Globally, the operation of nuclear power plants results in the production of a tremendous quantity of spent nuclear fuel. The methods for handling spent nuclear fuel can be categorized into three: storage, direct disposal and recycling. A technology designed to recycle accumulated spent nuclear fuel is pyropocessing. In pyroprocessing, various fission products (FPs) such as C-14, H-3, I-129 and Cs-137 are generated. Among these FPs, technetium (Tc-99) is a gaseous nuclear isotope with a long half-life and high mobility in the form of TcO4 - in aqueous solutions, making it essential to capture strictly in order to prevent radioactive contamination of the environment. In previous studies, ion-exchange or adsorption using MOFs (Metal Organic Frameworks) have been used to remove Tc-99. These methods, however, involve separation in aqueous solutions, not in the gaseous state. In this study, we developed a CaO-based adsorbent for capturing Re as a surrogate for radioactive Tc-99. Isopropyl alcohol (IPA) was employed as a pore-forming agent during the preparation of the adsorbents, and its effects on characteristics and adsorption performance were investigated. The size of the pores were analyzed from nitrogen (N2) adsorption isotherm analysis and mercury (Hg) intrusion curves. As a result, it was confirmed that the addition of IPA had a significant impact on the formation of macro-pores. Furthermore, this macroporous structure was found to enhance the adsorption performance of Re.

The disposal of spent nuclear fuel (SNF) poses a significant challenge due to its high radioactivity and heat generation. However, SNF contains reusable materials, such as uranium and trans-uranium, which can be recovered through aqueous reprocessing or pyrochemical processes. Prior to these processes, voloxidation is necessary to increase reaction kinetics by separating fuels from cladding and reducing the particle size. In the voloxidation, uranium dioxide (UO2) from SNF is heated in the presence of oxygen and oxidized to triuranium octoxide (U3O8), resulting a release of gaseous fission products (FPs), including technetium-99 (Tc-99), which poses a risk to human health and the environment due to its high mobility and long half-life of 2.1×105. To date, various methods have been developed to capture Tc in aqueous solutions. However, a means to capture the gaseous form of Tc (Tc2O7) is essential in the voloxidation. Due to the radioactive properties of technetium isotopes, rhenium is often used as a substitute in laboratory settings. The chemical properties of rhenium and technetium, such as their electronic configurations, oxidation states, and atomic radii, are similar and these similarities indicates that the adsorption mechanism for rhenium can be analogous to that for technetium. In the previous study, a disk-type adsorbent based on CaO developed was effective in capturing Re. However, this study lacked sufficient data on the chemical properties and capture performance of the adsorbent. Furthermore, the fabrication of disk-type adsorbents is time-consuming and requires multiple steps, making it impractical for mass production. This study introduces a simple and practical method for preparing CaO-based pellets, which can be used as an adsorbent to capture Re. The results provide a better understanding of the adsorption behavior of CaO-based pellets and their potential for capturing Tc-99. To the best of our knowledge, this is the first study to apply a CaO-based pellet to capture Re and investigate its potential for capturing Tc-99.