Light-Water Reactor

Definition

A light-water reactor (LWR) is a type of nuclear reactor that uses ordinary water (as opposed to heavy water) as the coolant and neutron moderator. It is the most widely used type of nuclear reactor for the generation of electric power.

5 Must Know Facts For Your Next Test

1. Light-water reactors use ordinary water (H2O) as both the coolant and the neutron moderator, slowing down the neutrons to increase the likelihood of fission.
2. The two main types of light-water reactors are the pressurized water reactor (PWR) and the boiling water reactor (BWR), which differ in how the water is used to generate steam.
3. Light-water reactors are designed to operate at high pressures, typically around 150 atmospheres, to prevent the water from boiling at the high temperatures inside the reactor core.
4. The fuel used in light-water reactors is typically low-enriched uranium, which contains a higher percentage of the fissile isotope U-235 than natural uranium.
5. Light-water reactors are known for their relatively simple design, high thermal efficiency, and good safety record, making them the most widely used type of nuclear reactor for commercial power generation.

Review Questions

• Explain the role of the coolant and moderator in a light-water reactor.
  • In a light-water reactor, the ordinary water (H2O) serves a dual purpose as both the coolant and the moderator. The coolant removes the heat generated by the fission process, while the moderator slows down the high-energy neutrons to increase the likelihood of further fission reactions. The water acts as a moderator by colliding with the fast neutrons, reducing their energy and allowing them to be more easily absorbed by the fuel, thus sustaining the chain reaction.
• Describe the two main types of light-water reactors and how they differ in the way they generate steam.
  • The two main types of light-water reactors are the pressurized water reactor (PWR) and the boiling water reactor (BWR). In a PWR, the water in the primary coolant loop is kept under high pressure to prevent it from boiling, and the heat is transferred to a secondary loop where steam is generated. In a BWR, the water in the reactor core is allowed to boil, and the steam generated is used directly to drive the turbines and generate electricity.
• Analyze the advantages and safety considerations of light-water reactors compared to other nuclear reactor designs.
  • Light-water reactors are the most widely used type of nuclear reactor due to their relatively simple design, high thermal efficiency, and good safety record. The use of ordinary water as both the coolant and moderator contributes to their safety, as water has a high heat capacity and can effectively remove heat from the reactor core. Additionally, the high-pressure operation and multiple safety systems in place help to mitigate the risk of accidents. However, light-water reactors also have some safety concerns, such as the potential for hydrogen buildup and the need for careful management of the radioactive waste produced.

Related terms

Fission:

The splitting of heavy atomic nuclei, such as those of uranium or plutonium, into lighter nuclei, which releases a large amount of energy.

Coolant: A substance, such as water or air, that is circulated through or around a nuclear reactor to remove or transfer heat.

Moderator:

A material, such as water, graphite, or heavy water, used in a nuclear reactor to slow down neutrons and increase the likelihood of further fission.