Radioactive Waste Disposal Site Research Articles

Adsorption of U(VI) on the natural soil around a very low-level waste repository

The behaviors of U(VI) in environmental media around radioactive waste disposal site are important for safety assessment of geological repositories. However, the estimation of environmental behaviors of U(VI) in natural media was insufficient. This work aimed to determine the adsorption of U(VI) on natural soil surrounding a candidate very low-level radioactive waste (VLLW) disposal site in southwest China. Results showed that the adsorption process of U(VI) on soils could be well supported by pseudo-second-order kinetic and Freundlich model. The adsorption of U(VI) was pH-dependent but temperature-independent. High ionic strength (NaCl) strongly affected the adsorption process at low pH (2.0–5.5). CO32− remarkably inhibited the U(VI) adsorption, while the adsorption of U(VI) was promoted by PO43− and SO42−. Naturally occurred soil organic matters (SOMs) showed high affinity for U(VI), while the presence of additional humic acid (HA) strongly inhibited U(VI) adsorption. The occurrence of ferrous iron could result in the reduction of U(VI) at low pH values (pH < 4), leading to the promotion of immobilization of U(VI). These findings would provide some guidance for the safety assessments of the VLLW disposal as well as the remediation of contaminated soil.

Geological interactions and radio-chemical risks of primordial radionuclides 40K, 226Ra, and 232Th in soil and groundwater from potential radioactive waste disposal site in Ghana

Geological interactions and radio-chemical risks of primordial radionuclides 40K, 226Ra, and 232Th in soil and groundwater from potential radioactive waste disposal site in Ghana

Selection of sites for the construction of radioactive waste disposal points

The article deals with the selection of sites for the construction of nuclear installations, radioactive waste disposal sites and other facilities for the use of nuclear energy. The review of modern approaches to the selection of sites for placement of near-surface radioactive waste disposal points shows that the system research in this area is not fully presented, and is mainly aimed at solving problems of an engineering-geological nature for the location area, as well as the choice of materials for engineering protection barriers. In this paper, using the example of radioactive waste disposal sites, we review the requirements set by the regulatory documents of the Russian Federation and the International Atomic Energy Agency in the field of site selection. The authors proposed additions to the methodology for selecting sites for the construction of low-and medium-level waste disposal sites based on the system and GIS analysis of the ALARA principles, as well as the method of weighted evaluation of criteria and their pairwise comparisons. The multi-criteria nature of the site selection problem is proposed to be described by GIS analysis of data with drawing the corresponding limiting and preferred requirements directly on the map of the area, which is shown in the article by the example of selecting sites for radioactive waste disposal points. Taking into account the necessary requirements at various stages of the life cycle, as well as their significance, can be assessed by weighted estimates and pairwise comparisons, followed by their introduction into the GIS analysis. This approach allows to choose rational options for placing potential sites, taking into account the life cycle of the object, in a rational way, with compliance with all necessary regulatory requirements.

A comprehensive study of the sorption mechanism and thermodynamics of f-element sorption onto K-feldspar

The mobility of heavy metal contaminants and radionuclides in the environment is directly controlled by their interactions with charged mineral surfaces, hence an assessment of their potential toxicity, e.g. in the context of radioactive waste disposal sites, requires understanding of sorption processes on the molecular level. Here, we investigate the sorption of a variety of rare earth elements (REE) and trivalent actinides (Am, Cm) on K-feldspar using batch sorption, time-resolved laser-induced fluorescence spectroscopy (TRLFS), and a surface complexation model. Initially, a reliable pKa for K-feldspar’s surface deprotonation reaction was determined as 2.5 ± 0.02 by column titration experiments, in excellent agreement with a measured pHIEP of 2.8. Batch sorption experiments over a broad range of experimental conditions in terms of mineral grain size, pH, [M3+], ionic radius, solid/liquid ratio, ionic strength, and equilibration procedures were carried out to quantify macroscopic retention. The trivalent d-block element Y, early, mid, and late lanthanides (La, Eu, Nd, Lu), as well as two minor actinides (Am, Cm) were used for batch sorption experiments and showed similar pH dependent uptake behavior, underlining their chemical analogy. In parallel, spectroscopic investigations provided insight into surface speciation. Cm TRLFS spectra indicate the formation of three inner-sphere sorption complexes with increasing hydrolysis. Additionally, a ternary K-feldspar/Cm/silicate complex was found for pH > 10, and batch and spectroscopic data at low pH (<4) point to small amounts of outer sphere sorption complexes. Based on TRLFS data, batch sorption, and titration data, a generic geochemical sorption model was developed, that describes sorption edges for all investigated M3+/K-feldspar systems satisfactorily. The derived stability constants for the binary sorption complexes (logK1-4 = −3.6, −7.7, −11.5, and −17.4, respectively) could successfully be used to reproduce literature data. The stability constants obtained for the surface complexes were included into the database for the Smart Kd-concept, which will further improve the safety assessment of potential repositories for radioactive waste.

SEM study of the early stages of Fe-bentonite corrosion—The role of naturally present reactive silica

The iron-bentonite interface will be important with respect to the long-term performance of high-level radioactive waste (HLW) disposal sites. Magnetite and Fe-silicates form at this interface due to anoxic corrosion. The corrosion mechanism, however, is still under debate. In the present study two bentonites differing with respect to their content of reactive silica were compared using electron microscopy. The presence of reactive silica immediately led to the formation of Fe-silicates while magnetite prevailed in the other sample. These results confirm recently published conceptual models describing the corrosion and point towards the importance of considering reactive silica in this system.

Influence of colloidal Fe(OH)3 on the adsorption characteristics of strontium in porous media from a candidate high-level radioactive waste geological disposal site

Colloids in groundwater or geological barriers generally play a key role in the migration of special nuclides. Adsorption characteristics of strontium were investigated on porous media in the presence of colloidal Fe(OH)3 from the Beishan Site, the only high-level radioactive waste disposal site candidate in China. The effects of colloid amounts, solid contents, and pH were determined and studied by batch texts. The results revealed that the presence of colloidal Fe(OH)3 in porous media contributed to promotion of the sorption effect, and the influencing factors had a significant impact on the adsorption process. The sorption ability increased with increasing colloid amount when the equilibrium time was approximately 10 h under an optimal solid-liquid ratio of 20 g L−1. The sorption effect in alkaline conditions was better than that under acidic conditions. The sorption kinetics indicated that the strong chemical interaction and/or surface complexation contributed primarily to strontium sorption. The sorption isotherms and model fitting revealed that the sorption of strontium onto porous media in the presence of colloidal Fe(OH)3 was a monolayer adsorption, and the presence of colloidal Fe(OH)3 is an important factor that greatly influences the removal of strontium from aqueous solutions. These findings provide useful information for the treatment of strontium in radioactive waste disposal sites.

АНАЛИЗ ДОЛГОВЕЧНОСТИ ИНЖЕНЕРНЫХ БАРЬЕРОВ БЕЗОПАСНОСТИ ИЗ БЕТОННЫХ ГЛИН

The durability and safety of the storage and burial sites of hazardous waste from metallurgical and chemical production should be ensured through the consistent implementation of the defense in depth concept. Engineering designs of safety barriers should meet the following requirements: limit contact of waste with natural waters; ensure the safety of waste under external influences; prevent the spread of hazardous industrial waste to the surrounding soil mass. Object safety indicators are durability and service life, which should be ta ken into account in scenarios of forecasting the durability of disposal systems.For an objective assessment of the degradation of engineering safety barrier s of radioactive waste disposal sites, evolution models of bentonite barriers are considered. The following models are considered: montmorillonite illitization model; bentonite chlorination model; model for calculating the swelling parameters; ion exchange model and a model of sorption of radionuclides by bentonite. Conclusions show that when assessing the long-term evolution of engineering safety barriers from bentonite during the chemical destruction of montmorillonite, changes can occur, in particular, an increase in the permeability of the barrier.

Plutonium migration in a rough single fractured granite

The insights into the transport mechanism of Pu in granite fractures are indispensable for a reliable safety-assessment of radioactive waste disposal sites. In this work, the study of transport behavior of Pu in a rough single fracture has been performed under different pH conditions. The results indicated that under strong acidic condition the sorption of Pu dominated by ion-exchange reaction is quite weak, reversible and not be affected by the change of flow rates, while under neutral condition the majority of Pu can be adsorbed onto granite surface, controlled by surface-complex reaction between Pu(OH)4(aq) and fracture surface hydroxyl groups.

Use of Routine Environmental Monitoring Data to Establish a Dose-based Compliance System for a Low-level Radioactive Waste Disposal Site.

A dose-based compliance methodology was developed for Waste Control Specialists, LLC, low-level radioactive waste facility in Andrews, Texas, that allows routine environmental measurement data to be evaluated not only at the end of a year to determine regulatory compliance, but also throughout the year as new data become available, providing a continuous assessment of the facility. The first step in the methodology is a screening step to determine the potential presence of site emissions in the environment, and screening levels are established for each environmental media sampled. The screening accounts for spatial variations observed in background for soil and temporal fluctuations observed in background for air. For groundwater, the natural activity concentrations in groundwater wells at the facility are highly variable, and therefore the methodology uses ratios for screening levels. The methodology compares the ratio of gross alpha to U + U to identify potentially abnormal alpha activity and the ratio of U to U to identify the potential presence of depleted uranium. Compliance evaluation is conducted for any samples that fail the screening step. Compliance evaluation uses the radionuclide-specific measurements to first determine (1) if the dose exceeds the background dose and if so, (2) the dose consequences, so that the appropriate investigation or action occurs. The compliance evaluation is applied to all environmental samples throughout the year and on an annual basis to determine regulatory compliance. The methodology is implemented in a cloud-based software application that is also made accessible to the regulator. The benefits of the methodology over the existing system are presented.

Experience of Space Geodesy Observations at Nuclear Facilities

The paper reviews observations of modern crustal movements (MCMs) using global navigation satellite systems (GNSS) at nuclear facilities (NF). In 1995–2002, observations were conducted at geodynamic test sites of the Novovoronezh, Kalinin, and Rostov NPPs. Following the results of GNSS observations, a conclusion was drawn about the stability of the Kalinin NPP test site: it was recommended that design solutions take into account deformation of the Earth’s surface in the north–south direction. The creation of a geodynamic test site for observing the activity of the Rostov NPP area based on GPS technology promoted the passage of a state environmental impact assessment during the launch of the first NPP reactor in 2001. In the construction area of Russia’s first deep-level radioactive waste disposal site (Krasnoyarsk krai), a geodynamic test site was created to observe MCMs, and a methodology was developed for processing and interpreting geodynamic observation data taking into account the large-scale spatiotemporal effect. For the first time, for the area at the junction of the largest tectonic structures—the Siberian Platform and the West Siberian Plate—the rates of horizontal crustal deformations were instrumentally measured and the cyclical nature of the geodynamic regime was established. Observations made in 2010–2016 showed that in 2010–2013, maximum changes in distances between observation points did not exceed 10 mm/year. In 2013–2014, the tectonic regime was activated, manifested by a change in the signs of compressional and extensional strain of the upper crust on the right and left banks of the Yenisei River. The annual rates of maximum change in the lengths of baselines during the activation period reached ±18 mm. The standard horizontal and vertical errors for 2012–2016 were 3.0–3.5 and 6.0–7.4 mm, respectively. To take into account the scale factor, methodological approaches to interpreting the observational data were developed, which made it possible to assess the extent of impact of MCMs on the stability of the natural insulating properties of rock massifs while substantiating the geoecological safety of radioactive waste disposal. Based on the observation results, the boundary conditions for modeling the stress–strain state of a rock massif were established and the site of the GKhK Mining and Chemical Combine was geodynamically zoned.

Physical and micro-structural characteristics of limestone after high temperature exposure

Temperature is a major factor affecting physical and mechanical rock properties. With increasing temperature, a series of variations enlarge the internal defects within rocks, resulting in physical and mechanical rock property variations. To explore the influence of temperature on the physical and micro-structure of limestone, the weighing test and P-wave velocity test were conducted on limestone after exposure to high temperature to reveal the evolution of the limestone mass and P -wave velocity. XRD, XRF, SEM, and mercury intrusion tests were also carried out to examine the mineral composition and content, micro-fracture morphology, porosity, and fractal dimension. The limestone mass and P-wave velocity decrease with increasing temperature. When T ≤ 400 °C, there is no obvious change in chemical composition and crystal structure; when T = 400–500 °C, the diffraction intensity of partial calcite decreases, and dolomite decomposes gradually; when T > 500 °C, illite decomposes gradually, while dolomite decomposes completely; and the diffraction intensity of calcite is significantly reduced. When T ≤ 200 °C, changes in trace minerals or impurities containing K2O and Na2O and the decomposition of illite oxide are dominant; when T = 400–600 °C, illite oxide, trace minerals, or impurities containing K2O and calcium hydroxide begin to decompose. When T = 600–800 °C, magnesite and dolomite begin to decompose. When T ≤ 200 °C, micro-fracture surfaces change slightly. When T = 200–500 °C, micro-fractures begin to develop and propagate gradually, most of which are intergranular cracks with a small number of transgranular cracks. When T > 500 °C, transgranular cracks occur in samples with locally broken crystals, and the cracking of the crystal structure occurs with increasing pore size. With increasing temperature, the limestone pore fractal dimension decreases gradually, and the higher the temperature, the greater the decrease. 400 °C to 500 °C is the temperature threshold interval that causes the pore structure change. These new pores, resulting from the increasing temperature, are primarily mesopores with a pore diameter of 1.0–10.0 μm. This research provides a scientific basis for the design and construction of rock engineering projects to be subjected to high temperatures, deep geological radioactive nuclear waste disposal sites, deep mines, and the exploitation of geothermal resources.

방폐장 입지정책에서 정부의 정치적 관리: 부안군 유치시도 및 경주시 유치선정 사례 비교

본 연구는 국내 방폐장 입지선정과정에서 정부(공공관리자)가 실행한 전략적 관리행위를 평가하고 분석하는데 목적이 있다. 이를 위해 Moore(1995)의 ‘정치적 관리’ 분석 틀을 활용하여 2004년 부안군 사례와 2005년 경주시 사례를 비교 분석하였다. 본 연구의 질문은 “동일한 정책이슈를 두고 상반된 정책결과가 나타난 이유는 무엇인가?”이며, 이에 대한 답을 찾기 위해 기존의 정책갈등관점, 정책수용성관점, 거버넌스관점, 민주주의관점에서 벗어나 정치적 관리(political management)라는 새로운 관점에서 공공관리자의 전략적 관리행위를 분석하였다. 먼저 정책문제로서 방폐장 입지정책의 성격을 분석한 결과, Heifetz(1994)의 문제상황모형에서 ‘Type 2’에 해당하고, Wilson (2001)의 규제정치모형에서 ‘기업가 정치’에 해당하여 업무의 성격이 적응적(adaptive)이고, 이해 관계 조정 및 정책홍보 등의 활동이 중요한 것으로 나타났다. 다음으로 Moore(1995)의 다섯 가지 기술에 따라 부안군과 경주시 사례를 비교 분석한 결과, 네 가지 기술의 측면에서 경주시가 부안군보다 우수했음이 확인되었으며, 특히 기업가적 옹호와 협상 전략에서 정부의 적극적이고 탁월한 정책활동이 전개되었음을 확인하였다. 이에 따라 본 연구에서는 방폐장 입지정책과 같이 난해(wicked)하고 기업가적(entrepreneurial)인 성격의 정책문제일수록 정치적 관리가 중요하게 작용함을 밝히고, 향후 공공관리 영역에서 이러한 전략적 측면의 중요성을 제언하였다.

Adsorption characteristic of Cs+ and Co2+ ions from aqueous solutions onto geological sediments of radioactive waste disposal site

The physico-chemical characteristics of clayey (CS) and brown sand (BSS1) sediments from the host geological formation of Inshas radioactive waste disposal site were explored and were correlated with the adsorption properties toward Cs+ and Co2+. Fe2O3 and SiO2 were the two most abundant chemical compounds in both sediments with greater percentage of the former in the CS which had platy surfaces (31.51 m2/g). FT-IR analyses evidenced the comparability between the contained low quantities of organic matter in both sediments. Geochemical study was carried out to investigate the weathering history and tectonic setting taken from the site area. Batch adsorption experiments of Cs+ and Co2+ reflected greater capacities of the CS which were correlated to the occurrence of hematite, kaolinite, vermiculite and plagioclase minerals, detected by XRD. All studied adsorption systems were kinetically controlled by the chemical sorption mechanism. The sorption isotherms ordered the adsorbed amounts to the following: Cs+/CS > Cs+/BSS1 > Co2+/CS > Co2+/BSS1. Langmuir, Freundlich, Dubinin-Radushkevitch and Temkin isotherm equations were applied to specify the affinities of CS and BSS1. Values of ΔH° reflected the exothermic natures for both systems of Cs+ and vice-versa regarding Co2+. Values of ∆G° revealed that the only spontaneous systems were the Cs+/CS at 298 and 313 K. The studied sediments gave good performance toward postponing the potential release of Cs+ and Co2+ into biosphere.

Effect of a humic acid colloid on the sorption behaviour of Sr onto soil in a candidate high-level radioactive waste geological disposal site

We explored the effect of the presence or absence of humic acid (HA) on the sorption behaviour of Sr onto soil. We examined three different experimental cases for Sr sorption: (1) sorption in the presence of only colloidal HA, (2) sorption in the presence of only soil and (3) sorption in the presence of both colloidal HA and soil (HS). A batch technique was used to study the influencing factors, including the amount of colloidal HA, solid content, pH, initial concentration of Sr and contact time. The experiments showed that the influencing factors significantly affected the sorption process. For example, in the case of soil and HS, the sorption percentage increased rapidly with increasing solid content at m/V < 20g/L, changing from 8.35% and 37.54% to 49.09% and 77.03%, respectively. Moreover, scanning electron microscopy and Fourier transform infrared spectroscopy were used to characterize samples. The kinetics and isotherms of Sr were best described by the pseudo-second-order and Langmuir models, which indicated that the process was controlled by chemisorption and uniform monolayer sorption with constant energy on the outer surface. These findings provide valuable information for predicting strontium migration in radioactive waste disposal sites.

Sorption of selenite on Tamusu clay in simulated groundwater with high salinity under aerobic/anaerobic conditions

The sorption behavior of selenite onto the Tamusu clay from a preselected high-level radioactive waste disposal site in Inner Mongolia, China, was first investigated in simulated groundwater with high salinity by batch sorption experiments under aerobic/anaerobic conditions. The results demonstrated that the Kd values rapidly decreased and then remained steady in the pH range of 2.0–8.0. However, selenite sorption was promoted when pH exceeded 8.0, which might be attributed to the coprecipitation between Ca2+ and SeO32−. Besides, the change trend of the Kd values as functions of various parameters was not affected by oxygen. The sorption kinetics and isotherms could be well fitted by the pseudo-second-order kinetic model and the Freundlich model for both aerobic and anaerobic conditions, and the calculated thermodynamic parameters (△G and △H) suggested that the selenite sorption process was a spontaneous and endothermic process. Additionally, the XPS results revealed that Se(IV) could be reduced to Se (0) only in anaerobic conditions and that the different amounts of Fe on the clay surface led to the discrepancy of the Se(IV) Kd values under aerobic and anaerobic conditions even in high-salt simulated groundwater. Overall, our findings in this study are significant in regards to the retardation of selenite on the host rock under high salinity conditions.

Sorption of U(VI) onto natural soils and different mineral compositions: The batch method and spectroscopy analysis

This research studied the sorption behavior of uranium(VI) onto two different kinds of soils: surface soil and undersurface soil that taken from the depth of 30 m undersurface. The soil samples were collected from a low and medium-level radioactive waste disposal site in the southwest of China. The effects of pH, solid-liquid ratio and contact time on the adsorption behavior were studied by batch adsorption method. The experiment results show that the mineral composition of soil and the speciation of U in natural groundwater are two main influencing factors. Muscovite and clinochlore, two of the main minerals of soil samples, dominate the sorption behavior of uranium onto natural soils at weak acidic and near neutral pH range. Under neutral and weak alkaline conditions, the thermodynamic calculation results show that Ca2+ and CO32− have significant influence on the species of uranium in aqueous solution. The U sorption reduced sharply due to the formation of the CaUO2(CO3)32− (aq) complex. This work provides a better insight of the sorption behavior of uranium onto natural soils, and gives an in-depth understanding about the influence of aqueous and surface speciation.

Thermodynamic study of the complexation of humic acid by calorimetry

Although the thermodynamic quantities (Gibbs free energy, reaction enthalpy, and entropy) of the complexation of humic acid are necessary for the discussion of the reaction thermodynamics, their accurate determination, especially concerning dissolved humic acid in deep groundwater, has not been carried out. In this study, a combination of potentiometry and calorimetry was used for the determination of the thermodynamic values of complexation of typical humic acid and groundwater humic acid, which was isolated from deep groundwater at Horonobe, Hokkaido, Japan, with copper (II) ions and uranyl (VI) ions. The apparent complexation constant of Horonobe humic acid was independent of the pH of the bulk solution, whereas that of typical humic acid was dependent on the pH. This observation indicates that the polyelectrolyte effect of Horonobe humic acid is negligible because of its relatively small molecular size. In addition, the effect of the heterogeneity of Horonobe humic acid was not significant. Moreover, the complexation enthalpy of Horonobe humic acid was consistent with that of homogeneous poly(acrylic acid), which means the complexation of Horonobe humic acid was not affected by the functional group heterogeneity. Consequently, the unique complexation mechanism of Horonobe humic acid was revealed based on the determined thermodynamic quantities. The migration of radionuclides in the deep underground environment must be affected by these characteristics; thus, the accurate determination of thermodynamic quantities of in situ humic substances is very helpful for the safety assessment of geological disposal, when disposal sites for radioactive waste are chosen.

Reconstructing Terrestrial Water Storage Variations from 1980 to 2015 in the Beishan Area of China

Terrestrial water storage (TWS) is a key element in the global and continental water cycle. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) has provided a highly valuable dataset, which allows the study of TWS over larger river basins worldwide. However, the lifetime of GRACE is too short to demonstrate long-term variability in TWS. In the Beishan area of northwestern China, which is selected as the most prospective site for high-level radioactive waste (HLRW) disposal, the assessment of long-term TWS changes is crucial to understand disposal safety. Monthly and annual TWS changes during the past 35 years are reconstructed using GRACE data, other remote sensing products, and the water balance method. Hydrological flux outputs from multisource remote sensing products are analyzed and compared to select appropriate data sources. The results show that a decreasing trend is found for GRACE-filtered and Center for Space Research (CSR) mascon solutions from 2003 to 2015, with slopes of −2.30 ± 0.52 and −1.52 ± 0.24 mm/year, respectively. TWS variations independently computed from the water balance method also show a similar decreasing trend with the GRACE observations, with a slope of −0.94 mm/year over the same period. Overall, the TWS anomalies in the Beishan area change seasonally within 10 mm and have been decreasing since 1980, keeping a desirable dry condition as a HLRW disposal site.

Попередня оцінка сумарної активності локалізованих радіоактивних відходів у модулі А-1 пункту захоронення радіоактивних відходів «Підлісний»

Попередня оцінка сумарної активності локалізованих радіоактивних відходів у модулі А-1 пункту захоронення радіоактивних відходів «Підлісний»

Reconstructing the Gyeongju Low to Intermediate Radioactive Waste Disposal Site Selection in Korea

Reconstructing the Gyeongju Low to Intermediate Radioactive Waste Disposal Site Selection in Korea