A review of near-field mass transfer in geologic disposal systems

AbstractA primary purpose of performance assessment of geologic repositories for radioactive waste is to predict the extent to which radioactive species are released from the waste solids and are transported through geologic media to the environment. Reliable quantitative predictions must be made of rates of release of radionuclides from the waste into the rock, transport through the geologic media, cumulative release to the accessible environment, and maximum concentrations in ground water and surface water. Here we review theoretical approaches to making the predictions of near-field release from buried waste solids, which provide the source terms for far-field release. The extent to which approaches and issues depend on the rock media and on regulatory criteria is discussed.

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A Study of Steady Buoyancy-Driven Dissipative Micropolar Free Convection Heat and Mass Transfer in a Darcian Porous Regime with Chemical Reaction

Nonlinear Analysis Modelling and Control ◽

10.15388/na.2007.12.2.14707 ◽

2007 ◽

Vol 12 (2) ◽

pp. 157-180 ◽

Cited By ~ 24

Author(s):

O. Anwar Bég ◽

R. Bhargava ◽

S. Rawat ◽

H. S. Takhar ◽

Tasweer A. Bég

Keyword(s):

Mass Transfer ◽

Velocity Field ◽

Heat And Mass Transfer ◽

Chemical Reaction ◽

Reaction Rate ◽

Near Field ◽

Packed Bed ◽

Darcy Number ◽

Reaction Model ◽

Chemical Reaction Rate

In the present paper we examine the steady double-diffusive free convective heat and mass transfer of a chemically-reacting micropolar fluid flowing through a Darcian porous regime adjacent to a vertical stretching plane. Viscous dissipation effects are included in the energy equation. Assuming incompressible, micro-isotropic fluid behaviour the transport equations are formulated in a two-dimensional coordinate system (x, y) using boundary-layer theory. The influence of the bulk porous medium retardation is modeled as a drag force term in the translational momentum equation. Transformations render the conservation equations into dimensionless form in terms of a single independent variable, η, transverse to the stretching surface. A simplified first order homogenous reaction model is also used to simulate chemical reaction in the flow. Using the finite element method solutions are generated for the angular velocity field, translational velocity field, temperature and species transfer fields. The effects of buoyancy, porous drag and chemical reaction rate are studied. Chemical reaction is shown to decelerate the flow and also micro-rotation values, in particular near the wall. Mass transfer is also decreased with increasing chemical reaction rate. Increasing Darcy number is shown to accelerate the flow. Applications of the study include cooling of electronic circuits, packed-bed chemical reactors and also the near field flows in radioactive waste geo-repositories.

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CFD Simulation of Human Coughs and Sneezes: A Study in Droplet Dispersion, Heat, and Mass Transfer

Volume 7: Fluid Flow, Heat Transfer and Thermal Systems, Parts A and B ◽

10.1115/imece2010-37331 ◽

2010 ◽

Author(s):

Amir A. Aliabadi ◽

Steven N. Rogak ◽

Sheldon I. Green ◽

Karen H. Bartlett

Keyword(s):

Mass Transfer ◽

Heat And Mass Transfer ◽

Cfd Simulation ◽

Near Field ◽

Dynamics Simulation ◽

Evaporation Process ◽

Buoyancy Effect ◽

Computational Fluid Dynamics Simulation ◽

Droplet Dispersion ◽

Ambient Relative Humidity

A Computational Fluid Dynamics simulation of near-field cough and sneeze droplet dispersion and heat and mass transfer is developed. In this study various sources of variability in cough and sneeze processes are considered. These are variations in injection volume (0.5l, 2.5l, and 5.0l) and ambient relative humidity (20%, 40% and 60%). There are a total of 9 simulations for coughs and sneezes in a quiescent background. A large ensemble (5000) of droplets are tracked with diameters in the range 1–500micron. Evaporation and dispersion are predicted as a function of droplet size. Generally, fine droplets evaporate faster than large droplets. Higher relative humidities slow the evaporation process. Larger droplets have greater axial penetration. They also exhibit greater vertical drop due to the effect of gravity. Sideway penetration is increased by higher injection volumes. The buoyancy effect due to thermal energy of the injection is very weak, at least for the 10-second computation duration.

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The elliptic whistler jet

Journal of Fluid Mechanics ◽

10.1017/s0022112099005923 ◽

1999 ◽

Vol 397 ◽

pp. 23-44 ◽

Cited By ~ 19

Author(s):

HYDER S. HUSAIN ◽

FAZLE HUSSAIN

Keyword(s):

Flow Visualization ◽

Near Field ◽

Major Axis ◽

Field Mass ◽

Vortical Structures ◽

Air Jet ◽

Mass Entrainment ◽

Circular Jets ◽

Secondary Vortices ◽

Axis Switching

Elliptic jets have decided advantages for technological applications over circular jets; this paper explores further advantages achieved by jet forcing due to self-excitation. Using hot-wire measurements and flow visualization, we have studied an elliptic whistler (i.e. self-excited) air jet of 2:1 aspect ratio which, in contrast to an elliptic jet issuing from a contoured nozzle, displays no axis switching, but significantly increased spread in the major-axis plane. Its near-field mass entrainment is considerably higher (by as much as 70%) than that of a non-whistling jet. Flow visualization reveals unexpected dynamics of the elliptic vortical structures in the whistler jet compared to that in the non-whistling jet. Vortices rolled up from the lip of the elliptic pipe impinge onto the collar, producing secondary vortices; interaction of these two opposite-signed vortices is shown to cause the different behaviour of the whistler jet.

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The Effect of Precipitation Fronts Induced by Radionuclide Chain Decay and Elemental Solubility Limits on Near-Field Mass Transport

MRS Proceedings ◽

10.1557/proc-257-705 ◽

1991 ◽

Vol 257 ◽

Author(s):

Karen J. Worcan ◽

Michael J. Apted

Keyword(s):

Mass Transport ◽

Near Field ◽

Field Mass ◽

Bentonite Buffer ◽

Diffusional Mass ◽

High Level Nuclear Waste ◽

Uranium Plutonium ◽

High Level ◽

Chain Decay ◽

Diffusional Mass Transport

ABSTRACTThe formation and impact of precipitation fronts on the diffusional mass transport of radionuclides from a high-level nuclear waste canister through a bentonite buffer has been investigated in a series of numerical simulations. The precipitation fronts arise from chain decay and ingrowth, coupled with differences in elemental solubility limits and sorption properties. The fronts influence particularly the behavior of uranium, plutonium and neptunium isotopes. The isotopic concentration profiles across the buffer differ considerably from results obtained with models that employ elemental solubility limits simply as a boundary condition at the waste-bentonite interface.

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Near-Field Transport of 129I from a Point Source in an In-Room Disposal Vault

MRS Proceedings ◽

10.1557/proc-353-535 ◽

1994 ◽

Vol 353 ◽

Author(s):

Miroslav Kolář ◽

Dennis M. Leneveu ◽

Lawrence H. Johnson

Keyword(s):

Mass Transport ◽

Point Source ◽

Groundwater Flow ◽

Near Field ◽

Single Point ◽

Boundary Integral ◽

Boundary Integral Method ◽

Field Mass ◽

Release Rates ◽

Manufacturing Defects

AbstractA very small number of disposal containers of heat generating nuclear waste may have initial manufacturing defects that would lead to pin-hole type failures at the time of or shortly after emplacement. For sufficiently long-lived containers, only the the initial defects need be considered in modelling of release rates from the disposal vault. Two approaches to modelling of near-field mass transport from a single point source within a disposal room have been compared: the finite-element code MOTIF (A Model Of Transport In Fractured/porous media) and a boundary integral method (BIM). These two approaches were found to give identical results for a simplified model of the disposal room without groundwater flow. MOTIF has been then used to study the effects of groundwater flow on the mass transport out of the emplacement room.

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Chemical durability of high-level waste glass in repository environment: main conclusions and remaining uncertainties from the GLASTAB and GLAMOR projects

MRS Proceedings ◽

10.1557/proc-932-95.1 ◽

2006 ◽

Vol 932 ◽

Cited By ~ 4

Author(s):

P. Van Iseghem ◽

K. Lemmens ◽

M. Aertsens ◽

S. Gin ◽

I. Ribet ◽

...

Keyword(s):

Near Field ◽

Chemical Durability ◽

High Level Waste ◽

Model Parameters ◽

Residual Rate ◽

Geological Disposal ◽

Glass Dissolution ◽

Geologic Disposal ◽

High Level

ABSTRACTThis paper reviews the main conclusions of two European Commission funded projects, GLASTAB and GLAMOR, on the durability of HLW glass in geological disposal, and the remaining uncertainties. The progress in GLASTAB relates to the characterization of the alteration layer, the modeling of glass dissolution, the interaction of glass with near field materials, the behaviour of radionuclides, and the calculation of HLW glass dissolution as part of geological disposal. The GLAMOR programme was focused on the decrease of the glass dissolution rate upon achieving silica saturation in solution. Two conclusions from this programme are the importance of the residual rate measured beyond silica saturation and the need to reduce the uncertainties in model parameters. The overall conclusion from the two projects is that strong progress has been achieved on basic dissolution mechanisms and interaction with disposal environments - HLW glass will act as a good barrier to the release of radionuclides in geologic disposal.

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