Subject : Power Plant Engineering

Topic: Chap 5- Nuclear Power Plants

Difficulty: Medium

In any chain reaction, the neutrons produced are fast moving neutrons. These are less effective in causing fission of U235 and they try to escape from the reactor. It is thus implicit that speed of these neutrons must be reduced if their effectiveness is carrying out fission is to be increased.

This is done by making these neutrons collide with lighter nuclei of other materials, which does not absorb these neutrons but simply scatter them. Each collision causes loss of energy and thus the speed of neutrons is reduced. Such a material is called a Moderator. The neutrons thus slowed down are easily captured by the fuel element at the chain reaction proceeds slowly.