The diagram shows a simple nuclear fission reactor - Leaving Cert Physics - Question 9 - 2006

A chain reaction in the fuel rods occurs when a neutron collides with a fissile nucleus, causing it to split and release further neutrons. These newly released neutrons can then collide with other fissile nuclei, continuing the reaction.

To control this chain reaction, control rods made of materials that absorb neutrons, like boron or cadmium, are used. By inserting or withdrawing these control rods from the reactor core, the rate of the reaction can be increased or decreased, thus maintaining a stable output of energy.

The purpose of shielding in a nuclear reactor is to protect personnel and the environment from harmful radiation emitted during fission reactions. This shielding helps to decrease radiation exposure. A material commonly used for shielding is concrete, which effectively absorbs radiation due to its density.

When the reactor is operational, the coolant circulates through the reactor to absorb the heat generated by the fission reactions. This heat causes the coolant to increase in temperature, ensuring it effectively transfers heat away from the reactor core to produce steam for electricity generation.

One potential effect of a nuclear fission reactor on the environment is the production of radioactive waste, which can contaminate land and water if not stored and managed properly.

When storing radioactive materials, it is crucial to ensure they are kept in a secure location, using safety signs to indicate hazards and locked storage to prevent unauthorized access.