A physics-based mesoscale phase-field model for predicting the uptake kinetics of radionuclides in hierarchical nuclear wasteform materials

Journal Article · Fri Mar 01 00:00:00 EST 2019 · Computational Materials Science

DOI:https://doi.org/10.1016/j.commatsci.2018.11.041· OSTI ID:1490317

Li, Y. L.; Zeidman, B. D.; Hu, S. Y.; Henager, C. H.; Besmann, T. M. ; Grandjean, A.

Multiscale, hierarchical, porous materials are promising nuclear wasteform materials with potential for efficiently adsorbing and sequestering radionuclides. However, fundamental understanding of such complex micro- and meso- structures on radionuclide diffusion and uptake kinetics is lacking, which is essential for designing advanced nuclear wasteform materials. In this work we developed a microstructural-dependent diffusion model which accounts for three-dimensional (3D) microstructural features, and heterogeneous thermodynamic and kinetic properties to predict the radionuclide uptake kinetics in complex porous structures. Na⁺ and Sr²⁺ ionic exchange in LTA zeolite multiscale materials in batch tests is taken as a model system to demonstrate the model and its application in hierarchical materials with multiscale porosity. It is found that the reduction of ionic mobility associated with chemistry, structure and/or phase changes has more profound impact on the uptake kinetics in a large 3D porous particle than that in a small particle. Uptake kinetics in large particles are limited by two diffusion processes, i.e., bulk diffusion and surface layer transport. Decreasing particle size and increasing mesoscale pore volume fraction changes the uptake kinetics from two diffusion processes to a single process and dramatically increase the uptake kinetics. Predicted uptake kinetics and the effect of microstructures on the effective capacity of radionuclides and uptake efficiency are consisted with the results observed in Ba²⁺ exchange experiments. The results demonstrate that the developed model should be highly adaptable to transport problems in other hierarchical material systems.

• Research Organization: Energy Frontier Research Centers (EFRC) (United States). Center for Hierarchical Waste Form Materials (CHWM); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1490317
• Report Number(s): PNNL-SA-137890
• Journal Information: Computational Materials Science, Vol. 159, Issue C; ISSN 0927-0256
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

Phase-field model
ionic exchange
porous silica
porous materials
radioactive waste storage
Hierarchically Porous Materials