It's intermediate half-lives that are problematic. Very long half lives (for example, billions of years, like Th 232) are not a problem, because they have low

It's intermediate half-lives that are problematic. Very long half lives (for example, billions of years, like Th 232) are not a problem, because they have low activity (few particles emitted per second). Very short half lives (for example, minutes) are not a long-term problem, because they are entirely gone after those minutes. It's the middling half lives that get you: short enough to be highly active, long enough to stick around for years. So, Cs 137 and I 90 stick around for a few hundred years. That's bad, and LFTR still produces these. On the other hand, it's a lot better than the situation with conventional U reactors, because those produce transuranic elements with intermediate half lives measured in tens of thousands of years. There is a qualitative difference to human civilisation between 300 years and tens of thousands of years. LFTR produces those transuranic elements too, but in orders of magnitude less quantity -- that combined with the liquid phase leads us to expect that would be a much smaller problem than with conventional reactors. Wikipedia suggests some other LFTR advantages here, which I haven't thought about: https://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reactor https://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reacto... Low mobility of radioactivity. Even if there is an accident beyond the design basis for the multiple levels of containment and passively cooled systems, fluorides do not easily enter the biome. The salts do not burn, explode, or chemically degrade in air and react only slowly with water. Fluorine combines ionically with most fission products to form stable fluorides. This is not only an MSFR's first level of containment, but also serves as a high inherent safety level during any beyond-design basis event. Fluoride is especially good at holding biologically active "salt loving" wastes such as cesium-137 and strontium-90, which are permanently bound as stable, nonvolatile CsF and SrF2. The fluoride salts of radioactive actinides and fission products are generally not soluble in water at lower temperatures. Even though Caesium fluoride is one of the fission product fluorides that is highly water soluble, its extremely high boiling point and chemical stability, combined with the lack of stored energy sources (hydrogen, steam, etc.) in the LFTR, prevent it from being blown into the air and carried with the wind to contaminate a large amount of land.[citation needed]