The waste is made up of a block of borosilicate glass conditioning matrix and its metal container, which is made of stainless steel and is covered by a 55mm-thick over-container made of low alloy steel. In tunnels 500 meters underground, these items will be positioned.
Weathering by water:
When there is water on the glass surface, a phenomena known as "weathering" can sometimes influence a glass container. Finding out how quickly and via what mechanisms the glass will deteriorate is the fundamental concern. A significant issue regarding the origin of the radionuclides is brought up by the long-term behaviour of this vitrified waste in contact with water. Because the glass can be altered by the water in the subsurface environment, also, some of the radionuclides may leak from this water. This all happens after erosion of the mineral casings when the geological site becomes saturated with water.
Nuclear glasses are made using physicochemical processes that are very comparable to those used to make silicate glasses in nature. The theoretical ideas created for these materials can therefore be used by researchers to their advantage. This is despite the large number of parameters that constitute difficulty, especially since the glass consists of more than thirty oxides with different compositions, and it is also breakable during its cooling after casting as a result of mechanical pressures, additionally, the temperature varies with respect to location, time, and the types of materials that are close to the glass.
The type of the chemical bonds within the vitreous structure and the characteristics of the dissolved species are all factors in the reactions that take place in nuclear glasses when there is water present. Silicon hydrolysis condensation reactions, and ion exchange reactions, are part of the main reactions. The precipitation of the crystallized secondary phases and the formation of a wet and inert porous layer are the results of the hydrolysis-condensation reactions of silicon. While alkalis, which bind weakly to the glass lattice, are mainly related to ion exchange. It was found that the ability of passivation appears on the wet layer due to the closure of its pores, and therefore the researchers conclude that the transport of solutes is strongly associated (at the mesoscopic scale) with the mentioned chemical reactions.
Because of the environment's introduction of potentially disruptive foreign elements like magnesium and iron, these layers of atteration have a considerable deal of chemical complexity. This complexity is partially a result of the glass's inherent properties.
- CHARACTERIZATION OF THE R7T7 LWR REFERENCE GLASS- PACAUD F.- FILLET C.- BAUDIN G. CEA Centre d'Etudes Nucléaires de la Vallée du Rhône, 30 Bagnols-sur-Ceze ^FR
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