scholarly journals Intrinsic formation of nanocrystalline neptunium dioxide under neutral aqueous conditions relevant to deep geological repositories

2015 ◽  
Vol 51 (7) ◽  
pp. 1301-1304 ◽  
Author(s):  
Richard Husar ◽  
René Hübner ◽  
Christoph Hennig ◽  
Philippe M. Martin ◽  
Mélanie Chollet ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Neptunium Dioxide ◽  
Deep Geological Repositories ◽  
Aqueous Conditions ◽  
New Formation

Simple dilution of an aqueous Np(iv) bicarbonate solution triggers the intrinsic formation of nanocrystalline neptunium dioxide (NpO2). This new formation route could be a likely scenario in the repository and disposal of radioactive waste.

Performance Assessment Modelling for the Geological Siting Regions for the L/ILW and HLW Repositories in the Context of the Swiss Site Selection Plan

2011 ◽  
Author(s):  
Andreas Poller ◽  
Ju¨rg W. Schneider ◽  
Piet Zuidema ◽  
Johannes Holocher ◽  
Gerhard Mayer
Keyword(s):  
Radioactive Waste ◽  
Nuclear Energy ◽  
Geological Conditions ◽  
Numerous Test ◽  
Three Stages ◽  
Deep Geological Repositories ◽  
National Cooperative ◽  
Stage 1 ◽  
Radionuclide Release ◽  
Energy Law

In Switzerland, the Nuclear Energy Law requires the disposal of all radioactive waste in deep geological repositories. The procedure for selecting the repository sites is defined in the Sectoral Plan for Deep Geological Repositories and consists of three stages. In Stage 1, the National Cooperative for the Disposal of Radioactive Waste (Nagra) proposed geological siting regions based on criteria relating to safety and engineering feasibility. As part of Stage 2, Nagra has to select at least one site within each siting region, to carry out a provisional safety analysis for each site and a safety-based comparison of the sites. In order to achieve these objectives, the state of knowledge of the geological conditions in the siting regions has to be sufficient to perform the provisional safety analyses. In October 2010, Nagra submitted a report which documents Nagra’s technical-scientific assessment of this precondition, based on a comprehensive list of processes and parameters relevant for safety and engineering feasibility. A part of this assessment consists of test calculations for the provisional safety analyses. This paper summarizes how the numerous test calculations have been identified, how the concepts of radionuclide release from the repository are implemented into numerical codes and how input data and results are organized in order to ensure transparency and traceability.

Assessment of Operational-Phase Safety of Deep Geological Repositories for Radioactive Waste

2004 ◽  
pp. 3540-3545 ◽  
Author(s):  
Ian G. McKinley ◽  
Kenichi Kaku ◽  
Fiona B. Neall ◽  
Hideki Kawamura ◽  
Hidekazu Asano
Keyword(s):  
Radioactive Waste ◽  
Operational Phase ◽  
Deep Geological Repositories

scholarly journals Deciphering porosity clogging at barrier interfaces in deep geological repositories for radioactive waste

2021 ◽  
Vol 1 ◽  
pp. 181-182
Author(s):  
Mara I. Lönartz ◽  
Jenna Poonoosamy ◽  
Yuankai Yang ◽  
Naila Ait-Mouheb ◽  
Guido Deissmann ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Transport Properties ◽  
Reactive Transport ◽  
Time Lapse ◽  
Mineral Dissolution ◽  
Microscopy Imaging ◽  
Deep Geological Repositories ◽  
Set Up ◽  
High Level

Abstract. The disposal of spent nuclear fuels and high-level radioactive wastes in deep geological repositories represents one of the greatest scientific-technical and societal challenges of our times. Most disposal concepts rely on a multibarrier system, consisting of a combination of engineered materials, geotechnical and geological barriers to provide a safe containment of the radioactive waste to protect humans and the environment against dangers arising from ionizing radiation. A reliable safety assessment of a deep geological repository over assessment time scales of several 100 000 years requires a profound and comprehensive understanding of the complex coupled physical (thermal, hydraulic, mechanical), chemical and biogeochemical (THM/CB) processes that govern the long-term evolution of the repository system. As a result of thermal and chemical gradients at the interfaces of different components and materials of the multi-barrier system (e.g. interfaces between metallic waste containers and bentonite backfill or between structural concrete and clay host rock), mineral dissolution and precipitation reactions are promoted; thus the (local) porosity, the volume filled with gas and/or water, can increase or decrease leading to changes in the macroscopic transport properties of the respective media. Although a reduction of the porosity (porosity clogging) appears to be desirable to inhibit radionuclide migration, it can also be detrimental, particularly in the case of gas pressure build-up due to canister corrosion or bacterial activity. So far, porosity clogging at barrier interfaces and associated consequences on solute or gas transport remain poorly understood; currently used mathematical descriptions of porosity clogging in reactive transport codes usually fail to capture respective experimental observations (Chagneau et al., 2015; Deng et al., 2021). In this context, we are developing a “lab-on-a-chip” set-up, which combines time lapse optical microscopy imaging and in operando Raman spectroscopy (Poonoosamy et al., 2019, 2020) to determine (i) whether complete clogging is possible and permanent, (ii) which parameters control the porosity clogging and (iii) which changes in transport properties of porous media are induced due to porosity clogging. Our approach comprises micronized counterdiffusion experiments with in situ visualization and monitoring of the evolution of mineralogy and microstructure/pore architecture with time. Complementary pore scale modelling will be used to derive key relationships that describe changes in transport properties due to mineral precipitation-induced porosity clogging. This approach will help to improve reactive transport codes and their predictive capabilities thus enhancing confidence and reduce uncertainties in long-term predictions, leading to more realistic descriptions of the evolution of complex repository systems.

Mechanical and SCC Behavior of an API5L Steel Casing Within the Context of Deep Geological Repositories for Radioactive Waste

2015 ◽  
Author(s):  
F. Bumbieler ◽  
S. Necib ◽  
J. Morel ◽  
D. Crusset ◽  
G. Armand
Keyword(s):  
Radioactive Waste ◽  
Host Rock ◽  
Mechanical Load ◽  
Early Stage ◽  
High Yield ◽  
General Corrosion ◽  
Short Term ◽  
In Situ Experiments ◽  
Deep Geological Repositories

Andra, the French national radioactive waste management agency, is in charge of studying the possibility of disposal of High Level activity Wastes (HLW) in deep geological repositories. The concept of HLW cells consists of horizontal micro-tunnels of about 0.7 m in diameter, equipped with a steel casing. In order to ensure the reliability of the casing, particularly with respect to Stress Corrosion Cracking (SCC), several in-situ experiments dedicated to the analysis of its short term mechanical and corrosion behavior have been performed at Andra’s Underground Research Laboratory (URL) as well as in surface laboratory. Reduced and full scale in-situ experiments consisting of equipping boreholes parallel to the major horizontal stress (σH) with instrumented steel tubing, have been performed to analyze the mechanisms involved in the casing/rock interface. The main characteristics of the short term mechanical load applied by the rock have been determined from local strain and convergence measurements. Although in-situ stress is isotropic in the section of boreholes parallel to σH, measurements exhibit a strongly anisotropic load. SCC experiments conducted on different steel grades, in contact with the clay host rock containing CO2/H2 revealed that general corrosion is the main type of corrosion expected for steel casings. However, the selected steel casing must have a sufficiently high yield strength (above 400 MPa) to reduce the risk of early stage plasticity due to host rock anisotropic convergence and thus to overcome SCC. API5LX65 steel seems to meet both mechanical and corrosion requirements, therefore being likely the appropriate material for the manufacture of the casing.

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