270 results found
Petrov VA, Ojovan MI, Yudintsev SV, 2023, Material Aspect of Sustainable Nuclear Waste Management, Sustainability (Switzerland), Vol: 15
Ojovan MI, 2023, The Flow of Glasses and Glass-Liquid Transition under Electron Irradiation., Int J Mol Sci, Vol: 24
Recent discovery and investigation of the flow of glasses under the electron beams of transmission electron microscopes raised the question of eventual occurrence of such type effects in the vitrified highly radioactive nuclear waste (HLW). In connection to this, we analyse here the flow of glasses and glass-liquid transition in conditions of continuous electron irradiation such as under the e-beam of transmission electron microscopes (TEM) utilising the configuron (broken chemical bond) concept and configuron percolation theory (CPT) methods. It is shown that in such conditions, the fluidity of glasses always increases with a substantial decrease in activation energy of flow at low temperatures and that the main parameter that controls this behaviour is the dose rate of absorbed radiation in the glass. It is revealed that at high dose rates, the temperature of glass-liquid transition sharply drops, and the glass is fully fluidised. Numerical estimations show that the dose rates of TEM e-beams where the silicate glasses were fluidised are many orders of magnitude higher compared to the dose rates characteristic for currently vitrified HLW.
Ojovan MI, Yudintsev SV, 2023, Glass, ceramic, and glass-crystalline matrices for HLW immobilisation, Open Ceramics, Vol: 14
We briefly overview the utilisation of glasses, ceramics and glass crystalline materials (GCMs) composed of both vitreous and crystalline phases focusing on nuclear waste immobilisation and potential use of some advanced waste forms for incorporation of the rare earth elements (REE) and minor actinide (MA: Am, Cm) fraction of high-level waste (HLW).
Poluektov VV, Petrov VA, Ojovan MI, et al., 2023, Uranium Retention in Silica-Rich Natural Glasses: Nuclear Waste Disposal Aspect, Ceramics, Vol: 6, Pages: 1152-1163
Uranium-containing glass samples with an age of 140–145 million years were collected within the volcanic rocks of the largest volcanic-related uranium ore deposit in the world. Main features of their composition are high concentrations of silica and uranium, the largest for the rocks of this type. In contrast to this, the ages of fresh (unaltered) low-silica natural glasses of a basic composition (basalts) usually do not exceed a few million years. The volcanic low-silica glass is unstable at longer times and in older ancient rocks is transformed into a crystalline mass. The geochemistry of uranium including the behavior in solids and solutions is similar to that of long-lived transuranic actinides such as radioactive Np and Pu from high-level radioactive waste. This allows uranium to be used as a simulant of these long-lived hazardous radionuclides both at the synthesis and for the study of various nuclear wasteforms: glasses, glass crystalline materials and crystalline ceramics. The data obtained on long-term behavior of natural glasses are of importance for prognosis and validation of stability of nuclear wasteforms disposed of in geological disposal facilities (GDF).
Darmaev MV, Ojovan MI, Mashanov AA, et al., 2023, The Temperature Interval of the Liquid-Glass Transition of Amorphous Polymers and Low Molecular Weight Amorphous Substances, APPLIED SCIENCES-BASEL, Vol: 13
Malkovsky VI, Zharikov AV, Ojovan MI, 2023, Modification of Pulse Decay Method for Determination of Permeability of Crystalline Rocks, Inventions, Vol: 8
An improvement of the pulse decay method of rock permeability measurement is presented. The technique is based on fitting experimental data to analytical and numerical solutions of the filtration equations derived with regard to the variation of flowing gas properties with temperature and pressure. A special apparatus and software for the implementation of this method were developed. A single experiment in which gas is used as a flowing medium enables determining both the permeability of a sample to water and the Klinkenberg constant. The permeability measurements on the samples of different types of rock with various reservoir properties were carried out and demonstrated satisfactory accuracy and efficiency of the method. An effective method for anisotropic permeability measurement is proposed as a development of this technique.
Malkovsky VI, Petrov VA, Yudintsev SV, et al., 2023, Influence of Rock Structure on Migration of Radioactive Colloids from an Underground Repository of High-Level Radioactive Waste, SUSTAINABILITY, Vol: 15
Drace Z, Ojovan MI, Samanta SK, 2022, Challenges in Planning of Integrated Nuclear Waste Management, Sustainability, Vol: 14, Pages: 14204-14204
<jats:p>Planning for integrated nuclear waste management (INWM) entails consideration of all generated waste from energy generation, nuclear fuel cycle and institutional facilities as well as waste from decommissioning and remediation of nuclear facilities, legacy waste, and eventual accident waste and requires establishment of different planning scenarios as well as control milestones to allow for adequate flexibility to address inevitable changes. An early assessment of waste management needs from development and use of advanced reactors and innovative nuclear fuel cycles is required to aid design and operation of such facilities as well as to understand their impact to overall waste management planning. Major prerequisites for approach to planning and establishment of INWM plans are discussed briefly. It is pointed out that five most important challenges in establishing and implementing the INWM plan needs to be addressed: (i) inventory; (ii) time frame for an integrated plan; (iii) assessment of facility needs; (iv) costs estimation (life-cycle cost analyses) and (v) funding and financing. The INWM has to promote strategic thinking within a broad framework resulting in a sustainable and sensible outcome for nuclear waste management at a strategic and national level.</jats:p>
Ojovan MI, Steinmetz HJ, 2022, Approaches to Disposal of Nuclear Waste, Energies, Vol: 15, Pages: 7804-7804
<jats:p>We present a concise mini overview on the approaches to the disposal of nuclear waste currently used or deployed. The disposal of nuclear waste is the end point of nuclear waste management (NWM) activities and is the emplacement of waste in an appropriate facility without the intention to retrieve it. The IAEA has developed an internationally accepted classification scheme based on the end points of NWM, which is used as guidance. Retention times needed for safe isolation of waste radionuclides are estimated based on the radiotoxicity of nuclear waste. Disposal facilities usually rely on a multi-barrier defence system to isolate the waste from the biosphere, which comprises the natural geological barrier and the engineered barrier system. Disposal facilities could be of a trench type, vaults, tunnels, shafts, boreholes, or mined repositories. A graded approach relates the depth of the disposal facilities’ location with the level of hazard. Disposal practices demonstrate the reliability of nuclear waste disposal with minimal expected impacts on the environment and humans.</jats:p>
Yudintsev SV, Nickolsky MS, Ojovan MI, et al., 2022, Zirconolite polytypes and murataite polysomes in matrices for the REE-actinide fraction of HLW, Materials, Vol: 15, ISSN: 1996-1944
Electron backscatter diffraction (EBSD) has been used for more than 30 years for analyzing the structure of minerals and artificial substances. In recent times, EBSD has been widely applied for investigation of irradiated nuclear fuel and matrices for the immobilization of radioactive waste. The combination of EBSD and scanning electron microscopy (SEM/EDS) methods allows researchers to obtain simultaneously data on a specimen's local composition and structure. The article discusses the abilities of SEM/EDS and EBSD techniques to identify zirconolite polytype modifications and members of the polysomatic murataite-pyrochlore series in polyphase ceramic matrices, with simulations of Pu (Th) and the REE-actinide fraction (Nd) of high-level radioactive waste.
Ojovan MI, 2022, Challenges in the long-term behaviour of highly radioactive materials, Sustainability, Vol: 14, Pages: 2445-2445, ISSN: 2071-1050
Ojovan MI, Louzguine-Luzgin DV, 2022, On structural rearrangements during the vitrification of molten copper, Materials, Vol: 15, Pages: 1-10, ISSN: 1996-1944
We utilise displacement analysis of Cu-atoms between the chemical bond-centred Voronoi polyhedrons to reveal structural changes at the glass transition. We confirm that the disordered congruent bond lattice of Cu loses its rigidity above the glass transition temperature (Tg) in line with Kantor–Webman theorem due to percolation via configurons (broken Cu-Cu chemical bonds). We reveal that the amorphous Cu has the Tg = 794 ± 10 K at the cooling rate q = 1 × 1013 K/s and that the determination of Tg based on analysis of first sharp diffraction minimum (FDSM) is sharper compared with classical Wendt–Abraham empirical criterion.
Tournier RF, Ojovan MI, 2022, Multiple Melting Temperatures in Glass-Forming Melts, SUSTAINABILITY, Vol: 14
Kovalenko ІО, Panasiuk МI, Skorbun АD, et al., 2021, Correlation between chemical composition and 90Sr concentrations in groundwater of the Chornobyl NPP industrial site., J Environ Radioact, Vol: 240
The volumetric activity of the divalent 90Sr ion in groundwater at the Chornobyl NPP industrial site ranges from 1 to 2 to 400-3800 Bq/l. The increase in groundwater radionuclides concentrations is associated with the reduced sorption properties of local sediments, which affect the migration capacity of radionuclides in the environment. The decrease of the 90Sr sorption properties of sediments is caused by changes in the chemical composition of groundwater. A new statistical method has been performed. Method based on the Monte Carlo method in order to evaluate the correlations between the 90Sr volumetric activity and the groundwater chemical composition components. Simulation results using this method suggest a correlation between the volumetric activity of 90Sr, the concentrations cations, the pH, and the oxidation index (organic contents). A direct correlation was established between the volumetric activity of 90Sr, Ca2+ concentrations and the pH of groundwater in the range from 7 to 12.4. It was revealed that the concentrations of Na+ and K+ do not affect the conditions of 90Sr migration with groundwater. There is an inverse correlation between the concentration of 90Sr and the oxidation index, which is an indirect indicator of the organic substances content in water. Thus, the presence of organic substances in the groundwater effectively promotes sorption of 90Sr. The proposed method of geochemical statistics enables a quantitative assessment of groundwater monitoring results.
Tournier RF, Ojovan MI, 2021, Comments about a recent publication entitled “Improving glass forming ability of off-eutectic metallic glass formers by manipulating primary crystallization reactions”, Scripta Materialia, Vol: 205, Pages: 114039-114039, ISSN: 1359-6462
Abdel Rahman RO, Ojovan MI, 2021, Toward Sustainable Cementitious Radioactive Waste Forms: Immobilization of Problematic Operational Wastes, SUSTAINABILITY, Vol: 13
Tournier RF, Ojovan MI, 2021, Prediction of second melting temperatures already observed in pure elements by molecular dynamics simulations, Materials, Vol: 14, Pages: 1-21, ISSN: 1996-1944
A second melting temperature occurs at a temperature Tn+ higher than Tm in glass-forming melts after heating them from their glassy state. The melting entropy is reduced or increased depending on the thermal history and on the presence of antibonds or bonds up to Tn+. Recent MD simulations show full melting at Tn+ = 1.119Tm for Zr, 1.126Tm for Ag, 1.219Tm for Fe and 1.354Tm for Cu. The non-classical homogeneous nucleation model applied to liquid elements is based on the increase of the Lindemann coefficient with the heating rate. The glass transition at Tg and the nucleation temperatures TnG of glacial phases are successfully predicted below and above Tm. The glass transition temperature Tg increases with the heating rate up to Tn+. Melting and crystallization of glacial phases occur with entropy and enthalpy reductions. A universal law relating Tn+ and TnG around Tm shows that TnG cannot be higher than 1.293Tm for Tn+= 1.47Tm. The enthalpies and entropies of glacial phases have singular values, corresponding to the increase of percolation thresholds with Tg and TnG above the Scher and Zallen invariant at various heating and cooling rates. The G-phases are metastable up to Tn+ because the antibonds are broken by homogeneous nucleation of bonds.
Ojovan MI, Tournier RF, 2021, On structural rearrangements near the glass transition temperature in amorphous silica, Materials, Vol: 14, ISSN: 1996-1944
The formation of clusters was analyzed in a topologically disordered network of bonds of amorphous silica (SiO2) based on the Angell model of broken bonds termed configurons. It was shown that a fractal-dimensional configuron phase was formed in the amorphous silica above the glass transition temperature Tg. The glass transition was described in terms of the concepts of configuron percolation theory (CPT) using the Kantor-Webman theorem, which states that the rigidity threshold of an elastic percolating network is identical to the percolation threshold. The account of configuron phase formation above Tg showed that (i) the glass transition was similar in nature to the second-order phase transformations within the Ehrenfest classification and that (ii) although being reversible, it occurred differently when heating through the glass-liquid transition to that when cooling down in the liquid phase via vitrification. In contrast to typical second-order transformations, such as the formation of ferromagnetic or superconducting phases when the more ordered phase is located below the transition threshold, the configuron phase was located above it.
Nabakhtiani G, Giorgadze I, Ojovan MI, 2021, IAEA-Assisted Treatment of Liquid Radioactive Waste at the Saakadze Site in Georgia, PROCESSES, Vol: 9
Kochkin B, Malkovsky V, Yudintsev S, et al., 2021, Problems and perspectives of borehole disposal of radioactive waste, Progress in Nuclear Energy, Vol: 139, Pages: 1-9, ISSN: 0149-1970
An overview is given of status of projects for the disposal of radioactive waste in very deep boreholes in crystalline rocks which demonstrates all main pros and cons of this technology. New opportunities offered by drilling long horizontal drillholes in ductile formations can provide the basis for projects that have the potential to overcome many of the disadvantages of deep boreholes. The concept of disposal in horizontal drillholes brings together the technologies of borehole and mined repositories using the advantages of both, and therefore deserves an expert discussion at international level.
Tournier RF, Ojovan MI, 2021, Dewetting temperatures of prefrozen and grafted layers in solid ultrathin films viewed as melt-memory effects, Physica B: Condensed Matter, Vol: 611, Pages: 1-10, ISSN: 0921-4526
Undercooled phase exists behind glass phase with superheated medium-range order between Tg and Tn+ > Tm. The ordered volume fraction stays equal to the percolation threshold F ≅ 0.15 of broken bonds up to Tn+. The difference ΔTg between Tg(bulk) of films with thickness (h > h0) and Tg(h) of ultrathin films of thickness (h < h0) is a linear function of (h-ho). Dense layer with minimum thickness hr is grafted against substrate by isothermal annealing, rinsed to reduce film thickness below hr/F, and finally dewetted at Tg. Similar thickness prepared and annealed near Tm and heated above Tm contains residual crystallized layer dewetting at Tn+. The prefrozen layer reproduces the glassy grafted layer in a crystallized state up to Tn+. Melting heat and melting temperature Tm are linear functions of h for h < h0. Prefrozen layers are due to melt-memories leading to new scenarios of crystallization.
Tournier RF, Ojovan MI, 2021, Building and breaking bonds by homogenous nucleation in glass-forming melts leading to transitions in three liquid states, Materials, Vol: 14, ISSN: 1996-1944
The thermal history of melts leads to three liquid states above the melting temperatures Tm containing clusters—bound colloids with two opposite values of enthalpy +Δεlg × ΔHm and −Δεlg × ΔHm and zero. All colloid bonds disconnect at Tn+ > Tm and give rise in congruent materials, through a first-order transition at TLL = Tn+, forming a homogeneous liquid, containing tiny superatoms, built by short-range order. In non-congruent materials, (Tn+) and (TLL) are separated, Tn+ being the temperature of a second order and TLL the temperature of a first-order phase transition. (Tn+) and (TLL) are predicted from the knowledge of solidus and liquidus temperatures using non-classical homogenous nucleation. The first-order transition at TLL gives rise by cooling to a new liquid state containing colloids. Each colloid is a superatom, melted by homogeneous disintegration of nuclei instead of surface melting, and with a Gibbs free energy equal to that of a liquid droplet containing the same magic atom number. Internal and external bond number of colloids increases at Tn+ or from Tn+ to Tg. These liquid enthalpies reveal the natural presence of colloid–colloid bonding and antibonding in glass-forming melts. The Mpemba effect and its inverse exist in all melts and is due to the presence of these three liquid states.
Ojovan MI, Petrov VA, Yudintsev SV, 2021, Glass Crystalline Materials as Advanced Nuclear Wasteforms, Sustainability, Vol: 13, Pages: 4117-4117
<jats:p>Glass crystalline materials (GCM) are of increasing interest as advanced nuclear wasteforms combining the advantages of vitreous and crystalline matrices. The GCM are versatile wasteforms envisaged for a wider use to immobilise various types of both radioactive and chemically hazardous wastes. They can be produced either via low temperature sintering using precursors composed of glass frit, oxides, and crystalline phases or through conventional melting aiming to produce first a parent glass, which is then crystallised by a controlled thermal schedule to obtain target crystalline phases within the GCM. Utilization of GCM is highlighted as a perspective wasteform for immobilization of partitioned radionuclide streams.</jats:p>
Ojovan MI, 2021, The Modified Random Network (MRN) model within the Configuron Percolation Theory (CPT) of glass transition, Ceramics, Vol: 4, Pages: 121-134, ISSN: 2571-6131
A brief overview is presented of the modified random network (MRN) model in glass science emphasizing the practical outcome of its use. Then, the configuron percolation theory (CPT) of glass–liquid transition is concisely outlined, emphasizing the role of the actual percolation thresholds observed in a complex system. The MRN model is shown as an important tool enabling to understand within CPT the reduced percolation threshold in complex oxide systems.
Ojovan M, 2021, Glass formation, Encyclopedia of Glass Science, Technology, History, and Culture, Editors: Richet, Publisher: Wiley
Tournier RF, Ojovan MI, 2021, Undercooled phase behind the glass phase with superheated medium-range order above glass transition temperature, Physica B: Condensed Matter, Vol: 602, Pages: 1-17, ISSN: 0921-4526
Rapidly quenched glass formers are amorphous and transformed into glass phases by relaxing enthalpy during the first heating. Two liquids give rise, at first, to an intermediate Phase 3 below T3 < Tg respecting the entropy constraints and then, the enthalpy increases towards that of the glass phase up to Tg. The negative activation energy shows that Phase 3 is hidden behind the glassy phase acting as an intermediate invasive phase during the second cooling. Phase 3 carries a medium-range order above Tg which can be superheated above the melting temperature up to Tn+. The two-liquid state model predicts the thermodynamic properties as well as the relaxation times from liquids 1 to 2. The configuron model is successfully applied to 54 glasses explaining the transitions by percolation and an ‘ordered’ fraction equal to the critical threshold Φc = 0.15 ± 0.01 from Tg to Tn+.
Laraia M, Rahman ROA, Ojovan MI, 2021, Terms and glossary relevant to nuclear cementitious systems, Sustainability of Life Cycle Management for Nuclear Cementation-Based Technologies, Pages: 629-646, ISBN: 9780128183298
Rahman ROA, Ojovan MI, 2021, Hydration process: Kinetics and thermodynamics, Sustainability of Life Cycle Management for Nuclear Cementation-Based Technologies, Pages: 125-160, ISBN: 9780128183298
Cements are hydraulic binders that react with water to form solidified phases; the hydration reaction plays an important role in determining the behavior of the cementitious systems through their life cycle. This chapter addresses the hydration reaction kinetics and thermodynamics and their impacts on the properties of the cement-based systems. In this respect, the hydration reactions and their roles in determining the setting time, mechanical properties, and heat release during the hydration process will be presented by overviewing the principals and advances in studying the kinetics of alite as the main and fast reacted major unhydrated cement phase. Properties of the hydrated Portland cement-based materials will be summarized, and the factors that control the hydration process will be discussed. The focus of this section is to identify the links between the factors that affect the hydration reactions and the attained cement properties. Hydration of innovative cements including calcium aluminate cement that is used for radioactive waste conditioning and is considered as a part of the low-pH cement in geological disposal will be overviewed, and main properties of these hydrated cements will be highlighted.
Rahman ROA, Ojovan MI, 2021, Preface, ISBN: 9780128183298
Rahman ROA, Ojovan MI, 2021, Behavior of cementitious SSC’s in mitigating accidents, Sustainability of Life Cycle Management for Nuclear Cementation-Based Technologies, Pages: 233-267, ISBN: 9780128183298
This chapter is devoted to present the factors that affect the sustainability of cementitious SSC’s under accidental conditions. In this respect, accidents in nuclear facilities, their scale, and initiators will be introduced. The types of hazard that can initiate an accident will be presented, and extent of damage in cementitious SSC’s in previous accidents will be reviewed. Methods to predict the behavior of cementitious SSC’s under accidental case will be summarized. Three cases were selected to be included in this chapter that represent different accidental conditions in three facilities, namely, radioactive waste disposal, dry spent fuel storage, and nuclear reactor containment. In each case, the development of the accidental conditions will be presented and models that could be used to describe the behavior of the respective cementitious SSC’s will be reviewed.
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