Geological Disposal Of High-level Waste Research Articles

Nuclear waste glass alteration under the influence of iron, claystone, and cementitious grout: An integral study

To prepare for the future deep geological disposal of high-level waste, the alteration of two inactive nuclear glasses was studied in the presence of claystone, iron, and cementitious grout at 50 °C for a period of 4 years. The materials were immersed together in a synthetic water representative of claystone solution composition. Blank experiments were also carried out to study the independent behaviors of iron and glass in the synthetic water. The evolution of the solutions’ chemistry was monitored. At the end of the experiments, the glass and iron, as well as the neoformed phases, were characterized. Results showed that Si, Ca, Mg, and Fe are key elements. A competition exists between the retention/integration of species into glass gels and clay-like neoformations. Magnesium tends to be leached from glasses and form Mg-silicates. It would only integrate into the gel if it was widely available in the solution. Furthermore, iron could form Fe-silicates. Whether for Mg or Fe, the formation of silicates was detrimental to the glass since it involved the creation of a silicon sink and thus the conservation of a high alteration rate. Concerning calcium, in these experiments it appeared that this species tends to be integrated/retained within the gels. In the pH conditions existing here, it seems that there is no competition with a neoformation. The specific impact of the cementitious grout was also studied, and the results showed that the presence of this material in the system had a beneficial effect on glass alteration due to a significant Si supply in the solution, enabling a reduction in the glass alteration rate.

Fractional Advection Diffusion Models for Radionuclide Migration in Multiple Barriers System of Deep Geological Repository

Based on the multiple barriers concept of deep geological disposal of high-level waste, fractional advection diffusion equations for radionuclide migration in multiple layers low-permeability porous media are proposed in this work. The presented fractional advection diffusion models in terms of different definitions of fractional derivative are analytically addressed via the Laplace integral transform method. This work provides a theoretical foundation for further simulations of radionuclide migration in the multiple barriers system of the high-level waste repository.

Evaluation of the technical options of radioactive waste management for utilization of MOX fuel: thermal impact of minor actinide separation with geological disposal of high-level waste

ABSTRACT The impact of disposal of mixed oxide (MOX) fuel from light water reactors (LWRs) has been considered from the viewpoint of the thermal properties and the number of the vitrified waste for various conditions of the nuclear fuel cycle. In addition, the effect of separation of the minor actinides (MAs) (Np, Am, Cm) that potentially influence the geological disposal area has been evaluated quantitatively. Review of the effect of MAs separation on heat generation in MOX fuel disposal has revealed that dedicated measures for thermal impact reduction need to be developed for the purpose of nuclear-fuel-cycle evaluation from the viewpoint of continuous utilization of Pu. Not only MA separation, but also the nuclear fuel cycle conditions, technical options, waste occupied area per waste package are strongly relevant to the thermal properties of the vitrified waste, and it is necessary to consider the combination of these factors together with the number of waste packages to progress the feasibility studies for geological disposal of MOX-LWR.

Подземная исследовательская лаборатория: преодоление неопределенностей в оценке сейсмических условий участка «Енисейский»

The article presents the basic principles and an algorithm allowing to arrange a seismological monitoring system for the Yeniseiskiy site selected for deep geological disposal of high-level waste. It describes the seismological monitoring system developed by NO RAO in 2018 also briefly considering the seismotectonic conditions of the area. The paper describes the process that has been followed to select the corresponding sites and equipment layouts in the areas fitted with seismological monitoring stations with relevant instrumental characteristics being provided. It shows that considering the current stage of research, higher sensitivity was provided in the area as compared to the one associated with available regional seismological observations. It demonstrates the efficiency of the built-up monitoring system with its sensitivity assessment provided both based on the calculated model and under real conditions. The long-term safety assessment performed for such a facility relies upon many factors with the seismic hazard level within the area of the monitored facility also taken into consideration. To provide most reliable evaluation of seismic parameters, continuous seismological monitoring should be performed over a several years’ period along with the sensitivity assessment of the selected monitoring system. The seismological monitoring system should focus not only on the general study of the monitored territory, but also on the areas assumed as zones of most probable seismic event occurrence, i.e. areas involving tectonic faults. The relevance of this task has been repeatedly emphasized in the course of multiple discussions on this issue featuring the representatives from SC Rosatom and the Scientific and Engineering Centre for Nuclear and Radiation Safety. The monitoring system fitted within the repository area meets relevant regulatory requirements. In accordance with the existing requirements, to reduce the uncertainties in the seismic hazard assessment of the territory, the implementation of certain measures was recommended during further development of the local seismological monitoring network to identify and assess the potential of hazardous geodynamic zones.

Preliminary modelling of radionuclide migration in the argillaceous sediments of the Sumer Formation (Northwestern Bulgaria)

In Bulgaria, from the preliminary analyses performed for site selection of deep geological disposal of high-level waste (HLW) and spent fuel (SF), it was concluded that the most promising host rocks are the argillaceous sediments of the Sumer Formation (Lower Cretaceous), situated in the Western Fore-Balkan Mts. The present paper aims to compare the transport of three major radionuclides from a hypothetical radioactive waste disposal facility, which incorporates an engineering barrier of bentonite into the argillaceous (marl) medium. The simulations were performed by using HYDRUS-1D computer programme. The results are used for a preliminary estimation of argillaceous sediments as a host rock for geological disposal of HLW.

Gamma (60Co) irradiation and thermal effect on redox behavior of interlayer iron in montmorillonite

Fe2+-montmorillonite (Mt) is expected to be one of the major altered clay minerals formed in the engineered barrier system proposed for deep geological disposal of high-level waste (HLW). The high energy radiations imparted by the radionuclides present in HLW as well as the temperature can impact the redox behavior of interlayer iron in clay. Therefore, we have studied the effect of γ- radiation (60Co) on the stability of Fe2+-Mt dispersed in water. Irradiation at a dose rate of 0.6 kGy/h for 18 h resulted in the oxidation of about 14% interlayer Fe2+ as indicated by Fe2+/Fetotal ratio. On further irradiation, these oxidized Fe3+ are reduced back to Fe2+. Such behavior was observed in inert, aerated, and N2O-saturated conditions.The effect of temperature was found to be similar to that of γ-irradiation, particularly on the reduction of interlayer Fe3+ from Fe3+-Mt. When the temperature was increased from 50 to 300 °C, > 90% reduction (Fe3+ → Fe2+) was observed, which is ascribed to the self-reduction mechanism. This sample is similar to that of Fe2+-Mt as evident from XRD, FTIR, TG and magnetic data anaysis. The increase in Fe2+/Fetotal ratio of the heat-treated samples enabled the solid-state reaction with o-phenanthroline (L) by in-situ complexation to form organo-modified Mt. (d001 = 18.5 Å) at room temperature (RT, 27 °C). Furthermore, the presence of Fe2+ in this heat-treated Mt. is evident from their reduction of aqueous CrVI. For instance, 55% of CrVI reduction occurred with Fe3+-Mt@200. On the other hand, the gradual oxidation of interlayer Fe2+ occurred when Fe2+-Mt was heated up to 300 °C. Only about 12% oxidation was observed when heated to 200 °C for 4 h. This is probably due to an equilibrium between oxidation and their self-reduction. In this heat treated sample, about 73% of CrVI reduction occurred, which is comparable to 80% reduction observed with freshly prepared Fe2+-Mt@RT. Thus, the redox behavior of interlayer iron was significantly influenced by γ-irradiation as well as thermal treatment. We believe the observations made here have significant implications on the plausible existence of clay minerals in the geothermal and extraterrestrial environment.

Static and coupled dynamic testing of granite for geological disposal of high-level waste

The Tianhu area of Xinjiang Province has been pre-selected for the geological disposal of high-level radioactive waste. To engineer the design of the disposal site, one must understand the static and dynamic properties of the granite in the borehole. In the present study, rock was sampled at the same depth in the same borehole, and its tensile and uniaxial-compression strengths were evaluated. Both strengths were steady and representative. The dynamic tensile and dynamic compression strengths increased with loading rate, confirming the loading rate effect on the brittle material. A coupled static-and-dynamic tension test was then carried out. Under increasing axial static stress, the dynamic tensile strength first increased and then decreased in a stable manner. The dynamic tensile strength was maximized when the static axial pre-pressure reached approximately 50% of the static-tensile strength. Meanwhile, the coupled static-and-dynamic strength increased under increasing axial static pressure, reaching approximately three times the static tension strength, and 1.5 times the dynamic tension strength. The failure model in the dynamic test was mainly tension failure, consistent with the static tension test. Therefore, the rock in this area is mechanically stable and putatively suitable for the geo-disposal of high-level waste (HLW). For a complete assessment, the rock should be tested by other methods such as seepage and in situ stress testing. After a detailed analysis of the rock in this area, the testing results and theoretical knowledge will become available for deep geo-engineering blasting and excavation, and HLW geo-disposal.

Corrosion of carbon steel components in the French high-level waste programme: evolution of disposal concept and selection of materials

ABSTRACTIn France, the reference concept for the geological disposal of high-level waste (HLW) consists of horizontal micro-tunnels, containing carbon steel casing and overpacks (around a stainless steel container containing vitrified waste). The overpacks and casing will be exposed to an environment that will evolve over time: from a hot and humid atmosphere containing oxygen, to an anoxic environment saturated with water at the geothermal temperature. Lots of corrosion experiments have been performed in representative environments to study steel corrosion modes (general corrosion, pitting and crevice corrosion, stress corrosion cracking, hydrogen embrittlement…) while taking into account the influence of temperature, radiation, mechanical stresses and microorganisms. Some key results have influenced the design of the HLW disposal cell, including the carbon steel grades and dimensions of the casing and overpacks, or the addition of an alkaline grout material between the casing and the host rock.This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

A methodology for scenario development based on understanding of long-term evolution of geological disposal systems

We have developed a “hybrid” scenario development method by combining bottom-up and top-down approaches and applied for the case of geological disposal of high-level waste. This approach provides a top-down perspective, by introducing a concept of safety functions for different periods and “storyboards”, which depict repository evolution with time on a range of spatial scales, and a bottom-up perspective, by identifying relationship between processes related to radionuclide migration and safety functions based on feature, event and process (FEP) management. Based on a trial study, we have specified work descriptions for each step of the hybrid scenario development methodology and confirmed that the storyboard provides a baseline and holistic overview for the FEP management and a common platform to involve close interaction with experts in various disciplines to understand the crossover phenomenological processes. We also confirmed that there is no conflict between the top-down approach and the bottom-up approach and the hybrid scenario development work frame fulfils the specified requirements for traceability, comprehensiveness, ease of understanding, integration of multidisciplinary knowledge and applicability to a staged approach to siting.

Comparison of Numerical Tools Through Thermo-Hydro-Gas Transport Modeling for a Geological Repository in Boom Clay

Two numerical codes, TOUGH2 with the EOS5 module and CODE_BRIGHT, were compared in a confidence building effort for multiphase flow problems in a geological repository in Boom Clay, Belgium. A model study comparison between two codes was carried out through three numerical examples, including a one-dimensional hydro-gas (HG) case, a two-dimensional (2-D) axisymmetrical HG case with a constant hydrogen production rate, and a 2-D axisymmetrical thermo-hydro-gas (THG) case with time-varying heat and gas production rate. This numerical study of modeling the gas-driven migration of pore water under constant or time-dependent thermal conditions in two dimensions is based on the current Belgian multibarrier repository design for geological disposal of high-level waste. Comparison between numerical results demonstrates that the two numerical tools give sufficiently similar results in all three cases, thus providing evidence for the consistency of these tools in solving HG and THG problems in Boom Clay. The differences in the results obtained by the two modeling tools were also discussed.

A Thermoelectric-Conversion Power Supply System Using a Strontium Heat Source of High-Level Radioactive Nuclear Waste

A thermoelectric-conversion power supply system with radioactive strontium in high-level radioactive waste has been proposed. A combination of Alkali Metal Thermo-Electric Conversion (AMTEC) and a strontium fluoride heat source can provide a compact and long-lived power supply system. A heat source design with strontium fluoride pin bundles with Hastelloy cladding and intermediate copper has been proposed. This design has taken heat transportation into consideration, and, in this regard, the feasibility has been confirmed by a three-dimensional thermal analysis using Star-CD code. This power supply system with an electric output of 1MW can be arranged in a space of 50m2 and approximately 1.1m height and can be operated for 15 years without refueling. This compact and long-lived power supply is suitable for powering sources for remote places and middle-sized ships. From the viewpoint of geological disposal of high-level waste, the proposed power supply system provides a financial base for strontiumcesium partitioning. That is, a combination of minor-actinide recycling and strontium-cesium partitioning can eliminate a large part of decay heat in high-level waste and thus can save much space for geological disposal.

Modelling sorption data for the actinides Am(III), Np(V) and Pa(V) on montmorillonite

The retention characteristics of the bentonite near-field engineered barrier proposed in most of the concepts for the deep geological disposal of high-level waste and spent fuel are an important component in repository performance assessment studies. Montmorillonite generally constitutes 65 to 90 wt.% of the bentonite. Sorption edge measurements have been performed at trace concentrations for the actinides Am(III), Np(V) and Pa(V) on purified and conditioned SWy-1 montmorillonite under anoxic, carbonate free conditions. To the best of the author´s knowledge, this is the first time a sorption data set has been measured for 233Pa(V) uptake on montmorillonite. In some earlier work, the 2 site protolysis non-electrostatic surface complexation and cation exchange quasi mechanistic sorption model has been used to model the sorption edges measured for 11 metals with valencies between II and VI. From this study a linear correlation between strong site surface complexation constants and the corresponding hydrolysis constants was established: a Linear Free Energy Relation (LFER). The new measurements for 241Am(III), 239Np(V) and 233Pa(V) fit very well on this previously established LFER. Through the LFER, a chemically consistent picture emerges which explains quantitatively why some metals tend to exhibit very high sorption and others only moderate to weak sorption.

Activation energy for diffusion of helium in water-saturated, compacted Na-montmorillonite

It is important to clarify the migration behavior of hydrogen gas dissolved in water-saturated, compacted bentonite, which is a promising material for geologic disposal of high-level waste and TRU waste disposal. The diffusion coefficients of helium, which can be detected under extremely low background conditions, in water-saturated, compacted Na-montmorillonite were determined as a function of temperature by a transient diffusion method. The activation energies for diffusion of helium were then obtained. The activation energies were from 6.9 ± 4.8 to 19 ± 2.8 kJ mol − 1 and were regarded to be independent of dry density. The activation energies of helium in water-saturated Na-montmorillonite were roughly equal to those in bulk water, 14.9 kJ mol − 1, and in ice, from 11 to 13 kJ mol − 1. It is possible that helium diffuses not only in pore water but also in interlayer water.

Effects of Calcium Ions on the Sorption of Am(III) and Eu(III) onto Kaolinite in the Presence of Humic Acid

The sorption of actinides onto minerals depending on groundwater chemistry plays an important role in the safety aspects of geological disposal of high-level waste. The effects of Ca(II) on the sorption of Am(III) and Eu(III) onto kaolinite in the presence of humic acid (HA) were examined in this study. Distribution coefficients (Kd) of Am(III) and Eu(III), and the fractional adsorption (fHA) of HA on kaolinite were determined by a batch method under initial Ca(II) concentrations of 0 to 1.0 × 10-3 M at a constant ionic strength of 0.1 M (NaClO4) and pH region from 3.5 to 10 in an N2 atmosphere at 298 K. The Kd increased with increasing Ca(II) concentrations in regions higher than 1.0 X10-4 M and in the range of pH 7 to 10. In this pH region, fHA was also enhanced by introducing Ca(II). Concentrations higher than 1.0 × 10-4 M Ca(II) can be regarded as a bridge between kaolinite and HA. It is very likely that the increase in the adsorbed HA on kaolinite, where the HA includes very stable Am(III) and Eu(M) humates, results in an increase in the Am(III) and Eu(IH) distribution coefficients.

A Modest Proposal: A Robust, Cost-Effective Design for High-Level Waste Packages

ABSTRACTAn alternative waste-package design for the geological disposal of high-level waste (HLW) glass is presented. In conventional designs, a massive buffer of compacted bentonite is placed around a thick-walled, mild-steel overpack; in the revised design, a much thinner buffer is placed within a thin-walled, mild-steel overpack. This simple expedient eliminates certain performance concerns in existing waste-package designs, while not necessitating the study of any new materials. This integrated waste package (IWP) design has comparable release-rate performance as current package designs for HLW. In addition, the 1WP design requires far-less rock excavation, permits significantly higher temperatures for longer periods, leads to a 20-50% reduction in repository area, and is more cost efficient than previous designs.

What will be the engineered barriers for deep disposal of high level radioactive wastes in the future? : Plas, F; Jorda, M; Atabek, R; Robinet, J C; Hoorelbeke, J M; Bellet, J Proc 1st Annual Topical Meeting on High Level Radioactive Waste Management, Las Vegas, 8–12 April 1990V1, P650–658. Publ La Grange Park: ANS/ASCE, 1990

Two sealing approaches are currently being developed in France for deep geological disposal of high-level wastes. One is based on the use of swelling clay in order to restore the initial permeability of the host formation at all points of the disposal area. In the case of the second concept, granular materials are considered with an appropriate design of the disposal area and the local emplacement of impermeable dams in the drifts and at the bottom of access shafts to avoid any short-circuit between the disposal site and the biosphere. The characteristics and present limits of each concept are presented and discussed, leading to outline the main research and development future axes.

The Engineered Barrier System: Performance Issues

ABSTRACTThe engineered barrier system (EBS) for geologic disposal of high-level waste may typically consist of the waste solid, a container, and a porous backfill. Whether the surrounding rock is part of the EBS is arguable, but the properties of the surrounding rock strongly affect the EBS performance. The EBS functions and performance issue are addressed.

Evaluation of predictive models of temperature distribution in geological disposal of high-level waste: influence of thermal conductivity of formation : Palancar, M C; Aragon, J M; Luis, P; Diez, M Radioact Waste ManageV14, N3, 1990, P207–219

A theoretical model for the prediction of temperature distribution in a geological formation containing a cylinder of high-level waste is evaluated experimentally at small scale. The heat generation of the waste is simulated by electrical heating of a cylinder and the geological formation by a mass of compacted common salt. It has been observed that the model only gives good predictions if a temperature dependence of the thermal conductivity is assumed

1989 Joint International Waste Management Conference

Reviewed is the as-titled conference, held in October 23 to 28, 1989, in Kyoto, Japan, sponsored by American Society of Mechanical Engineers, Japan Society of Mechanical Engineers, and Atomic Energy Society of Japan, with other co-sponsoring societies. In the Conference, all the aspects of radioactive waste management were discussed, including policies and general strategies for waste management, solidification and incineration of low-, and intermediate-level wastes (LLW and ILW), shallow-land burial disposal of LLW/ILW and its safety assessment, decommissioning, storage and transportation of spent fuels, vitrification of high-level wastes (HLW), deep geologic disposal of HLW and its safety assessment by natural analogs, and partitioning and transmutation. The significance of the Conference is found in that the informations of Japan's waste management activities, which do not always reach audience in other part of the world, were conveyed in detail in the Conference. More papers were presented for LLW/ILW...

Performance Assessment of a High-Level-Waste Repository in Clay

ABSTRACTPerformance assessment studies have been undertaken on the geological disposal of high-level waste in a clay layer in the framework of the CEC project PAGIS. The methodology applied consists of two consecutive steps : a scenario and a consequence analysis. The scenario analysis has indicated that scenarios of normal evolution, of human intrusion, of climatic change, of secondary glaciation effects and of faulting should be evaluated. For the consequence analysis as well deterministic “best estimate” as stochastic calculations, including uncertainty, risk and sensitivity analyses, have been elaborated.The calculations performed show that most radionuclides decay to negligible levels within the first fewjneters of the clay barrier. Just a few radionuclides, 99Tc, 135Cs and 237Np with its daughter nuclides 233U and 229Th can eventually reach the biosphere. The maximum dose rates arising from the geological disposal of HLW, as evaluated by the “best-estimate” approach are about 10−11 Sv/y for river pathways. If the sinking of a water well into the 150 m deep aquifer layer in the vicinity of the repository is considered together with a climatic change, the maximum calculated dose rate rises to a value of 3×10−7 Sv/y. The maximum dose rates evaluated by stochastic calculations are about one order of magnitude higher due to the considerable uncertainties in the model parameters. In the case of the Boom clay the estimated consequences of a fault scenario are of the same order of magnitude as the results obtained for the normal evolution scenario. The maximum risk is estimated from the results obtained through stochastic calculations to be about 5×10−8 per year. The sensitivity analysis has shown that the effective thickness of the clay layer, the retention factors of Tc, Cs and Np, and the Darcy velocity in the aquifer are parameters which strongly influence the calculated dose rates.