Jean Shao, Twitter asked:
What it is about newer plants that make them safer? So what have we learned from the last 40 years of nuclear development in order to make safe plants?
We’ve learned to make designs that really take advantage of physics. It’s probably misnamed by calling it passive safety, but I would call it better using and understanding the physics. We use gravity, natural convection, those sort of things to help cool the plant after it shuts down. So GE Hitachi’s ESBWR has the ability to remove heat passively without any electricity, without any operator actions for well over 7 days. The PRISM reactor can do that for a very, very long time and if not, forever. So that's where reactor vendors like GE Hitachi have learned “what do we need to do to these designs to make them better and to make them safer?"
Even the first gen of nuclear reactors are some of the safest machines the human race has ever conceived, certainly its only the word nuclear, a sensationalist media and social memory of the cold war that makes us think they are unsafe. it is true however that they can be safer, and should be. without employing hyperbole and without making light of sufferings, even the worst nuclear disasters have had very low body counts. so with objective perspective looking at pure risk vrs reward, nuclear power is by far and away the best choice for our future. Kellzea, Sat, 31st Mar 2012
One thing they employ in nuclear reactors are control rods controlled with electromagnets. This is so that, in case of a complete power failure, the control rods will be completely dropped into the reactor core, completely stopping the reaction. Lab Rat, Sun, 7th Oct 2012
Here is an alternative view: