Channeling and its Potential Consequences for Radionuclides Transport

1987 ◽  
Vol 112 ◽  
Author(s):  
Luis Moreno ◽  
Ivars Neretnieks
Keyword(s):  
Water Flow ◽  
Granitic Rock ◽  
Flow Distribution ◽  
Crystalline Rock ◽  
Fractured Media ◽  
Radionuclide Transport ◽  
Rock Matrix ◽  
Sorption Coefficient ◽  
The Matrix ◽  
Large Flow

SummaryRadionuclide transport through fractured media is usually calculated assuming that water flows in most of the fractures. Several observations in the field and the laboratory show that flow is very unevenly distributed in fractured crystalline rock. These observations indicate that most of the water flow takes place in a limited number of channels. The channels are seldom wider than a few meters and are often much narrower. This means that the surface of the fracture in contact with the flowing water (wetted surface) is less than one might expect.This low value of the wet surface of the fracture may considerably influence the transport of radionuclides through fractured media. If the channels do not intersect over a certain distance, then the channels may be modelled as a bundle of independent channels. Channels with a large flow and small sorption surface will carry the tracer rapidly and in large amounts.Calculations are performed for cases where channeling is assumed to take place. The most important entities to assess are the water flow distribution in the different channels, the wetted surface of the channels, the diffusivity into the rock matrix, and the sorption coefficient in the matrix. Experimental data for the water flow distribution are used and the transport of nuclides is calculated for the different channels. From these values the concentration of the effluent is determined. The results show that the retardation for the nonsorbing nuclides is negligible. Retardation is only important for the nuclides which are strongly sorbed on the granitic rock. Calculations are also done assuming other channel frequencies and other overall water flowrates.

Diffusion in the Matrix of Granitic Rock Field Test in the Stripa Mine

1987 ◽  
Vol 112 ◽  
Author(s):  
Lars Birgersson ◽  
Ivars Neretnieks
Keyword(s):  
Granitic Rock ◽  
Nuclear Waste Repository ◽  
Filling Material ◽  
Rock Matrix ◽  
In Situ Experiment ◽  
Undisturbed Rock ◽  
Disturbed Zone ◽  
The Matrix ◽  
Stress Environment

AbstractThree similar migration experiments in the matrix of granitic rock are presented. The experiments have been carried out in “undisturbed” rock, that is rock under its natural stress environment. Since the experiments were performed at the 360 m level (in the Stripa Mine), the rock was subjected to nearly the same conditions as the rock surrounding a nuclear waste repository as proposed in the Swedish concept (SKB).A mixture of three non-sorbing (conservative) tracers, Uranine, Cr-EDTA and I−, were injected into the granitic rock matrix for time periods of months up to years. The subsequent overcorings of the injection holes showed that the tracers had in some cases migrated at least ≈ 400 mm (measuring limit) into the rock matrix for the experiment with the longest injection time. It could also be seen that there were large differences in migration distance into the rock matrix for samples taken fairly close to each other. One example where the tracers have diffused through fissure coating (filling) material located in “undisturbed” rock is also presented.The results from all three experiments show that all three tracers have migrated through the disturbed zone close to the injection hole, through the fissure coating material and a distance into the “undisturbed” rock matrix.These results therefore indicate that dissolved compounds may migrate into the rock matrix. This migration into the rock matrix will increase the area available for sorption of radionuclides significantly and may therefore increase the migration times for radionuclides by order(s) of magnitude.Diffusivities and hydraulic conductivities obtained in this in-situ experiment compare well with those obtained in laboratory experiments.

Determination of the Flow-Wetted Surface in Fractured Media

2000 ◽  
Vol 663 ◽  
Author(s):  
Luis Moreno ◽  
Erik Svensson ◽  
Ivars Neretnieks
Keyword(s):  
Analytical Solutions ◽  
Large Volume ◽  
Accurate Determination ◽  
Fractured Media ◽  
Open Fractures ◽  
Flowing Water ◽  
Radionuclide Transport ◽  
Rock Matrix ◽  
Borehole Data

ABSTRACTDiffusion and sorption in the rock matrix are important retardation mechanisms in radionuclide transport in fractured media. The surface area in contact with the flowing water so called flow-wetted surface controls the interaction with the rock matrix. The flow-wetted surface, FWS, may be determined from the frequency of open fractures intersecting a borehole. The choice of the packer distance used in these hydraulic measurements is however crucial. If the packer distance is large, several open fractures may be found in the same packer interval. Analytical solutions and numerical calculations are used in order to address the determination of the flow-wetted surface from borehole data. The study is focused in two important aspects of the fieldwork, namely the distance used between the packers and b) the number of measurements that are required in order to obtain a accurate determination of the flow-wetted surface. A large volume of hydraulic data in Sweden obtained by using quite small packer distance is revised. The most usual packer distance was 3 meters. However, for some boreholes or sections of them even smaller packer distances were used. From these data, the flow-wetted surface was determined at several sites in Sweden. In some sites, the used packer distance was too large that no accurate determination of the flow-wetted surface could be done.

Colloid and Radionuclide Transport in Granite Under Low Water Flow Rates Expected in a Geological Repository

2009 ◽  
Vol 1193 ◽  
Author(s):  
Nairoby Albarran ◽  
Tiziana Missana ◽  
Ursula Alonso ◽  
Miguel Garcia-Gutierrez ◽  
Manuel Mingarro ◽  
...  
Keyword(s):  
Water Flow ◽  
Fractured Rock ◽  
Water Flow Rate ◽  
Test Site ◽  
Crystalline Rock ◽  
Low Flow ◽  
Radionuclide Transport ◽  
Hydrodynamic Conditions ◽  
Flow Rates ◽  
High Level

AbstractColloids generated from the engineered barriers of a high level radioactive waste repository (HLWR) emplaced in crystalline rock could play a significant role in radionuclide transport and they are of concern for the safety assessment of these repositories.The main objectives of this study are: a) to analyze the transport properties of colloids in a crystalline fractured rock under hydrodynamic conditions as similar as possible to those expected in a repository (i.e. low flow rates) and b) to discuss the effects of their presence on the transport of radionuclides.Transport experiments with bentonite and latex colloids in a fractured granite column from the Grimsel Test Site (Switzerland) were carried out, under geochemical conditions ensuring colloid stability (alkaline and low ionic strength water). Transport experiments were also carried out with 85Sr and 233U and the results with and without the presence of bentonite colloids were compared.Colloid filtration in the fracture was always observed, even when colloids presented high stability and the conditions were unfavorable to colloid attachment to rock surfaces, being both the colloids and the rock negatively charged and the fracture surface smooth. The retention in the fracture depended on the water flow rate, increasing the retention as the water flow decreased.This work illustrates as both the mobile and retained fraction of colloids, which strongly depend on the hydrodynamic conditions, are of importance in the overall radionuclide mobility.

Diffusion in the Matrix of Granitic Rock Field Test in the Stripa Mine Part 2.

1983 ◽  
Vol 26 ◽  
Author(s):  
Lars Birgersson ◽  
Ivars Neretnieks
Keyword(s):  
Laboratory Experiments ◽  
Granitic Rock ◽  
Nuclear Waste Repository ◽  
Rock Matrix ◽  
Injection Hole ◽  
Undisturbed Rock ◽  
Natural Stress ◽  
The Matrix ◽  
Migration Experiment ◽  
Stress Environment

ABSTRACTA migration experiment in the rock matrix is presented. The experiment has been carried out in “undisturbed” rock, that is in rock under its natural stress environment. Since the experiment was performed at the 360 m-level (in the Stripa mine), the rock was subject to nearly the same conditions as the rock surrounding a nuclear waste repository as proposed in the Swedish concept (KBS).The results show that all three tracers (Cr-EDTA, Uranine and 1-) have passed the zone disturbed by the presence of the injection hole and migrated some distance into “undisturbed” rock.These results indicate the existence of a connected micro fissure system in undisturbed rock, in which tracers (and therefore radionuclides) can migrate. Diffusivities obtained in this experiment are comparable to those obtained in laboratory experiments.

Aqueous Phase Diffusion in Crystalline Rock

1981 ◽  
Vol 11 ◽  
Author(s):  
M.H. Bradbury ◽  
D. Lever ◽  
D. Kinsey
Keyword(s):  
Radioactive Waste ◽  
Aqueous Phase ◽  
Water Movement ◽  
Degradation Products ◽  
Crystalline Rock ◽  
Crystalline Rocks ◽  
Radionuclide Transport ◽  
Fracture Networks ◽  
Phase Diffusion ◽  
Main Factors

One of the options being considered for the disposal of radioactive waste is deep burial in crystalline rocks such as granite. It is generally recognised that in such rocks groundwater flows mainly through the fracture networks so that these will be the “highways” for the return of radionuclides to the biosphere. The main factors retarding the radionuclide transport have been considered to be the slow water movement in the fissures over the long distances involved together with sorption both in man-made barriers surrounding the waste, and onto rock surfaces and degradation products in the fissures.

Allocation of fracturing intervals and justification of fracture parameters in the pre-Jurassic deposits

2021 ◽  
pp. 9-19
Author(s):  
P. A. Boronin ◽  
N. V. Gilmanova ◽  
N. Yu. Moskalenko
Keyword(s):  
Permeability Coefficient ◽  
Complex Structure ◽  
High Flow ◽  
Well Testing ◽  
Rock Matrix ◽  
Unconventional Reservoir ◽  
Flow Rates ◽  
Matrix Permeability ◽  
The Matrix ◽  
Standard Set

The object of research in this article is the productive deposits of the pre-Jurassic complex. The pre-Jurassic complex is of great interest, this is an unconventional reservoir with a complex structure and developed fractured zones. High flow rates cannot be determined by the rock matrix, since the matrix permeability coefficient is on average 2−3 md. In this regard, there is the problem of separation of fractured intervals according to a standard set of well testing.

Diffusion Measurements on Crystalline Rock Matrix

1994 ◽  
Vol 353 ◽  
Author(s):  
Kari Hartikainen ◽  
A. HautojÄrvi ◽  
H. Pietarila ◽  
J. Timonen
Keyword(s):  
Power Law ◽  
Gas Flow ◽  
Crystalline Rock ◽  
New Technique ◽  
Matrix Diffusion ◽  
Rock Matrix ◽  
Model Calculations ◽  
Short Time ◽  
Drill Cores

AbstractA new gas flow technique is introduced such that experiments on very long samples are possible. This new technique together with increased accuracy of the measurements, allows the observation of power law tails in the break-through curves. Dispersion in these experiments can be controlled in great detail, and therefore the power law tails can be used to determine very accurately the parameters relevant in matrix diffusion. Results for rock and metal samples are shown, and they are fitted with model calculations which include both dispersion and matrix diffusion. The introduced technique, which is designed for ordinary drill cores, is suitable for scanning a large number of samples in a very short time.

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