Novel insights into the long-term retardation of GMZ01 to U(VI): based on molecular dynamics and numerical simulation

Abstract

The long-term retardation performance of Gaomiaozi Na-bentonite (GMZ01) to uranium (U(VI)) is still technically challenging due to its high toxicity and the complexity of environmental conditions. This present groundbreaking study fills this gap by using molecular dynamics (MD) technique combined with numerical simulation to study the long-term retardation behavior of GMZ01 to high-level waste (HLW) under the thermal–hydraulic-mechanical-chemical (THMC) coupling conditions in Beishan groundwater from micro to macro for the first time. The results show that in compacted GMZ01, (1) uranyl combines with groundwater substances in the process of self-diffusion to form a cluster, and its self-diffusion is mainly affected by the species size, the net charge, the bonding numbers of U-ob and the bond numbers of OS-Na-ob. (2) The upper limit adsorption capacity of montmorillonite for uranyl is 1.359E-3 site/Å2. (3) The migration of U(VI) in GMZ01 is dominated by diffusion behavior. (4) The GMZ01 with a dry density of 1.7 g/cm3 and a thickness of 0.6 m can guarantee that the repository has a safe period of 10,000 years under 60 °C. This combined method provides a totally new direction for studying the migration of HLW and the design of repository under deep geological disposal.