There is no excuse for any power reactor to not be “walk-away safe”.
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Yeah that’s part of the genius of thorium lftr reactors. they are walk away safe.
My understanding is that the French pebble bed uranium reactors are totally walkaway safe. Pellets of uranium are encapsulated in ceramics (think space shuttle tiles) that both keep the pellets at a uniform distance and also prevent meltdown should the water evaporate.