I remember working in the early 90s on a training simulation of the reactor safety shutdown equipment for a UK AGR reactor - this device was pretty critical as

I remember working in the early 90s on a training simulation of the reactor safety shutdown equipment for a UK AGR reactor - this device was pretty critical as it as responsible for sequencing the shutdown operations during a scram. It was designed in the 1960s using technology they were completely confident would work and keep working - so it was basically 1940s electro-mechanical technology: relays, worm gears etc. I don't think they really trusted electronics at that point, let alone computing devices for something so super critical. No idea how that is done now though!