Separating and sorting

Sorting radioactive waste has advantages

As with household waste, sorting can prove really useful when it comes to managing radioactive material. It is performed industrially during reprocessing. The sorting or separation of radioactive material is also often called partitioning.

At the La Hague plant, partitioning is limited to the recovery of the uranium and plutonium considered to be reusable from the spent fuel from reactors. Partitioning has advantages. By removing the mildly radioactive uranium – which represents more than 90% of the mass of the spent fuel – you can reduce the volume of waste. The plutonium can be burned in a reactor to produce energy. Recovering the plutonium reduces the radioactive toxicity of the waste and the amount of heat it releases.

The glass residues from reprocessing, produced at the La Hague plant, are less toxic and release less heat than the spent fuel they come from. But because the separation process is not yet complete, they still contain some long-lived radioactive atoms (minor actinides). By removing these radioelements, it is possible to obtain lighter glass that will be back to the level of activity of natural uranium after three centuries, instead of the 10,000 or so years it would take for normal glass or the 200,000 years for spent fuel.

Partitioning radioactive atoms is a hot chemistry operation only made possible by the use of robotization. There are other difficulties too, of chemical origin. The heavy atoms to be separated out all have very similar properties. Partitioning is difficult in many respects, and active research into it is under way in France and elsewhere.

What do you do with the radioactive nuclei once they have been removed? The ideal solution would be to turn them into non-radioactive nuclei or nuclei that are still radioactive but would lose their radioactivity more quickly. That is the difficult task of transmutation. At present transmutation is used for plutonium, a fissile element.

Partitioning without transmutation can be useful. For example, if a radioactive element releases a lot of heat but disappears quickly, it can be conditioned separately for entreposing until it disappears. The waste that would ultimately need to be buried would release less heat and be less radioactive.