Patent Number: 051805421
Section: description

Referring now to FIGS. 1 and 2, part of a container 10 is shown, the container 10 being rectangular in plan and comprising a base 12 and side walls 14, 16. Crossed rails 18 forming a grid structure are disposed on the base 12, and define rectangular recesses 19 in which a highly absorbent cementitious material 20 is disposed for absorbing any liquids, for example, seepage of liquid from compacted boxes 22 (shown in broken line). The compacted boxes 22 contain material and articles (not shown) contaminated with radionuclides and for subsequent storage in vaults or caves. By compacting the boxes 22, a high packing density can be achieved to make the most effective use of the space inside the vault or cave. The space between the compacted boxes 22 inside the container 10 is filled with a known cementitious grout (not shown),--see for example GB-A-2196548, and the container 10 is capped with a lid (not shown). The cementitious material 20 comprises OPC with the addition of a clay, such as sodium bentonite, and provides a liquid absorption capability of about 75% by volume. A preferred sodium bentonite clay is sold under the Trade Marks "Volclay" and "Steebent". "Volclay" sodium bentonite clay (Civil Engineering Grade) is sold by: Volclay Limited, Wallasey, Merseyside, England. "Steebent" sodium bentonite clay (Civil Engineering Grade) is sold by Steetley Minerals Limited, Woburn Road, Woburn Sands, Milton Keynes, England. Examples of the preparation of suitable cementitious material 20 are as follows: EXAMPLE I A hydrated clay slurry was prepared by adding Volclay sodium bentonite clay to water to make a 5% (by weight) solution, the hydrated clay slurry then being allowed to stand for twenty four hours. A Portland cement slurry was prepared in batches using a water/cement ratio of about 0.45 in a low shear mixing system for about 15 minutes. The cement slurry was then mixed with the hydrated clay slurry and high sheared in a mixer for a further one hour. The amount of hydrated clay slurry was arranged so that the resulting mixture had a water/solids ratio of about 1.5/1. The mixture was poured into moulds and allowed to stand for twenty four hours at ambient temperature. The mixture was then removed from the moulds as individual blocks of 130.times.180.times.250 mm, and placed in an oven for drying at between 50.degree. C. and 100.degree. C. for between 5 and 6 days. After drying the blocks were allowed to cool to ambient temperature and then stored in airtight enclosures until required in the container 10. The cementitious blocks had a liquid absorption capability of about 75% by volume. EXAMPLE II Example I was repeated but with a hydrated clay slurry made using a 6% (by weight) solution of Steebent sodium bentonite clay. In other respects Example II was the same as Example I. The cementitious blocks had a liquid absorption capability of about 70% by volume. As an alternative in Examples I and II, the blocks before drying may be broken into granules, for example, between 5 and 70 mm, and the granules subsequently dried in the oven. The dried granules may then be used in the recesses 19 instead of the blocks of Examples I and II. It is considered that the high porosity of the cementitious mixtures of Examples I and II is due to a large extent to the physical characteristics of the clay. The reference to water/cement and water/solids ratios herein refers to the volume of water (liters) and the weight of cement or solids (grammes).