Assessing the effect of radioactive waste glass dissolution on early-stage radionuclide migration using simplified geological repository Monte Carlo transport models

The vitrification of radioactive waste within glass and subsequent disposal within a geological disposal facility (GDF) requires a comprehensive understanding of the effect of glass dissolution on GDF performance. This paper aims to analyse the effect of both high-level and intermediate-level waste (HLW and ILW) glass dissolution source terms on radionuclide release into the geosphere just above the disposal vault (the ‘crown’). Radionuclide migration was simulated in GoldSim for HLW in either granite or clay host rocks with a bentonite buffer using carbon steel or copper canisters, whereas ILW simulations considered either granite or clay host rocks, in either bentonite buffer or cement backfill, using concrete or cast-iron canisters. Glass dissolution source terms were varied by coupling GoldSim and MATLAB to modify the initial, residual, and resumption dissolution rates of the glass or by applying the analytical GRAAL model to glass dissolution. HLW glass results indicate no preference of granite over clay host rocks for a given canister type but that a copper canister is preferable to steel. ILW results suggest that a granite–bentonite–cast-iron environment yields lowest crown activities with cast-iron preferable to concrete as the canister, bentonite preferable to cement as the buffer/backfill, and granite preferable to clay as the host rock. Varying glass dissolution source terms (initial, residual, and resumption dissolution rates) had an understood effect on radionuclide migration, although changes were arguably insignificant considering peak crown activity for both HLW and ILW.

A Multiple Investigation of Aqueous Eu(III)−Oxalate Complexes: the Reduction Coordination Number and Validation of Spectral Linear Correlation

Detailed information on the An(III) /Ln(III) complexation properties in solution is essential for separation chemistry and prediction of the potential for radionuclide migration from a nuclear waste repository into natural...

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.

Near field evolution of a spent fuel repository in an argillaceous rock formation and impact on radionuclide migration

<p>In August 2015, the German government approved the national programme for the responsible and safe management of spent nuclear fuel (SNF) and radioactive waste proposed by the Federal Ministry for the Environment, Nature Conservation, Building and Reactor Safety (BMU). The assumption is that about ~ 1 100 storage casks (10 500 tons of heavy metal) in the form of spent fuel assemblies will be generated in nuclear power plants and will have to be disposed. However, a decision on the disposal concept for high-level waste is pending and an appropriate solution has to be developed with a balance in multiple aspects. All potential types of host rocks, clay and salt stones as well as crystalline formations are under consideration. In the decision process, evaluation of the risk of different waste management options and scenarios play an enormous role in the discussion. Coupled physical and chemical processes taking place within the engineered barrier system of a repository for high-level radioactive waste will define the radionuclide mobility/retention and the possible radiological impact. The objective of this work is to assess coupled processes occurring in the near-field of a generic repository for spent nuclear fuel in a high saline clay host rock, integrating complex geochemical processes at centimetre-scale. The scenario considers that radionuclides can be released during a period of thousands of years after full saturation of the bentonite barrier and the thermal phase.</p><p>Transport parameters and the discretization of the system, are implemented in a 2D axisymmetric geometry. The multi-barrier system is emplaced in clay and a solubility limited source term for the selected radionuclides is assumed. Kinetics and chemical equilibria reactions are simulated using parameters obtained from experiments. Additionally, porosity changes due to mineral precipitation/dissolution and feedback on the effective diffusion coefficient are taken into account. Protonation/deprotonation, ion exchange reactions and radionuclide inner-sphere sorption is considered.</p><p>Numerical simulations show, that, when the canister corrosion starts, the redox potential decreases, magnetite precipitates and H<sub>2</sub> is formed. Furthermore, the aqueous concentration of Fe(II) increases due to the presence of magnetite. By considering binding to montmorillonite via ion exchange reactions, the bentonite acts as a sink for Fe(II). Additionally, magnetite forms a chemical barrier offering significant sorption capacity for many radionuclides. Finally, a decrease of porosity in the bentonite/canister interface leads to a further deceleration of radionuclide migration. Due to the complexity of reactive transport processes in saline environments, benchmarking of reactive transport models (RTM) is important also to build confidence in those modelling approaches. Development of RTM benchmark procedures is part of the iCROSS project (Integrity of nuclear waste repository systems - Cross-scale system understanding and analysis) funded by both the Helmholtz Association and the Federal Ministry of Education and Research (BMBF).</p><p> </p>

Ultramicrobacteria from Nitrate- and Radionuclide-Contaminated Groundwater

The goal of the present work was to investigate the physicochemical and radiochemical conditions and the microbial diversity in groundwater collected near the Lake Karachai (Russia), which was formerly used for the disposal of liquid radioactive waste, to isolate the dominant bacteria, and to determine their taxonomy and the physiological characteristics responsible for their adaptation to this environment. Groundwater samples contained high concentrations of acetate, oxalate, nitrate, and sulfate, as well as radionuclides. High-throughput sequencing and analysis of the clone libraries revealed lower microbial diversity in the most strongly contaminated groundwater and a predominance of bacteria of the genera Polynucleobacter, Pusillimonas, Candidatus Pelagibacter, and of the candidate phylum Parcubacteria; these groups include species with an ultra small cell size. Archaeal sequences in the libraries belonged to ammonium oxidizers of the phylum Thaumarchaeota and methanogens of the phylum Euryarchaeota. Pure cultures of obligate and facultative ultramicrobacteria belonging to the genera Chryseobacterium, Microbacterium, Salinibacterium, Pusillimonas, Roseomonas, and Janibacter were isolated from water samples. In genomes of Pusillimonas and Roseomonas strains the genes associated with nitrate reduction, resistance to heavy metals and metalloids were revealed. Several isolates are able to participate in the geochemical process of nitrate conversion to N2 using acetate; this results in decreasing redox potential, which in turn may stimulate radionuclide reduction and decrease radionuclide migration in groundwater.