GB2049261A

GB2049261A - Method of disposal of tritium- containing water wastes

Info

Publication number: GB2049261A
Application number: GB8013241A
Authority: GB
Original assignee: Kernforschungszentrum Karlsruhe GmbH
Current assignee: Karlsruher Institut fuer Technologie KIT
Priority date: 1979-04-27
Filing date: 1980-04-22
Publication date: 1980-12-17
Also published as: FR2455341A1; DE2917060A1; JPS55147397A; GB2049261B; CH644965A5; BE881627A; FR2455341B1; DE2917060C2; JPS60638B2

Abstract

A method of disposing of tritium- containing aqueous wastes in which the wastes are mixed with a bentonite, cement or a cement-sand mixture added to act as a bonding agent, the still liquid cement mix packaged in a suitable material and allowed to set, the packaged material then being suitable for sinking into the sea. The bentonite may be mixed first either with the tritium- containing wastes, or with the cement or cement-sand mixture. The third component is then added. Values are given for the relative ratios of the various components for the two methods.

Description

SPECIFICATION Method of disposal of tritium-containing water wastes The present invention relates to a method of preparing tritium-containing water wastes for sinking into the sea, in which the HTO-containing water wastes are mixed with an inorganic bonding agent, the mixture thus produced being packaged and being allowed to set in the packaging, the solidified product, together with the packaging, then being suitable for sinking into the sea.

It is well known to dispose of radioactive tritium in the form of HTO-containing water wastes by solidifying the wastes with an inorganic bonding agent such as cement and then sinking it into the sea. For this purpose tritium containing effluents have to be fixed and packaged. No demands are made as to the quality of the fixing and packaging.

The transport and container costs for such a method of disposal are very high. Accordingly, it is extremely desirable that the packaging material, usually a drum, contains as high as possible percentage water (and hence tritium) content. Prior art methods accordingly require the mixing water and cement in a weight ratio of from 0.35:1 to 0.8:1. There are thus obtained cement blocks which have a water content of from 50% to 70% by volume. A higher water content cannot be obtained utilising such method because the cement settles out and the water located thereabove remains in a liquid state.

The present invention seeks to provide a method by means of which a higher HTO content in the end product compared with known methods can be obtained. The invention also seeks to provide a method in which expense and costs of transportation of such solidified products are reduced.

In accordance with the present invention, there is provided a method of disposal of tritiumcontaining water wastes in which the HTO-containing water wastes are mixed with an inorganic bonding agent, the mixture then being packaged and allowed to set in the packaging, the solidification product and the packaging then being suitable for sinking into the sea, comprising the steps of mixing tritium-water or water containing synthetic radionuclides and tritium water with a bentonite which is capable of swelling and is water absorbent, the weight ratio of water to bentonite lying with the range of 10:1 to 4:1, adding cement or a cement and sand mixture to the bentonite-water mixture in a ratio by weight which is not less than 1::5 so as to produce a mortar which sets to a cement stone or concrete having a water-cement value of from 1.0 to 4.0, charging the liquid cement or mortar thus obtained into a plastics material or metalenvelope and allowing the liquid cement or mortar to set in such envelope, the solidified product and packaging being suitable for sinking into the sea.

Also in accordance with the present invention, there is provided a method of disposal of tritium-containing water wastes, in which the HTO-containing water wastes are mixed with an inorganic bonding agent, the mixture then being packaged and allowed to set in the packaging, the solidification product and the packaging then being suitable for sinking into the sea comprising the steps of mixing swellable, water absorbent bentonite with cement in a weight ratio lying in the range of 1 :9 to 1::1 and subsequently adding tritium water or water containing synthetic radionuclides and tritium water in an amount sufficient to produce a watercement value of from 1.0 to 4.0, charging the liquid cement or mortar thus obtained into a plastics material or metal envelope and allowing the liquid cement or mortar to set in such envelope, the solidified product and packaging being suitable for sinking into the sea.

The standards of the International Atomic Energy Authority regarding the tritium-water solidification product are not particularly stringent. It is merely necessary that the product must have a density of at least 1.3 g.cm-3. The density of a mixture of water, cement and clay (bentonite), assuming that water has a density of 1 g.cm-3 and that cement and clay have a density of approximately 3 g.cm-3 may be estimated according to the equation: D = 100/ (Z + T) + W where Z is the percentage of cement, T is the percentage of clay and W is the percentage of water, all percentages being by weight.

To achieve a density of 1.3 g.cm-3, the water to solids ratio must be not more than 1.9. The invention will be further described, by way of illustration only, with reference to the following exemplary experiments: 1. Experiments to in crease the maximum water absorbtion capacity in the solids mixture.

The following table shows the effects on the water absorbtion capacity of Portland cement 350 of the addition of a substantially non-swellable and of a highly swellable bentonite: Bentonite W/Z value content Maximum water/solids ratio with swellin solids able bentonite mixture non-swelling swellable (weight %) bentonite bentonite 0 0.75 0.75 0.75 10 0.8 0.95 1.06 20 0.85 1.05 1.3 50 1.1 3.0 6.0 Products which have a very high bentonite content and a high water content are not, however, adequately solid. In products in which the solids are 50% bentonite, the limit water solids ratio is 2, which is a W/Z value of 4. A further limitation on the usefulness of setting water and solids mixtures is provided by the requirement that the density must not be below 1.3. By increasing the water - solids ratio of cement products by the addition of swellable bentonite thereto not only reduces the volume of the product, but also provides a weight reduction which is significant because of the reduction brought about thereby in transportation costs. The following table shows the relative increases of density, volume and weight in various water - solids contents compared with water. Cement and swellable bentonite is assumed to have a density of 3 for the purposes of this table.

Water/ Density Volume Weight Solids increase factor increase factor 0.33 2 2 4 0.5 1.8 1.67 3 0.8 1.59 1.42 2.25 1.0 1.5 1.33 2 1.2 1.43 1.28 1.83 1.5 1.36 1.22 1.67 1.9 1.30 1.18 1.53 oo 100% 1 1 1 (water)

Claims

1. A method of disposal of tritium-containing water wastes in which the HTO-containing water wastes are mixed with an inorganic bonding agent, the mixture then being packaged and allowed to set in the packaging, the solidification product and the packaging then being suitable for sinking into the sea comprising the steps of mixing tritium-water or water containing synthetic radionuclides and tritium water with a bentonite which is capable of swelling and is water absorbent, the weight ratio of water to bentonite lying within the range of 10:1 to 4:1, adding cement of a cement and sand mixture to the bentonite-water mixture in a ratio by weight which is not less than 1 ::5 so as to produce a mortar which sets to a cement stone or concrete having a water-cement value of from 1.0 to 4.0, charging the liquid cement or mortar thus obtained into a plastics material or metal envelope and allowing the liquid cement or mortar to set in such envelope, the solidified product and packaging being suitable for sinking into the sea.

2. A method of disposal of tritium-containing water wastes in which the HTO-containing water wastes are mixed with an inorganic bonding agent, the mixture then being packaged and allowed to set in the packaging, the solidification product and the packaging then being suitable for sinking into the sea comprising the steps of mixing swellable, water absorbent bentonite with cement in a weight ratio lying in the range of 1: 9 to 1:1 and subsequently adding tritium water or water containing synthetic radionuclides and tritium water in an amount sufficient to produce a water-cement value of from 1.0 to 4.0, charging the liquid cement or mortar thus obtained into a plastics material or metal envelope and allowing the liquid cement or mortar to set in such envelope, the solidified product and packaging being suitable for sinking into the sea.

3. A method of disposal of tritium containing waste waters substantially as hereinbefore described.