Volumetric lattice Boltzmann method for pore-scale mass diffusionadvection process in geopolymer porous structures

Porous materials present significant advantages for absorbing radioactive isotopes in nuclear waste streams.To improve absorption efficiency in nuclear waste treatment,a thorough understanding of the diffusion-advection process within porous structures is essential for material design.In this study,we present advancements in the volumetric lattice Boltzmann method(VLBM)for modeling and simulating pore-scale diffusion-advection of radioactive isotopes within geopolymer porous structures.These structures are created using the phase field method(PFM)to precisely control pore architectures.In our VLBM approach,we introduce a concentration field of an isotope seamlessly coupled with the velocity field and solve it by the time evolution of its particle population function.To address the computational intensity inherent in the coupled lattice Boltzmann equations for velocity and concentration fields,we implement graphics processing unit(GPU)parallelization.Validation of the developed model involves examining the flow and diffusion fields in porous structures.Remarkably,good agreement is observed for both the velocity field from VLBM and multiphysics object-oriented simulation environment(MOOSE),and the concentration field from VLBM and the finite difference method(FDM).Furthermore,we investigate the effects of background flow,species diffusivity,and porosity on the diffusion-advection behavior by varying the background flow velocity,diffusion coefficient,and pore volume fraction,respectively.Notably,all three parameters exert an influence on the diffusion-advection process.Increased background flow and diffusivity markedly accelerate the process due to increased advection intensity and enhanced diffusion capability,respectively.Conversely,increasing the porosity has a less significant effect,causing a slight slowdown of the diffusion-advection process due to the expanded pore volume.This comprehensive parametric study provides valuable insights into the kinetics of isotope uptake in porous structures,facilitating the development of porous materials for nuclear waste treatment applications.

A review:applications of the phase field method in predicting microstructure and property evolution of irradiated nuclear materials

Complex microstructure changes occur in nuclear fuel and structural materials due to the extreme environments of intense irradiation and high temperature.This paper evaluates the role of the phase field method in predicting the microstructure evolution of irradiated nuclear materials and the impact on their mechanical,thermal,and magnetic properties.The paper starts with an overview of the important physical mechanisms of defect evolution and the significant gaps in simulating microstructure evolution in irradiated nuclear materials.Then,the phase field method is introduced as a powerful and predictive tool and its applications to microstructure and property evolution in irradiated nuclear materials are reviewed.The review shows that(1)Phase field models can correctly describe important phenomena such as spatial-dependent generation,migration,and recombination of defects,radiation-induced dissolution,the Soret effect,strong interfacial energy anisotropy,and elastic interaction;(2)The phase field method can qualitatively and quantitatively simulate two-dimensional and three-dimensional microstructure evolution,including radiation-induced segregation,second phase nucleation,void migration,void and gas bubble superlattice formation,interstitial loop evolution,hydrate formation,and grain growth,and(3)The Phase field method correctly predicts the relationships between microstructures and properties.The final section is dedicated to a discussion of the strengths and limitations of the phase field method,as applied to irradiation effects in nuclear materials.

Phase-field model of pitting corrosion kinetics in metallic materials

Pitting corrosion is one of the most destructive forms of corrosion that can lead to catastrophic failure of structures.This study presents a thermodynamically consistent phase field model for the quantitative prediction of the pitting corrosion kinetics in metallic materials.An order parameter is introduced to represent the local physical state of the metal within a metal-electrolyte system.The free energy of the system is described in terms of its metal ion concentration and the order parameter.Both the ion transport in the electrolyte and the electrochemical reactions at the electrolyte/metal interface are explicitly taken into consideration.The temporal evolution of ion concentration profile and the order parameter field is driven by the reduction in the total free energy of the system and is obtained by numerically solving the governing equations.A calibration study is performed to couple the kinetic interface parameter with the corrosion current density to obtain a direct relationship between overpotential and the kinetic interface parameter.The phase field model is validated against the experimental results,and several examples are presented for applications of the phase-field model to understand the corrosion behavior of closely located pits,stressed material,ceramic particles-reinforced steel,and their crystallographic orientation dependence.