The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Describe the reactions in a nuclear reactor and the means that engineers use to control reaction rates. (E)

A nuclear reactor is a device that uses nuclear reactions to produce energy, typically in the form of heat, which is then converted into electricity. The nuclear reactions in a reactor occur when atomic nuclei collide with one another, releasing large amounts of energy. The most commonly used nuclear fuel in reactors is Uranium-235 (U-235). In this exercise, we will be focusing on the reactions happening inside a nuclear reactor and how engineers control the reaction rates to optimize the energy production and ensure its safe operation.

The primary nuclear reaction that takes place in a reactor is called nuclear fission. In this process, a heavy nucleus (such as U-235) absorbs a neutron and then splits into two smaller nuclei, along with releasing several neutrons and a significant amount of energy. The released neutrons can go on to cause fission in other U-235 nuclei, leading to a chain reaction. The energy released in the form of heat is utilized to produce steam, which drives turbines and generates electricity.

In order to maintain a stable and safe operation of a nuclear reactor, it is crucial to control the rate at which nuclear reactions occur. This is primarily done by controlling the number of neutrons that are available to initiate further fission reactions. Engineers use a combination of the following methods to achieve this control: 1. Control rods: These are rods made of neutron-absorbing materials, such as boron or cadmium, which are inserted or removed from the reactor core to regulate the number of neutrons available for fission. By adjusting the position of control rods, engineers can influence the rate at which the chain reaction proceeds. 2. Moderator: A moderator is a material used in the reactor core to slow down the neutrons produced during fission, making them more likely to be absorbed by the fuel and continue the chain reaction. Water, heavy water, or graphite are commonly used as moderators. By adjusting the properties or presence of the moderator, the neutron speed and subsequent fission rates can be manipulated. 3. Coolant: A coolant is used in a nuclear reactor to remove the heat generated during fission. The flow rate and temperature of the coolant can be adjusted to impact the reactions occurring in the reactor core. Higher coolant flow rates can remove more heat from the core, reducing its temperature and affecting the reaction rate. In summary, nuclear reactors utilize fission reactions of heavy nuclei like U-235 to produce energy. These reactions release neutrons, which can go on to cause additional fission reactions. Engineers control the reaction rates inside the reactor by adjusting the number of available neutrons using control rods, moderators, and coolant flow rates in order to maintain a stable and safe operation while optimizing energy production.