Self answering question.

I believe the answer for your question is fission energy.

Most, or more accurately to say, that, all nuclear power reactors in the world today are based on fission process. A fission reactor uses heavy elements such as uranium and plutonium as fuels. Uranium are by far, the most common element used in the fission reactor, as plutonium does not exist naturally, but have to be 'create'. To do so, we bombard uranium with neutrons, so that uranium would become a new radioisotopes, before decaying into neptunium and finally decay into plutonium.

Fission is the process of disintegration of heavy nuclide to lighter one to achieve stability. During the process, the energy is released as thermal and kinetic energy.

Let say A ~> B + 3n + energy
where A=the unstable atom (called parent nuclide)
B=the stable atom (called daughter nuclide)
n= neutron produced as by product (3n is only average)

The neutrons can induced disintegration of another atom
n + C ~> C unstable
C unstable ~> D + 3n + energy

So, u see, this rection is a chain reaction.

Another example is nuclear reactor. But in a nuclear reactor, the process is being control by manipulating the control rod made of carbon(or boron) to absorb the neutrons released during disintegration. Thus, we can slow down the reaction.

But in atomic bomb, the reaction is intentionally uncontrolled so that the disintegration rate would increase, thus increasing the energy released. The energy released is what we see as a gigantic explosion.(Becoz its energy is expanding so rapidly)

Do u remember the Chernobyl catastrophy. During that accident, the fission reaction was uncontrolled because the operator carelessly forgot to brought down the control rod. So the reactor became hot and finally exploded. The reaction is similar to atomic bomb but on a smaller scale.



Fusion reaction is the process of combining the lighter element to form heavier element. (opposite to fussion)
But similar to fussion, it also release a lot of energy during the process. The light element that i mentioned is hidrogen.

H + H ~> He + energy

This technology required a lot of energy to combine the atoms. Usually we use laser to provide energy to make the atoms collide each other. But in the case of hydrogen bomb, we use small atomic bomb to give sufficient energy for the atoms to combine.

Until todays, no hydrogen bomb was used by any nations. But the Soviet and US have unofficially used it during test. Hydrogen bomb provide greater power that the atomic bomb. Hydrogen bomb need a very advanced technology to acquire it.

Another example of fusion reaction is the sun. The sunlight is actually the energy released during fusion reaction.

The hydrogen bomb is described as cleaner that the atomic bomb. Becoz atomic bomb will produce radioactive waste. And becoz of this characteristic, many countries opt to use it in the future.

note that there is no nuclear power reactor that used fusion reaction since it need a very high energy that even can easily vaporized metal.There is no fusion reactor that has been used to generate electricity. However, there are some experimental reactor that based on fusion process.