Nuclear Reactor

- Overview

A nuclear reactor, formerly known as an atomic reactor, is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reaction. Nuclear reactors are used in nuclear power plants to generate electricity and for nuclear ship propulsion. 

The heat from nuclear fission is transferred to the working fluid (water or gas), which in turn flows through the steam turbine. They either drive the ship's propeller or turn the shaft of a generator. Steam from nuclear energy can in principle be used for industrial process heating or district heating. Some reactors are used to produce isotopes for medical and industrial use, or to produce weapons-grade plutonium.

- Heat Generation

The reactor core generates heat in a number of ways: 

• The kinetic energy of fission products is converted to thermal energy when these nuclei collide with nearby atoms.
• The reactor absorbs some of the gamma rays produced during fission and converts their energy into heat. 
• Heat is produced by the radioactive decay of fission products and materials that have been activated by neutron absorption. This decay heat source will remain for some time even after the reactor is shut down.

A kilogram of uranium-235 (U-235) converted via nuclear processes releases approximately three million times more energy than a kilogram of coal burned conventionally (7.2 × 1013 joules per kilogram of uranium-235 versus 2.4 × 107 joules per kilogram of coal). 

The fission of one kilogram of uranium-235 releases about 19 billion kilocalories, so the energy released by 1 kg of uranium-235 corresponds to that released by burning 2.7 million kg of coal.