On Monday, 17 June 2024 13:39:35 BST Wols Lists wrote: > On 17/06/2024 12:17, Alan Mackenzie wrote: > > Sadly, the FBR never made it into commercial deployment. > > Was that the one with the heavy water moderator? So a thermal runaway > was impossible because you'd have no moderator left?
No, that was another design of water-cooled reactor with the same instability problem: it could have melted down long before the moderator was lost. I used to know the differences between reactor designs, but that was 40 or 50 years ago. Pressurised water reactor; boiling water reactor, ... I'm still convinced that the gas-cooled design is the best, and that's not just because we were the first to market with it. The fast breeder reactor at Dounreay used uranium and plutonium fuel (I think) and was cooled with liquid sodium - yes, really. It used the fast, Multi-MeV neutrons directly from the fission of uranium, not needing a moderator to bounce them around and cool them to thermal energies, 2KeV, as in all other uranium-fuelled reactors. The core was the size of a largish, red-hot dustbin and generated 120 MW. A quite astonishing power density. Frightening, too. That will no doubt be why it was built at the most remote site in mainland Britain. The breeding aspect is that it created thorium while it was operating, which could then be used as the fuel in other reactors. There's still a school of thought that thorium would make a much safer, more economical reactor. I don't know why the FBR programme was cancelled; I thought it held great promise at the time, but perhaps the chemical challenges were too great: liquid sodium flying around in steel pipes, and so on. -- Regards, Peter.
