What is the main purpose of a moderator in a thermal nuclear reactor? A to shield the surroundings from ionising radiations B to decrease the number of fission chain reactions C to decrease neutron speeds D to prevent the core from overheating - AQA - A-Level Physics - Question 29 - 2021 - Paper 2

The main purpose of a moderator in a thermal nuclear reactor is to decrease the speeds of neutrons. By slowing down the neutrons, they become more likely to interact with fissile material, such as uranium-235 or plutonium-239, thereby increasing the probability of successful fission and allowing for a sustained nuclear chain reaction. This is crucial for maintaining a controlled reaction within the reactor.