Groundwater Colloid Properties and their Potential Influence on Radionuclide Transport

1996 ◽  
Vol 465 ◽  
Author(s):  
C. Degueldre
Keyword(s):  
Steady State ◽  
Water Flow Rate ◽  
Clay Fraction ◽  
Radionuclide Transport ◽  
Transport Mechanisms ◽  
Transport Models ◽  
Contaminated Aquifer ◽  
Suspension Process ◽  
Alkali Elements ◽  
Respective Concentration

ABSTRACTColloid facilitated transport is still an issue in radioactive waste management. Sophisticated phenomenological transport models are available, but progress is required to fully understand mechanisms and parameters. This study lead in this direction. Investigation of the marl groundwater colloids in steady-state conditions at Wellenberg, shows that their concentration is independent of the water flow rate. Their generation is caused by the re-suspension of the rock clay fraction only. The re-suspension process is presently being studied under flow transient conditions. Extension of our measurements to other safety relevant systems as well as a literature survey show that the colloid concentration under steady-state conditions is correlated to the concentration of alkali elements and earth alkali elements. The higher their respective concentration, the fewer colloids are occurring. Considerations on colloid contamination models are also included. The paper emphasises various colloid transport mechanisms including colloid generation from the irreversibly contaminated aquifer.

The anterior and posterior ‘stomach’ regions of larval Aedes aegypti midgut: regional specialization of ion transport and stimulation by 5-hydroxytryptamine

1999 ◽  
Vol 202 (3) ◽  
pp. 247-252 ◽  
Author(s):  
T.M. Clark ◽  
A. Koch ◽  
D.F. Moffett
Keyword(s):  
Steady State ◽  
Aedes Aegypti ◽  
Ion Transport ◽  
Malpighian Tubules ◽  
Transport Mechanisms ◽  
Regional Specialization ◽  
Negative Deflection ◽  
Electrical Polarity

The ‘stomach’ region of the larval mosquito midgut is divided into histologically distinct anterior and posterior regions. Anterior stomach perfused symmetrically with saline in vitro had an initial transepithelial potential (TEP) of −66 mV (lumen negative) that decayed within 10–15 min to a steady-state TEP near −10 mV that was maintained for at least 1 h. Lumen-positive TEPs were never observed in the anterior stomach. The initial TEP of the perfused posterior stomach was opposite in polarity, but similar in magnitude, to that of the anterior stomach, measuring +75 mV (lumen positive). This initial TEP of the posterior stomach decayed rapidly at first, then more slowly, eventually reversing the electrical polarity of the epithelium as lumen-negative TEPs were recorded in all preparations within 70 min. Nanomolar concentrations of the biogenic amine 5-hydroxytryptamine (5-HT, serotonin) stimulated both regions, causing a negative deflection of the TEP of the anterior stomach and a positive deflection of the TEP of the posterior stomach. Phorbol 12,13-diacetate also caused a negative deflection of the TEP of the anterior stomach, but had no effect on the TEP of the posterior stomach. These data demonstrate that 5-HT stimulates region-specific ion-transport mechanisms in the stomach of Aedes aegypti and suggest that 5-HT coordinates the actions of the Malpighian tubules and midgut in the maintenance of an appropriate hemolymph composition in vivo.

scholarly journals Elements Present in Leach Solutions from Unsaturated Spent Fuel Tests

1993 ◽  
Vol 333 ◽  
Author(s):  
P. A. Finn ◽  
J. K. Bates ◽  
J. C. Hoh ◽  
J. W. Emery ◽  
L D. Hafenrichter ◽  
...  
Keyword(s):  
Performance Assessment ◽  
Radionuclide Transport ◽  
Spent Fuel ◽  
Major Fraction ◽  
Transport Models ◽  
Preliminary Results ◽  
J 13

ABSTRACTPreliminary results for the composition of the leachate from unsaturated tests at 90°C with spent fuel for two successive periods of ~60 days each with pretreated J-13 groundwater are reported. The pH of the leachate solutions ranged from 4 to 7. The americium concentration was 104 to 105 greater than that reported for saturated spent fuel tests in which the leachate pH was 8. The major fraction of material in the leachate was present as colloids containing both americium and curium. The presence of actinides in a form not currently directly included in repository radionuclide transport models provides information that can be used in spent fuel reaction modeling, the performance assessment of the repository and the design of the engineering barrier system.

Building Confidence in Radionuclide Transport Models for Fractured Rock: The Nagra/JNC Radionuclide Retardation Programme

2000 ◽  
Vol 663 ◽  
Author(s):  
K. Ota ◽  
W.R. Alexander ◽  
P.A. Smith ◽  
A. Möri ◽  
B. Frieg ◽  
...  
Keyword(s):  
Fractured Rock ◽  
Test Site ◽  
Process Models ◽  
Swiss Alps ◽  
Radionuclide Transport ◽  
Transport Models ◽  
North East ◽  
Host Rocks ◽  
Experimental Technology

ABSTRACTThe joint Nagra/JNC Radionuclide Retardation Programme has now been ongoing for 15 years with the main aim of direct testing of radionuclide transport models in as realistic a manner as possible. A large programme of field, laboratory and natural analogue studies has been carried out at the Grimsel Test Site in the central Swiss Alps and the Kamaishi In Situ Test Site in north-east Japan. The understanding and modelling of both the processes and the structures influencing radionuclide transport/retardation in fractured host rocks have matured as has the experimental technology, which has contributed to develop confidence in the applicability of the underlying research models in a repository performance assessment. In this paper, the successes and set-backs of this programme are discussed as is the general approach to the thorough testing of the process models and of model assumptions. In addition, a set of key findings is presented, involving discussions on the enhancement of confidence through the program.

scholarly journals Use of experimental isotope-exchange fluxes in reversible enzyme and membrane transport models, assessed by simultaneous computer simulation of unidirectional and net chemical rates

1992 ◽  
Vol 286 (1) ◽  
pp. 295-303 ◽  
Author(s):  
I W Plesner
Keyword(s):  
Steady State ◽  
Exchange Rates ◽  
Membrane Transport ◽  
Isotope Exchange ◽  
Transport Model ◽  
Total Concentration ◽  
Rate Equations ◽  
Tracer Transport ◽  
Transport Models ◽  
Experimental Conditions

Steady-state rate equations for unidirectional (isotope-exchange) rates can become so complex, even for rather simple (reversible) enzyme or membrane transport models, that they are useless for detailed data analysis. In this paper a procedure is described for simultaneous simulation of net (chemical) and isotope-exchange rates. The method employs an expanded version of the basic model to monitor explicitly the fate of the label in an experiment. The procedure is quite general, and can be used for steady-state as well as transient kinetic situations, or it can be used in conjunction with existing interactive computer programs for steady-state model analysis. Three numerical examples are presented. First, it is shown, using the conventional (Post-Albers) model for Na+/K(+)-ATPase, that the change in concentration of a labelled intermediate after a change in experimental conditions does not in general reflect the change in the total concentration of that intermediate, and thus labelled intermediate concentrations may be misleading. Second, using a standard co-transport model and a prototype active-transport model (equivalent to a ligand-ATPase), it is shown that the ratio of tracer transport fluxes at steady state yields transport stoichiometries which depend on the experimental conditions, are different from the net apparent stoichiometries, and whose changes with conditions are also different from that of the net stoichiometries. It follows that conclusions drawn on the basis of experimentally determined tracer fluxes should be viewed with some caution. Specifically, a measured influx stoichiometry ligand/ATP (in the ATPase case) of higher than 1:1 does not necessarily imply the existence of more than one site for either ligand on the enzyme.

Data Reduction for Radionuclide Transport Codes Used in Performance Assessments: An Example of Simplification Process

1997 ◽  
Vol 506 ◽  
Author(s):  
B. Dverstorp ◽  
B. Mendes ◽  
A. Pereira ◽  
B. Sundström
Keyword(s):  
Data Reduction ◽  
Transport Model ◽  
Computer Experiments ◽  
Simple Calculation ◽  
Radionuclide Transport ◽  
Transport Pathway ◽  
Transport Models ◽  
Transport Pathways ◽  
Flow Parameters ◽  
Spatially Varying

ABSTRACTThe input data required for transport models for use in long-term risk assessments of repositories for radioactive waste, in geological media, are intrinsic to the performance of the models. The flow parameters utilized in these models typically come from 2 or 3D hydro-geological calculations done in a prior phase of an assessment. This paper examines some of the standard simplifications introduced when hydrogeological data are reduced to ID as is often required for radionuclide transport models. Two key aspects of data reduction are the determination of average properties of fractured media between and along transport pathways. To quantify possible errors associated with these reduction procedures, two computer experiments have been done. We show that the use of effective flow parameters, representing the average properties of a set of independent transport pathways, in a 1 D radionuclide transport model can result in an underestimation of peak releases by one order of magnitude or more. This result is valid for short-lived nuclides whenever retardation is an important factor. On the other hand, averaging of spatially varying transport properties along a transport pathway may lead to unjustified conservatism. A simple calculation example using Monte Carlo technique, shows that a model that does not take into account spatially varying retardation properties along the transport pathways may overestimate peak release rates by several orders of magnitude. We conclude that more sophisticated transport models taking into account available hydrogeological information on spatial variability are needed to fully understand the potential errors associated with consequence calculations in the performance assessment

scholarly journals NON-GAUSSIAN DISTRIBUTION IN RANDOM TRANSPORT DYNAMICS

1994 ◽  
Vol 08 (28) ◽  
pp. 3887-3961 ◽  
Author(s):  
MISAKO TAKAYASU ◽  
HIDEKI TAKAYASU ◽  
Y-H. TAGUCHI
Keyword(s):  
Steady State ◽  
Diffusion Equation ◽  
Mass Distribution ◽  
Power Law ◽  
Gaussian Distribution ◽  
Discrete Space ◽  
Transport Models ◽  
Fluid Turbulence ◽  
Transport Dynamics ◽  
Non Gaussian

Statistical properties of random transport models defined on discrete space-time are investigated both numerically and analytically. As an extreme limit we first consider aggregation limit of massive particles. With the presence of permanent injection we have a nontrivial steady state where the mass distribution follows a power law. It is shown that the steady state is universal and very robust. Next, we analyze the cases of imperfect aggregation that a finite portion is transported at a time. We have a Gaussian fluctuation governed by the ordinary diffusion equation in the nonaggregation limit, while the system converges to the power law steady state in the aggregation limit even without injection. In the intermediate cases the fluctuations are always between Gaussian and the power law. Underlying relations to the exponential-like distributions in fluid turbulence are also discussed.

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