The French "loi de 2006" stipulates that certain nuclear wastes must be reconditioned for storage in accordance with current standards. This is particularly the case for "technical wastes" from the dismantlement of the Marcoule vitrification plant, which conditioned wastes from the site's installations between 1978 and 1997.
These technical wastes could be incorporated into cement rather than glass or bitumen, since this process is less costly than vitrification and presents fewer ignition risks than bitumen. All that is needed is to just evaluate the irradiation resistance of the selected cements:
- calcium silicate, the most common (Portland): portllandite Ca(OH)2,
- calcium aluminate, reputed to be more thermally and chemically resistant: katoite Ca3Al2(OH)12 and gibbsite Al(OH)3,
- phosphomagnesium, usable in the presence of aluminum: brucite Mg(OH)2.
More specifically, the researchers studied the response to the irradiation of crystalline hydrates, which are produced by hydrating the cement during its manufacture. For this purpose, they used the Sirius electron accelerator at the laboratory for irradiated solids in Palaiseau.
The structure of the examined hydrates was preserved up to 300 megagrays. Doses that were ten times higher (3 gigagrays) induced different microstructural variations. In particular, this resulted in deformations of the crystal mesh, which were then characterized.
No phase change (amorphization) was observed, allowing the researchers to conclude that the studied hydrates are resistant to the irradiation conditions specified for these storage facilities.