Most realistic depiction of a nuclear bomb on Film
Terminator 2 depicts the closest thing to the truth when it comes to a nuclear explosion. James Cameron (the director) received a letter from a nuclear laboratory thanking him for Terminator 2 and for the most realistic depiction of a nuclear bomb going off they had ever seen.
There are much better videos on Youtube. T2 sets out to be entertainment, rather than information. You are not seeing the wider scale of the impact or the aftermath (nuclear winter).