what is a controlled nuclear chain reaction?

Answer 1

A controlled chain reaction is one in which
the neutron flux, (density of slow neutrons that
cause fission), is controlled in some way to
limit the speed of the reaction.
This may be done grossly by limiting the density,
(closeness), of the fuel elements, and in fine,
by introducing control elements, (eg. cadmium rods).

Answer 2

As a uranium atom fissions, it releases 2 to 3 neutrons. However, it doesn't release the neutrons all at once. There are prompt neutrons and delayed neutrons. There is just enough time between the prompt and delayed neutrons that a reactor maintained at just barely critical can be controlled at time frames approaching seconds which is slow enough for humans and their control systems to respond to it. The control is the use of control rods which absorb neutrons. When just the right balance of neutrons are maintained, there is one neutron born for every neutron that causes a fission. The rest of the neutrons can be leaked or absorbed by other elements than uranium. When this ratio is very close to 1.000, the reactor is controlled.

Answer 3

It's a chain reaction which the decaying atoms are controlled by the emission of radiation.

Example:

Adding (Cd) and (B) atoms to a Uranium Fission Reaction, that absorb Neutrons and so controlling the emission of radiaton.

Answer 4

its the process that powers nuclear power plants that produce electricity.