METHOD AND COMPOSITION FOR LIMITING PERMEABILITY OF A MATRIX TO LIMIT LIQUID AND GAS INFLOW

Abstract

A method of limiting or reducing liquid and/or gas inflow through a porous matrix, comprising delivering to said porous matrix a coagulable polymer emulsion or colloid for contacting with at least one selected additive which interacts with said polymer emulsion or colloid to form a sealing barrier to reduce liquid and/or gas inflow through the porous matrix wherein said coagulable polymer emulsion or colloid contains at least one selected additive including one or a combination of radiation stabilisers to confer radiation resistance; and wherein said sealing barrier is formed by contacting said polymer emulsion or colloid with a further selected additive to cause coagulation of said polymer emulsion or colloid to form said sealing barrier. The sealing composition, which has low toxicity, preferably contains carbon black as radiation stabiliser conferring radiation resistance for the sealing barrier in the range 1 to 100 MRad.

Claims

1. A method of limiting or reducing liquid and/or gas inflow through a porous matrix, comprising delivering to said porous matrix a coagulable polymer emulsion or colloid for contacting with at least one selected additive which interacts with said polymer emulsion or colloid to form a sealing barrier to reduce liquid and/or gas inflow through the porous matrix wherein said coagulable polymer emulsion or colloid contains at least one selected additive including one or a combination of radiation stabilisers to confer radiation resistance on said sealing barrier; and wherein said sealing barrier is formed by contacting said polymer emulsion or colloid with a further selected additive to cause coagulation of said polymer emulsion or colloid to form said sealing barrier.

2. The method of claim 1, wherein said sealing composition is introduced to said porous matrix by injection through injection holes drilled in the matrix.

3. The method of claim 2, wherein said injection holes are drilled by push drilling.

4. The method of claim 3, wherein said injection holes are drilled and sealing composition injected to form a cylindrical containment barrier for radioactive waste.

5. The method of claim 3, wherein said injection holes are drilled and sealing composition injected to form a conical containment barrier for radioactive waste.

6. The method of claim 3, wherein said injection holes are drilled and sealing composition injected to form a rectilinear containment barrier for radioactive waste.

7. The method of claim 1 wherein said sealing composition forms a containment barrier mechanically resistant to at least 1 MRad.

8. The method of claim 7 wherein said sealing composition comprises a latex emulsion or colloid and a radiation stabiliser selected from the group consisting of carbon black, zinc oxide both in particulate form and essentially insoluble in water; ortho di-substituted phenols, hydroxyphenyl propionates, hydroxybenzyl compounds, aromatic amines, sterically hindered amines, phosphites and organic sulphur compounds.

9. The method of claim 8 wherein said sealing composition contains carbon black as radiation stabiliser, preferably being present in the latex emulsion or colloid in proportion of 0.1 to 3 wt %.

10. A sealing composition comprising a coagulable polymer emulsion or colloid contactable with at least one selected additive which interacts with said polymer emulsion or colloid to form a coagulated mass for forming a sealing barrier against liquid or gas inflow through a porous matrix, wherein said polymer emulsion or colloid contains at least one further selected additive including one or a combination of radiation stabilisers to confer radiation resistance on said sealing barrier.

11. The sealing composition of claim 10 wherein said sealing composition comprises a latex emulsion or colloid and a radiation stabiliser selected from the group consisting of carbon black, zinc oxide both in particulate form and essentially insoluble in water; ortho di-substituted phenols, hydroxyphenyl propionates, hydroxybenzyl compounds, aromatic amines, sterically hindered amines, phosphites and organic sulphur.

12. The sealing composition of claim 11 containing carbon black as radiation stabiliser, and being present in the latex emulsion or colloid in proportion of 0.1 to 3 wt %.

13. The sealing composition of claim 12, passing regulatory limits for (a) metals selected from the group consisting of arsenic, cadmium, chromium, lead, mercury, selenium and silver; (b) VOC and, SVOC; and (c) organochlorine pesticides as set down by the US Environmental Protection Agency, SW-846, Method 1311 Toxicity Characteristic Leaching Procedure.

14. The method of claim 7, wherein said containment barrier is mechanically resistant to at least 10 MRad.

15. The method of claim 7, wherein said containment barrier is mechanically resistant to up to 100 MRad.

16. The sealing composition of claim 12, wherein carbon black is present in the latex emulsion or colloid in proportion less than 1 wt %.

17. The sealing composition of claim 12, wherein carbon black is present in the latex emulsion or colloid in proportion in the range 0.5 to 0.7 wt %.

18. A sealing composition comprising a coagulable polymer emulsion or colloid contactable with at least one selected additive which interacts with said polymer emulsion or colloid to form a coagulated mass for forming a sealing barrier against liquid or gas inflow through a porous matrix, wherein said polymer emulsion or colloid contains at least one further selected additive including one or a combination of radiation stabilisers selected from the group consisting of carbon black, zinc oxide both in particulate form and essentially insoluble in water; ortho di-substituted phenols, hydroxyphenyl propionates, hydroxybenzyl compounds, aromatic amines, sterically hindered amines, phosphites and organic sulphur compounds to confer radiation resistance on said sealing barrier, said radiation stabiliser or combination of radiation stabilisers being present in the latex emulsion or colloid in proportion less than 1 wt %.

19. A method for forming a radiation resistant containment barrier which limits or reduces liquid or gas inflow through a porous matrix, comprising delivering to said porous matrix by injection a coagulable polymer emulsion or colloid for contacting with at least one selected additive which interacts with said polymer emulsion or colloid to form a radiation resistant containment barrier to reduce liquid and/or gas inflow through the porous matrix, said coagulable polymer emulsion or colloid containing at least one selected additive including one or a combination of radiation stabilisers to confer radiation resistance on said containment barrier; wherein said sealing barrier is formed by contacting said polymer emulsion or colloid with a further selected additive to cause coagulation of said polymer emulsion or colloid to form said sealing barrier; and wherein said containment barrier is mechanically resistant to a radiation level of at least 1 MRad.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0029] The method and composition of the present invention may be better understood from the following description of preferred embodiments and examples and with reference to the accompanying drawings, in which:

[0030] FIG. 1 is a schematic cross-sectional view of a ground formation surrounding a vessel holding liquid radioactive waste having cracks or apertures in the matrix surrounding the vessel that requires sealing in accordance with a first embodiment of the sealing method to prevent or minimise water inflow into the vessel;

[0031] FIG. 2 is a schematic illustration of a radioactive waste storage facility where the sealing method of the invention is applied to form a tank farm containment barrier of a first rectilinear geometry.

[0032] FIG. 3 is a schematic illustration of the radioactive waste storage facility of FIG. 2 showing one section of the tank farm containment barrier of first rectilinear geometry.

[0033] FIG. 4 is a schematic illustration of a radioactive waste storage facility where the sealing method of the invention is applied to form a tank containment barrier of a second cylindrical geometry.

[0034] FIG. 5 is a schematic illustration of a radioactive waste storage facility where the sealing method of the invention is applied to form a tank containment barrier of a third conical geometry.

[0035] Referring to FIG. 1, the sealing method of one embodiment of the invention is applied to treatment of a vessel 14 holding aqueous radioactive waste associated with a nuclear installation located in a porous matrix 32 being a ground formation surrounding a vessel 14, through which contaminated water penetrates through cracks 30 in the wall 31 of vessel 14, and face 34, the cracked wall 31 also forming a porous matrix requiring sealing to prevent outflow of contaminated water into the surrounding ground formation 32.

[0036] Hydraulic parameters of the porous matrix 32 must also be determined. The nature and extent of the hydraulic field in the porous matrix 32 beyond vessel 14 must be understood if effective sealing is to be effected. In order to determine hydraulic parameters of connectivity, penetration and spread of water inflow, a suitable dye, such as a tracer dye, having the same flow characteristics as water but being coloured so as to clearly contrast against the vessel 14 and the site, is introduced through suitable injection holes (not shown). Seepage of the dye outward from the vessel 14 and through the porous matrix 32 can be timed and visually assessed to determine permeation of water outflow as well as any other water flows through the matrix which may add to a radioactive waste contamination problem. Reporting of dye indicates where water flow is occurring and flow rate of the dye is measured to determine flow properties of the dye within the matrix 32 when introduced at a particular rate and pressure. This gives an indication of the flow rates of a solution of the sealing composition, so that it can be determined when to introduce suitable additives and at what concentrations.

[0037] Having reference to parameters ground and water temperature, water pH, mineral content and salinity levels as well as flow properties of water in and around the vessel 14, the porosity of matrix 32 and of temperature of the site, components and the respective concentrations of said components of the sealing composition can be suitably selected as well as the estimated volume of sealing composition needed. Further description of the sealing composition is provided below. One option is to drill passages 38 and 40 through to the vessel 14 so that sealing composition can be introduced to seal the cracks 30 through and form a sealing barrier against flow of contaminated water.

[0038] In a further embodiment described with reference to FIGS. 2 to 5, the sealing method could be used for forming containment barriers for restricting liquid or gaseous leakage from a radioactive waste storage facility 110 having a number of tanks 114 for holding liquid radioactive waste and surrounding structure 120 with side walls and floor also constructed of a radiation resistant barrier according to a second containment method as known in the art and, for example, including lead shielding. The waste may be low, medium or high level radioactive waste. Such containment barriers could be constructed 1) during construction of waste storage facility 110, 2) after construction of the waste storage facility, prior to filling of tanks 114 with aqueous radioactive waste, or 3) as a repair strategy for a waste storage facility 110 which has deteriorated over time to provide a barrier seal to protect against possible leaks from the tanks 114 into surrounding ground 150 and porous matrix or formation 170.

[0039] The containment barrier 130 may be formed in a number of geometries as described below.

[0040] Referring to FIGS. 2 and 3, the containment barrier 130 is of rectilinear geometry and arranged within the surrounding containment structure 120 which may be subject to cracking and require sealing treatment. In FIG. 2, injection holes 135 are disposed parallel in a rectangular pattern viewed in plan and sealing composition, as described below, is introduced into the injection holes 135 drilled into sandy overburden 125 surrounding tanks 114 to form, after lateral spreading, a rectangular box shaped containment barrier to prevent waste leakage into surrounding porous matrix or formation 170 and any existing water table as well as surrounding ground 150. FIG. 3 indicates how the rectilinear containment barrier 130 can be constructed in sections, one section 130A of which is shown in FIG. 3. Injection holes 135A have been drilled into sandy overburden 125 but not yet used for grouting to form the containment barrier. One injection hole 135 is shown with grouting for section 130A completed.

[0041] A containment barrier may also be required on the floor of the surrounding containment structure 120 of FIGS. 2 and 3. Such a containment barrier may be constructed prior to construction of containment barrier 130. The containment barrier 130 extends to just below the height of surrounding containment structure 120 above surrounding ground 150. Containment barrier 130 extends into surrounding formation 170 a depth calculated with reference to the permeability of the surrounding formation 170 to the radioactive waste. It will be understood that FIGS. 2 and 3 are schematic for ease of illustration. If surrounding formation 170 is fractured or porous, further sealing treatment may be applied to form containment barriers within the surrounding formation as well. Such treatment may, depending on the geology and hydrology of surrounding formation 170, require higher injection pressures than used for forming a containment barrier within the waste treatment facility 110.

[0042] Referring to FIG. 4, an individual tank 114 is provided with a cylindrically shaped containment barrier 230 which is prepared by injecting sealing composition, as described below, through injection holes 235 disposed in a circular array about tank 114. Injection holes 235 drilled through sandy overburden 125 surrounding tank 114 are arranged parallel and injection of sealing composition forms, after lateral spreading, the cylindrically shaped containment barrier to prevent waste leakage into surrounding formation 170 and any existing water table. As with the embodiments of FIGS. 2 and 3, further sealing treatment of the containment structure 120 and surrounding formation 170 may be performed as required.

[0043] Referring to FIG. 5, containment barrier 330 for a tank 114 has a conical geometry and is constructed for a deteriorating facility where leakage from tank 114 is becoming a risk. Such a containment barrier is formed by drilling injection holes 335 into the surrounding containment structure 120 and surrounding formation 170 at intervals around the tank 114. The hydraulic parameters for the matrix are either determined or known from methods such as those described above. In contrast to the embodiment of FIG. 4, the injection holes 335 are drilled through sandy overburden 125 surrounding tank 114 at an angle, each injection hole 335 converging and intersecting at the apex 332 of the conical containment barrier 330. To reduce cost, while allowing effective sealing, the layout of injection holes 335 should minimise the number of injection holes 335 required. To this end, injection holes 335 are disposed at regular and substantially equidistant intervals in a circular array around tank 114 as indicated by FIG. 5.

[0044] As the waste storage facility 110 is a high radiation level site, drilling cuttings or fines cannot be brought to the level of surrounding ground 150. The injection holes 135, 135A, 235, 335 are drilled by push drilling using push rods to prevent cuttings or fines from drilling reaching surface of ground 150. This contrasts with other non-radiation applications where percussive drilling could be used.

[0045] During initial phases of introduction of the multi-component composition by injection into the various injection holes 135, 135A, 235, 335, the sealing composition is formulated with an inhibitor to provide an extended set time so as to allow for optimum spread and penetration of sealing composition into matrix 120, 170 specifically to form the containment barriers 130, 230, 330. It is undesirable for the sealing composition to set too close to the injection holes 135, 135A, 235, 335 as this then requires drilling of further injection holes, at a cost, in order to enable introduction of additional sealing composition.

Sealing Composition

[0046] The selected grout component of the sealing composition used to form the seal and containment barriers of FIGS. 1 to 5 contains a major proportion of a latex emulsion or colloid, having a near uniform dispersion of polymeric particles desirably having a particle size distribution with 100% of polymer particles having size less than 2 microns. This particle size compares with a particle size range of 5 to 30 microns inorganic cement particles for Portland cement and a Tamcrete product in which 58% of the inorganic particles have particle size greater than 2 microns and 100% of the inorganic particles have particle size less than 40 microns. The difference in particle sizing is beneficial for the selected latex emulsion based sealing composition since it can flow into and permeate fine cracks at lower pressure and without the risk of undesirable hydro-fracturing that a cement based sealing composition would indicate. A minor proportion of the grout component of the sealing composition was comprised of a lauric acid salt, ammonium laurate, as well as further selected additives as described further below.

[0047] By major proportion of latex emulsion or colloid is intended an emulsion or colloid containing sufficient latex to form an effective seal once the emulsion or colloid is in situ within the passages to be sealed (here crack 30) and setting or coagulation is initiated. Typically, latex will be supplied in emulsion or colloidal suspension with water. The preferred latex is a natural rubber latex such as is readily available from a number of sources in various grades. Latex emulsions of purity greater than 20% to 60% and above are preferred for the grout component of the exemplary sealing composition. Further description of the characteristics of suitable latex emulsions is provided in the Applicant's Australian Patent Nos. 2009253842 and 2013266018, the contents of which are incorporated herein by reference.

[0048] The radiation stabilisers may, for example, include one or a combination of additives selected from the group consisting of carbon black, zinc oxide, ortho di-substituted phenols, hydroxyphenyl propionates, hydroxybenzyl compounds, aromatic amines, sterically hindered amines, phosphites and organic sulphur compounds such as thiobisphenols and thioethers. Preferably, the compound is selected for suitability for the containment application, compatibility with latex and cost as well as the transport properties to the sealing site.

[0049] Meeting these requirements, carbon black is preferably included as a radiation stabiliser, preferably being present in the latex in proportion of less than 1 wt % of the sealing composition, for example 0.6 wt %, and at the requisite particle size as indicated above. Carbon black may be available as a furnace black or a special black. Furnace blacks are a relatively low cost commodity chemical typically produced from heating heavy residual oil in the absence of oxygen.

[0050] In one example, prior to injectionas described belowapproximately 1260 kg (6-210 Kg drums) of latex containing a small amount of coconut oil (sufficient to achieve a lauric acid concentration of about 0.03 wt % in the final sealing composition) was mixed with an additive mixture comprising 2.5 kg of KT powder (coagulation inhibitor), ground to the required sizing, 1-5 kg of KOH and about 8 kg of carbon black. Required quantities of sealing composition for the sealing application will be determined following measurement of the hydraulic parameters as mentioned above. As the hydraulic parameters are monitored using a computer control and data acquisition unit, quantities may be re-calculated and further sealing composition made available as required. A suitable control and data acquisition unit is described in U.S. Pat. No. 6,801,814, the contents of which are hereby incorporated herein by reference.

[0051] The sealing composition is pumped to provide gas/liquid containment barriers 130, 230, 330 about tanks 114. While the Applicant has used pumping at pressures up to 20 MPa in rock formations to enable sealing of large cracks, such pressures are not required for forming containment barriers 130, 230, 330 in waste treatment facility 110. Injection of sealing composition at pressures less than 1 MPa, for example about 0.6 MPa may be sufficient.

[0052] Coagulation or setting of the sealing composition may be done in a number of ways using coagulation accelerators and curing agents for example as described in the Applicant's Australian Patent Nos. 2009253842 and 2013266018 incorporated herein by reference. Acids provide a convenient example. Shear may also cause coagulation or setting though is unlikely to be sufficient alone.

Radiation Resistance

[0053] Samples of a sealing composition or grout, containing carbon black anti-rad as described above, were subjected to irradiation by a .sup.60Co source at doses of 1 MRad, 10 MRad and 100 MRad. An un-irradiated control was also included.

[0054] As to qualititative observations, the un-irradiated sample had an acetate smell. An unpleasant acrid odour arose from the more highly irradiated samples. A slight oily film developed with increasing radiation dose. Samples became stiffer with increasing radiation dose. Rippling of sample grouts was observed at 1 MRad through 100 MRad where erosion was encountered.

[0055] No significant dimensional changes occurred for the sample grouts with irradiation as evident from the following Table.

TABLE-US-00001 Dose Dimensional Stability 0 0.89 1 MRad 1.05 10 MRad 1.02 100 MRad 0.95
However, there was a significant increase in density from 0 MRad to 1 MRad, consistent with increased cross-linking. Density decreased over the range 10 to 100 MRad consistently with increased chain scission. Low levels of radiation may even be effectively curative, inducing a requisite degree of cross-linking and setting in the grout and increasing seal effectiveness.

[0056] Irradiation, particularly above 1 MRad, made the samples more elastic, even hyperelastic, and less plastic. Sample grouts ruptured at 800% elongation at 1 MRad irradiation, falling to a still acceptable 200% elongation at 100 MRad irradiation. However, erosion channeling presents some issues at this radiation level.

[0057] The tests indicate that sample grouts would form effective sealing compositions and containment barriers even up to 100 MRad irradiation and compare favourably with studies showing significant changes in properties of poly(ether-block-amide) thermoplastic elastomers in the 5 to 20 MRad dose range and substantial loss of mechanical properties of vulcanized chlorobutyl rubbers at 2.5 MRad.

Toxicity Analysis

[0058] Toxicity analysis was conducted to assess compliance with US regulatory levels for a number of contaminants as regulated by SW-846, Method 1311: Toxicity Characteristic Leaching Procedure (TCLP), herein incorporated by reference. TCLP organic results for the sample grouts showed no detectable amounts of regulated VOC, SVOC or commonly used organochlorine pesticides. TCLP results for As, Cd, Cr, Pb, Hg, Se and Ag were all below regulatory limits and below detectable limits. The sample grouts were TCLP compliant.

[0059] Modifications and variations to the sealing method and composition as described herein and as would be apparent to the skilled addressee are deemed to be within the scope of this invention.