According Wikipedia there are two types of nuclear fission:

One type, discovered by German physicist Otto Hahn, 1938, produces pure energy (in the shape of steam) at nuclear power plants under moderated conditions.

Another, very nasty type producing destruction, invented by an American clown under military secrecy 1942/5 is the following: Until destruction is desired, it is kept subcritical - in the case of a uranium bomb, it is achieved by keeping the fuel in a number of separate pieces, each below the critical size. No fission occurs! To produce destruction, the pieces of uranium are brought together rapidly - to become critical - to drive the instantaneous explosion FLASH of the nuclear weapon into the atmosphere. It lasts some nanoseconds and vaporizes and radiates innocent people that happen to be in the way.

The second, nasty type fission is pure pseudoscience to scare you and a BIG JOKE. Evidently bringing two separate subcritical pieces of uranium in contact with each other does not produce one solid piece with a critical mass that suddenly detonates. Two metal pieces cannot become one by compressing them together ... and even if they can, they will not detonate.

Metal cannot explode!

Nuclear fission is only possible under moderated and controlled conditions to produce energy in form of electricity and heat. Fission producing destruction is nonsense. You should wonder why Wikipedia cannot say so!