Low — and intermediate-level wastes

A wide range of techniques is available for processing low — and intermediate — level waste. Because waste volume is one of the parameters that determine the price of disposal to the waste generator, volume reduction is often an important component of waste treatment. It may be achieved in a number of ways, the most straightforward of which is compaction. Here the wastes are simply forced down into a container. Super-compaction requires much greater forces because here whole waste drums are crushed into a puck-shaped form. These are usually concreted into an overpack. Another volume reduction technique is incineration. Wastes that are often treated this way are cellulosic materials and contaminated oil. The resulting ash, which will have a higher specific activity than the original waste, is usually immobilised using concrete. The final volume reduction method is re-melting. This is used for contaminated metal wastes, often encountered during decommissioning of nuclear facilities. Re-melting, which may be preceded by decontamination, aims to remove any remaining contamination in the form of slag so that the metal is clean enough to be recycled. Even if the metal is not recyclable, re-melting may still be economic because it produces a significant reduction in the volume of waste requiring disposal.

By far the commonest method of waste immobilisation is encapsulation with a cement grout. With wastes that contain magnesium or aluminium, reaction with the high pH pore fluids may generate hydrogen gas and require the container to be vented. Another technique, now not so favoured, is encapsulation in bitumen. Technologies that are gaining ground are vitrification, which can be used for a wide range of wastes,8 and pyrolysis, which has been found to be useful for organic ion exchange resins.