The problem with PU is that fast neutrons make it split. With reactors that use thermal /or slow neutrons you have more control. If the substance slowing down the neutrons gets hot , less slow neutrons get made so the reactor is self adjusting that way. PU is great for bombs because the fast neutrons continue the reaction quickly so it all gets used up fast. Perfect for bombs!
Fast reactors are also required to have a negative temperature coefficient.
Bruh did you even read about the IFR? It’s 1970s tech a pool sodium reactor has be design a negative Doppler coefficient heating it up automatically due to the base laws of the universe slows the critical reaction rate down.
They pulled the rods out at full power trying to spike it they could not the negative Doppler coefficient kicks in immediately.
Pool cooled sodium reactor are an order of magnitude safer than BWR or PWR for that matter both can melt down a pool sodium reactor simply cannot. It’s thermal mass and secondary guard vessel air cooling by convection keeps the sodium below the boiling point under any conditions.
You can pull the rods AND kill the pumps it will shut down and convention decay heat cool indefinitely.
Literally walk away safe. The humans could be dead and it will just sit there cooling down. Eventually The sodium will freeze and seal it up for good. In a true end of the world scenario. The double top cover and argon cover gas should last thousands if not tens of thousands of years this doesn’t include the impact rated concrete building around all of that.