I think you are having a tough time distinguishing a nuclear bomb from a nuclear reaction.
A nuclear warhead is built different and when the fission starts it is, let's say, less controlled. There is a dramatic split of atoms and BANG... you have a nuclear explosion.
If a nuclear reactor core is not cooled properly and allowed to heat it begins to melt everything around it and you have a nuclear disaster on your hands...not a simple battery acid leak.
Have you ever heard of Chernobyl?
Chernobyl was a city in the Soviet Union and also was powered by a nuclear reactor. The nuclear reactor had a total meltdown and it killed 56 people outright and wrecked the environment. A city of 336,000 people had to be evacuated and remains abandoned to this very day. A modern ghost town. 800,000 Soviets were exposed to radiation and there have been about 4000 deaths attributed to the meltdown.
Thats some battery leak!
Yes! I remember the warnings that went accross Canada about Chernobyl and the wind back sometime around 1980.
But, you say "there is a dramatic split of atoms" that is excatly how an A-bomb works. Now I know nuclear warheads are really atomic warheads.