The greater part of radioactive waste results from the production of electricity in nuclear power plants (85% In France).
The remaining 15% originates from the medical sector, from industry, from research and from the military sector.
Two categories of waste can be identified, according to the intensity of the radiation they emit and their lifespan (the period during which they remain radioactive).
Here we will restrict ourselves to the management of radioactive wastes resulting from the nuclear industry for the production of electricity.
Low level short-lived waste: taking account of the rate of radioactive decay (what is called the half-life), within 300 years they will have a radioactivity level equal to that of natural background radioactivity. It is largely waste resulting from operations linked to the maintenance of nuclear power plants - the tools and cleaning rags brought into the radioactive zone for maintenance purposes and spare parts (valves, filters …) that have been replaced.
In France the volume of this waste has been drastically reduced (by a factor of 3 in the last 10 years). Today it represents
100 cubic metres per reactor
per year.
The waste is packed into units called parcels, in steel or in concrete. The waste is then completely covered by a matrix, a material whose role is to render inert the waste and to contain the radioactivity. The parcels have the effect of isolating the wastes from the environment. In 300 years time, their radioactivity level will be indistinguishable from background radioactivity levels.
Medium to high level, long-lived waste: this is waste linked to the nuclear fuel. It represents 10% of nuclear waste.
The uranium used in nuclear power plants is withdrawn after 3 or 4 years and replaced by new fuel.
The irradiated fuel is a highly radioactive waste, which remains active for a very long period. It can be stocked as it is, that is to say, the totality of the fuel assemblies must be stocked.
Or these fuel elements can be retreated, in such a way as to recycle the matter containing energy.
This retreatment-recycling operation is undertaken in France, for example.
After the separation operations, we recover:
- the sheathing of the fuel: the fuel rods into which the fuel is stacked;
- the
most active matter
(U238 and plutonium), about 97% of the spent fuel;
- the wastes generated by the fission: fission products and minor actinides (elements formed by the absorption of neutrons into the uranium nucleus).
Retreatment, by recovering the matter that is most active, results in the volume
of wastes to be stocked being divided by a factor of three.
This high activity, long-lived waste is vitrified, that is to say cast into glass, a material that is resistant to the heat and radiation. The glass is packed into metallic drums made of stainless steel, which are lowered into concrete wells, ventilated to ensure cooling. This storage solution can continue for several more decades, whilst waiting for a definitive solution. Because of the retreatment operations, the volumes are quite small.
France, for example, puts its know-how at the
disposal of other countries and retreats waste on behalf of Germany, Belgium, Japan, etc. The totality of the volumes treated in France is then returned to the country of origin: both the energetic matter and the ultimate waste.
In England, at Sellafield, there is a retreatment plant that undertakes the same operations.
In Finland and Sweden a different solution has been found: that of deep geological storage. A site is under construction in Finland (due to be opened in 2020) and potential sites are being studied in Sweden. In the United States, a storage centre for waste of military origin has existed since 1996. For the moment, spent fuel is guarded in the nuclear power plants.
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