Safety Of Geological Disposal Research Articles

Modelling of failure and fracture development of the Callovo-Oxfordian claystone during an in-situ heating experiment associated with geological disposal of high-level radioactive waste

To ensure the safety of geological disposal of high-level radioactive waste, in-situ experiments have been carried out to examine the behavior of rocks in underground research laboratories (URLs). At the Meuse/Haute-Marne URL in France, the French National Radioactive Waste Management Agency (Andra) has been assessing the Callovo-Oxfordian claystone (COx) as potential host rock of geological disposal by subjecting the COx to in-situ heating mimicking exothermic radioactive waste. Results of the in-situ experiments are used to validate and bolster the numerical simulators for predicting the thermo-hydromechanically (THM) coupled behavior of the COx. The numerical simulators are, however, yet to be tested for predicting the failure and fracture development of the COx during heating, which is of paramount importance to the safety of the geological disposal. In this research, we modelled a recently carried out in-situ experiment at the Meuse/Haute-Marne URL using the TOUGH-FLAC simulator to predict the failure and fracture development of the COx during heating. The objectives are to examine the effects of (i) the weak bedding planes, (ii) the softening rate of matrix/weak plane strengths, and (iii) the stiffness anisotropy of the COx on the development of shear and tensile fractures during heating. Results show that considering failure along the weak planes enabled accurate predictions of fracture development. Also, fracture development intensified at a softening rate beyond a threshold level and the geometry of fractures was significantly affected by the stiffness anisotropy. These results will help boost the reliability of the safety and performance assessment of geological disposal in claystone.

Composition‐dependent leaching behavior in ion‐irradiated borosilicate glasses: A corrosion mechanism study

AbstractEvaluating the corrosion behavior of borosilicate glass after irradiation holds vital importance for the safe geological disposal of high‐level radioactive waste. This study examined the leaching properties of three kinds of sodium‐borosilicate (RNa2O‒B2O3‒KSiO2, denoted as “NBS”) glasses with the same R but varying K under 5 MeV Xe‐ion radiation to decipher the correlation between the corrosion mechanism and glass composition. After Xe‐ion radiation, an increase in [BO3] units was observed, indicative of the glass network depolymerization. Irradiated glasses exhibited a more significant change in [BO3] units over the leaching time compared to their pristine counterparts. There is a strong correlation between the initial dissolution rates of pristine glasses, the K value, and the proportion of Na. Additionally, the initial Si dissolution rate of the NBS glasses has been accelerated by heavy ion irradiation. For the same R value over the glass series, the initial Si dissolution rates in ternary borosilicate glasses change at similar rates after irradiation. This study concluded that the variation trend in the initial dissolution rate of Si and Na differs under ion radiation.

What the Flux? – Water-Rock-Microbe Interactions and Crustal Gases in the Deep Subsurface

The deep, dark fracture zones of the continental crust host a fascinating interplay between water, rocks, and microbes, resulting in the production and consumption of gases, including methane, volatile organic compounds (VOCs), and hydrogen. Various geological factors influence the formation and release of these crustal gases, including the local rock type with its concentration of radioactive elements and carbon, temperature, and the connectivity and dynamics of fracture systems with each other and to the surface. To understand the formation, accumulation, and release of crustal gases, methodologies of hydrogeochemistry, biogeochemistry, and isotope geochemistry can be employed. Sample collection from drill holes and mines, coupled with on-line monitoring of gas flux rate and composition, provides important data. Furthermore, the integration of molecular biological methods enhances our understanding of the water-rock-microbe interactions that shape the deep subsurface gas realm. Crustal gases have crucial implications for life in extreme environments, including those outside of our planet Earth, but potentially also pose significant challenges to drilling, mining, and their environmental impact. Moreover, crustal gases hold relevance for the energy sector, contributing to both the long-term safety of geological disposal of nuclear waste, carbon footprint of geothermal wells, and the exploration of hydrogen as a sustainable energy resource.

Disposal of high-level radioactive waste in crystalline rock: On coupled processes and site development

Safe disposal of high-level radioactive nuclear waste (HLW) is crucial for human health and the environment, as well as for sustainable development. Deep geological disposal in sparsely fractured crystalline rock is considered one of the most favorable methods for final disposal of HLW. Extensive research has been conducted worldwide and many countries have initiated their own national development programs for deep geological disposal. Significant advancements of national programs for deep geological disposal of HLW in crystalline rock have been achieved in Sweden and Finland, which are currently under site development stage, focusing on detailed site characterization, repository construction, and post-closure safety analysis. Continued research and development remain important in the site development stage to ensure long-term safety of the HLW disposal repository. This work presents an overview and discussion of the progress as well as remaining open scientific issues and possibilities related to site development for safe disposal of HLW in crystalline rock. We emphasize that developing a comprehensive and convergent understanding of the coupled thermal, hydraulic, mechanical, chemical and biological (THMCB) processes in fractured crystalline rock remains the most important yet challenging topic for future studies towards safe disposal of HLW in crystalline rock. Advancements in laboratory facilities/techniques and computational models, as well as available comprehensive field data from site developments, provide new opportunities to enhance our understanding of the coupled processes and thereby repository design for safe geological disposal of HLW in crystalline rock.

Current status of the geological disposal programme and an overview of the safety case at the pre-siting stage in Japan

In Japan, high-level radioactive waste and specific low-level radioactive waste which includes long-lived radionuclides are planned to be disposed of in the geological formations at depths greater than 300 ​m. The disposal site will be selected through a stepwise site investigation process that consists of a Literature Survey, Preliminary Investigation, and Detailed Investigation phases. In October 2020 a Literature Survey was launched in Japan at two municipalities in Hokkaido for the first time since NUMO initiated a nationwide call for volunteer municipalities in 2002, and the outcomes are currently being compiled. To enhance the public’s understanding of how to implement safe geological disposal in Japan based on the latest scientific knowledge and technology, NUMO, as the implementing organisation, developed and published a safety case for geological disposal at the pre-siting stage. This safety case provides multiple lines of arguments and evidence to demonstrate the feasibility of the geological disposal and a basic structure for a safety case that will be applicable to any potential sites in Japan. The safety case also presented some R&D challenges to enhance the technical confidence of the project, including the R&D topics related to rock mechanics. This report presents the current status of the geological disposal programme in Japan, together with the status of the Literature Survey phase and an overview of the NUMO safety case.

Precipitation sequence of fracture-filling calcite in fractured granite and changes in the fractionation process of rare earth elements and yttrium

This study has focused on the paragenetic sequence, and variation in rare earth elements with yttrium (REY) composition, of fracture-filling calcite in the Toki Granite in the Mizunami area, central Japan. The morphological, chemical, and isotopic characteristics of the calcite and chemistry of fluid inclusions reveal that the calcite in the Toki Granite can be differentiated into four discrete generations: Calcite I (oldest) to Calcite IV (most recent). The precipitation history of calcite reflects the changes in the hydrogeochemical regime of paleo-groundwaters, controlled by the evolution of groundwater by seawater infiltration associated with marine transgression and surface water infiltration associated with marine regression and uplift. The post-Archean average shale-normalized REY patterns in each generation of calcite show no significant Ce anomaly, negative Eu anomaly, and a light REY (LREY)-depleted pattern dominates. These features are also common to the Toki Granite. The consistency of the features in each generation of calcite indicates that REY was supplied from the Toki Granite by water-rock interaction. The lack of a Ce anomaly in the calcite demonstrates that groundwaters have maintained reducing conditions during the calcite precipitation. However, the fractionation of LREY and heavy REY in each generation of the calcite is more pronounced than in the granite. The fractionation process in the paleo-groundwaters from which each generation of calcite precipitated closely relates to the systematic variation of carbonate complex in the REY series and/or pH in palaeo-groundwater. The findings of this study will be important for assessing the long-term safety of geological disposal of high-level radioactive waste.

Pyrite oxidation by nitrate and nitrite in sodium bicarbonate solution under anoxic and abiotic conditions

Pyrite reactivity with nitrate and nitrite was assessed in long-term batch tests to assess its possible oxidation in anoxic conditions at pH 8.5, at room temperature and atmospheric pressure. This was done in the frame of compatibility studies of nitrate-containing radioactive waste with a pyrite-containing clay host rock for geological disposal. Abiotic pyrite suspensions were prepared under inert atmosphere in 15 mM bicarbonate medium, as this simulates the inorganic carbon and pH conditions in the pore water of Boom Clay, which is a potential host rock for geological disposal in Belgium. Two forms of pyrite powder were used, formed via different genetic pathways and exhibiting a different morphology, namely pyrite obtained by crushing a large crystal cluster and pyrite extracted from Boom Clay by flotation. The reactivity of these two pyrite forms with nitrate and nitrite is reported and compared. Overall, after 2–2.5 years under abiotic conditions and inert atmosphere, no significant reaction between crushed pyrite and nitrate was detected, while a very limited reaction was observed between Boom Clay pyrite and nitrate. Between pyrite and nitrite, which is known to be more reactive than nitrate, a slow reaction took place for both forms of pyrite, with no significantly higher reactivity with the Boom Blay pyrite. The variability between the replicates of Boom Clay pyrite were also larger than for crushed pyrite. Overall, nitrate and nitrite induced a very limited, if any, oxidation reaction of the pyrite powders. These observations are important in assessing the safety of geological disposal of nitrate-containing radioactive waste.

Assessment of sensor performance in the context of geological radwaste disposal—A first case study in the Belgian URL HADES

Monitoring in the context of geological disposal of radioactive waste is considered to play a relevant role in the stepwise implementation of the disposal. Such monitoring however implies particular conditions for the sensing equipment to be deployed. The experience gathered with experimental setups in underground research laboratories (URLs) is very valuable to improve the reliability of sensors envisaged for this monitoring. In Belgium, many experimental setups have been implemented in the HADES URL. With its construction started in 1980, it is the longest operational facility in a clay formation in Europe that is dedicated to investigate the feasibility and safety of geological disposal of radioactive waste. Technical experts use it to develop and test technologies for constructing, operating and closing a waste repository in a deep clay formation. Scientists conduct large-scale experiments to assess the safety of disposal in poorly indurated clay. As a result, thousands of sensors have been installed in the HADES URL over the past four decades. Many of them are regularly providing measurement data up to now. To obtain an insight in the factors that determine their performance, a research programme has been launched to assess the sensor performance of the HADES monitoring setups one by one. This paper describes the methodology for this assessment. It is based on a systematic screening of each individual sensor according to a set of indicators. As a first case, the CLIPEX instrumented setup was selected. It was installed more than 20 years ago to monitor the clay host rock response to gallery construction works. The assessment provided the performance data of the different sensor types, which allowed to make a performance appraisal of the respective sensor types. Based on the results of this first case, the assessment methodology will be applied to the other setups to extend the performance database of the different sensor types.

Boom Clay pore water geochemistry at the Mol site: Experimental data as determined by in situ sampling of the piezometers

In many countries, geological disposal in clay is the primary option for the final disposal of high-level radioactive waste and spent fuel. In Belgium, the Boom Clay is studied as a potential host rock for the disposal of radioactive waste. In this frame, the pore water geochemistry of the Boom Clay is an essential feature for evaluating the performance and long term safety of geological disposal in a host rock because: (1) it determines the speciation and solubility of radionuclides, and (2) it is required as initial or boundary condition to evaluate the interactions with other repository components, i.e. the different waste forms and the engineered barrier system (e.g. overpack materials, backfill), as well as to evaluate the influence of the repository construction (e.g. oxidation, interaction with the liner if present). In this study, we report a unique, first of its kind data set of the in situ sampled pore waters of the Boom Clay at the Mol site, covering a depth interval of 65 m. The thorough screening of the collected data for potential geochemical perturbations and sampling artifacts led to a reference data set of 195 pore waters complemented with 39 in situ gas and pH analyses. A statistical analysis was applied to this dataset and a reference pore water composition was derived for the Boom Clay pore water at the Mol site. The reported ranges of the elemental concentrations reflect pore water natural variations at formation scale, whereas in situ sampled pCO2 and pH values are limited to the depth interval enveloped by HADES URL at 196–200 m below sea level. Thus, uncertainty remains on the variations of the pCO2 and pH at the scale of Boom Clay Formation. The reference pore water chemistry dataset will help to update current geochemical pore water chemistry model. At the same time, the presented data set can improve geochemical modelling strategies developed for low permeability sediments, like argillites and shales, where direct pore water sampling is technically difficult.

A tentative useful-for-all definition of “safety” in the context of radioactive waste disposal

Abstract. Most, if not all, national programmes for radioactive waste management pledge their overall commitment to safety or – in the case of radioactive waste disposal – to long-term safety. Therefore, it may be somewhat surprising to find that the term “safety” is hardly defined in these programs. The same holds for some of the core international guidance literature on the deep geological repository (DGR) “safety case” concept. With respect to stakeholder concern over the safety of geological disposal, it seems, however, advisable to seek common ground in the understanding of the idea of “safety”. Hotzel and Schröder (2018) reviewed the most relevant international guidance literature for explicitly or implicitly provided definitions of “safety” in the context of radioactive waste disposal. Based on this study – and on the finding that a practical, useful-for-all definition of “safety” is not provided in the scanned literature – they developed a tentative dictionary-style definition of “safety” that is suitable for everyday use in the DGR context. In the current contribution I embed, expand and update the 2018 study at both ends: As an enhanced introduction to the 2018 study, I lay out a basic concept of “sound” glossary definitions, namely glossary definitions being both practical and correct (and what this means). The thesis is that sound glossary definitions can facilitate mutual understanding between different stakeholder groups. As an update to the actual proposal for the definition of “safety” from the Hotzel and Schröder (2018) paper, that was presented and discussed at the Waste Management Conference 2018, I review the latest international guidance literature and the stakeholder concerns raised at the 2018 conference in order to present a revised definition. As a seed of discussion, it may help to eventually expose possible mismatches in the base assumptions of safety experts and other stakeholders and thereby support meaningful communication.

Experimental study on gas permeability of granite close to natural joint

The metal corrosion, organic degradation and waste radiolysis in the geological disposal repository of high-level radioactive waste (HLW) will lead to gas generation and form additional pressure, which will drive the nuclide migration and thereby influence the long-term safety of geological disposal. It is crucial to study the gas permeability of the host rock for the geological disposal of HLW. Therefore, the gas permeability of some granite samples close to a natural joint in the Beishan pre-selected area for China’s geological disposal project was studied in this paper. Firstly, the effective gas permeability under different confining pressures, different gas pressures and different directions was measured by the quasi-steady method. Secondly, the absolute gas permeability and slip factor were obtained according to Klinkenberg’s law. Finally, the effect of confining pressure, direction and distance to the joint surface on gas permeability were analyzed. The gas seepage in granite is found to conform to Klinkenberg’s law. The absolute gas permeability is gradually decreased with the increase of the confining pressure. The gas permeability of granite is isotropic and homogeneous because the intrinsic permeability measured in different directions and at different distances from the joint is found to be similar. The above results can provide references for the performance assessment of the surrounding rock of the HLW disposal repository.

Adsorption of iodine from aqueous solutions by aminosilane-grafted mesoporous alumina

Adsorptive removal of iodine from aqueous waste streams is an efficient way of minimizing the environmental footprints associated with radioactive species, however, developing highly efficient, durable, adsorbents is key to this technique’s success. Here, we investigated the iodine adsorption performance of aminosilane-grafted mesoporous alumina using various aminosilanes, including 3-Aminopropyl-triethoxysilane (APS), N-methylaminopropyl-trimethoxysilane (MAPS), and 3-N,N-dimethylaminopropyl-trimeth-oxysilane (DMAPS). The successful incorporation of amine moieties within the mesopores of alumina was confirmed by FTIR and elemental analysis. From the iodine adsorption tests, Al-APS, Al-MAPS and Al-DMAPS exhibited capture capacities of 124, 223 and 241 mg/g, respectively, while the bare alumina had a capacity of 107 mg/g. Assessing the iodine adsorption front on the Al-DMAPS sample revealed sharp adsorption kinetics from 0 to 4 h followed by a gradual increase from 4 to 24 h, indicating that the aminated Al2O3 had high affinity towards the contaminate. Increasing the Al-DMAPS loading from 30 to 50 wt% revealed only a 4% enhancement in iodine adsorption capacity, implying that the lower aminosilane concentration was optimal. The equilibrium uptake and kinetics of iodine adsorption over aminosilane-grafted mesoporous alumina were represented by Langmuir and pseudo-second-order models, respectively. Meanwhile, the leach test results revealed that amine grafting moderately enhanced the material’s ability to permanently trap iodine for safe geological disposal, however, further waste consolidation is required to improve the iodine retention in these adsorbents.

Safer-than: Making Nuclear Waste Disposal More Familiar

ABSTRACT Geological disposal has been proposed as the solution for managing the most radioactive nuclear wastes. These wastes stay hazardous for periods better measured in geological rather than human time. This challenges the capacity of science to accurately predict the future evolution and safety of geological disposal facilities. Thus nuclear waste management organisations, such as the Finnish Posiva, utilise a broad range of historical and cultural evidence and discursive tactics to support their scientific argumentation for the long-term safety of geological disposal. Posiva, for instance, makes its safety case by anchoring its disposal project in broader international scientific settings and engineering practices; by giving the abstract disposal concept form and tangible through mundane objects and spaces and in so doing presenting geological disposal as an extension of the everyday; and finally by juxtaposing the underground and the aboveground to depict the underground as more predictable and knowable, essentially as ‘safer than.’ By invoking and imagining geological disposal through the familiar, Posiva negotiates the limits of scientific knowledge, and undermines the nuclearity of geological disposal to make its case for the implementability, manageability and safety of geological disposal and, crucially, to present geological disposal as the only available option for long-term nuclear waste management.

Natural and Anthropogenic Analogues for High-Level Nuclear Waste Disposal Repositories: A Review

ABSTRACTProjects involving deep geological disposal of nuclear waste are unique in that predictive models of long-term safety often involve geological timeframes. This manuscript provides a review of natural and anthropogenic analogues for high-level nuclear waste disposal in a deep geological repository. We also occasionally highlight analogues that have been used for low- and intermediate-level waste. Most studies define natural analogues as either naturally occurring or anthropogenic systems. In this paper, we distinguish between natural analogues and anthropogenic analogues because the latter generally provide non-technical (anecdotal) illustrations of concepts and processes for the safety case, whereas the former can provide technical and quantitative information. In addition, natural analogues can provide information over geological time scales (millions of years) and spatial scales (kilometers), whereas anthropogenic analogues provide information over a much more limited time scale (hundreds or thousands of years). Regardless of the definition, analogue studies provide one of the multiple lines of evidence intended to increase confidence in the safe geological disposal of high-level nuclear waste. They are deemed necessary because they complement the experiments that are carried out over a period of months or years. They also provide a way to validate numerical long-term safety assessment models with information and data covering geological time scales and spatial scales.The first part of this review describes the analogue concept. The second and third parts provide examples of natural and anthropogenic analogues for engineered barrier systems and natural barriers. Part four describes analogues for complex coupled transport processes. Finally, we discuss general and specific areas of future research.A concerted effort should be made to ensure that there is a transfer of data from the complex, natural analogue field studies to simplistic models which, by necessity, are used to evaluate the long-term safety of deep geological repositories. Field analogue studies should be planned to interface with laboratory experiments and, ultimately, with in situ field experiments, when the final repository site is selected. This will involve using natural analogue data in a quantitative way to support the deep geological repository safety case.

Towards best possible safety – current regulatory research for the German site selection process for high-level radioactive waste disposal

Abstract. The Federal Office for the Safety of Nuclear Waste Management (BASE – Bundesamt für die Sicherheit der nuklearen Entsorgung) is the German federal regulatory authority for radioactive waste disposal. It supervises the German site selection process and is responsible for the accompanying public participation. Task related research is an integral part of BASE's activities. The projects MessEr and übErStand compiled the state-of-the-art science and technology regarding surface based exploration methods suitable for addressing the criteria and requirements specified in the German Site Selection Act. The results support BASE to review and define the surface-based exploration programs to be executed by the national implementer BGE (Bundesgesellschaft für Endlagerung mbH). To support BASE in reviewing the application of the exclusion criteria “active fault zones” according to the Site Selection Act, the project KaStör reviewed the current knowledge on active faults and fault zones in Germany and recommends methodological approaches to date and identify the activity of faulting. For the time being, the Site Selection Act defines 100 ∘C as a draft limit on the temperature at the outer surface of a repository container for all host rocks. The project Grenztemperatur studied the temperature dependency of the different thermal-hydraulic-mechanical-chemical/biological (THMC/B) processes according to available features-events-processes (FEP) catalogues for rock salt, clay stone, and crystalline rock and describes ways to defining host rock specific maximum temperatures based on specific disposal and safety concepts. Safety oriented weighting of different criteria and comparison of different potential regions and sites are key challenges during the siting process. The project MABeSt studied and reviewed methodological approaches to this weighting and comparison problem with special emphasis on multi criteria analysis (MCA) and multi criteria decision analysis (MCDA). A key requirement for safe geological disposal of nuclear waste is barrier integrity. The project PeTroS performed the first triaxial flow-through experiments on natural rock salt samples at disposal relevant p−T conditions and studied potential percolation mechanisms of fluids within rock salt. The data substantiate that the minimum stress criterion and/or the dilatancy criterion are the prime “percolation thresholds” in rock salt. The research results support BASE in fulfilling its tasks as national regulator according to state-of-the-art science and technology and are also relevant to other stakeholders of the siting process.

Effect of Cations on Interlayer Water Dynamics in Cation-Exchanged Montmorillonites Studied by Nuclear Magnetic Resonance and X-ray Diffraction Techniques

To ensure the safety of geological disposal of radioactive wastes, understanding the migration behavior of radioactive species in montmorillonite clays has become increasingly important. However, there are still many indeterminate aspects about the influence of cation species and humidity on the interlayer water dynamics and swelling properties of montmorillonite clays. In this work, by using XRD and 1H-NMR spin-lattice relaxation rate (1/T1) techniques, we aimed to clarify the relation between water layer thickness and molecular dynamics in various cation-exchanged montmorillonites (Mn+-MMTs; Mn+ = Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+, Ba2+, La3+, Sm3+, and Lu3+) in the temperature range of -40 °C to 50 °C. XRD measurements showed that layer thickness in Mn+-MMTs increased with increasing hydrated water according to the order of structure-breaking chaotropic K+, Rb+, Cs+ ions, structure-making kosmotropic and borderline Li+, Na+, Ba2+ ions, divalent ions, and trivalent lanthanide ions. It was found t...

An active microbial community in Boom Clay pore water collected from piezometers impedes validating predictive modelling of ongoing geochemical processes

Safe geological disposal of radioactive waste requires a detailed understanding of the geochemical conditions present in the host formation. Consequently, analysis of pore water is essential, as its composition determines among others, the speciation and solubility of radionuclides. Boom Clay is considered a potential host formation in Belgium. Although the elemental composition of Boom Clay pore water is relatively well known, the real mechanisms controlling the pCO2 (g) and the pH, the two most important parameters, are not completely understood. Currently, these parameters are under investigation based only on inorganic chemistry. Borehole waters of different Underground Research Facilities (URF) harbour an active microbial community; however, their possible impact on the geochemistry of Boom Clay pore water extracted from piezometers is not yet examined. The present study discusses the evolution of the geochemistry and the microbial community in the pore water from the piezometers around the PRACLAY gallery of the HADES URF during 7 years after installation of the piezometers. Overall, the elemental composition seemed to vary during the first 4 years, while afterwards it remained quite stable. However, the pCO2 values varied substantially over time, while the pCH4 increased in all filters. The presence of an active microbial community in the piezometers, could explain why experimental pCO2 – pH data do not correspond to the data obtained by predictive modelling, hampering validation of current predictive models of the ongoing geochemical processes. Moreover, the nature of the sampling equipment and the sampling procedure possibly stimulated the present microbial community, resulting in increased methane production rates. To improve predictive modelling, microbial processes are needed to be taken into account together with inorganic geochemistry considered at the current stage, which necessitates detailed microbial and geochemical monitoring in future studies.

The Single Deposit Scale Scenario at Granite Area in A Long-Term Safety Assessment of A Radioactive Waste Repository

Deep geological disposal is internationally accepted as a feasible and safe way to dispose of high-level radioactive waste (HLW). Long-term safety assessment of a radioactive waste repository is vital to building confidence in safety of geological disposal of radioactive waste. Many countries with nuclear power industries have carried out this work. The aim of this paper is to study the influence by a fracture intersecting the deposition hole or excavation damaged zone at repository located in granite area. Furthermore, it is also of interest for addressing important aspects of the internal evolution of the canister. This paper analysed two representative scenarios for the single deposit scale scenario at granite area. These results show that the influence of the fracture zone is enormous. The convective transport mass is far more than the diffusive transport mass. Moreover, the leading path of convective is the fracture zone. The transport mass which across the granite boundary is very little. These results also a convenient case for the construction of final geological repositories in China

Characterization and degradation of a polyaryl ether based superplasticizer for use in concrete barriers in deep geological repositories

Superplasticizers are important additives used in concrete barriers in geological waste repositories. Superplasticizers have been a major concern in the long-term assessments of safe geological disposal for radioactive waste since superplasticizers and their degradation products can act as complexing ligands and thereby increase the mobility of radionuclides. In this work a new type of superplasticizer, based on a polyaryl ether polymer, has been characterized. It was found that the superplasticizer combines the structural features of polycarboxylate ether based superplasticizers and sulfonated naphthalene-formaldehyde based superplasticizers and that it contains organophosphate charged groups. A novel method for evaluating the rate of degradation of the superplasticizer under alkaline conditions was elaborated and the degradation products and rate constant of the process was determined. The results demonstrate that degradation occurs rapidly compared to the typical lifetime of a repository.

Dissolution Behavior of Lead Borate Glass under Simulated Geological Disposal Conditions

ABSTRACTDevelopment of an iodine immobilization technique that can fix radioactive iodine in waste form for a long period and constrain its leaching into pore water is necessary in order to secure the long-term safety of geological disposal of transuranic (TRU) waste.Lead borate glass vitrified at a low temperature is regarded as one of the promising immobilization materials of Iodine-129 which will be removed from spent AgI filters generated from reprocessing plants and may have a significant effect on long term safety of geological disposal.Leaching experiments in bentonite-equilibrium water have been conducted to understand the lead borate glass dissolution behaviors in possible geological disposal conditions. Boron dissolved with the highest rate in all types of the solutions and was regarded as an index element to represent the glass dissolution rate. On the other hand, lead dissolved with a far slower rate. The chemical species and possible precipitating minerals of lead were examined by a geochemical calculation code for typical underground water. Altered glass surfaces were investigated by SEM, TEM and XRD. XRD analysis showed that the main constituent phase of the altered layer was hydrocerussite, Pb3(CO3)2(OH)2, that was predicted by the geochemical simulation as well.