With nuclear accidents happening occasionally around the world, the safety of nuclear plants has come into question and the concern, if these are safe, has arisen in the past years. However, to dispel this fear, we need to understand as to how do the nuclear power plants work.
Nuclear reactors always have multiple layers of the safety system and if one layer fails, the other takes over. Control rods and nuclear poison are the two important components in any nuclear plant which prevent any accident in the nuclear plant.
It should be understood here that control rods are present in all kinds of nuclear plants and can shut it down within minutes of any potential accident. The nuclear poison which is essentially Boron is present only in pressurized water reactors.
This (boron) kind of nuclear poison is capable of terminating a nuclear reaction within minutes, in case something goes wrong in a nuclear reactor.
However, the threat of any fatal accident occurring in the nuclear reactors is grim as the history of accidents is very well documented and lessons are always learnt from any such previous accidents. In recent history also only three major nuclear accidents have occurred. Three Mile Island, Fukushima and Chernobyl are the only known nuclear accidents and these were contained without any major loss of human life, thus strengthening the thought that nuclear plants are safe.