A highly effective technique for protecting against radiation from radioactive bodies is to concentrate and then condition them in an inert form that prevents them from migrating into the environment, particularly as a result of action by water. Waste is placed inside containers to form solid, stable packages that are easy to handle and transport, ready for interim storage or permanent disposal.
A variety of media are used to trap radioactive atoms, including cement, bitumen, thermoset resins, glass and ceramics. Together with the container, the resulting "containment matrix" in which the radioactive elements are embedded forms a protection barrier. The choice of medium depends on the radioactivity in the waste. Considering the very long term, a repository in a geological medium will perform the containment role, when the container and containment matrix have disappeared or been degraded.
The potential for embedding waste in ceramics is being researched, due to the exceptional water resistance of such materials, but ceramics are currently still costly to produce.
Intermediate-level long-lived waste (ILW-LL), which is produced in greater volumes than high-level waste (HLW), was until recently embedded in an inert material such as bitumen or concrete. Since 2002, this category of waste is compacted and placed inside a stainless steel container similar to those used for vitrified waste.
Low-level radwaste contains little radioactive material. There are benefits in compacting it to reduce its volume. This category of waste is cast in cement, bitumen or resins enabling it to be placed in drums.
Plutonium recovered during reprocessing operations is conditioned as insoluble oxide (PuO2) in sealed boxes pending reuse in MOX fuel. The boxes are small to prevent any risk of criticality.
Completing the list, some highly radioactive spent fuels unloaded from reactors remain to be conditioned. These non-reprocessed irradiated fuel assemblies are currently stored in pools or silos. These delicate, highly radioactive structures measuring more than 4m in length are cumbersome. When the time comes to dispose of them, they will be inserted into large, heavy transport containers, as in the USA and Sweden.
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