Another advance: resistant glass
The second major industrial advance is the highly resistant borosilicate glass used at La Hague. According to CEA's estimates, this glass loses only a thousandth of its volume in 10,000 years, and 10% after a million years. The silica dissolved in the water of a geological environment would slow its erosion. A protective gel would form, increasing the material's longevity. After these timescales, the radioactivity would have practically disappeared, if humans were still around to notice it.
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