Patent Number: 048427730
Section: summary

FIELD OF THE INVENTION The invention relates to a method for producing a suitable solid product containing cement for terminally storing water containing tritium (tritium water) wherein the tritium water is mixed with cement and bentonite. The tritium water is mixed with bentonite, which is capable of swelling, to produce a water-bentonite suspension. The suspension obtained in this manner undergoes a swelling operation and thereafter cement is added to the swollen suspension. BACKGROUND OF THE INVENTION German Pat. No. 29 17 060 describes a method for solidifying tritium water. A minimum density of 0.3 grams/cm.sup.3 is a boundary condition for the product to be cured. The basis for the formulation used in the above reference is a mixture of cement, bentonite and tritium water. The method described and the product correspond to laboratory experiments. An attempt was made to produce a product for terminally storing tritium water on the basis of the formulation of the above-mentioned German Pat. No. 29 17 060. When translating this mixture developed in the laboratory to a semi-technical scale (university experiments and in the technical scale of 1:1), it was shown however that the terminal storage of the tritium water is not possible because the requirements imposed on large containers having an interior volume of approximately 8 m.sup.3 could not be fulfilled. These requirements include a solid product having the highest possible water content and no residual water. All large specimens which were produced having a water content of more than 60% by weight have residual water during and after curing. Such an occurrence is not permissible for the terminal storage, for example, in a terminal storage mine according to the requirements of the authorities empowered to grant a permit for this purpose. On the other hand, a content of water below 60% is not worthwhile in view of economic considerations. SUMMARY OF THE INVENTION It is an object of the invention to provide a method of the kind described above with which a solid product can be produced containing cement and which is suitable for terminal storage. It is a further object of the invention to provide such a solid product which has a higher water content without the danger of residual water being present. The method of the invention is for producing a solid product containing cement for terminally storing tritium water. The method according to the invention includes the steps of: feeding tritium water and activated bentonite capable of swelling to a dispersion pump wherein high shearing forces are developed; dispersingly mixing the tritium water and the bentonite in the dispersion pump by subjecting the tritium water and the bentonite to high shearing forces to obtain a suspension thereof; subjecting the suspension to a swelling operation; and, admixing cement with the swollen suspension. Thus, it is a feature of the invention that the activated bentonite, which is capable of swelling, is dispersingly mixed with the tritium water under the action of high shearing forces and the suspension obtained in this manner is subjected to a swelling operation. Thus, in the method of the invention, activated bentonite capable of swelling is utilized. In activated bentonite, the earth alkali ions built into the crystal lattice are for the most part replaced by sodium ions. This can be obtained with a chemical treatment. The bentonite is dispersingly mixed and sheared with the tritium water under the action of high shearing forces and thereby opened. The grain aggregate of the bentonite is substantially entirely mechanically broken up by means of the shearing forces to form a suspension. The suspension obtained in this manner is thereafter subjected to a swelling operation and then mixed with cement. The above method steps advantageously make it possible to produce a product with approximately 85 to 90% by weight of water content without residual water having been detected. Pursuant to an advantageous embodiment of the invention, the tritium water is dispersingly mixed with the bentonite in a mass ratio range of approximately 10:1 to approximately 20:1. Preferably, this mass ratio is approximately 12.5:1. This ratio is higher than previously obtained in the state of the art described above. In a discontinuous method, the tritium water-bentonite suspension is subjected to the swelling operation in a swelling container. For this purpose, it is advantageous to circulate the suspension in the swelling container. In a continuous method, the tritium water-bentonite suspension passes through a retention segment which effects a hold-up time of at least 10 minutes. In this way, an adequate bentonite swelling is obtained. In a further advantageous embodiment of the invention, the swollen suspension is mixed with a cement which contains only a small portion of calcium or releases only a small quantity of calcium ions. In this way, a deactivation of the bentonite is prevented. In still another advantageous embodiment of the invention, the swollen suspension is dispersingly mixed with the cement under the action of high shearing forces whereby an additional break up of the suspension and an improved homogenization of the solid product are obtained. The product is still capable of flowing and can be filled into a gas-tight container. A filling level of at least 92% by volume can be obtained without additional technical assisting means. Since no residual water occurs, present day official requirements for the terminal storage in an accessible terminal storage facility can be fulfilled.