Describe and explain how a constant rate of fission is maintained in a reactor by considering what events or sequence of events may happen to the released neutrons. (6 marks)

In one fission reaction 2 or 3 neutrons are released at once, to ensure the effectiveness and the safety of the reaction this must be controlled. A neutron is first slowed down by a moderator, which is usually water. The energy of the neutrons is absorbed by the moderator through collisions and it takes about 50 collisions to reach thermal speed. The neutron could also be absorbed by a control rod which is typically made out of boron. Then the neutron is absorbed by uranium 235 to cause a fission event which goes on to cause a further fission event.