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I've got one question... The main issue is that now at Fukushima there are products like Cesium-90 in the sea, contaminating the entire sealife, which have cra

I've got one question... The main issue is that now at Fukushima there are products like Cesium-90 in the sea, contaminating the entire sealife, which have crazy long half-life (ninety years). Thankfully they're "heavy" so they go down towards the center of the earth, but only at about 5 cm per year. So in ten years the're going to be highly radioactive Cesium-90 at 50 cm behind rocks still polluting the sealife. In case the worst sht happens: the worst SNAFU conceivable... Would MSRs also generate highly products like Cesium-90? I mean: I don't care about all the security and the great design meaning an uncontrolled reaction shall never happen. I know: it won't happen. Just like Fukushima. It didn't happen because it couldn't. We got your point. It IS safe. But I tell you: a sht you didn't expect is going to happen (maybe an asteroid striking your reactor or whatever). What then? Would MSRs pollute less than Uranium based reactors in the worst of the worst scenario? If so I'm all for it.

thingification 14y ago
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]
DennisP 14y ago
For starters, on NPR I heard the scientist who measured the Fukushima cesium in fish. He said the level of radioactivity was a small fraction of the amount naturally in the fish. But to your question, the answer is yes, MSRs would pollute less in the worst scenario. It's true they will generate cesium, because that's one of the things left after you fission atoms. However, since it's liquid fuel, the cesium can be removed continually and taken away to storage. (I think the idea is to encase it in glass and bury it.) The amount of cesium in the reactor at any given time is much smaller than for solid-fuel reactors. Also, fission products like cesium are chemically contained in the molten salt. If something breaks open the reactor, the salt will escape, quickly cool, and solidify, containing the cesium. You'll get hot rocks at the reactor site but no radioactive cloud over your community. Many of the engineers claim the reactor wouldn't need water cooling, so it wouldn't have to be on a shoreline. Put it in the desert if you want.

thingification 14y ago

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]

DennisP 14y ago

For starters, on NPR I heard the scientist who measured the Fukushima cesium in fish. He said the level of radioactivity was a small fraction of the amount naturally in the fish. But to your question, the answer is yes, MSRs would pollute less in the worst scenario. It's true they will generate cesium, because that's one of the things left after you fission atoms. However, since it's liquid fuel, the cesium can be removed continually and taken away to storage. (I think the idea is to encase it in glass and bury it.) The amount of cesium in the reactor at any given time is much smaller than for solid-fuel reactors. Also, fission products like cesium are chemically contained in the molten salt. If something breaks open the reactor, the salt will escape, quickly cool, and solidify, containing the cesium. You'll get hot rocks at the reactor site but no radioactive cloud over your community. Many of the engineers claim the reactor wouldn't need water cooling, so it wouldn't have to be on a shoreline. Put it in the desert if you want.