Let us imagine that, by a hundred years, our descendants decide to get rid of long lived fission products by sending them beyond the solar system, and they fire a rocket loaded with 11 tons technetium, the production of technetium during 10 years by the 60 French reactors. Unfortunately, the rocket taking these 11 tons ended up in a mountain lake a cubic kilometer volume in which everything has dissolved technetium What would the impact of this disaster? The calculation shows that one should drink about one cubic meter of water from this lake to be exposed to a dose equal to one year of exposure to natural radioactivity.