For the longest time, nuclear energy has divided opinions across the globe. Countries with this resource have always been considered more powerful. This is understandable, considering the energy can be catastrophically destructive, especially if used in atomic bombs or fail.

However, did you know that nuclear is the world’s second-largest source of low-carbon power? It’s vital for producing clean energy and can be used better. One of the components that makes nuclear efficient is the nuclear reactors. Here are some nuclear reactor facts to get you started.

1. Nuclear Reactors are the Heart of Nuclear Plants

Nuclear reactors are to nuclear plants what the heart is to humans. They control all the nuclear chain reactions needed for the plant to produce the much-needed heat. They do this in a process known as nuclear fission, resulting in spinning turbines that produce electricity.

2. Uranium is the Basic Nuclear Reactor Fuel                  

As with other plants, nuclear reactors require regular refueling, usually after 12, 18, or 24 months. Uranium is the most used fuel, with the uranium-U-235 specifically being the most preferred option (it’s easy to split apart.

Operators open the reactor vessel to refuel and fill it with small, processed ceramic uranium pellets. The process involves replacing about a third of the fuel with new rods. While uranium is the most commonly used fuel, this may vary depending on the type of nuclear reactor and its needs.

For instance, a 1000 MWe class PWR can use about 51,000 fuel rods containing about 18 million pellets.

3. Several Power Ratings of Nuclear Reactors Are Available

The efficiency and power output of a nuclear reactor are quoted in the following ways:

Thermal MWt

Megawatts thermal (MWt) refers to the power input a heat engine can produce. For nuclear reactors, their MWt depends on their quality and quantity. The bigger the nuclear reactor, the higher the output.

Gross Electrical MWe

The gross electrical MWe measures the power from the nuclear reactor’s steam turbine and generator. In some cases, it can also tell the temperature of the condenser circuit.

Net Electrical MWe

This refers to the power the nuclear reactor can supply to the main grid. It accounts for the remaining power after removing the one needed to run the reactor itself. Both net and gross electrical MWe are affected by weather, so slightly lower figures are used in specific seasons.

4. Nuclear Reactors Have Several Components

Apart from fuel, nuclear power reactors have other components that allow them to run efficiently. They include the moderator, control rods/blades, coolant, containment, and steam generator. Pressure vessels or tubes are also necessary for transporting the coolant within the nuclear reactor system.

5. There are Different Types of Nuclear Reactors

Over time, countries have developed different types of nuclear reactors to keep up with the demands. The Pressured Water Reactor (PWR) is the most common option. It has about 300 operable reactors tasked with producing power and others for naval propulsion. Water is its primary coolant and moderator.

Countries like France, the USA, Russia, Japan, South Korea, and China are the most common users of PWRs. The states have a total of 307 pressured water reactors. PWRs have the highest GWe ratings, with 292.8.

The other types of nuclear reactors include the following:

Boiling Water Reactor (BWR)

The only significant difference between a boiling water nuclear reactor and the pressured water reactor is that the former has one circuit in which the water has lower pressure, allowing it to boil in the core at about 285 degrees Celsius. This makes BWRs a better option for mode following mode compared to PWRs.

However, few countries have adopted BWRs, with only Japan, Sweden, and USA being active users. Only 60 units of boiling water reactors are available and shared across the 3 users.

Pressured Heavy Water Reactor (PHWR)

With about 47 pressured heavy water reactors available, Canada and India are the only known active users. PHWR relies on heavy water (deuterium oxide D20) as its neutron moderator and coolant. It is a 235 MWe nuclear reactor (pressure tube type) that adopts the CANDU design from Canada.

Light Water Graphite Reactor (LWGR)

The light water graphite reactor is almost similar to the pressured heavy water reactor, only using light water as a coolant. It contains pressure tubes full of fuel and is often surrounded by a graphite moderator. With a GWe rating of 7.4, Russia is the only active state with these reactors, with 11 units available.

The advanced gas-cooled reactor (AGR), Fast Neutron Reactor (FNR), and High Temperature Gas-cooled Reactor (HTGR) are the lesser-known/used examples of nuclear reactors.

6. First Generation Nuclear Reactors Have Been Retired

Due to nuclear energy’s efficiency, there is always a need to improve the designs of nuclear reactors. As new generations come in, the old ones (the first generation) have been retired. Apart from improving productivity, newer designs are necessary for reducing the cost of operation and improving general safety.

Even though the II-generation reactors are now commonly used, countries like Japan have used the much-improved III-generation reactors since 1996. They come with advantages such as:

  • Standard designs and licensing
  • Are easier to operate
  • Longer operating life – up to 60 years
  • Has a better grace period after shutdown. Gives operators about 72 hours before requiring intervention
  • Uses fuel more efficiently
  • Less susceptible to operational upsets.

The retired 1st generation nuclear reactors had high operation costs, needed much human intervention, and could fail anytime.

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Last Update: August 9, 2023