Cesium Distribution Coefficients Research Articles

Predicting the distribution coefficient of cesium in solid phase groups using machine learning

The migration and retention of radioactive contaminants such as 137Cesium (137Cs) in various environmental media pose significant long-term storage challenges for nuclear waste. The distribution coefficient (Kd) is a critical parameter for assessing the mobility of radioactive contaminants and is influenced by various environmental conditions. This study presents machine-learning models based on the Japan Atomic Energy Agency Sorption Database (JAEA-SDB) to predict the Kd values for Cs in solid phase groups. We used three different machine learning models: random forest (RF), artificial neural network (ANN), and convolutional neural network (CNN). The models were trained on 14 input variables from the JAEA-SDB, including factors such as the Cs concentration, solid-phase properties, and solution conditions, which were preprocessed by normalization and log-transformation. The performances of the models were evaluated using the coefficient of determination (R2) and root mean squared error (RMSE). The RF, ANN, and CNN models achieved R2 values greater than 0.97, 0.86, and 0.88, respectively. We also analyzed the variable importance of RF using an out-of-bag (OOB) and a CNN with an attention module. Our results showed that the environmental media, initial radionuclide concentration, solid phase properties, and solution conditions were significant variables for Kd prediction. Our models accurately predict Kd values for different environmental conditions and can assess the environmental risk by analyzing the behavior of radionuclides in solid phase groups. The results of this study can improve safety analyses and long-term risk assessments related to waste disposal and prevent potential hazards and sources of contamination in the surrounding environment.

New Sorbents Based on Polyacrylonitrile Fiber and Transition Metal Ferrocyanides for 137Cs Recovery from Various Composition Solutions

For the first time, new sorbents based on polyacrylonitrile (PAN) fiber and transition metal ferrocyanides were obtained. The main difference between the obtained sorbents and the existing ones is the stage of preliminary preparation of the initial support by converting it into the forms PAN-Fe(OH)3 or PAN-MnO2, due to which additional ion exchange groups (carboxyl, carbonyl, etc.) are formed, which increases the amount of ferrocyanide fixed to the support. The best components and conditions for the synthesis of new sorbents were determined (concentration (0.1–0.2 mol/L), as well as pH (1 for sorbents based on PAN-Fe(OH)3, and 1–5—PAN-MnO2) of potassium ferrocyanide solution, concentration of transition metal salts (0.02 mol/L), temperature conditions). The influence of the studied solution composition (pH, concentration of Na+, K+, NH4+ ions) on the cesium distribution coefficients during its recovery by the obtained sorbents was assessed. The possibility of cesium recovery from solutions with pH 1–9 containing macro quantities of cations was demonstrated. The sorbents derived were characterized by modern structural methods such as infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy with EDS analysis. A study of the trace amount sorption of 137Cs was carried out in comparison with commercially available highly efficient sorbents (FNS-10 and Termoksid-35), and it was shown that the resulting sorbents are not inferior to industrial ferrocyanide sorbents and can be used for 137Cs selective sorption from technological solutions and natural waters.

ЭКСТРАКЦИЯ ЦЕЗИЯ И СТРОНЦИЯ ИЗ АЗОТНОКИСЛЫХ РАСТВОРОВ КРАУН-ЭФИРАМИ В ТЯЖЕЛЫХ РАЗБАВИТЕЛЯХ

The extraction ability of crown-ethers has been studied with respect to cesium and strontium from nitric acid solutions in heavyweight polar organic solvents: chloroform; 1,2-dichloroethane; bis(2-chloroethyl)ether; nitrobenzene; 1,1,7-trihydrododecafluoroheptyl alcohol. Using bis(2-chloroethyl)ether as a new polar solvent in the extraction processes of dibenzo21-crown-7 and 4,4' (5')-ditretbutyldibenzo-18-crown-6, rather high distribution coefficients of cesium are achieved (DCs) from solutions with a nitric acid concentration of 1-5 mol / dm3. In the extraction of dicyclohexyl-18-crown-6 strontium, the highest DSr values were obtained, using chlorine-substituted hydrocarbons and bis(2-chloroethyl)ether with an extraction maximum of 1-3 mol / dm3 HNO3, depending on the diluent used. Extraction systems based on selective crown-ethers in a solvent mixture for the joint extraction of cesium and strontium from chemically complex nitric acid solutions are proposed.

Basic Study on Applicability to Artificial Barriers for Radioactive Waste Disposal Facility for Various Zeolites

Artificial barriers are being considered for the burial disposal of low-level radioactive waste in Japan. The artificial barrier consists of i) a low permeable layer made of bentonite materials that suppresses migration of nuclides due to advection, and ii) a low diffusion layer that uses cementitious materials that suppresses migration of nuclides due to diffusion. In addition, as methods of disposing of radioactive waste generated by the accident at the Fukushima Daiichi Nuclear Power Station, controlled disposal and isolation-type disposal are being considered. We thought that it would be effective to add adsorption performance to the performance of suppressing migration of such radioactive substances. In this study, we designed and experimented on the adsorption performance of mortar mixed with various zeolites, which had never been examined. As evaluation methods, i) fluidity, ii) strength, iii) low diffusivity, and iv) distribution coefficient of cesium and iodine were obtained. Based on the results, we reexamined the composition and conducted experiments to examine the applicability to high-adsorption artificial barriers. As a result, it was confirmed that the mass transfer resistance tends to be low due to the zeolite being porous. It was also shown that the strength of mortar mixed with zeolite depends on the cement matrix. As a result of this research, the distribution coefficient of cesium in cementitious materials using zeolite with a high cation exchange capacity designed in this research is higher than that of cementitious materials for low-level radioactive waste disposal facilities currently in operation 1,500 times was obtained. On the other hand, we were able to discover the possibility of examining construction on a full-scale regarding fluidity and compressive strength. As a future task, it was found that it is necessary to investigate a more practical artificial barrier by increasing the strength and densification of the cement paste.

Dimension reduction for uncertainty propagation and global sensitivity analyses of a cesium adsorption model

This paper presents an efficient method to perform uncertainty and sensitivity analyses in a cesium adsorption model upstream chained with a pore water composition model. As the number of uncertain input parameters is about twenty for each of the two models, a dimension reduction technique is implemented to build a polynomial approximation of the cesium distribution coefficient in a reduced subspace. Two approaches are tested depending on the water composition and adsorption models are treated as a single block or two separate blocks. In view of assessing the robustness of the approaches, three initial cesium concentrations are considered to explore different regimes of the adsorption model. The interpretation of the linear transformations projecting the original inputs to the reduced coordinates is broadly consistent with the geochemical features of the model. Validation results show that the relative error levels of the surrogate models are around a few percent for both approaches with only one thousand realizations of the chained model. Global sensitivity analysis highlights that the variance of the cesium distribution coefficient is overwhelmingly governed by the adsorption model. Still, this conclusion is nuanced when considering the whole cumulative distribution function for which the interaction effects between the two models account for a fifth.

Effect of radioactive cesium-rich microparticles on radioactive cesium concentration and distribution coefficient in rivers flowing through the watersheds with different contaminated condition in Fukushima

Radioactive cesium-rich microparticles (CsMPs) derived from the Fukushima Daiichi Nnuclear Power Plant accident were detected from soils and river water around Fukushima Prefecture, Japan. Because CsMPs are insoluble and rich in radioactive cesium (RCs), they may cause the overestimation of solid-water distribution coefficient (Kd) for RCs in the water. Previous studies showed the proportion of RCs derived from CsMPs on RCs concentration in soils collected from areas with different contaminated levels. Because the proportion of RCs concentration derived CsMPs to the RCs concentration of soils in the less contaminated areas is higher than that in the highly contaminated areas, the effect of CsMPs on particulate RCs concentration in river water may be larger in the less contaminated areas. However, the difference in the effects of CsMPs on the particulate RCs concentration and Kd in river water flowing through watersheds with different contaminated levels has not been clarified. In this study, we investigated the effect of CsMPs on the particulate RCs concentration and Kd in two rivers, Takase River and Kami-Oguni River, flowing through the watersheds with different RCs contaminated levels in Fukushima Prefecture.CsMPs might enter rivers due to soil erosion because they were detected only in some samples collected from both rivers during flood events. CsMPs accounted for more than half of particulate RCs concentration in some water samples collected in the flood condition. In particular, the proportion of CsMPs in particulate RCs for the Kami-Oguni River was greater than that for the Takase River. However, when evaluating for the entire water sampling in the flood condition, a proportion of RCs concentration derived from CsMPs in the average RCs concentrations per unit mass of SS in both river waters collected in the flood condition was not large. CsMPs might temporarily increase the particulate RCs concentration and Kd in the flood event, but CsMPs did not significantly affect them when evaluated throughout the event.

Effect of Csmps on Radioactive Cesium Concentration and Distribution Coefficient in Rivers Flowing in the Watersheds with Different Contaminated Condition in Fukushima

Effect of Csmps on Radioactive Cesium Concentration and Distribution Coefficient in Rivers Flowing in the Watersheds with Different Contaminated Condition in Fukushima

Effect of Csmps on Radioactive Cesium Concentration and Distribution Coefficient in Rivers Flowing in the Watersheds with Different Contaminated Condition in Fukushima

Effect of Csmps on Radioactive Cesium Concentration and Distribution Coefficient in Rivers Flowing in the Watersheds with Different Contaminated Condition in Fukushima

Effective removal of radioactive cesium from contaminated water by synthesized composite adsorbent and its thermal treatment for enhanced storage stability

A composite adsorbent for the removal of radioactive cesium (137Cs) was synthesized by immobilizing potassium cobalt ferrocyanide in the micro pores of the zeolite chabazite. The synthetically optimized composite adsorbent demonstrates a rapid cesium adsorption rate under both salt-free and high-salt conditions with a high distribution coefficient of cesium (≥105 mL/g). Although both components have the same ion-exchange reaction between potassium and cesium, the reaction by ferrocyanide component was predominant, which derived hundred times higher distribution coefficient of the composite adsorbent than that of pure chabazite. A thermal stabilization process was studied for improving the storage and/or disposal stability of the spent adsorbent. The formation of a eutectic system within the spent adsorbent reduced the stabilization temperature to 1000 °C from 1200 °C. Accordingly, the leaching of cesium was remarkably reduced by the remineralization to the stable pollucite. The stable impregnation of ferrocyanide component in the chabazite pores derived the reduction of cesium volatility enabling the high temperature stabilization method. Our experimental results provide evidence that the composite adsorbent has clear advantages on the cesium removal from contaminated water and its stabilization via thermal-treatment.

Decontamination of seawater from 137Cs and 90Sr radionuclides using inorganic sorbents

In this work, we have studied sorption of 137Сs and 90Sr radionuclides from seawater under batch conditions by ferrocyanide sorbents based on hydrated titanium and zirconium dioxides (Т-35, NPF-HTD), clinoptilolite and glauconite (NPF-GL, NPF-CL) natural aluminosilicates, zirconium phosphate (T-3A), modified hydrated titanium dioxide (T-3K) as well as by manganese dioxide based on hydrated titanium dioxide (MD-HTD). Isotherms of sorption and dependences of cesium distribution coefficients on salt content and calcium concentration were obtained. Distribution coefficients of cesium and strontium were calculated. Stability of spent sorbents against radionuclides leaching was studied in from the point of view of their further treatment.The NPF-GL and NPF-HTD sorbents are recommended for treatment of seawater-based liquid radioactive waste with various salinity; these sorbents possess high distribution coefficients of cesium 104 and 105 ml/g even at the salinity of waste as high as 100 g L−1. Distribution coefficients of strontium from seawater were (1.0–1.9)·102 ml/g for all sorbents that is conditioned by the presence of colloidal species of strontium (34 ± 7%) in the simulated seawater. Capacities of the sorbents for strontium varied within 200–310 mg/g. The sorbents strongly retain adsorbed radionuclides: the total percentage of leaching for 28 days was 4.4%, 2.2% and 3.1% for 137Cs leaching from the NPF-HTD, T-35 and T-3A sorbents respectively and 10.7% for 90Sr leaching from the NPF-CL sorbent.

Preparation and ion exchange studies of cesium and strontium on sodium iron titanate

Sodium iron titanate (NaFeTiO) inorganic ion exchanger was synthesized and the ion exchange behaviour of cesium, strontium and europium ion on NaFeTiO was studied. The sodium iron titanate was prepared by the hydrolysis of tetraethyl ortho titanate with sodium hydroxide in the presence of ferric chloride at the Ti/Fe mole ratio of 25.7. The ion exchange material was characterized by elemental analysis, sodium exchange capacity, X-Ray diffraction, thermogravimetry, and Raman spectroscopy. The distribution coefficient (Kd, mL/g) of cesium, strontium and europium on NaFeTiO was measured as a function of pH of the aqueous phase, duration of equilibration, concentration of sodium, cesium, strontium and europium ion in aqueous phase. The Kd of cesium gradually increased with increase of pH, and that of strontium also increased up to pH 6 followed by saturation in Kd values. However, the distribution coefficient of europium increased up to pH 4 followed by the precipitation of europium at higher pH values. The rate of ion exchange of cesium and strontium on NaFeTiO was rapid in the initial stages of equilibration followed by the establishment of equilibrium occurring after 200 min. The kinetics of extraction was fitted in to pseudo-first order and -pseudo-second order rate equations. The NaFeTiO was found to follow the ion exchange mechanism, in which the sodium ion from NaFeTiO was exchanged with cesium or strontium ion from aqueous phase. The strontium exchange capacity on NaFeTiO was determined to be 233 mg g−1. The loaded metal ions was recovered using 0.5 M nitric acid.

Очистка морской воды от радионуклидов цезия и стронция

The article deals with the study of sorption (under batch conditions) of cesium and strontium radionuclides from sea water with ferrocyanidic sorbents based on hydrated titanium and zirconium dioxides (Т-35, NPF-HTD), glauconite and clinoptilolite natural aluminum silicates (NPF-G, NPF-C), zirconium phosphate (Т-3А), modified hydrated zirconium dioxide (Т-3К), and manganese dioxide based on hydrated titanium dioxide (MD-HTD). We have obtained the sorption isotherms, defined the cesium and strontium distribution coefficients. Dependences of the cesium distribution coefficient by the sorbents in seawater saline content have been obtained. The authors recommend NPF-G and NPF-HTD sorbents for treatment of liquid radioactive waste based on seawater with various salt content. Coefficients of the cesium distribution between solid and liquid phases were 1,0∙105 and 1,0∙104 mg/l, respectively, even at solutions with the salt content of 100 g/l. In the process of strontium sorption from seawater, the strontium distribution coefficients do not exceed 1,9·102 ml/g, this is connected with big proportion (34±7 %) of stable colloidal forms of strontium in the simulated seawater.

Состав, структура и селективная сорбция ионов цезия алюмосиликатным сорбентом, полученным из отходов калийногопроизводства ОАО «Беларуськалий»

Представлены результаты комплексного исследования алюмосиликатного сорбента, полу-ченного в результате кислотно-водной обработки образца глинисто-солевого шлама – крупнотоннаж-ного отхода калийного производства ОАО «Беларуськалий» Республики Беларусь. Установлен его вещественный состав и коллоидно-химические характеристики. По минералогическому составу алюмосиликатный сорбент относится к гидрослюдистой группе. Выявлена высокая эффективность извле-чения данным сорбентом ионов цезия из водного раствора. Определены коэффициенты распределе-ния цезия и значения сорбционной селективной емкости цезия для двух типов сорбционных центров алюмосиликатного сорбента.

Electromigration experiments for studying transport parameters and sorption of cesium and strontium on intact crystalline rock

This study aims to determine upscaling factors for the radionuclides' distribution coefficients (Kd) on crushed rocks to intact rock for the safety analysis of radionuclide migration from spent nuclear fuel in bedrock towards biosphere. Here we report the distribution coefficients for intact rock determined by electromigration sorption experiments and compare the results with those from recently performed batch sorption experiments. In total 34 rock samples, representing three typical rock types from Olkiluoto Finland, were studied in order to determine distribution coefficients, effective diffusion coefficients and porosities using the electromigration sorption experiments, formation factor experiments and porosity measurement. The parameters determined represent the three main parameters of geosphere used in the safety assessment of spent nuclear fuel disposal. The distribution coefficients of cesium and strontium on intact rock varied between (0.12–26.2) × 10−3 m3/kg and (1.4–13.3) × 10−3 m3/kg, respectively, whereas recent results for crushed rock varied between (2–57) × 10−3 m3/kg and (17–40) × 10−3 m3/kg, respectively. This implies that crushing increases the distribution coefficient significantly and upscaling factors from 3 to 33 were determined for scaling the distribution coefficients of crushed rock to ones of intact rock. The determined distribution coefficients of cesium and strontium for intact rock can be directly applied in the safety assessment whereas the upscaling factors can be used to convert distribution coefficients determined for crushed rock into ones for intact rock. Based on the results for porosities and effective diffusion coefficients it was concluded that they do not seem to correlate with sorption parameters. However, an alteration state, heterogeneity and mineral content seem to be important factors affecting the distribution coefficients and upscaling factors.

The effect of the synthesis method on the parameters of pore structure and selectivity of ferrocyanide sorbents based on natural minerals

Ferrocyanide sorbents were obtained via thin-layer and surface modification of natural clinoptilolite and marl. The effect of modification method on surface characteristics of these sorbents and their selectivity for cesium was studied. It was shown that the modification resulted in an increase of selectivity of modified ferrocyanide sorbents to cesium as compared with the natural clinoptilolite in presence of Na+, as well as in an increase of cesium distribution coefficients in presence of K+. The nickel–potassium ferrocyanide based on the clinoptilolite showed the highest selectivity for cesium at sodium concentrations of 10−4—2 mol L−1: cesium distribution coefficient was lg K d = 4.5 ± 0.4 L kg−1 and cesium/sodium separation factor was α(Cs/Na) = 250. In the presence of NH4 +, all modified sorbents showed approximately equal selectivity for 137Cs. Probable applications of the sorbents were suggested.

Analysis on distribution coefficients of Strontium and Cesium for safety assessment studies

The distribution coefficients of strontium and cesium in an Italian nuclear site were studied. Distribution coefficient is a fundamental parameter in safety assessment studies on radionuclide migration into the environment. A sensitivity analysis to identify the main influencing factors on the variation of distribution coefficient in subsoil was carried out. Cation exchange capacity was identified as the main influencing parameter, thus a correlation between cation exchange capacity and distribution coefficient was estimated. In this way, the determination of cation exchange capacity, that is less consuming, makes it possible to easily obtain a preliminary, but reliable distribution coefficient on extensive sites.

Cesium sorption and diffusion on crystalline rock: Olkiluoto case study

The sorption and diffusion behavior of cesium was studied to support the interpretation of the ongoing in-situ experiments in the Olkiluoto test site. The distribution coefficients of cesium in the Olkiluoto pegmatitic granite, veined gneiss and their main minerals were obtained by batch sorption experiments and the diffusion of cesium was studied in rock cubes. The results were modelled with PHREEQC and Comsol Multiphysics. The distribution coefficients of cesium were largest in biotite and veined gneiss. The effective diffusion coefficients of cesium from the diffusion model were 3 × 10−13 m2 s−1 for veined gneiss and 4 × 10−13 m2 s−1 for pegmatitic granite.

Interfacial insights on the dibenzo-based crown ether assisted cesium extraction in [BMIM][Tf2N]–water binary system

The distribution coefficient of Cs is estimated using dibenzo-21-crown-7 (DB21C7) and di-benzo-18-crown-6 (DB18C6) in 1-butyl-3-methylimidazolium bis (trifluroromethanesulphonyl) imide (BMIMTF2N) ionic liquid by performing solvent extraction experiments. In addition, molecular dynamics studies on the extraction of cesium (Cs+) ion transfer from the aqueous phase to the BMIMTF2N phase is reported. The experimental findings gave a cesium distribution coefficient of 0.218 and 0.326, which agrees closely with the values of 0.2 and 0.5 obtained from MD simulation for the ionophores DB18C6 and DB21C7, respectively. Thus MD simulation may be helpful in screening the solvents prior to the experiments.

Distribution coefficients of cesium and radium in coastal region of India

The distribution coefficient (Kd) values are used in determining the fate of radionuclide behavior in marine environment. The paper presents the results of the variation in the distribution coefficient (Kd), in field condition. The geometric mean of Kd for cesium and radium along west coast was 2.5 × 103 and 3.5 × 103, along south coast 2.2 × 102 and 2.1 × 104 and along east coast 2.3 × 103 and 1.4 × 104 respectively. Higher Kd value of 137Cs was observed in west coast while, minimum Kd was observed in the south coast. Higher radium Kd at few locations reflects existence of high deposits of Th and U bearing sediments.

Sorption of cesium radionuclides from aqueous solutions onto natural and modified aluminosilicates

Sorption of 137Сs from aqueous solutions onto natural aluminosilicates and onto those modified with mixed nickel potassium (NPF) and iron potassium (IPF) ferrocyanides was studied. The support being modified influences the composition, structure, and thermal stability of the formed ferrocyanide compounds and the sorption properties of the resulting sorbents. The modification increases the cesium distribution coefficients and static exchange capacity; it also extends the pH range of aluminosilicate operation. The most effective sorbents for cesium were obtained on the basis of glauconite (Gl) and clinoptilolite of the Shivertui deposit (ClSh). The cesium distribution coefficient on NPF-ClSh sorbent in the concentration range 10–7–10–5 mg L–1 was logKd [mL g–1] = 7.0 ± 1.0, and on NPF-Gl and NPF-ClSh samples in the concentration range 10–4–102 mg L–1, logKd [mL g–1] = 5.0 ± 0.3 and 5.7 ± 0.4, respectively. The cesium uptake at concentrations in solution ≥100 mg L–1 occurs owing to precipitation of mixed nickel cesium ferrocyanides in the pore space of the sorbents, which considerably enhances their capacity. The static exchange capacity for cesium of NPF-Gl was 220 ± 23, and that of NPF-ClSh, 500 ± 60 mg g–1.