I don’t think the problem was ever solved, the focus was on developing Uranium, and Plutonium reactors. I believe that there was just one Thorium reactor as a

I don’t think the problem was ever solved, the focus was on developing Uranium, and Plutonium reactors. I believe that there was just one Thorium reactor as a trial project, which didn’t progress so the technology hasn’t matured. It didn’t have the impetus.