Natural glass and glass for waste
The durability of naturally-occurring glass provides a guide to the strength of such materials over very long periods. Volcanic obsidian can be compared with a sample of R7T7 glass, which is used for waste. (It goes without saying that the sample being held in the photo has not been filled with radioactive atoms). Experts estimate the life of such glass to be well in excess of 10,000 years, after which time the initial radioactivity will have decayed by a factor of more than 1,000.