CN105181552A - Experimental method for obtaining nuclide migrating parameters in clay by utilizing flexible-wall permeameter - Google Patents

Abstract

The invention belongs to the technical field of research of soil analytical methods, in particular relates to an experimental technical method of quickly obtaining nuclide migrating parameters in clay by utilizing a flexible-wall permeameter. The experimental method comprises the following steps: I. pressing a clay material into a plurality of cylindrical samples with determined dry densities, and respectively putting into a pressure chamber of the flexible-wall permeameter for saturation; after finishing the saturation, uniformly adding tracer nuclides into the bottoms of the samples, and setting different pressure values to carry out an experiment, meanwhile, regularly collecting percolate at outlets, and calculating the percolation rates; II. stopping the experiment when the tracer nuclides occur in the percolate of the samples under the highest pressure, and taking the samples out and cutting into thin sheets of 1mm along the axial directions, performing dissipation, and measuring the concentration of the nuclides so as to obtain a nuclide concentration distribution curve of a plurality of groups of nuclides along the axial directions of soil columns; III. performing experimental calculation. The experimental method can be applied to the field of measurement of the nuclide migrating parameters.

Description

Flexible wall permeameter is utilized to obtain the experimental technique of clay Radionuclide Migration parameter

Technical field

The invention belongs to the studying technological domain of soil analysis method, particularly relate to a kind of experimental technique method utilizing flexible wall permeameter to obtain clay Radionuclide Migration parameter fast, can be used for nuclein migration parameter testing field.

Background technology

The migratory behaviour research of nucleic in clay medium material for radioactive waste repository design, addressing, construction and safety evaluation provide technical basis.The main method of current research nuclein migration has laboratory experiment, analog computation and site test three kinds, is being obtained on the basis of nuclein migration correlation parameter by lab and field test, utilizes numerical simulation calculation to assess the migration situation of long-time rear nucleic.But the low-permeability due to clay class dielectric material and the strong adsorbability to nucleic, make to adopt traditional laboratory experiment (post method, diffusion cell method, capillary tube technique etc.) technology to obtain the nuclein migration Experiment Parameter cycle very very long, often need the some months even longer time.The present invention proposes the measuring method of a kind of fast and simple acquisition nucleic transfer parameter in clay class dielectric material, save time and cost.

Document comparative analysis shows, the flexible wall permeameter that the present invention proposes obtains the experimental technique method of clay Radionuclide Migration parameter fast, and at home and abroad association area does not find the patent identical with this inventive principle and document.

Summary of the invention

The object of the invention is: the technical method that a kind of quick obtaining nucleic transfer parameter in the clay class dielectric materials such as bentonitic clay is provided, have that experimental period is short, measuring accuracy is high, simple operation and other advantages.

Technical scheme of the present invention: utilize flexible wall permeameter to obtain the experimental technique of clay Radionuclide Migration parameter, this experimental technique comprises the steps:

One, clay-like material is pressed into the multiple Cylindrical Samples determining dry density, puts into flexible wall permeameter pressure chamber respectively saturated; Saturated complete after, add tracer nuclide at sample bottom even, setting different pressures carries out experiment, exit timed collection transudate, calculates seepage flow speed;

When two, there is tracer nuclide in the transudate of sample under top pressure, stop experiment, each sample is taken out cutting vertically and, in 1mm thin slice, clear up, measure nuclide concentration, obtain polykaryon element along the axial nuclide concentration distribution curve of earth pillar;

Three, experimental calculation: 1, this experiment is one dimension migration models, and source item is impulse source, then the Transport of nucleic in earth pillar can adopt one dimension convection-dispersion equation to represent:

$\frac{\∂C}{\∂t}=\frac{D}{R_d}\frac{{\∂}^{2}C}{\∂z^2}-\frac{u}{R_d}\frac{\∂C}{\∂z}-\mathrm{\λ}C---\left(1\right)$

In formula: D-hydrodynamic dispersion coefficient, cm ²/ s; The concentration of C-nucleic in water, g/mL; The pore velocity of water in u-earth pillar, cm/s; R _d-retardation factor; λ-nuclide emission disintegration constant, 1/s; Z-axial distance, seepage direction is just, adding source place is 0, mm; T-time, s;

Under this experiment condition, source item adopts impulse source, and initial boundary conditions is:

C(x,t)| _t＝0＝0，C(x,t)| _t→∞＝0，(2)

${\∫}_0^{\mathrm{\∞}}Cndx=m---\left(3\right)$

In formula: n-factor of porosity; M-unit nucildic mass is injected in discharge area, g/cm ²

Calculating acquisition nucleic distribution values solution in earth pillar is:

$c\left(x,t\right)=\frac{m}{2\sqrt{\mathrm{\π}\frac{D}{R_d}t}}\exp \left(-\mathrm{\λ}t-\frac{{\left(x-\frac{u}{R_d}t\right)}^2}{4\frac{D}{R_d}t}\right)---\left(4\right)$

2, by above-mentioned experimental result according to formula 4 matching, reduced parameter, then can obtain nuclide concentration peak value migration distance is ut/R _d, Binding experiment time and seepage flow speed obtain retardation factor R _d, and then obtain hydrodynamic dispersion coefficient D; Different pressures can obtain multiple hydrodynamic dispersion coefficient D;

3, hydrodynamic dispersion coefficient can be expressed as:

D＝D _m+α|u|(5)

In formula: D _m-molecular diffusivity, cm ²/ s; α-dispersity;

Seepage flow speed corresponding with it for the hydrodynamic dispersion coefficient obtained under different pressures mapped according to formula 5, then this straight slope is dispersity α, and intercept is molecular diffusivity D _m.

Ultimate principle: nucleic seepage flow speed in interstitial medium material is directly proportional to seepage pressure, under utilizing flexible wall permeameter to carry out different osmotic power, the migration of nucleic in clay is tested, and obtains the concentration profile of nucleic in earth pillar by decomposing earth pillar; This experiment is approximate thinks one dimension nuclein migration model, source item is impulse source, adopt one dimension convection-dispersion equation to calculate the numerical solution obtaining nucleic Transport in earth pillar, experiment is obtained result and numerical solution matching, contrast obtains hydrodynamic dispersion coefficient and nuclide concentration peak value migration distance; Utilize outflow liquid mass and nuclide concentration peak value migration distance, obtain current and nuclein migration speed respectively, and then obtain retardation factor; Under different pressures, can obtain many group hydrodynamic dispersion coefficients, utilize the flow rate under hydrodynamic dispersion coefficient and this pressure to make rectilinear, then this straight slope is dispersity, and intercept is molecular diffusivity.

Beneficial effect: the method has the following advantages: be 1. adapted to nucleic and be less than 1 × 10 at infiltration coefficient ^-9the test of transfer parameter in the clay-like material of m/s; 2. experimental period is short, and flexible wall permeameter is the totally-enclosed system that can provide 0 ~ 2MPa pressure, improves the speed of nuclein migration, greatly shortens experimental period; 3. experimental result precision is high, and in permeability test process, sample is wrapped up by flexible material, effectively overcomes the experimental error that rigid walls permeameter lateral leakage brings under confined pressure effect, prevents nucleic percolating fluid to pollution and the seepage of permeating external environment; 4. data acquisition is convenient, can realize the Real-time Collection of percolating fluid in process of osmosis, chemical monitoring and analysis, release solid-liquid reaction and change in sample by the consecutive variations of ingredient properties is counter; 5. experimental provision is easy to dismounting, cleaning and changes, and the post-processed of sample is easy to realize, and this device has stronger anticorrosion and soil resistant performance simultaneously, is beneficial to carry out and repeats experiment.For nuclein migration parameter testing research work, the method can obtain nuclein migration parameter within comparatively short period, greatly saves measuring period and cost.

Accompanying drawing explanation

Below in conjunction with accompanying drawing, the present invention is further illustrated.

Fig. 1 nucleic concentration profile in earth pillar; Fig. 2 hydrodynamic dispersion coefficient and flow rate relation curve.

Embodiment

Embodiment 1, utilize flexible wall permeameter to obtain the experimental technique of clay Radionuclide Migration parameter, this experimental technique comprises the steps:

One, clay-like material is pressed into the multiple Cylindrical Samples determining dry density, puts into flexible wall permeameter pressure chamber respectively saturated; Saturated complete after, add tracer nuclide at sample bottom even, setting different pressures carries out experiment, exit timed collection transudate, calculates seepage flow speed;

When two, there is tracer nuclide in the transudate of sample under top pressure, stop experiment, each sample is taken out cutting vertically and, in 1mm thin slice, clear up, measure nuclide concentration, obtain polykaryon element along the axial nuclide concentration distribution curve of earth pillar;

Three, experimental calculation: 1, this experiment is one dimension migration models, and source item is impulse source, then the Transport of nucleic in earth pillar can adopt one dimension convection-dispersion equation to represent:

$\frac{\∂C}{\∂t}=\frac{D}{R_d}\frac{{\∂}^{2}C}{\∂z^2}-\frac{u}{R_d}\frac{\∂C}{\∂z}-\mathrm{\λ}C---\left(1\right)$

In formula: D-hydrodynamic dispersion coefficient, cm ²/ s; The concentration of C-nucleic in water, g/mL; The pore velocity of water in u-earth pillar, cm/s; R _d-retardation factor; λ-nuclide emission disintegration constant, 1/s; Z-axial distance, seepage direction is just, adding source place is 0, mm; T-time, s;

Under this experiment condition, source item adopts impulse source, and initial boundary conditions is:

C(x,t)| _t＝0＝0，C(x,t)| _t→∞＝0，(2)

${\∫}_0^{\mathrm{\∞}}Cndx=m---\left(3\right)$

In formula: n-factor of porosity; M-unit nucildic mass is injected in discharge area, g/cm ²

Calculating acquisition nucleic distribution values solution in earth pillar is:

$c\left(x,t\right)=\frac{m}{2\sqrt{\mathrm{\π}\frac{D}{R_d}t}}\exp \left(-\mathrm{\λ}t-\frac{{\left(x-\frac{u}{R_d}t\right)}^2}{4\frac{D}{R_d}t}\right)---\left(4\right)$

2, by above-mentioned experimental result according to formula 4 matching, reduced parameter, then can obtain nuclide concentration peak value migration distance is ut/R _d, Binding experiment time and seepage flow speed obtain retardation factor R _d, and then obtain hydrodynamic dispersion coefficient D; Different pressures can obtain multiple hydrodynamic dispersion coefficient D;

3, hydrodynamic dispersion coefficient can be expressed as:

D＝D _m+α|u|(5)

In formula: D _m-molecular diffusivity, cm ²/ s; α-dispersity;

Seepage flow speed corresponding with it for the hydrodynamic dispersion coefficient obtained under different pressures mapped according to formula 5, then this straight slope is dispersity α, and intercept is molecular diffusivity D _m.

Under different pressures, flow rate is different, and can obtain many group hydrodynamic dispersion coefficient D, do the relation curve of hydrodynamic dispersion coefficient and flow rate, as shown in Figure 2, then this straight slope is dispersity, and intercept is molecular diffusivity.

Claims (3)

1. utilize flexible wall permeameter to obtain the experimental technique of clay Radionuclide Migration parameter, it is characterized in that: this experimental technique comprises the steps:

One, clay-like material is pressed into the multiple Cylindrical Samples determining dry density, puts into flexible wall permeameter pressure chamber respectively saturated; Saturated complete after, add tracer nuclide at sample bottom even, setting different pressures carries out experiment, exit timed collection transudate, calculates seepage flow speed;

When two, there is tracer nuclide in the transudate of sample under top pressure, stop experiment, each sample is taken out cutting vertically and, in 1mm thin slice, clear up, measure nuclide concentration, obtain polykaryon element along the axial nuclide concentration distribution curve of earth pillar;

Three, experimental calculation: 1, this experiment is one dimension migration models, and source item is impulse source, then the Transport of nucleic in earth pillar can adopt one dimension convection-dispersion equation to represent:

In formula: D-hydrodynamic dispersion coefficient, cm ²/ s; The concentration of C-nucleic in water, g/mL; The pore velocity of water in u-earth pillar, cm/s; R _d-retardation factor; λ-nuclide emission disintegration constant, 1/s; Z-axial distance, seepage direction is just, adding source place is 0, mm; T-time, s;

Under this experiment condition, source item adopts impulse source, and initial boundary conditions is:

C(x,t)| _t＝0＝0，C(x,t)| _t→∞＝0，(2)

In formula: n-factor of porosity; M-unit nucildic mass is injected in discharge area, g/cm ²

Calculating acquisition nucleic distribution values solution in earth pillar is:

2. by above-mentioned experimental result according to formula 4 matching, reduced parameter, then can obtain nuclide concentration peak value migration distance is ut/R _d, Binding experiment time and seepage flow speed obtain retardation factor R _d, and then obtain hydrodynamic dispersion coefficient D; Different pressures can obtain multiple hydrodynamic dispersion coefficient D.

3. hydrodynamic dispersion coefficient can be expressed as:

D＝D _m+α|u|(5)

In formula: D _m-molecular diffusivity, cm ²/ s; α-dispersity;

Seepage flow speed corresponding with it for the hydrodynamic dispersion coefficient obtained under different pressures mapped according to formula 5, then this straight slope is dispersity α, and intercept is molecular diffusivity D _m.