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The trouble with molten salt thorium reactors is that they need an attached chemical plant that processes molten sodium mixed with radioactive elements.
This is not something a utility wants to own, maintain, and operate.
Here are some studies on such plants.[1] No full scale long-running salt reprocessing plant has ever been built. The great thing about boiling water reactors is that you just have to handle water. The radioactive portion of the systems is simple. Which is good, because it can't be maintained much during the entire lifespan of the plant. When you look at the history of nuclear reactors, almost all the problems involve plumbing.
The less that can go wrong with the plumbing, over 60 years or so, the better. For molten salt reactors, the physics is promising, the chemistry is a pain (fluorine, for starters), and the plumbing has major corrosion and clogging problems (high temperature radioactive molten salts and pipes just do not get along, even with really exotic alloys.) It's not impossible. But it's going to be prone to expensive problems, some of which probably will not be anticipated. Remember Ft. St. Vrain, the helium gas cooled reactor. Great idea. Ran for ten years. Even used some thorium. Troubles in the radioactive portion of the gas plumbing system meant it had to be shut down and dismantled.[2] That was sad, because it actually worked well for years. [1] https://www.osti.gov/servlets/purl/1484689 [2] https://en.wikipedia.org/wiki/Fort_Saint_Vrain_Nuclear_Power... |
Online reprocessing of nuclear fuel necessary for some thorium fuel cycle designs (reprocessing inside the nuclear power plant) could increase the risk of nuclear proliferation. U.S. government, as a general policy, doesn't like when non-weapon states do nuclear reprocessing.