Coolant is used to remove the heat produced from the reactor core. This heat is then transferred to the electrical generators or the environment. Water, liquid sodium, helium and carbon dioxide are most commonly used coolants.

The energy released due to a loss in mass during the process of nuclear fission and fusion is called nuclear energy. In both these processes, the loss in mass gets converted into energy in accordance with Einstein's mass-energy relation $E=mc^2$.

Uranium $238$ is used in nuclear reactor for fission reaction.

Nuclear fission carried out in a nuclear power plant is a controlled chain reaction which can be controlled to stop if required.

The yield of nuclear energy is enormous and hence it has extraordinary potential as an energy source.

Nuclear radiations are extremely harmful to human health. They can cause:

A self sustaining reaction where the neutrons bombard an atom resulting in the fission process which leads to the release of more neutrons which then bombards more atoms and the cycles goes on.

Splitting of a large atomic nucleus into smaller particles is called nuclear fission.

Nuclear energy can be of two types: nuclear fission and nuclear fusion. Both the types is used for the generation of electricity.

1 kg of coal can light the bulb for 8 hours whereas 1 kg of uranium can light the bulb for 3 x 10$^4$ years.

Energy generation from the nuclear energy is greater than from any non-conventional sources of energy. But it has some disadvantages too, such as:

With a complete combustion or fission, approx. $8 \ kWh$ of power can be generated from $1\  kg$ of coal, approx. $12 \ kWh$ power from $1\  kg$ of mineral oil and around $24,000,000\  kWh$ of power from $1 \ kg$ of Uranium-$235$.

Waste products formed during nuclear reactions are highly radioactive in nature and cannot be disposed into the environment directly. Wastes needs to be processed before releasing it into the environment.

1 kg of coal can light the bulb for 8 hours whereas 1 kg of uranium can light the bulb for 3 x 10$^4$ years.

Radiation from the radioactive elements pollutes not only the environment but also the civilization coming in contact with it. It causes radiation sickness which left untreated causes fatality.

Kaiga Generating Station is a nuclear power generating station situated at Kaiga, near the river Kali, in Uttar Kannada district of Karnataka, India. The plant has been in operation since March 2000 and is operated by the Nuclear Power Corporation of India. The plant is fueled by indigenous Uranium.

Nuclear fuels are non-renewable sources of energy and large amount of radioactive materials, which are toxic in nature, are released in the environment which are extremely hazardous to the health of living being for thousands of years. Thus nuclear energy also has some harmful effects.

Atomic energy 

A 

In hydrogen bomb we use the process of fusion.

Nuclear fusion is a nuclear reaction in which two or more atomic nuclei at a very high speed and join to form a new type of atomic nucleus. Fusion reactions are high energy reactions in which two lighter atomic  nuclei fuse to form a heavier nucleus. This fusion reaction is taking place in hydrogen bomb.