Numerical simulation of subsurface uranium (u) leaching and migration under geologic carbon storage conditions

Abstract

Geologic carbon storage (GCS) is the process to store large amount of carbon dioxide (CO 2 ) captured from stationary CO 2 emission sources in deep subsurface for permanent storage. GCS is widely recognized as a promising strategy to reduce emissions of greenhouse gas (GHG). However, the potential for mobilization of radioactive uranium (U) from U-bearing minerals in deep subsurface due to CO 2 injection remains a concern. In this study, A TOUGHREACT model was developed to investigate the potential of U-bearing mineral (UO 2 ) dissolution in a hypothetical deep CO 2 storage reservoir. An average reservoir temperature of 67.5 °C, an average reservoir pressure of 18.7 MPa and a CO 2 injection rate of 0.1 MMT/year (3.17 kg/s) were used in this study. Numerical simulation results show that HCO 3– concentration increased as a result of CO 2 dissolution after injection of CO 2 , which led to release of [UO 2 (CO 3 ) 3 ] 4– . However, released [UO 2 (CO 3 ) 3 ] 4– did not migrate toward the shallow aquifer through leakage pathways specified in the model, while CO 2 could migrate upward through the leakage pathways. In summary, the area of uranium contamination is restrained in deep subsurface and notable migration of uranium to shallow aquifer caused by CO 2 injection does not occur.