Transient Diffusion from the Near-Field, A 3-D Model

1991 ◽  
Vol 257 ◽  
Author(s):  
A. Bengtsson ◽  
B. Grundfelt ◽  
H. Widén
Keyword(s):  
Source Term ◽  
Near Field ◽  
Three Dimensional ◽  
Bentonite Clay ◽  
Spent Fuel ◽  
Radionuclide Migration ◽  
Transient Transport ◽  
Mass Transport Rate ◽  
D Model ◽  
Low Solubility

ABSTRACTA study of near-field radionuclide migration is presented. The study [1] has been performed in the context of the SKB91 study which is a comprehensive performance assessment of disposal of spent fuel. The objective of the present study has been to enable the assessment of which nuclides can be screened out because they decay to insignificant levels already in the near-field of the repository.A numerical model has been used which describes the transient transport of radionuclides through a small hole in a spent fuel canister imbedded in bentonite clay into a fracture in the rock outside the bentonite. Calculations for more than twenty nuclides, nuclides with both high and low solubility, have been made. The effect of sorption in the bentonite backfill is included. Materials data for bentonite where taken from [2]. The size of the penetration hole was assumed to be constant up to the time when the calculations were terminated, 500 000 years after the deposition. The mass transport rate is controlled by diffusion. The model is three dimensional.This paper describes the geometry of the modelled system, the assumptions concerning the transport resistances at the boundary conditions, the handling of the source term and obtained release curves.

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

2020 ◽  
Author(s):  
Vanessa Montoya ◽  
Orlando Silva ◽  
Emilie Coene ◽  
Jorge Molinero ◽  
Renchao Lu ◽  
...  
Keyword(s):  
Ion Exchange ◽  
Radioactive Waste ◽  
Nuclear Fuel ◽  
Reactive Transport ◽  
Spent Nuclear Fuel ◽  
Near Field ◽  
Spent Fuel ◽  
Exchange Reactions ◽  
Radionuclide Migration ◽  
High Level

<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>

The Near-Field Transport Code Tullgarn and its Use in Performance Assessment

1992 ◽  
Vol 294 ◽  
Author(s):  
Patrik Sellin ◽  
Nils Kjellbert
Keyword(s):  
Performance Assessment ◽  
Near Field ◽  
Steel Corrosion ◽  
List Type ◽  
Spent Fuel ◽  
Radionuclide Migration ◽  
Transport Code ◽  
Damaged Zone ◽  
Chain Decay ◽  
Resistance Network Model

ABSTRACTThe near-field radionuclide migration code Tullgarn has been developed for performance assessment purposes. As a part of the PROPER-code package it has been successfully applied in the SKB 91 safety analysis.The features and processes included in the code are:- Radioactive chain decay- Different canister failure mechanisms (copper corrosion from sulphide attack, steel corrosion, internal overpressure and initially defective canisters) - Spent fuel dissolution. The model is based on the assumption that the dissolution rate is proportional to the α-dose rate- Transport calculations are done with a resistance-network model. Tullgarn calculates the stationary release of radionuclides from a defect in the canister through the buffer and out into a fracture in the rock or up to the damaged zone under the deposition tunnel.Tullgarn can be used as a stand-alone model for near-field release calculations or as a submodel in an integrated assessment. In the SKB 91 analysis, Tullgarn gave the source term to the far-field model.

Modelling Radionuclide Mobility of Spent Fuel in a Deep Geological Repository Located in a Clay Bedrock

2009 ◽  
Author(s):  
Lara Duro ◽  
Abel Tamayo ◽  
Jordi Bruno ◽  
Aurora Marti´nez-Esparza
Keyword(s):  
Source Term ◽  
Spent Nuclear Fuel ◽  
Near Field ◽  
Radioactive Decay ◽  
Secondary Phase ◽  
Diffusive Transport ◽  
Deep Geological Repository ◽  
Spent Fuel ◽  
Geological Repository ◽  
Source Term Model

Source term models are widely used to assess the behaviour of spent nuclear fuel after final disposal. However, most models do not take into account some phenomena which are expected to control the transport of radionuclides through the near field. Some uncertainties arise from this fact, thus making it difficult to obtain proper simulations of radionuclide behaviour in the near field. In this work, we have used a compartmental code to build up an integrated source term model in an attempt to overcome the abovementioned drawbacks. The model developed takes into account radiolytically-mediated matrix dissolution, radioactive decay chains, diffusive transport, and retardation by sorption and secondary phase precipitation, among other processes. In addition, this model has been used to estimate radionuclide mobility from spent fuel located in a conceptual clay geological repository.

Near-Field Modelling in the Safety Assessment SR-Can

2008 ◽  
Vol 1107 ◽  
Author(s):  
C. Fredrik Vahlund
Keyword(s):  
Numerical Modelling ◽  
Input Data ◽  
Safety Assessment ◽  
Spent Nuclear Fuel ◽  
Fractured Rock ◽  
Near Field ◽  
Spent Fuel ◽  
Radionuclide Migration ◽  
Field Modelling ◽  
Swelling Clays

AbstractSpent nuclear fuel from the Swedish energy programme will be stored in an underground repository situated in saturated fractured rock at a depth of approximately 500 m. This paper describes numerical simulations of radionuclide migration in the near-field (consisting of a canister filled with spent fuel and an engineered system backfilled with swelling clays) for the recently completed safety assessment SR-Can [1] using a Matlab / Simulink code. Handling of input data for the models from the site descriptive programme from on-going investigations at two candidate sites and the numerical modelling concept are discussed.

scholarly journals Imaging of bi-anisotropic periodic structures from electromagnetic near-field data

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Dinh-Liem Nguyen ◽  
Trung Truong
Keyword(s):  
Inverse Scattering ◽  
Maxwell Equations ◽  
Field Data ◽  
Periodic Structures ◽  
Near Field ◽  
Scattering Problem ◽  
Three Dimensional ◽  
Inverse Scattering Problem ◽  
Factorization Method ◽  
Unique Determination

AbstractThis paper is concerned with the inverse scattering problem for the three-dimensional Maxwell equations in bi-anisotropic periodic structures. The inverse scattering problem aims to determine the shape of bi-anisotropic periodic scatterers from electromagnetic near-field data at a fixed frequency. The factorization method is studied as an analytical and numerical tool for solving the inverse problem. We provide a rigorous justification of the factorization method which results in the unique determination and a fast imaging algorithm for the periodic scatterer. Numerical examples for imaging three-dimensional periodic structures are presented to examine the efficiency of the method.

Three-Dimensional Finite-Difference Time-Domain Method Modeling of Nanowire Optical Probe

2014 ◽  
Vol 602-605 ◽  
pp. 3359-3362
Author(s):  
Chun Li Zhu ◽  
Jing Li
Keyword(s):  
Finite Difference ◽  
Time Domain ◽  
Finite Difference Time Domain ◽  
Incident Light ◽  
Near Field ◽  
Three Dimensional ◽  
Polarization Direction ◽  
Near Field Imaging ◽  
Difference Time ◽  
Field Imaging

In this paper, output near fields of nanowires with different optical and structure configurations are calculated by using the three-dimensional finite-difference time-domain (3D FDTD) method. Then a nanowire with suitable near field distribution is chosen as the probe for scanning dielectric and metal nanogratings. Scanning results show that the resolution in near-field imaging of dielectric nanogratings can be as low as 80nm, and the imaging results are greatly influenced by the polarization direction of the incident light. Compared with dielectric nanogratings, metal nanogratings have significantly enhanced resolutions when the arrangement of gratings is perpendicular to the polarization direction of the incident light due to the enhancement effect of the localized surface plasmons (SPs). Results presented here could offer valuable references for practical applications in near-field imaging with nanowires as optical probes.

A Numerically Efficient Method for Analysis of Very Large Articulated Floating Structures

1998 ◽  
Vol 42 (03) ◽  
pp. 174-186
Author(s):  
C. J. Garrison
Keyword(s):  
Hydrodynamic Interaction ◽  
Near Field ◽  
Three Dimensional ◽  
Computational Effort ◽  
Floating Structure ◽  
Complete Structure ◽  
Field Interaction ◽  
Floating Structures ◽  
Computing Effort ◽  
The Individual

A method is presented for evaluation of the motion of long structures composed of interconnected barges, or modules, of arbitrary shape. Such structures are being proposed in the construction of offshore airports or other large offshore floating structures. It is known that the evaluation of the motion of jointed or otherwise interconnected modules which make up a long floating structure may be evaluated by three dimensional radiation/diffraction analysis. However, the computing effort increases rapidly as the complexity of the geometric shape of the individual modules and the total number of modules increases. This paper describes an approximate method which drastically reduces the computational effort without major effects on accuracy. The method relies on accounting for hydrodynamic interaction effects between only adjacent modules within the structure rather than between all of the modules since the near-field interaction is by far the more important. This approximation reduces the computational effort to that of solving the two-module problem regardless of the total number of modules in the complete structure.

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