Some Important Mechanisms and Processes in the Near Field of the Swedish Repository for Spent Nuclear Fuel

1992 ◽  
Vol 294 ◽  
Author(s):  
Ivars Neretnieks
Keyword(s):  
Molecular Diffusion ◽  
Spent Nuclear Fuel ◽  
Dominant Role ◽  
Near Field ◽  
Water Flow Rate ◽  
Crystalline Rock ◽  
Diffusive Transport ◽  
Actual Design ◽  
Natural Analogues ◽  
And Performance

ABSTRACTIn repositories for nuclear waste there are many processes that will be instrumental in damaging the canisters and releasing the nuclides. Based on experiences from studies of the performance of repositories and of an actual design, the major mechanisms influencing the integrity and performance of a repository are described and discussed. The paper addresses only conditions in crystalline rock repositories. The low water flow rate in fractures and channels plays a dominant role in limiting the interaction between water and waste. Molecular diffusion in the backfill and rock matrix, as well as in the mobile water, is an important transport process, but actually limits the exchange rate because diffusive transport is slow. Solubility limits of both waste matrix and of individual nuclides are also important. Complicating processes include alpha-radiolysis, which may change the water chemistry in the near-field. The sizes and locations of water flowpaths and damages in the canisters considerably influence the release rates. Uncertainties in data are large. Nevertheless the system is very robust in the sense that practically no reasonably conceivable assumptions or data will lead to large nuclide releases. Several natural analogues have been found to exhibit similarities with a waste repository and help to validate concepts and to increase our confidence that all major issues have been considered.

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.

The Spread of Pollutants from Harbour Sludge Depots

1984 ◽  
Vol 16 (3-4) ◽  
pp. 623-633
Author(s):  
M Loxham ◽  
F Weststrate
Keyword(s):  
Time Scales ◽  
Molecular Diffusion ◽  
Near Field ◽  
Parameter Analysis ◽  
Migration Patterns ◽  
Long Time ◽  
Dilution Effects ◽  
Short Time ◽  
Harbour Sludge

It is generally agreed that both the landfill option, or the civil techniques option for the final disposal of contaminated harbour sludge involves the isolation of the sludge from the environment. For short time scales, engineered barriers such as a bentonite screen, plastic sheets, pumping strategies etc. can be used. However for long time scales the effectiveness of such measures cannot be counted upon. It is thus necessary to be able to predict the long term environmenttal spread of contaminants from a mature landfill. A model is presented that considers diffusion and adsorption in the landfill site and convection and adsorption in the underlaying aquifer. From a parameter analysis starting form practical values it is shown that the adsorption behaviour and the molecular diffusion coefficient of the sludge, are the key parameters involved in the near field. The dilution effects of the far field migration patterns are also illustrated.

scholarly journals The boundary condition for the vertical velocity and its interdependence with surface gas exchange

2017 ◽  
Author(s):  
Andrew S. Kowalski
Keyword(s):  
Boundary Condition ◽  
Vertical Velocity ◽  
Molecular Diffusion ◽  
Classical Mechanics ◽  
Vertical Motion ◽  
Diffusive Transport ◽  
Eddy Diffusivities ◽  
Air Stream ◽  
Upward Transport ◽  
Definition Of

Abstract. The law of conservation of linear momentum is applied to surface gas exchanges, employing scale analysis to diagnose the vertical velocity (w) in the boundary layer. Net upward momentum in the surface layer is forced by evaporation (E) and defines non-zero vertical motion, with a magnitude defined by the ratio of E to the air density, as w = E⁄ρ. This is true even right down at the surface where the boundary condition is w0 = E⁄ρ0. This Stefan flow velocity implies upward transport of a non-diffusive nature that is a general feature of the troposphere but is of particular importance at the surface, where it assists molecular diffusion with upward gas migration (of H2O, e.g.) but opposes that of downward-diffusing species like CO2 during daytime. The definition of flux-gradient relationships (eddy diffusivities) requires rectification to exclude non-diffusive transport, which does not depend on scalar gradients. At the microscopic scale, the role of non-diffusive transport in the process of evaporation from inside a narrow tube – with vapour transport into an overlying, horizontal air stream – was described long ago in classical mechanics, and is routinely accounted for by chemical engineers, but has been neglected by scientists studying stomatal conductance. Correctly accounting for non-diffusive transport through stomata, which can appreciably reduce net CO2 transport and marginally boost that of water vapour, should improve characterizations of ecosystem and plant functioning.

Digital autoradiography on C-14-labelled PMMA impregnated rock samples using the BeaverTM

MRS Advances ◽  
2018 ◽  
Vol 3 (21) ◽  
pp. 1161-1166 ◽  
Author(s):  
Mikko Voutilainen ◽  
Juuso Sammaljärvi ◽  
Eveliina Muuri ◽  
Jérôme Donnard ◽  
Samuel Duval ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Spent Nuclear Fuel ◽  
Rock Sample ◽  
Crystalline Rock ◽  
Imaging Plate ◽  
Heterogeneous Distribution ◽  
Heterogeneous Structures ◽  
In Situ Diffusion

In Finland and Sweden the KBS-3 concept has been chosen for the disposal of spent nuclear fuel in crystalline rock. Recent experiments have shown that heterogeneity of rock may play a major role in the transport of radionuclides. Autoradiographic methods have been proven to be able to assist the characterization of heterogeneous structures. In this study we tested a novel filmless autoradiographic device called BeaverTM which applies a micro patterned gaseous detector in order to quantitatively map beta emissions from C-14 atoms. The studied samples were impregnated with C-14-labelled methylmethacrylate (C-14-MMA) and polymerized to C-14-PMMA with thermal initiator. The BeaverTM was then used to determine the spatial distribution of the C-14-PMMA by measuring the C-14 emissions. The porosity is determined from the amount of C-14-PMMA in the rock sample and results were compared to ones from phosphor imaging plate autoradiography. The resulting images show a heterogeneous distribution of porosity which arises from the different minerals. The samples were chosen from three sites that have been used recently for in situ diffusion experiments: Olkiluoto (Finland), Äspö (Sweden) and Grimsel (Switzerland).

scholarly journals IDA-Pay: a secure and efficient micro-payment system based on Peer-to-Peer NFC technology for Android mobile devices

2012 ◽  
Vol 8 (4) ◽  
pp. 117 ◽  
Author(s):  
Luca Mainetti ◽  
Luigi Patrono ◽  
Roberto Vergallo
Keyword(s):  
Mobile Devices ◽  
Near Field ◽  
Operating Mode ◽  
Peer To Peer ◽  
Payment System ◽  
Third Party ◽  
Payment Systems ◽  
Shopping Experience ◽  
And Performance ◽  
System Effectiveness

The evolution of modern mobile devices towards novel Radio Frequency (RF) capabilities, such as Near Field Communication, leads to a potential for delivering innovative mobile services, which is still partially unexplored. Mobile proximity payment systems are going to enhance the daily shopping experience, but the access to payment security resources of a mobile device (e.g. the “Secure Element”) by third party applications is still blocked by smartphone and Operating System manufacturers. In this paper, the IDA-Pay system is presented, an innovative and secure NFC micro-payment system based on Peer-to-Peer NFC operating mode for Android mobile phones. It allows to deliver mobile-to-POS micro-payment services, bypassing the need for special hardware. A validation scenario and a system evaluation are also reported to demonstrate the system effectiveness and performance.

scholarly journals Reactive transport calculations to evaluate sulphide fluxes in the near-field of a SF/HLW repository

2019 ◽  
Vol 98 ◽  
pp. 10005
Author(s):  
Marek Pękala ◽  
Paul Wersin ◽  
Veerle Cloet ◽  
Nikitas Diomidis
Keyword(s):  
Reactive Transport ◽  
Spent Nuclear Fuel ◽  
Near Field ◽  
Opalinus Clay ◽  
High Level Waste ◽  
Waste Containment ◽  
Geological Repository ◽  
High Level ◽  
Reducing Bacteria ◽  
Hlw Repository

Radioactive waste is planned to be disposed in a deep geological repository in the Opalinus Clay (OPA) rock formation in Switzerland. Cu coating of the steel disposal canister is considered as potential a measure to ensure complete waste containment of spent nuclear fuel (SF) and vitrified high-level waste (HLW) or a period of 100,000 years. Sulphide is a potential corroding agent to Cu under reducing redox conditions. Background dissolved sulphide concentrations in pristine OPA are low, likely controlled by equilibrium with pyrite. At such concentrations, sulphide-assisted corrosion of Cu would be negligible. However, the possibility exists that sulphate reducing bacteria (SRB) might thrive at discrete locations of the repository’s near-field. The activity of SRB might then lead to significantly higher dissolved sulphide concentrations. The objective of this work is to employ reactive transport calculations to evaluate sulphide fluxes in the near-field of the SF/HLW repository in the OPA. Cu canister corrosion due to sulphide fluxes is also simplistically evaluated.

Notating Action-Based Music

2011 ◽  
Vol 21 ◽  
pp. 65-72 ◽  
Author(s):  
Juraj Kojs
Keyword(s):  
Direct Relationship ◽  
Dominant Role ◽  
Music Notation ◽  
Enactive Cognition ◽  
Graphic Scores ◽  
Physical Gestures ◽  
And Performance

The author discusses the notation of action-based music, in which physical gestures and their characteristics, such as shape, direction and speed (as opposed to psychoacoustic properties such as pitch, timbre and rhythm), play the dominant role in preserving and transferring information. Grounded in ecological perception and enactive cognition, the article shows how such an approach mediates a direct relationship between composition and performance, details some action-based music notation principles and offers practical examples. A discussion of tablature, graphic scores and text scores contextualizes the method historically.

Key Issues Influencing the Performance of Near-Field Barriers

1992 ◽  
Vol 294 ◽  
Author(s):  
P.W. Tasker ◽  
S.J. Wisbey ◽  
C.B. Boyle
Keyword(s):  
Near Field ◽  
Performance Assessments ◽  
Gas Generation ◽  
Human Environment ◽  
Factors Affecting ◽  
Control Factors ◽  
Natural Analogues ◽  
Physical Barriers ◽  
Key Issues ◽  
And Control

ABSTRACTIn developing a national strategy for the disposal of radioactive wastes, each country will consider isolation options that are appropriate to the types of waste that are produced. The options are developed in response to specific national regulatory requirements, and thus will focus on different aspects of performance. However, there are a number of technical concerns that are common to all programmes. The major issues concerning the behaviour of the chemical and physical barriers in the near field of a radioactive waste repository are discussed in this paper.The description of key issues has been divided into the following categories: barrier design, barrier evolution, scientific understanding through modelling, and validation of performance. The near-field barriers are selected and designed to provide appropriate radionuclide containment and control. Factors affecting the evolution of these barriers, such as container degradation and gas generation, determine the subsequent release of radionuclides to the human environment. Modelling repository evolution is therefore an integral feature of performance assessments, and issues such as the treatment of inhomogeneities and non-equilibrium chemistry may need to be addressed. However, the use of mathematical and computer models implies a requirement for validation. The use of demonstration experiments and natural analogues builds confidence in the predictions of repository performance models, and provides a degree of validation for otherwise inaccessible timescales.

New insight studies of the secondary phase formation under repository conditions

MRS Advances ◽  
2020 ◽  
Vol 5 (11) ◽  
pp. 539-547
Author(s):  
N. Rodríguez-Villagra ◽  
L.J. Bonales ◽  
J. Cobos
Keyword(s):  
Raman Spectroscopy ◽  
Spent Nuclear Fuel ◽  
Near Field ◽  
Aqueous Media ◽  
Secondary Phase ◽  
Ambient Atmosphere ◽  
Secondary Phases ◽  
Γ Radiation ◽  
Radiation Fields ◽  
Groundwater Environment

ABSTRACTIn a deep geological repository (DGR) scenario, uranium oxidized in aqueous systems will be stabilized as UO22+ (hexavalent uranium), as a consequence of tetravalent uranium oxidation by radiolytic byproducts. Uranyl cationic species (UO22+) in different speciation forms are expected to be found at the whole pH range conditions. The importance of UO22+ lies in its potential incorporation of trace radioelements onto secondary uranyl phases. In view of the difficulty of U chemistry in natural groundwater, it is necessary to improve speciation assessment techniques so as to understand chemical processes. Raman spectroscopy has been shown as a powerful tool to analyze the speciation of various actinyl (UO22+,NpO2+ and PuO22+) and to determine the distribution of those elements which are more likely to be stable in a near-field groundwater environment. Therefore, the aim of this work is to follow UO22+ changes as a consequence of γ radiation in aqueous media under DGR conditions, and to understand the behavior of UO22+ as a function of aqueous media, which help to understand and predict the potential precipitation of the solid phases formed. In this work, the use of Raman spectroscopy adapted to the empirical analysis of different nuclear applications for initial uranium concentrations 0.04M at ambient atmosphere is shown, i.e. as monitoring tool for UO22+ precipitation as a function of pH, studying UO2(NO3)2·6H2O stability in aqueous solutions representative of groundwater, in particular at ionic strength I = 0.02 – 0.4 M and pH from 7 to 13.2; and to evaluate the effect of γ radiation fields. At 10−4-10-3 M of radiolytically formed H2O2 concentration, the amount of uranium in solution decreased, as a results of secondary phases precipitation. The results obtained will be useful to the performance assessment studies of the Spent Nuclear Fuel (SNF) stored in DGRs. The work performed provides a partial picture of secondary phase formations, as a result of corrosion of SNF in a DGR.

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