▶ Date: 2024. 03. 07(Thu)

▶ Time: 4:30 ~ 5:30PM

▶ Venue: Research Building I, #310

▶ Speaker: Dr. Seonggyu Choi(KAERI)

▶ Title: Understanding the Radionuclide Retention Mechanisms in Geological Barrier Systems: Utilization of Thermodynamic Sorption Modeling

▶ Abstract:

The safe management of spent nuclear fuel (SNF) and associated contaminated by-products, which are classified as high-level radioactive waste (HLW), has emerged as a serious concern in numerous countries operating nuclear power plants. In south Korea, there have been productive R&D activities and societal discussions regarding the direct disposal of HLW without reprocessing, where the concept of deep geological disposal (DGD) stands out as the most proven technological option to prevent significant release of radionuclides into biosphere and ultimately secure the long-term safety of entire disposal system. The DGD system consists of multiple engineering and natural barriers, and migration of dissolved radionuclides released from the waste canister can be effectively retarded as they chemically sorb onto the relevant mineral components.

The sorption phenomena of dissolved chemical species onto mineral adsorbents have been widely described and quantified based on the definition of sorption-desorption distribution coefficient (Kd). However, since the simple Kd concept does not incorporate any mechanistic essence of the surficial interaction, an empirical Kd value is eventually dependent on the experimental conditions (pH, temperature, S/L, etc.) under which it was assessed. In this framework, application of thermodynamic sorption modeling (TSM), based on the chemical principle of mass action laws, has been suggested and actively investigated to geochemically parametrize the sorption phenomena more reliably under a wide range of aquatic conditions, especially in the context of modeling radionuclide migration within the DGD environment.

As part of a national R&D program on SNF storage and disposal launched in 2021, there has been a concerted effort to construct a robust thermodynamic sorption database of major radionuclides onto mineral adsorbents, which is aimed to be utilized as an essential input dataset in the operation of a process-based total system performance assessment framework, Apro. This seminar provides overviews on the DGD concept, geochemical behaviors of radionuclides, and utilization of TSM. Additionally, it also presents a case study focusing on the application of TSM for highly soluble fission products with montmorillonite purified from Bentonil-WRK bentonite, which is a new Ca-type research reference clay introduced in Korea Atomic Energy Research Institute (KAERI).