Behavior of glass matrices in geological disposal
On January 27, the Agence France Presse (AFP) published a news report about an American study on the behavior of glasses in which high-level radioactive waste (HLW) is packaged. According to this study, the corrosion of the glass or ceramic used to confine this waste is "significantly accelerated" under certain conditions. This dispatch was the subject of many occasions in the press and on social networks. But the results of this study cannot be transposed to Cigéo: find out why.
The published study looks at the American geological disposal project, the Yucca Mountain project, the concept of which is different from Cigéo. Consequently, the conclusions on the behavior of glasses referred to in this study cannot be transposed to Cigéo.
Indeed, the long-term safety of Cigeo relies on the Callovo-Oxfordian clay layer which was selected for its excellent properties of confinement of radioactive elements (low permeability, thickness of the layer, physico-chemical properties, etc.). Thus the geological environment limits and slows down the movement of radioactive elements for hundreds of thousands of years.
The geological barrier is supplemented by several complementary barriers, such as glass serving as a matrix for high-level waste. In a cautious approach and to take into account the residual uncertainties on the behavior of the glasses, Andra conducts safety analyzes which consider precisely the repository conditions and integrate all the repository elements (clay, concrete, steel, glass…), as well as the possibility of the glass dissolving faster than expected.
Many studies involving Andra and radioactive waste producers have been undertaken by the Research and Development division of the French Alternative Energies and Atomic Energy Commission (CEA) on the behavior of glass in the repository, and are based in particular on experiments carried out in the underground laboratory at Bure. This work concerns in particular the temperature within the repository, the presence of water from the Callovo-Oxfordian, the saturated and unsaturated water conditions, contact with the Callovo-Oxfordian, contact with steel and its corrosion products. and more recently the presence of water vapour, the presence of low pH cementitious water, and the effect of radiation.