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.

Following the previous study, the toxicity of a single subcutaneous administration of the Thyrokitty injection (I-131) and the side effects that may occur at therapeutic doses were confirmed. The Thyrokitty injection (I-131) was administered subcutaneously once at a dose of 0, 2.0, 6.0, and 18.0 mCi/kg, 5 male and female rats per group, and mortality, general symptom observation, and weight measurement were performed for 2 weeks, followed by observation of autopsy findings. There were no deaths, and no statistically significant weight change was observed. Mild hair loss, fissures, and crusting were observed by general symptom observation, but it was not a toxic change related to the Thyrokitty injection (I-131). Gastric atrophy and a decrease in the size of the spleen were observed by the autopsy. As a results of single subcutaneous administration of the Thyrokitty Injection (I-131) to rats at a maximum dose of 18.0 mCi/kg, a decrease in the size of the spleen and gastric atrophy were observed as the dose of the Thyrokitty Injection (I-131) increased, which may be related to the test substance. No abnormal findings related to the Thyrokitty injection (I-131) were observed. Therefore, the approximate lethal dose of the Thyrokitty injection (I-131) was 18.0 mCi/kg or more. In addition, as reported for the treatment of feline hyperthyroidism with radioiodine (131I), side effects of the Thyrokitty injection (I-131) are expected to be extremely rare. Temporary dysphagia and fever may occur, but it will recover naturally. It should be administered with caution in cats with diseases such as urinary system, cardiovascular system, gastrointestinal system and endocrine system, especially with kidney disease. And it should not be used in cats who are pregnant, lactating, or likely. It is expected that the Thyrokitty injection (I-131) can be used for clinical treatment in Korea as a veterinary drug.

Radioiodine (131I) has been used for the treatment of feline hyperthyroidism since the 1990s in the USA and Europe, and it is recommended as the most effective treatment for feline hyperthyroidism because it has a high therapeutic effect, small side effects, and does not require anesthesia. In this study, the pharmacological properties of the Thyrokitty injection (I-131), which is being developed as a treatment for feline hyperthyroidism, using radioiodine (131I) as an active ingredient, was tested. The %cell uptake of the Thyrokitty injection (I-131) in FRTL- 5 thyroid cells was 0.410 ± 0.016%, which was about 18 times higher compared to Clone 9 hepatocytes, and it was decreased by 30.7% due to the competitive reaction with iodine (sodium iodide). In addition, the %cell growth of the FRTL-5 thyroid cells was reduced by 25.0% by treatment with the Thyrokitty injection (I-131). As a result of the tissue distribution test, the Thyrokitty injection (I-131) was distributed at the highest concentration at 0.083 hours (5 minutes) after subcutaneous administration to animals in most organs except the stomach, small intestine, large intestine, muscle and thyroid gland, and it was excreted mainly through the kidneys. The stomach and thyroid gland showed a typical distribution pattern observed when radioiodine (131I) was administered. In addition, about 78.45% of the total amount of excretion was excreted within 48 hours, of which more than 85% was excreted in urine. In conclusion, the Thyrokitty injection (I-131) has the same mechanism of action, potency, absorption, distribution, metabolism and excretion characteristics as radioiodine (131I) reported in connection with the treatment of feline hyperthyroidism. In the future, using the results of this study, it is expected that the Thyrokitty (I-131) could be safely used in the clinical treatment of feline hyperthyroidism.

According to the Nuclear Safety and Security Commission (NSSC) Notice No. 2021-26 “Delivery Regulations for the Low- and Intermediate Level Radioactive Waste (LILW)”, the activity of 3H, 14C, 55Fe, 58Co, 60Co, 59Ni, 63Ni, 90Sr, 94Nb, 99Tc, 129I, 137Cs, 144Ce, and gross alpha must be identified. Currently, the scaling factor of the dry active waste (DAW) for LILW is applied as an indirect evaluation method in Korea. The analyses are used the destructive methods and 55Fe, 60Co, 59Ni, 63Ni, 90Sr, 94Nb, 99Tc, and 137Cs, which are classified as nonvolatile nuclides, are separated through sequential separation and then measured by gamma detector, liquid scintillation counter (LSC), alpha/beta total counter (Gas Proportional Counter, GPC), and ICP-MS. We will introduce how to apply the existing nuclide separation method and improve the measurement method to supplement it.

Organic complexing agents may affect the mobility of radionuclides at low- and intermediate-level radioactive waste repositories. Especially, isosaccharinic acid (ISA) is the main cellulose degradation product under high pH conditions in cement pore water. ISA can combine with radionuclides and form stable complexes that adversely influence adsorption in the concrete phase, resulting in radionuclides to leach to the near- and far-fields of repositories. This study focuses on investigating the sorption of ISA onto engineered barriers such as concrete, thereby studying adsorption isotherms of ISA on concrete and comparing various isotherm models with the experimental data. The adsorption experiment was conducted in three background solutions, groundwater (adjusted to pH 13 using NaOH), State 1 (artificial cement pore water, pH 13.3), and State 2 (artificial cement pore water, pH 12.5), in a batch system at a temperature of 20°C. Concrete was characterized using BET, Zeta-potential analyzer, XRD, XRF, and SEM-EDS. ISA concentrations were detected using HPLC. The experimental data were best fitted to one-site Langmuir isotherm; On the other hand, either two-site isotherm or Freundlich isotherm couldn’t give reasonable fitting to the experimental data. The observed ISA sorption behavior on concrete is crucial for the disposal of radioactive waste because it can significantly lower the concentration of ISA in the pore water. Although one-site Langmuir isotherm might effectively represent the sorption behavior of ISA on concrete, the underlying mechanism is still unknown, and further investigation should be done in the near future.