Currently, non-volatile nuclides such as 94Nb, 99Tc, 90Sr, 55Fe, and 59/63Ni are used a sequential separation. In this study, we developed a separation for 99Tc and 90Sr by a carbonate precipitation. Sodium Carbonate (Na2CO3) was inserted in the aqueous sample from a Dry Active Waste (DAW) and a carbonate precipitation was produced. The precipitate is composed of di- or tri-valent element such as Co, Sr, Fe, Ni and the supernatant is composed of mono-valent element (Cs) and anion materials (ReO4 -, TcO4 -). In DAW, it was confirmed that the recovery of 90Sr (precipitate) and 99Tc (supernatant) were > 90%, respectively. The precipitate and supernatant separated by using a Sr-resin and an anion-exchange resin, respectively. The separated samples were measured by a Liquide Scintillation Counter (LSC, 90Sr) and Induced-Coupled Plasma-Mass Spectroscopy (ICPMS, 99Tc).

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.

A low- and intermediate-level radioactive waste repository contains different types of radionuclides and organic complexing agents. Their chemical interaction in the repository can result in the formation of radionuclide-ligand complexes, leading to their high transport behaviors in the engineered and natural rock barriers. Furthermore, the release of radionuclides from the repository can pose a significant risk to both human health and the environment. This study explores the impact of different experimental conditions on the transport behaviors of 99Tc, 137Cs, and 238U through three types of barrier samples: concrete, sedimentary rock, and granite. To assess the transport behavior of the samples, the geochemical characteristics were determined using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fouriertransform infrared spectroscopy (FTIR), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and Brunauer-Emmett-Teller (BET) analysis. The adsorption distribution coefficient (Kd) was used as an indicator of transport behavior, and it was determined in batch systems under different conditions such as solution pH (ranging from 7 to 13), temperature (ranging from 10 to 40°C), and with the presence of organic complexing agents such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and isosaccharinic acid (ISA). A support vector machine (SVM) was used to develop a prediction model for the Kd values. It was found that, regardless of the experimental parameters, 99Tc may migrate easily due to its anionic property. Conversely, 137Cs showed low transport behaviors under all tested conditions. The transport behaviors of 238U were impacted by the order of EDTA > NTA> ISA, particularly with the concrete sample. The SVM models can also be used to predict the Kd values of the radionuclides in the event of an accidental release from the repository.

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.

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.

Radionuclides can be leached into groundwater or soil over a long period of time due to unexpected situations even after being permanently disposed of in a repository. Therefore, it is necessary to investigate the mobility of radionuclides for the safety assessment of radioactive waste disposal. In this study, the effects of organic complexing agents such as ethylenediaminetetraacetic acid (EDTA) and isosaccharinic acid (ISA) on the sorption behavior of 239Pu and 99Tc over cementitious (concrete and grout) and natural rock samples (granite and sedimentary rock) were investigated in batch sorption experiments. For characterization of rock samples, XRD, XRF, FT-IR, FE-SEM, BET, and Zeta-potential analyses were performed. For the evaluation of mobility, the distribution coefficient (Kd) was selected and compared. The adsorption experiment was carried out at two pHs (7 and 13), a temperature of 20°C, and a range of organic complexing agents concentrations (10-7~10-2 M and 10- 5~10-2 M for 239Pu and 99Tc, respectively). The radionuclides concentrations in adsorption samples were analyzed using ICP-MS. The Kd values for 239Pu in all rock samples reduced significantly due to the presence of EDTA, even at low concentrations such as 10-5 M. In the case of ISA, the limiting noeffect concentration was much higher than that of EDTA. On the other hand, 99Tc showed relatively lower Kd values than 239Pu, and the sorption behavior of 99Tc was almost unaffected by the organic complexing agents for all rock samples. Therefore, it is possible to assume that the increased mobility of radionuclides, especially, 239Pu, in groundwater caused by the lowering of sorption at even low concentrations of organic complexing agents may result in the transport of radionuclides to the nearand far-field location of the repository.

Technetium-99 (99Tc) is a challenging radionuclide from presents many problems related to safe disposal. The measurement of 99Tc is of particular interest due to its high mobility, and the fact that it is a beta-emitter with a long half-life (t1/2=2.13×105 years) with long-term radiological effects[1]. As an isotopes of 99Tc, 99mTc has been widely applied for medical diagnosis and medical research. It is reported that the 99mTc has been used in 80% of diagnostic nuclear medicine procedures and almost 30 million examinations are conducted worldwide using this isotope. Because 99mTc has a short half-life of 6 h and decays to 99Tc, monitoring and safe disposal of 99Tc from human urine is very important, and concern is increasing every day as global use of 99mTc has increased by more than 4.5×1014 Bq per week and is increasing continuously[2]. However, the current methods for the detection of this radionuclide in such mdium are time consuming and can not satisfy for the low level urine sample analysis. In this work, a method for rapid determination of 99Tc in urine samples was developed. The sample was firstly pre-treated with K2S2O8 to decompose the organic matters combined with 99Tc in 0.5 mol·L−1 HNO3 medium at 100°C. Then the sample solution was loaded to a TEVA column (2 mL) for 99Tc separation and purification. The target element was finally measured by high resolution inductively coupled plasma mass spectrometry (HR-ICPMS). The developed analytical method was proved to be reliable and can be used to rapid determine low-level 99Tc in urine samples.

99Tc is a long-lived radioactive fission product whose mobility in the subsurface is largely governed by its oxidation state. Migration of Tc from a waste repository may be prevented by immobilizing Tc(IV) in durable glass forms. Thus, efficient incorporation and high retention of Tc by glasses is very important for radioactive waste management and environmental remediation. Tc(IV) oxidation to higly volatile Tc(VII) (TcO4 −) at glass vitrification temperatures results in poor Tc retention in the final waste glass. Retention of Tc in the glass is generally improved by reducing conditions since Tc(IV) is not volatile. However, experiments with Tc-magnetite under high temperature and oxic conditions showed re-oxidation of Tc(IV) to volatile pertechnetate. To understand this phenomenon, we employed ab initio molecular dynamics simulations to study structural and electronic properties of Tc-incorporation in magnetite. The study provides the ramification of high temperature on Tc mobilization and changes of Tc retention in magnetite. Theory predictions also indicated enhanced Tc retention in the presence of 1st row transition metal dopants in Tc-incorporated magnetite that was confirmed by experiments. Furthermore, the overwhelming concentration of Cr(VI) co-mingled with Tc(VII) within the secondary waste form where Cr(VI) is more readily reduced than Tc(VII) by reduction potential metrics. Experiments with Tc-magnetite under high temperature and oxic conditions showed re-oxidation of Tc(IV) to volatile pertechnetate. Experiments also showed that magnetite transforms to maghematite resulting in disproportionation and re-oxidation of Tc. This transformation can be suppressed through incorporation of trace elements such as Co, Ni, Zn into magnetite forming spinel. In this talk, I will present results from ab initio molecular dynamics simulations and experiments on the structural and electronic properties of Tc and/or Cr incorporation in magnetite. I will also discuss the temperature effect on Tc/Cr mobilization and changes of Tc/Cr retention in magnetite. In addition, I will discuss the effect of Tc/Cr concentration and 1st row transition metal dopants on their incorporation in magnetite.

Mechanism and kinetics of Rhenium complexes as a surrogate of Technetium-99 (99Tc) is worthy of study from radioactive waste safe disposal perspective. Re(IV)-EDTA was synthesized via the reduction of Re(VII) with Sn(II) in the presence of Ethylenediaminetetracetic acid (EDTA). The Re(IV)-EDTA was then degraded by H2O2 (7–30%) at pH of 3–11 in ionic strength I = 0–2 M solution. The Re- EDTA was observed to degrade more rapidly at pH of ≤ 3–4 than one of ≥ 10–11 and remained stable at pH = 7–9. At a low acidic pH, the complex degradation process was facilitated by protonation and corresponded to the exponential model (y = k. e–nt). In contrast, at an alkaline pH, the degradation was facilitated OH– complexation with Re(IV) and corresponded to a linear model (y = –mt + C). Complex degradation followed the zero-order rate kinetics for the H+ and Re-EDTA parameters, apart from a pH of 3, for which degradation was a better fit to first order kinetics. A higher Re(IV)-EDTA stability at a pH of 7–9 demonstrated that Re(IV)-EDTA (or 99Tc(IV)-EDTA) tends to be more persistent in natural environmental conditions.

Rare earth elements, which are important components of motors, are in high demand and thus constantly get more expensive. This tendency is driven by the growth of the electric vehicle market, as well as environmental issues associated with rare-earth metal manufacturing. TC 298 of the ISO manages standardization in the areas of rare-earth recycling, measurement, and sustainability. Korea, a resource-poor country, is working on international standardization projects that focus on recycling and encouraging the domestic adoption of international standards. ITU-T has previously issued recommendations regarding the recycling of rare-earth metals from e-waste. ISO TC 298 expands on the previous recommendations and standards for promoting the recycling industry. Recycling-related rare earth standards and drafts covered by ISO TC 298, as well as Korea’s strategies, are reviewed and discussed in this article.

Since the ISO decided to deal with rare-earth elements at the 298th Technical Committee (TC) in 2015, Korea has participated in four plenary meetings and proposed four standards as of June 2019. The status of ISO TC 298, the standards covered by the TC, and the standardization strategies of Korea are summarized. Korean delegations are actively engaged in WG2, which deals with recycling, proposing four standards for fostering the rare-earth recycling industry. However, the participation of domestic experts is still low compared with the increase in the number of working groups and the number of standards in TC 298. The aim of this article is to summarize the current status of ISO international standards related to rare-earth elements, to encourage relevant experts to participate in standardization, and to develop international standards that accurately reflect the realities of the industry.

As a rule, geological disposal is considered a safe method for final disposal of high-level radioactive waste. However, some long-lived fission products like 99Tc and 129I contained in spent nuclear fuel are highly mobile as less sorbing anionic species in the subsurface environment and can mainly cause exposure dose to the ecosystem by emission of beta rays in the hundreds of keV range. Therefore, if these two nuclides can be separated and converted with high efficiency into radioactively unharmful nuclides, this would have a positive effect on disposal safety. One candidate method is to transmute these two nuclides in nuclear reactors into short-lived nuclides or into stable nuclides. For this purpose, it is necessary to evaluate which reactor type is more efficient in burning these two nuclides. In this study, the simulation results of nuclear transmutation of 99Tc and 129I in light water reactor (PWR), heavy water reactor (CANDU) and fast neutron reactor (SFR, MET-1000) are compared and discussed.