> if input power fails fission ultimately stops AIUI fission was stopped basically immediately. The problem was removing the decay heat from the fission by-pro

> if input power fails fission ultimately stops AIUI fission was stopped basically immediately. The problem was removing the decay heat from the fission by-products; without pumps to move cooling water that didn't happen. I think modern reactor designs have enough passive cooling that this failure mode can't happen. There are a lot of active reactor plants where it still could be possible though.