Fission in Uranium would take billions of years when its left to its own devices. Because of radioactive decay, it would either release alpha or beta radiation, or fission. The earth would have to be really old for that to maybe happen. Besides, Only less than 1% of Uranium is U-235, which is the only isotope of uranium that would fission, is found on earth.
Plutonium I think.
We look to the naturally occurring element uranium as a nuclear fuel.
In every nuclear reactor that is operating
Fusion ocurs in the stars including our sun. I don't know of fission occurring naturally anywhere, but there is evidence it once did in a few places on earth a long time ago. At that time there would have been more U-235 which has now reduced by decay. It may occur elsewhere in the universe in planets like earth, but we have no way of knowing this. Natural nuclear fission: Oklo - please see the related link, below
nuclear fission
Because uranium-235 can easily be made to fission in a reactor with a moderator to slow the neutrons down, a chain reaction can be sustained, and heat is generated which can be harnessed for electricity. Uranium is usually used because it is the largest naturally occurring atom. A smaller atom would not split as easily, and a larger atom would first need to be created before it could be split.Also Uranium-235 is the only isotope capable of undergoing fission and supporting a chain reaction of any element on earth that occurs naturally at high enough levels (0.72% of natural Uranium) to make it economically extractable. Other fissionable materials have to be produced in sufficient quantities in "breeder reactors" where the radiation converts certain non-fissionable elements into other fissionable elements through neutron capture. Because uranium is much more common that was believed early in the development of nuclear reactors, it is much more economical to refine naturally occurring uranium (separating the U-235 from U238) than to use breeder reactors to convert non-fissionable isotopes into fissionable ones and then refine the result to produce more nuclear fuel.A very slightly different world (e.g. older) and nuclear energy and weapons might never have been possible at all.
The idea of nuclear fusion occurring at room temperature is called cold fusion.
Nuclear fission happens spontaneously in nature. Uranium-235 does this, and is the only commonly occurring natural isotope that does. Nuclear fission can be induced by crashing a neutron into a fissionable atom. Some things other than Uranium-235 are fissionable, notably Uranium-238. Fission has been induced in various experiments. It happens in nuclear reactors and in nuclear bombs.
You get nuclear fission in:nuclear fission reactorsatomic fission bombs
nuclear fission
nuclear fission
krypton and barium are both naturally occurring non-radioactive elements. krypton can be extracted from air by fractional liquefaction. barium ore can be mined and barium extracted.