I-129 is one of the imporant nuclides that must be determined in the disposal process of radioactive waste in many countries. This radionuclide emits gamma-ray and x-ray photons within the energy range of 29 to 39 keV, consequently, an x-ray detector with high resolution performance is required for the analysis of I-129 activity. An n-type coaxial HPGe detector exhibits higher efficiency characteristics compared to a planar-type HPGe detector, however, its resolution is lower than a planar type. So it is difficult to completely deconvolute and fit the gamma-ray and xray peaks in the spectrum using a general gamma-ray spectrum analysis program such as GammaVision. To address this problem, in a previous study introduced the developed algorithm for the fitting and analysis of I-129 gamma-ray and x-ray spectum by fixing their emission ratios. In this study, we improved the algorithm by considering the variation of the efficiency in the HPGe spectrum, which reflects the actual HPGe crystal condition. And algorithm tests were performed using measured I-129 sample spectra with interfering nuclides acting as background curve are introduced.

Radiation from spent nuclear fuel (SNF) is one of key factors affecting the dissolution process of SNF and the source term from repository. The dissolution rate of uranium dioxide (UO2) matrix of SNF is expected to control the release of radionuclides from SNF in contact with water under geological disposal conditions. Based on the oxidative dissolution mechanism, the solubility of UO2 can increase significantly if the reducing environment near the fuel surface is altered by water radiolysis caused by radiation from SNF. Therefore, the analysis of water radiolysis products such as radicals (·OH, ·OH2, eaq, ·H) and molecules (H3O+, H2, H2O2) is perquisite for studies on the rate of such dissolution process to determine oxidation/dissolution mechanism and related rate constants. In this study we examined the two-known spectroscopic methods developed for H2O2 determination; one is the luminol-based chemiluminescence (luminol-CL) method and the other is the spectrophotometry using ferrous oxidation-xylenol orange complexation (FOX). Their applicability for quantitative analysis of H2O2 in potential aqueous samples from SNF dissolution studies was evaluated in terms of the analytical dynamic range (ADR), the limit of detection (LOD) and the interfering effects of various metal ions possibly present in real samples. The luminol-CL method exploits the chemiluminescence reaction caused by luminol; when in the presence of a metallic catalyst (e.g., Cu2+, Co2+), luminol emits a blue light (425 nm) at pH 10- 11 in response to oxidizing agents such as hydrogen peroxide. Although a flow-through reaction system is routinely employed to enhance the analytical sensitivity we achieved the ADR up to ~200 μM and LOD < 1 μM by a batch-wise CL detection using conventional cuvette cells and an intensified charge-coupled device (ICCD). Interestingly, it turned out that the interfering effects of other metal ions (e.g., UO2 2+, U4+, Fe2+ and Fe3+) is minimal, which should be advantageous for the luminol-CL method to be employed for samples potentially containing other metal ions. On the other hand, the FOX method spectrophotometrically analyzes H2O2 based on the difference in color (or absorption spectra) of Fe-xylenol orange (XO) complexes. Initially, the Fe2+-XO complex was provided in working solutions at pH 3, which was subsequently mixed with samples having H2O2 and allowed for quantitative oxidation of Fe2+ to Fe3+. Typically, by monitoring the absorbance of Fe3+-XO complex at 560-580 nm (λmax) the ADR up to ~100 μM and LOD ~1.6 μM were achieved. However, it is found that interfering effects from M3+ and M4+ ions are significant; these interfering metal ions can form XO complexes so as to directly contribute the measured absorbance. In contrast, the influence from M2+ ions was found to be negligible. To summarize we conclude that both methods can be applied for H2O2 determination for aqueous samples taken from SNF dissolution tests. However, prior to applying the FOX method the metal ion composition in those samples should be thoroughly identified not to overestimate the H2O2 concentration of samples. More details of underlying chemical reactions in both methods will be discussed in the presentation.

Mobility of radionuclides (RNs) in natural water systems can be increased by complex formation with organic materials. In alkaline cement pore-water conditions, cellulose materials in radwastes such as woods and papers are degraded fast to small organic materials. As a major cellulose degradation product, isosaccharinate (ISA) has been paid attention recently due to its effect on facilitating RNs migration. ISA contains a carboxyl and four hydroxyl functional groups, which cooperatively interact to form chelating bonds with positively charged radionuclides. In our previous study, we determined thermodynamic formation constants, reaction enthalpy and entropy of trivalent americium complexes with ISA, Am(ISA)n (3-n)+ (n=1, 2), in weak acidic condition by conducting temperature-dependent UVVis absorption spectroscopy. Based on those thermodynamic constants along with the experimental results from time-resolved laser induced fluorescence spectroscopy and DFT calculations, we suggested two different chelating-modes of ISA on Am(III). It is more relevant to study Am(III)-ISA complexation under alkaline conditions around pH 12.5, which correspond to the pore-water condition of calciumsilicate- hydrate. Under the alkaline conditions, deprotonated hydroxyl groups of ISA can form more strong interactions with Am. Aquatic hydroxide group can also act as a ligand to form ternary Am(III) -ISA-OH complexes. In this study, absorption spectra of Am-ISA systems were monitored with two variations: first, pH variation (5.5–13) in the presence of constant 30 mM ISA, and second, ISA concentration variation (20 μM – 30 mM) at constant pH of 12.5. As increasing the pH at constant 30 mM ISA, absorption spectra of Am(ISA)2 + were red-shifted from 506.3 to 509.5 nm. The samples showed stable absorption spectra over 30 days. On the other hand, samples with lower ISA concentrations below 10 mM at pH 12.5, showed gradual decrease in the absorbance as sample aging time. By examining filtrates after ultrafiltration (1 kDa), we confirmed that aqueous Am(III)-ISA complexes were formed in the presence of 30 mM ISA at pH 12.5, while colloidal particles and precipitations were formed in the conditions of ISA concentrations lower than 10 mM. In this presentation, we will discuss about probable ternary complex forms of Am(III)-ISA-OH, colloidal forms, and solubility of Am(III) as a function of ISA concentration under alkaline conditions. Absorption and luminescence spectroscopic properties of the Am(III)-ISA-OH ternary system will also be presented.

The bioreduction process from soluble U(VI) to insoluble U(IV) has been extensively studied in the field of radionuclides migration. Since acetic acid (AcOH) is widely used as an electron donor for bioreduction of U(VI), it is necessary to understand the effect of U(VI)-AcOH complexes that exist in different species depending on pH on this process. Changes in samples before and after bioreduction can be compared using time-resolved laser luminescence spectroscopy (TRLLS), which measures the characteristic luminescence spectra of different U(VI) species. Although luminescence properties of U(VI)-AcOH species were reported, experiments were conducted under conditions below pH 4.5. In this study, spectrophotometry and TRLLS for U(VI)-AcOH species (10−100 μM U(VI) and 20 mM AcOH) were performed in pH ranges extending to neutral and alkaline pH regions similar to groundwater conditions as well as acidic pH region. Two different complexes (UO2(AcO)+, UO2(AcO)2 with U(VI) and acetate ratios of 1:1, 1:2) were observed in the acidic pH region. The 1:1 complex, which appears as the pH increases, has no luminescence properties, but its presence can be confirmed because it serves to reduce the luminescence intensity of UO2 2+. In contrast, the 1:2 complex exhibits distinct luminescence properties that distinguish it from UO2 2+. The 1:3 complex (UO2(AcO)3 -) expected to appear with increasing pH was not observed. Two different complexes ((UO2)3(OH)5 +, (UO2)3(OH)7 - with U(VI) and OH ratios of 3:5, 3:7) were observed as the major species in the neutral pH region, but their luminescence lifetimes are remarkably short compared those in the absence of AcOH. Solid U(VI) particles were observed in the alkaline pH region, and they also had completely different luminescence properties from the aforementioned U(VI)-AcOH and U(VI)-hydrolysis species. Based on these results, the effect of pH in the presence of AcOH on the bioreduction process from U(VI) to U(IV) will be discussed.

Sulfide concentrations critically affect worker safety and the integrities of underground facilities, such as deep geological repositories for spent nuclear fuel. Sulfide is highly sensitive to oxygen, which can oxidize sulfide to sulfate. This can hinder precise measurement of the sulfide concentration. Hence, a literature review was conducted, which revealed that two methods are commonly used: the methylene blue and sulfide ion-selective electrode (ISE) methods. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used for comparison with the two methods. The sulfide ISE method was found to be superior as it yielded results with a higher degree of accuracy and involved fewer procedures for quantification of the sulfide concentration in solution. ICP-OES results can be distorted significantly when sulfide is present in solution owing to the formation of H2S gas in the ICP-OES nebulizer. Therefore, the ICP-OES must be used with caution when quantifying underground water to prevent any distortion in the measured results. The results also suggest important measures to avoid problems when using ICP-OES for site selection. Furthermore, the sulfide ISE method is useful in determining sulfide concentrations in the field to predict the lifetime of disposal canisters of spent nuclear fuel in deep geological repositories and other industries.

Carbonates are inorganic ligands that are abundant in natural groundwater. They strongly influence radionuclide mobility by forming strong complexes, thereby increasing solubility and reducing soil absorption rates. We characterized the spectroscopic properties of Am(III)-carbonate species using UV-Vis absorption and time-resolved laser-induced fluorescence spectroscopy. The deconvoluted absorption spectra of aqueous Am(CO3)2 − and Am(CO3)3 3− species were identified at redshifted positions with lower molar absorption coefficients compared to the absorption spectrum of aqua Am3+. The luminescence spectrum of Am(CO3)3 3− was red-shifted from 688 nm for Am3+ to 695 nm with enhanced intensity and an extended lifetime. Colloidal Am(III)-carbonate compounds exhibited absorption at approximately 506 nm but had non-luminescent properties. Slow formation of colloidal particles was monitored based on the absorption spectral changes over the sample aging time. The experimental results showed that the solubility of Am(III) in carbonate solutions was higher than the predicted values from the thermodynamic constants in OECD-NEA reviews. These results emphasize the importance of kinetic parameters as well as thermodynamic constants to predict radionuclide migration. The identified spectroscopic properties of Am(III)-carbonate species enable monitoring time-dependent species evolution in addition to determining the thermodynamics of Am(III) in carbonate systems.

Time-resolved laser fluorescence spectroscopy (TRLFS) and excitation-emission matrix (EEM) spectroscopy were used to study the interaction of U(VI) and natural organic matters (NOMs) in groundwater. Various types of groundwaters (DB-1, DB-3 from KURT site and OB-1, OB-3 from a U deposit in Ogcheon metamorphic belt) were used as samples. Pulsed Nd-YAG laser at 266 nm (Continuum Minilite) was used as the light source of TRLFS. The laser pulse energy of 1.0 mJ was fixed for all measurements. The luminescence spectrum was recorded using a gated intensified chargecoupled device (Andor, DH-720/18U03 iStar 720D) attached to the spectrograph (Andor, SR-303i). EEM spectra were measured using a spectrofluorometer (Horiba Scientific, Aqualog) equipped with a 150 W ozone-free xenon arc lamp. Excitation spectra were recorded by scanning the excitation wavelength from 200 to 500 nm. Emission spectra were measured using a CCD in the wavelength range of 242–823 nm. In the case of the recently collected DB-1 samples, it was observed that the U and NOM quantities decreased compared to the samples collected before 2016. For some DB-1 samples, the amount of dissolved organic carbon indicating the presence of NOM was significantly reduced, and changes consistent with this phenomenon were observed in the EEM spectrum. The time-resolved luminescence characteristics (peak wavelengths and lifetime) of U(VI) in the DB-1 samples agree well with those of Ca2UO2(CO3)3(aq). This U(VI) species remains stable, even in samples taken five years ago. The estimated amounts of U and NOM from the spectroscopic data of DB-3, OB-1, and OB-3 samples are relatively low compared to DB-1 samples. When a known amount of U(VI) was mixed in each groundwater, the time-resolved luminescence spectrum exhibited a characteristic spectral shape different from the expected luminescence intensity. This phenomenon is presumed to be due to the interaction between U(VI) and NOM in groundwater. The results of this study suggest that the chemical speciation of NOM as well as U(VI) is required to understand U behavior in groundwater.

We observed the symbiotic star AG Dra for a total of 61 nights between April 2004 and December 2021 using the 1.8-m telescope and the high-resolution Echelle spectrograph BOES at the Bohyunsan Optical Astronomy Observatory and obtained 355 frames of spectroscopic data to investigate the variations in its spectral lines. Overnight short-term and long-term changes in prominent emission lines are examined. No short-term changes are found in the line profiles. However, the peak intensity of the Hα emission line exhibits very small variation. In the long-term period, many emission lines including He I λ5875, λ6678, λ7065 and Fe II λ5018 are found to vary reflecting the symbiotic outburst activities. It is noted that He II λ4686 and Raman-scattered O VI λ6830, λ7088 are exceptions, where no significant variations are discernible. One of the noticeable lines is the λ5018 line. Its appearance and disappearance pattern are different from other emission lines, and the line is found to appear in outburst states. The Hα and Hβ lines remain very similar in our spectroscopic monitoring campaign.

To predict the long-term behaviors of actinides in aqueous environments, complexation behaviors of actinides should be understood. Various organic ligands of chelating aromatic structure appearing in humic substances are known to form stable aqueous complexes. In this study, a benzene diol (or catechol) derivative, i.e., 4-nitrocatechol (nCA) is selected and its chemical equilibria including acid dissociation and complexation with U(VI) ion were examined using spectroscopic methods. In addition, the effect of ionic strength (Is) on those equilibria was evaluated by adjusting the level of NaClO4 in aqueous solutions. First, the experiments to determine the acid dissociation constant (pKa) of nCA were carried out in aqueous solutions with different ionic strengths from 0.01–2.0 M. The acid dissociation constants of nCA (pKa1) were measured to 6.73 ± 0.07, 6.69 ± 0.03, 6.38 ± 0.03, 6.09 ± 0.12, and 6.04 ± 0.07 at Is = 0.01, 0.1, 0.5, 1.0, and 2.0, respectively. These results were confirmed through the UV-Vis absorption spectral data analysis using the HypSpec program. As the pKa1 decreases as the ionic strength increases, except for Is = 2.0, these data were further analyzed with SIT (Specific ion Interaction Theory). Typically, as the solution becomes basic, a red shift is shown in the absorption spectrum. This effect can be understood from the intramolecular charge transfer (ICT) occurring in the deprotonated structures of nCA. At higher pH similar trends were also observed for measurement of pKa2. However, the determination of pKa2 is found not to be straightforward since a dimer formation equilibrium of nCA was observed as the ionic strength increased. This phenomenon will be discussed in detail with other supporting experimental results. Second of all, the complexation between the U(VI) and nCA in aqueous solutions was also examined. It was shown that nCA can easily form complexes with U(VI) ions at a wide range of pH via the deprotonation of their hydroxyl groups. U(VI)-nCA complexation will be further characterized by UV-Vis spectroscopy, IR and NMR by varying the solution ionic strength. The metal-ligand binding stoichiometry will be confirmed, for example, through the Job’s method. Finally, the acid dissociations constant and stability constants that were determined in this study will be used to provide species diagrams of aqueous U(VI)-nCA systems at a wide range of pH considering the effect of solution ionic strengths.