scholarly journals Diffusive Transport of Dissolved Gases in Potential Concretes for Nuclear Waste Disposal

2021 ◽  
Vol 13 (18) ◽  
pp. 10007
Author(s):  
Elke Jacops ◽  
Quoc Tri Phung ◽  
Lander Frederickx ◽  
Séverine Levasseur
Keyword(s):  
Diffusion Coefficients ◽  
Host Rock ◽  
Dissolved Gases ◽  
Spent Fuel ◽  
Gas Generation ◽  
Boom Clay ◽  
Barrier Materials ◽  
Diffusion Technique ◽  
Geological Repository ◽  
Intermediate Level Radioactive Waste

In many countries, the preferred option for the long-term management of high- and intermediate level radioactive waste and spent fuel is final disposal in a geological repository. In this geological repository, the generation of gas will be unavoidable. In order to make a correct balance between gas generation and dissipation by diffusion, knowledge of the diffusion coefficients of gases in the host rock and the engineered barriers is essential. Currently, diffusion coefficients for the Boom Clay, a potential Belgian host rock, are available, but the diffusion coefficients for gases in the engineered concrete barriers are still lacking. Therefore, diffusion experiments with dissolved gases were performed on two concrete-based barrier materials considered in the current Belgian disposal concept, by using the double through-diffusion technique for dissolved gases, which was developed in 2008 by SCK CEN. Diffusion measurements were performed with four gases including helium, neon, methane and ethane. Information on the microstructure of the materials (e.g., pore size distribution) was obtained by combining N2-adsorption, mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and water sorptivity measurements. A comparison was made with data obtained from cement-based samples (intact and degraded), and the validity of existing predictive models was investigated.

Process Model of Gas-Related Phenomena Associated With a Proposed L/ILW Repository in Switzerland

1997 ◽  
Vol 506 ◽  
Author(s):  
Rainer Senger ◽  
Peter Gribi ◽  
Markus Hugi ◽  
Piet Zuidema
Keyword(s):  
Radioactive Waste ◽  
Host Rock ◽  
Process Model ◽  
Structural Integrity ◽  
Gas Production ◽  
Pore Waters ◽  
Gas Generation ◽  
Free Gas ◽  
Intermediate Level Radioactive Waste ◽  
National Cooperative

ABSTRACTNAGRA (National Cooperative for the Disposal of Radioactive Waste) has been investigating the feasibility for siting a low- and intermediate-level radioactive waste (L/ILW) repository in subsurface geologic environments. The design of the L/ILW repository consists of a horizontally accessed cavern system located beneath Wellenberg in the low-permeability unit of Valanginian marl. One of the concerns for the safety analysis is the effect of gas generation (primarily hydrogen) from anaerobic corrosion and degradation of waste material. The development of a free gas phase and the concomitant pressure buildup can result in the displacement of contaminated pore waters from the repository. Moreover, excess buildup of pressures in the repository can impact the structural integrity of the engineered barrier and of the surrounding host rock. For the investigation of the gas-related phenomena in a proposed L/ILW repository, a process model was developed to simulate the different performance periods of the repository which include: (1) construction/operation period of the repository resulting in desaturation of the host rock caused by pressure decline and ventilation in the cavern, and (2) post-closure period after backfilling and sealing of the caverns resulting in resaturation of the host rock and of the cavern, and in the release of waste-generated gas. Period (1) takes into account degassing of dissolved gas (methane) in the formation water due to the pressure decline around the cavern, and period (2) considers dissolution of free gas caused by the pressure increase associated with the resaturation and with the gas production in the cavern.

scholarly journals The Dependency of Diffusion Coefficients and Geometric Factor on the Size of the Diffusing Molecule: Observations for Different Clay-Based Materials

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-16 ◽  
Author(s):  
Elke Jacops ◽  
Marc Aertsens ◽  
Norbert Maes ◽  
Christophe Bruggeman ◽  
Rudy Swennen ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Effective Diffusion Coefficient ◽  
Tritiated Water ◽  
Effective Diffusion ◽  
Geometric Factor ◽  
Opalinus Clay ◽  
Dissolved Gases ◽  
Exponential Relationship ◽  
Boom Clay

In order to investigate in more detail the relation between the size of diffusing molecules and their diffusion coefficients (and geometric factors), diffusion experiments with gases of different size and tritiated water (HTO) have been performed on different clayey samples (Boom Clay, Eigenbilzen Sands, Opalinus Clay, Callovo-Oxfordian Clay, and bentonite with different dry densities). We observed that, for unreactive gases in clayey materials, the effective diffusion coefficient varies with the size of the diffusing molecule and this variation can be described by an exponential or a power law function. The variation of the geometric factor can also be described by an exponential function. The observed experimental relations can be used to estimate diffusion coefficients; by measuring experimentally in clay the effective diffusion coefficient of two unreactive dissolved gases with a different size, the diffusion coefficients of other dissolved gases (with a size in between the two measured gases) can be estimated by using the fitted exponential relationship.

Spent fuel dissolution in Belgian Supercontainer conditions: source term and compatibility

2012 ◽  
Vol 1475 ◽  
Author(s):  
K. Lemmens ◽  
Th. Mennecart ◽  
C. Cachoir
Keyword(s):  
Host Rock ◽  
Spent Nuclear Fuel ◽  
Spent Fuel ◽  
Boom Clay ◽  
Surface Areas ◽  
Diffusion Controlled ◽  
Radiological Safety ◽  
And Performance ◽  
Radionuclide Release

ABSTRACTIn the frame of the Safety and Feasibility Case 1 development, the Belgian agency for radioactive waste (ONDRAF/NIRAS) has to demonstrate that the geological disposal of spent nuclear fuel in the Boom Clay host rock following the Supercontainer design provides sufficient radiological safety in the long term. This safety relies on the containment of the radionuclides by the overpack, the limitation of radionuclide release from the waste matrix, the diffusion controlled transport of the radionuclides, and their low solubility and sorption on the Boom Clay host rock. This paper presents an evaluation of the main processes considered for the limitation of radionuclide release by the Spent Fuel in Supercontainer conditions, characterized by the presence of a concrete buffer and hyperalkaline pore water. We present a description of the main expected processes with their potential impact on the fuel alteration mechanisms, and potential reference fuel matrix alteration rates and effective fuel surface areas for use in safety and performance assessment models.

scholarly journals SiLiF Neutron Counters to Monitor Nuclear Materials in the MICADO Project

Sensors ◽  
2021 ◽  
Vol 21 (8) ◽  
pp. 2630
Author(s):  
Luigi Cosentino ◽  
Quentin Ducasse ◽  
Martina Giuffrida ◽  
Sergio Lo Meo ◽  
Fabio Longhitano ◽  
...  
Keyword(s):  
Radioactive Waste ◽  
Detector Response ◽  
Nuclear Materials ◽  
Spent Fuel ◽  
Neutron Detectors ◽  
Intermediate Level Radioactive Waste ◽  
Eu Project ◽  
Interim Storage ◽  
Waste Drums

In the framework of the MICADO (Measurement and Instrumentation for Cleaning And Decommissioning Operations) European Union (EU) project, aimed at the full digitization of low- and intermediate-level radioactive waste management, a set of 32 solid state thermal neutron detectors named SiLiF has been built and characterized. MICADO encompasses a complete active and passive characterization of the radwaste drums with neutrons and gamma rays, followed by a longer-term monitoring phase. The SiLiF detectors are suitable for the monitoring of nuclear materials and can be used around radioactive waste drums possibly containing small quantities of actinides, as well as around spent fuel casks in interim storage or during transportation. Suitable polyethylene moderators can be exploited to better shape the detector response to the expected neutron spectrum, according to Monte Carlo simulations that were performed. These detectors were extensively tested with an AmBe neutron source, and the results show a quite uniform and reproducible behavior.

Determination of gas diffusion coefficients in saturated porous media: He and CH4 diffusion in Boom Clay

2013 ◽  
Vol 83-84 ◽  
pp. 217-223 ◽  
Author(s):  
Elke Jacops ◽  
Geert Volckaert ◽  
Norbert Maes ◽  
Eef Weetjens ◽  
Joan Govaerts
Keyword(s):  
Porous Media ◽  
Diffusion Coefficients ◽  
Gas Diffusion ◽  
Saturated Porous Media ◽  
Boom Clay

The Effect of Bromide on Oxygen Yields in Homogeneous α-radiolysis

MRS Advances ◽  
2017 ◽  
Vol 2 (13) ◽  
pp. 711-716 ◽  
Author(s):  
Lovisa Bauhn ◽  
Christian Ekberg ◽  
Patrik Fors ◽  
Kastriot Spahiu
Keyword(s):  
Radiation Field ◽  
Spent Nuclear Fuel ◽  
Radiation Doses ◽  
Deep Geological Repository ◽  
Spent Fuel ◽  
Mass Spectrometric Measurement ◽  
Α Decay ◽  
Geological Repository ◽  
Dissolved Ions ◽  
Dissolved Hydrogen

ABSTRACTIn a scenario where ground water enters a canister for spent nuclear fuel in a deep geological repository, the presence of dissolved ions in the water could possibly influence the fuel dissolution due to effects on radiolysis yields. One species of particular interest in this context is bromide, which has a proven ability to scavenge hydroxyl radicals much faster than molecular hydrogen does. As a result, bromide could inhibit the beneficial effect of dissolved hydrogen, which has been shown in γ-radiolysis experiments. However, already a few hundred years after repository closure, α-decay starts to dominate in the radiation field from the spent fuel. Hence, the effects of α-radiolysis are expected to govern the fuel dissolution over the geological timeframes of the repository. In the present work, α-radiolysis experiments have been performed to determine the effect of bromide ions on the yield of hydrogen peroxide by mass spectrometric measurement of its decomposition product oxygen. The use of high activity 238Pu solutions has made it possible to study this effect during pure α-radiolysis from a homogeneously distributed radiation field. To simulate deep bedrock repository conditions, and to minimize the influence of in-leaking O2 from air, the studies were performed using graphite sealed stainless steel autoclaves with an initial atmosphere of 10 bar H2. The results show that addition of 1 mM Br- to the solution gives no significant effect on the O2 yield for radiation doses up to 2 MGy. This lack of effect is most likely explained by the limited radical escape yields from radiation tracks in pure α-radiolysis.

The Integrated Project NF-PRO: Recent Advances in European Research on the Near-Field System

2007 ◽  
Author(s):  
Alain Sneyers ◽  
Bernd Grambow ◽  
Pedro Herna´n ◽  
Hans-Joachim Alheid ◽  
Jean-Franc¸ois Aranyossy ◽  
...  
Keyword(s):  
European Commission ◽  
Near Field ◽  
Framework Programme ◽  
European Research ◽  
Spent Fuel ◽  
Field System ◽  
Geological Repository ◽  
Integrated Project ◽  
High Level ◽  
Sixth Framework Programme

The Integrated Project NF-PRO (Sixth Framework Programme by the European Commission) investigates key-processes in the near-field of a geological repository for the disposal of high-level vitrified waste and spent fuel. The paper discusses the project scope and content and gives a summary overview of advances made by NF-PRO.

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