Patent Number: 051805421
Section: summary

This invention relates to a container, and more particularly to a container for material contaminated with a toxic substance or with a radionuclide. In the nuclear industry, material such as mechanical components, rubber gloves, or liquids such as oils can become contaminated with radionuclides, for example, iodine 129, uranium, radium 226, and thorium 232. It is the normal practice to place such material in suitable containers, and subsequently to store the containers in specially designed vaults or caves. In order to make more effective use of the space in the vaults or caves a high packing of the contaminated material is desirable. According to one aspect of the present invention, in a container for material contaminated with at least one toxic material or a radionuclide, there is provided highly absorbent cementitious material for absorbing liquid in the container. The container may be adapted to receive compacted receptacles containing the contaminated material, and the liquid may be leakage from said compacted receptacles. Preferably, the cementitious material has a voidage of at least 40% by volume. Desirably, the cementitious material comprises cement hydrated beyond 25% thereof. The cementitious material may be made by a method comprising forming a cement slurry and a bentonite clay slurry, subsequently mixing together the cement slurry and the clay slurry, and heating the resulting mixture at a temperature such as to remove capillary water from the mixture without to a substantial extent dehydrating any hydrated cement. Preferably, the temperature is at least 50.degree. C. Advantageously, the mixed cement slurry and clay slurry has a water/solids ratio of about 1.5/1. The cement may comprise typical Portland cement (OPC). The water absorption capacity of cementitious material depends inter alia on the internal porosity of the material. Hence, to produce a cementitious material having a relatively high absorption capability it is necessary to use a high water content in its preparation. Whilst the maximum water/cement ratio that can be achieved using a low shear system is about 0.45, a water/solids ratio up to about 1.5/1 can be achieved by the addition of a suitable clay, viz: bentonite clay. When such a clay/cement/water mixture is heated to drive out the capillary water without dehydrating any hydrated cement to a substantial extent, an internal porosity of up to 75% by volume may be achieved. Provided that the cement has hydrated beyond 25% thereof, the ratio of hydrated to unhydrated cement should have little influence on the absorption capacity of the dried cementitious material in the short term, on the assumption that the water in the setting cement material is evenly distributed.