Thanks, I had no idea lead-bismuth reactors existed. It seems the large number of unstable lead isotopes and their long decay chain would assure a long cooldown requirement before any maintenance could be done in the reactor compartment/primary coolant system. Not only that, but this stuff would present a huge disposal problem. https://en.wikipedia.org/wiki/Isotopes_of_lead

It seems the Alfa class was decommissioned for scrapping, though one was refitted with a pressurized water reactor for a while. https://en.wikipedia.org/wiki/Alfa-class_submarine#Decommiss...

An interesting issue with this design is that if the Pb-Bi coolant ever solidified, the reactor control rods became frozen in place.