chain reactions
No nuclear fission occurs in the body.
A critical assembly of fissile material
Currently, it can't. May be it could be in future.
The term fission generally means to split into parts. When we talk about splitting the atom, we generally apply the term nuclear fission to the process. Nuclear fission, the breaking apart of an atomic nucleus, can occur spontaneously, or it can occur as the result of the bombarding of a nucleus with radiation. Nuclear fission is covered in another related question, and it is linked below.
Uranium does two things because it is unstable. It will either undergo radioactive decay, or spontaneous fission. The processes have some general similarities, but are distinctly different. And both events occur naturally, though spontaneous fission occurs much less often. Additionally, both events result in the emission of particulate and electromagnetic radiation.
Nuclear energy
No nuclear fission occurs in the body.
Nuclear fission, the fission or "splitting" of an atomic nucleus, can happen in two basic ways. One is a form of natural radioactive decay called spontaneous fission. The atom just "splits" apart. The other involves the absorption of a neutron, and fission can occur as a result of this as well. Both spontaneous fission and neutron absorption are described in separate questions here on WikiAnswers. You'll find links to them below.
A critical assembly of fissile material
Currently, it can't. May be it could be in future.
The term fission generally means to split into parts. When we talk about splitting the atom, we generally apply the term nuclear fission to the process. Nuclear fission, the breaking apart of an atomic nucleus, can occur spontaneously, or it can occur as the result of the bombarding of a nucleus with radiation. Nuclear fission is covered in another related question, and it is linked below.
Nuclear fission splits an atom of one element into two atoms of two different elements. This is not usually called transmutation. However, fission is accompanied by subsequent steps, which usually include transmutation.
Uranium does two things because it is unstable. It will either undergo radioactive decay, or spontaneous fission. The processes have some general similarities, but are distinctly different. And both events occur naturally, though spontaneous fission occurs much less often. Additionally, both events result in the emission of particulate and electromagnetic radiation.
first it occur in nature and second it occur in power plant
Transitions between various stages of electron excitement.
A nuclear disaster may occur when the radioactive materials are mishandled and which may lead to radioactive exposure or a chain reaction of nuclear fission, fusion. Most of these disasters are induced by the man made mistakes.
The main consequence is the production of quantities of highly active fission products which would not occur naturally, and which will have to be carefully stored for thousands of years.