Uranium is the basic material for nuclear programs. Uranium is mined in open pit and underground mines. Uranium is found naturally around the world, but few ore deposits are found. It is a radioactive, silvery-white metal that is hard and dense and easy to form. It has a high density and reacts well with cold water when refined.
In the atmosphere, it is covered with uranium oxide, so it can rise quickly. U fights against steam and acid solutions. Uranium can be found in combination with other metals in solid-state. When some uranium atoms break down into a chain reaction, energy is released. This is called nuclear fission. In nuclear power plants, fission is slow and very rapid in nuclear weapons.
In both cases, there is complete control over the fission. Nuclear fission works best when uranium-235 or plutonium-239 is used. When the U-235 atom splits, it emits two out of two neutrons. More U-235 atoms were planted. The number of neutrons is multiplied. An evolutionary chain reaction occurs. Only a sufficient chain of U-235 atoms can sustain a chain reaction.
The amount of matter that causes this is called critical mass. Of the 1,000 naturally occurring atoms, only seven are U-235 and the remaining 993 are U-238.