Thermal conductivity of compacted bentonite is one of the parameters affecting the behaviour of high-level radioactive waste (HLW) repositories, where the bentonite will be used as a buffer. Because ...the heat released from the HLW will be diffused across the buffer, understanding the thermal properties of buffer materials is necessary to accurately assess the thermal performance of the HLW repository. In this study, the thermal conductivity of compacted Gaomiaozi (GMZ07) and Wyoming (MX80) bentonites was measured and investigated under different testing conditions: temperature, water content and dry density. The obtained results showed that the thermal conductivity of compacted bentonites increased with increasing temperature. The thermal conductivity increased noticeably with temperature above 60 °C, while the change in thermal conductivity with temperature was small at temperature ranging from 5 to 60 °C. The temperature effect on thermal conductivity decreased with increasing dry density, and for a dry specimen, the thermal conductivity was negligibly changed with temperature.
•Thermal conductivities of two bentonites increased with increasing temperature.•Thermal conductivity increased noticeably with temperature above 60C.•Temperature effect of thermal conductivity decreased with dry density.•Thermal conductivity was negligibly changed with temperature for dry specimen.
Soil thermal properties are essential for investigating the thermal performance of many kinds of underground thermal engineering structure. To investigate the influences of microstructure alteration ...on soil thermal properties, thermal conductivity, thermal diffusivity and specific heat capacity were measured for both undisturbed and compacted lateritic clay specimens subjected to drying and wetting with the thermal probe method. Results revealed that thermal conductivity and diffusivity of undisturbed specimens were higher than that of compacted specimens. The specific heat capacity of the undisturbed and compacted specimens was roughly the same. For the same volumetric water content, thermal conductivity of specimens produced by drying was higher than that by wetting due to hysteresis effects. Test results from the scanning electron microscope and mercury intrusion porosimetry confirmed that compared with compacted specimens, the undisturbed specimens have a relatively uniform pore system that improves the extent or quality of heat transfer paths through the contact points and water bridges, thus have higher thermal conductivity. The hysteresis effects on soil thermal conductivity can be explained by the ink-bottle effect, effects of pore size distributions induced by shrinkage and swelling, and differences in the volume of entrapped air between drying and wetting.
•Thermal conductivity and diffusivity of undisturbed specimens are higher than that of compacted one.•Specific heat capacity of the undisturbed and compacted specimens is roughly the same.•Thermal conductivity of specimens produced by drying is higher than that by wetting.•Microstructure effects on the thermal properties of lateritic clay is noticeable.•The mechanism of hysteresis effects on thermal conductivity is revealed.
•A mathematical model is established to simulate the heat conduction and moisture transport at the repository site.•The present model can simulate the temperature field more accurately in the nuclear ...waste repository.•The temperature and moisture distributions near the waste canister are obtained.
In this paper, coupled governing equations were proposed to simulate three-dimensional heat conduction and moisture transport in the nuclear waste repository. Because there will be a large temperature gradient near inner and outer boundaries of the bentonite buffer layer, and the heat driven moisture transport is introduced in the governing equation of moisture transport. By applying the Fourier and Laplace transforms, the governing equations were converted to the Bessel equations, and the Laplace-domain solutions to temperature and moisture distributions were derived through the inverse Fourier transform. The reliability of the proposed solutions was verified through comparative analysis with the line heat source model. These analytical solutions were applied to obtain the evolutions of temperature field and moisture distribution near the waste canister. Finally, a sensitivity study was performed to analyze the effects of relevant parameters on the heat driven moisture transport.
Bentonite pellets or their mixtures with powdered bentonite are potential buffer/backfill materials for the deep geological disposal of high-level radioactive waste (HLW) and are used to backfill the ...joints between neighbouring bentonite blocks or the construction gaps between bentonite blocks in the buffer layer and surrounding rock. Knowledge of the thermal properties of buffer/backfill materials is essential for the thermal evaluation and design of HLW repositories. The thermal properties were measured on a mixture of GMZ07 bentonite pellets and powdered bentonite with 70% pellet content over a wide range of water contents, dry densities, and temperatures. The test results revealed that the thermal conductivity of the specimen compacted with pure bentonite powder was higher than that of the mixture. This was due to the different pore-size distributions that influenced the conductive heat transfer in the specimens. The difference in thermal conductivity between the two types of specimens made by different methods decreased with increasing dry density, which was mainly attributed to the preparation of bentonite pellets using a compaction–crushing method. In addition, the destruction of bentonite pellets increased gradually with increasing dry density. The thermal conductivity, thermal diffusivity, and volumetric heat capacity of the mixture increased with increasing temperature. For a given dry density, the size of the inter-aggregate pores and aggregates of the mixture was larger than that of compacted pure GMZ07 bentonite, resulting in a decrease in the extent or quality of connections between neighbouring aggregates and a reduction in the thermal conductivity.
The thermal conductivity of compacted bentonite is one of the most crucial parameters for the safe operation of high-level radioactive waste (HLW) repositories where bentonite can act as a feasible ...buffer. In this study, the potential effects of aging on the thermal conductivity of Gaomiaozi (GMZ07) and Wyoming (MX80) bentonites were investigated experimentally. The bentonite specimens were prepared under different conditions, such as varying water content and dry density, through the static compaction method in a special mould. The water content of the compacted bentonite specimens was kept constant during curing periods of 0, 5, 15, 30, 60, and 100 d under constant volume conditions, and the thermal conductivity of the two bentonites was then measured using the thermal probe method. The test results showed that the thermal conductivity decreased with increasing aging time for both of the compacted bentonites, with a trend that decreased significantly at the early aging periods and then tended to be constant when the aging time exceeded 60 d. The effects of aging are more pronounced for specimens with higher dry densities and water contents. Mercury intrusion porosimetry (MIP) test results confirmed that the reduction in thermal conductivity with aging time could be attributed to smectite hydration within the bentonites during the aging process. With this hydration, part of the soil water moves into the interlayer spaces of smectite crystals, resulting in a decrease in the pore water outside the bentonite particles, which decreases the thermal conductivity of the bentonites.
•Thermal conductivity of two compacted bentonites decreases with aging time.•Thermal conductivity tends to be constant when the aging time exceeds 60 days.•Effect of aging on the thermal conductivity increases with water content.•Reduction in thermal conductivity of bentonite is due to the hydration of smectites.
In a deep geological repository (DGR) system, the buffer layer is indispensable to ensuring the safe disposal of high-level radioactive nuclear waste (HLW). Because the heat generated by the decay of ...the spent nuclear fuel in a canister is released to the surrounding buffer layers, the bentonite buffer material experiences long-term high-temperature conditions. Therefore, the variations in physical properties of bentonite buffer material under high-temperature conditions are one of the important parameters in the DGRs for HLW. A series of tests on the specific gravity, specific surface area (SSA), Atterberg's limits, and free swelling ratio of MX80 bentonite after heating for different times at a high temperature of 200 °C were conducted, to investigate the influence of thermal ageing time on its physical properties. Then, the microscopic investigations, including X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), were conducted to explain the aforementioned variations from the microscopic point of view. Based on the crystal layer structure characteristics of montmorillonite, the quantitative relationships between the physical properties of bentonite and its mineral composition or bound water content were established to further explain the mechanism by which thermal ageing affects the physical properties of MX80 bentonite. The results indicate that with increasing heating time, the specific gravity, SSA, liquid limit, plastic limit, plastic index and free swelling ratio decrease sharply by 2.5%, 4.5%, 3.1%, 5.5%, 2.8% and 30.2%, respectively, within 15–30 days of heating. After 30 days of heating, their variations are negligible. Under high-temperature conditions, the transformation of mineral composition, desorption of bound water, and changes in the micro-morphology are the fundamental reasons for the variations in the physical properties of bentonite, and they influence and interact with each other.
•Specific gravity of MX80 bentonite decreases with increasing thermal ageing time.•Specific surface area of MX80 bentonite decreases with increasing thermal ageing time.•Liquid and plastic limit of MX80 bentonite decrease with increasing thermal ageing time.•Free swelling ratio of MX80 bentonite decreases with increasing thermal ageing time.•Montmorillonite in MX80 bentonite will be transformed into sodium mica at high temperature.
Human activities have increased with urbanisation in the Erhai Lake Basin, considerably impacting its eco-environmental quality (EEQ). This study aims to reveal the evolution and driving forces of ...the EEQ using water benefit-based ecological index (WBEI) in response to human activities and policy variations in the Erhai Lake Basin from 1990 to 2020. Results show that (1) the EEQ exhibited a pattern of initial degradation, subsequent improvement, further degradation and a rebound from 1990 to 2020, and the areas with poor and fair EEQ levels mainly concentrated around the Erhai Lake Basin with a high level of urbanisation and relatively flat terrain; (2) the EEQ levels were not optimistic in 1990, 1995 and 2015, and areas with poor and fair EEQ levels accounted for 43.41%, 47.01% and 40.05% of the total area, respectively; and (3) an overall improvement in the EEQ was observed in 1995-2000, 2000-2005, 2005-2009 and 2015-2020, and the improvement was most significant in 1995-2000, covering an area of 823.95 km
and accounting for 31.79% of the total area. Results also confirmed that the EEQ changes in the Erhai Lake Basin were primarily influenced by human activities and policy variations. Moreover, these results can provide a scientific basis for the formulation and planning of sustainable development policy in the Erhai Lake Basin.
Knowledge of soil thermal properties is necessary for the thermal evaluation and design in geotechnical engineering. In this study, the soil thermal properties of undisturbed lateritic clay with and ...without free iron oxides were measured during drying and wetting. Furthermore, mercury intrusion porosimetry and scanning electron microscopy tests were conducted on specimens to investigate how the free iron oxides affect the soil microstructure. Test results revealed that the thermal conductivity and diffusivity of the undisturbed lateritic clay with the free iron oxides removed (i.e., treated specimens) were higher than those with the free iron oxides (i.e., untreated specimens). The hysteresis effect on the soil thermal conductivity had reduced after removing the free iron oxides. Investigations showed that the microstructure of the treated specimens was denser, and the debris and granular units considerably increased compared with those of untreated specimens. The number and size of soil pores in the treated specimens was lower and smaller than those of untreated specimens. The difference in thermal conductivity and diffusivity between the treated and untreated specimens was mainly attributed to the different extent or quality of connections between neighbouring soil particles that affected the conductive heat transfer in specimens. After removing the free iron oxides, the connection and inclusion of the stable aggregates were destroyed; thus, the relatively large soil pores disappeared. The further dispersion of the soil particles forming the aggregates filled the relatively small pores in specimens, which increased the heat transfer path between neighbouring soil particles.
Advances in technology have increased the use of endovascular therapy for lower extremity revascularization (LER), but the impact on hybrid surgery has not been studied. This study aims to (1) ...investigate the contemporary national trends in frequency of hybrid LER and (2) compare the outcomes of open bypass (BYP) and hybrid surgery for isolated femoropopliteal revascularization.
Using the national Vascular Quality Initiative database from 2010 to 2017, all patients receiving bypass or hybrid LER for PAD were identified. A trend of all hybrid LER compared with open LER was obtained. Next, only patients who underwent hybrid or open isolated femoropopliteal LER were identified. Patients treated with hybrid surgery underwent femoral endarterectomy and antegrade endovascular intervention of the femoropopliteal vessels (HYB), whereas patients treated with BYP underwent femoral endarterectomy and femoropopliteal bypass. These two groups of patients were matched based on age, gender, race, indication, ambulatory status, emergency status, diabetes, hypertension, coronary artery disease, chronic obstructive pulmonary disease, and hemodialysis. Patient characteristics and the perioperative and 1-year outcomes of the two groups were compared.
The overall rate of hybrid LER procedures increased from 6.1% in 2010 to 32% in 2017 (P = .03). Hybrid LER was significantly more commonly used in patients with claudication (47%) and BYP surgery was used in patients with tissue loss (38.5%; P = .019). There were 456 HYB and 2665 BYP for isolated femoropopliteal revascularization. After propensity matching, the cohort comprised 425 patients in each group. HYB was associated with lower rate of myocardial infarction (1.9% vs 5.7%; P = .005) and renal complications (2.1% vs 6.7%; P = .003), length of stay (4.7 vs 6.1 days; P = .001), and higher rate of discharge to home (90.8% vs 81.4%; P < .001) compared with BYP. There was no significant difference in 30-day mortality (HYB 1.5% vs BYP, 2.5%; P = .44). The 1-year outcomes comparison suggested that patients in the BYP group had a higher likelihood of improvement in ambulatory status compared with patients in HYB group (16.7% vs 7.7%; P = .044). However, Kaplan-Meier analysis showed no difference in overall survival (P = .13) or amputation-free survival (P = .057) between the two groups. There was no statistical difference in graft patency, limb loss, or secondary interventions.
Hybrid LER for PAD has been increasingly used and accounts for up to one-third of open LER in the Vascular Quality Initiative. Hybrid femoropopliteal revascularization improves perioperative outcomes compared with femoropopliteal bypass. However, the 1-year outcomes between the two procedures are comparable, suggesting that hybrid femoropopliteal revascularization should be favored in high-risk patients because of its perioperative advantages.
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Despite a national decrease in emergency department visits in the United States during the first 10 months of the pandemic, preliminary Consumer Product Safety Commission data indicate increased ...firework-related injuries. We hypothesized an increase in firework-related injuries during 2020 compared to years prior related to a corresponding increase in consumer firework sales.
The National Electronic Injury Surveillance System (NEISS) was queried from 2018 to 2020 for cases with product codes 1313 (firework injury) and narratives containing "fireworks". Population-based national estimates were calculated using US Census data, then compared across the three years of study inclusion. Patient demographic and available injury information was also tracked and compared across the three years. Firework sales data obtained from the American Pyrotechnics Association were determined for the same time period to examine trends in consumption.
There were 935 firework-related injuries reported to the NEISS from 2018 to 2020, 47% of which occurred during 2020. National estimates for monthly injuries per million were 1.6 times greater in 2020 compared to 2019 (p < 0.0001) with no difference between 2018 and 2019 (p = 0.38). The same results were found when the month of July was excluded. Firework consumption in 2020 was 1.5 times greater than 2019 or 2018, with a 55% increase in consumer fireworks and 22% decrease in professional fireworks sales.
Firework-related injures saw a substantial increase in 2020 compared to the two years prior, corroborated by a proportional increase in consumer firework sales. Increased incidence of firework-related injuries was detected even with the exclusion of the month of July, suggesting that the COVID-19 pandemic may have impacted firework epidemiology more broadly than US Independence Day celebrations.
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