• Nuclear Engineering and Technology
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• v.56 no.1
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• pp.167-179
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• 2024

This study explores the feasibility of employing (U, Th)-based accident tolerant fuels (ATFs), specifically (_0.8UO₂, _0.2ThO₂), (_0.8UN, _0.2ThN), and (_0.8UC, _0.2ThC). The investigation assesses the overall performance of these proposed fuel materials in comparison to the conventional UO₂, focusing on deep neutronic and thermal-hydraulic (Th) analyses. Neutronic analysis utilized the MCNPX code, while COMSOL Multiphysics was employed for thermal-hydraulic analysis. The primary objective of this research is to overcome the limitations associated with traditional UO₂ fuel by exploring alternative fuel materials that offer advantages in terms of abundance and potential improvements in performance and safety. Given the limited abundance of UO₂, long-term sustainable nuclear energy production faces challenges. From a neutronic standpoint, the U-Th based fuels demonstrated remarkable fuel cycle lengths, except (_0.8UN, _0.2ThN), which exhibited the minimum fuel cycle length and, consequently, the lowest fuel burn-up. Regarding thermal-hydraulic performance, (_0.8UN, _0.2ThN) exhibited outstanding performance with significant margins against fuel melting compared to the other materials. Overall, when considering the integrated performance, the most favourable results were obtained with the use of the (_0.8UC, _0.2ThC) fuel configurations. This study contributes valuable insights into the potential benefits of (U, Th)-based ATFs as a promising avenue for enhanced nuclear fuel performance.

• Geomechanics and Engineering
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• v.38 no.1
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• pp.15-28
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• 2024

The rapid development of the economy has compelled the widen of highways, and the main challenge of this undertaking lies in the uneven settlement of road embankments. Through field and numerical experiments, this study explores the deformation mechanism of shallow buried pipelines due to road widening. The utilization of Plaxis3D software, which is adapt at simulating complex engineering geological conditions, enables the simulation of the settlement of both the central and right-side road embankments. Comparing with other numerical software such as ABAQUS and COMSOL, Plaxis provided more constitutive models including HS, HSS and Hoek-Brown model. The work concludes that the uneven settlement of road cross-sections is positively correlated with the horizontal distance from the pipeline, with a maximum settlement of 73 mm observed after construction. Furthermore, based on the Winkler's assumption, theoretical settlement and stress calculation methods are established. Results indicate that the maximum difference between the calculated values of this formula and simulated values is 1.9% and 7%, respectively. Additionally, the study investigates the stress and settlement of the pipeline's top under different angles to understand its behavior under various conditions. It finds that with traffic loads applied to the new embankment, a lever effect occurs on the lower pipeline, with the fulcrum located within the central isolation zone, leading to a transition in curve type from "single peak and single valley" to "double peak and single valley." Moreover, the settlement of pipelines on both sides of the central isolation zone and the normal stress of the pipeline's top section are symmetrical.

• Geomechanics and Engineering
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• v.23 no.2
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• pp.151-163
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• 2020

Grouting method is an effective way of reinforcing cracked rock masses and plugging water gushing. Current grouting diffusion models are generally developed for horizontal cracks, which is contradictory to the fact that the crack generally occurs in rock masses with irregular spatial distribution characteristics in real underground environments. To solve this problem, this study selected a cement-sodium silicate slurry (C-S slurry) generally used in engineering as a fast-curing grouting material and regarded the C-S slurry as a Bingham fluid with time-varying viscosity for analysis. Based on the theory of fluid mechanics, and by simultaneously considering the deadweight of slurry and characteristics of non-uniform spatial distribution of viscosity of fast-curing grouts, a theoretical model of slurry diffusion in an oblique crack in rock masses at constant grouting rate was established. Moreover, the viscosity and pressure distribution equations in the slurry diffusion zone were deduced, thus quantifying the relationship between grouting pressure, grouting time, and slurry diffusion distance. On this basis, by using a 3-d finite element program in multi-field coupled software Comsol, the numerical simulation results were compared with theoretical calculation values, further verifying the effectiveness of the theoretical model. In addition, through the analysis of two engineering case studies, the theoretical calculations and measured slurry diffusion radius were compared, to evaluate the application effects of the model in engineering practice. Finally, by using the established theoretical model, the influence of cracking in rock masses on the diffusion characteristics of slurry was analysed. The results demonstrate that the inclination angle of the crack in rock masses and azimuth angle of slurry diffusion affect slurry diffusion characteristics. More attention should be paid to the actual grouting process. The results can provide references for determining grouting parameters of fast-curing grouts in engineering practice.

• Tunnel and Underground Space
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• v.30 no.1
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• pp.39-62
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• 2020

In this study, Barcelona Basic Model (BBM) was implemented into TOUGH2-MP/FLAC3D for the numerical analysis of coupled thermo-hydro-mechanical (THM) behavior of unsaturated soils and the prediction of long-term behaviors. Similar to the methodology described in a previous study for the implementation of BBM into TOUGH-FLAC, the User Defined Model (UDM) of FLAC based on the Modified Cam Clay Model (MCCM) and the FISH function of FLAC3D were used to extend the existing MCCM module in FLAC3D for the implementation of BBM into TOUGH2-MP/FLAC3D. In the developed BBM module in TOUGH2-MP/FLAC3D, the plastic strains due to change in suction increase (SI) in addition to mean effective stress are calculated. In addition to loading-collapse (LC) yield surface, suction increase (SI) yield surface is changed by hardening rules in the developed BBM module. Several numerical simulations were conducted to verify and validate the implementation of BBM: using an example presented in the FLAC3D manual for the standard MCCM, simulation results using COMSOL, and experimental data presented in SKB Reports. In addition, the developed BBM analysis module was validated by simultaneously performing a series of modeling tests that were performed for the validation of the Quick tools developed for the purpose of effectively deriving BBM parameters, and by comparing the Quick tools and Code_Bright results reported in a previous study.