pressures and the residual capillary pressures decrease as temperature increases.