The Basics:

The main principle behind most traditional sources of electrical generation is to use an energy dense fuel like coal, oil, natural gas, or in the case of nuclear power, uranium as the energy source. That source is used to heat water to its boiling point so that it is turned into steam, which then turns a turbine that is connected to a generator thereby creating electricity. The steam then passes through a condenser, where it is condensed back to liquid and the process is repeated. 

Source: Union of Concerned Scientists Basic Diagram of a Boiling Water Reactor

Source: Union of Concerned Scientists

Basic Diagram of a Boiling Water Reactor


Uranium is an extremely energy dense fuel. Through a process known as fission, the uranium atoms are bombarded by neutrons. The neutrons split the uranium atoms, which in turn send out more neutrons, splitting even more uranium atoms, creating a chain reaction. As a byproduct, the chain reaction creates an excess of heat, referred to as an exothermic reaction, which is a chemical reaction that releases energy by light or by heat – and in a chemical equation: reactants → products + energy. By making use of this exothermic reaction, water is heated to roughly 520 degrees Fahrenheit, causing it to create steam and turn the turbine. Nuclear power reactors throughout the world rely on fission to create electricity. Unfortunately, fission by-products remain radioactive for thousands of years.

Arnie Gundersen standing adjacent to a model of the Cross Section of a Reactor Vessel in Japan

Arnie Gundersen standing adjacent to a model of the Cross Section of a Reactor Vessel in Japan

  • Control Rods: Help absorb neutrons during the atomic power chain reaction so that the fission process doesn't get out of control. By inserting or removing some of the control rods from the reactor core, operators manage the rate of the atomic reaction that then determines the amount of electricity produced
  • Reactor Vessel: The thick metal structure that houses the nuclear reactor core where the fission reaction takes place 
  • Fuel Rods: A long tube often made of Zirconium, which is filled with fuel pellets. These rods are arranged into bundles and are then loaded into the reactor core. 


Reactor Types:

Nuclear reactors are most often classified by their coolant type. The most common reactor type is the Water Cooled Reactor. Water used in these reactors is the commonly occurring H2O.  The water-cooled reactor types can be broken down into Boiling Water Reactors (BWRs) and Pressurized Water Reactors (PWRs). The main difference between BWRs and PWRs is that:

  • In BWRs, the water is brought to a boil and allowed to turn to steam through direct contact with the fuel rods.
  • In PWRs, the water in contact with the fuel rods is pressurized so that it does not boil. The hot pressurized water is then circulated through pipes and the heat is transferred to a separate body of water. This secondary body of water is not pressurized so it does boil and turns to steam, completing the rest of the generation process. PWRs keep the water that is in direct contact with the fuel rods in a closed loop system, separate from the water that is turned to steam so as to keep the radiation better contained. 

Because the BWR or the PWR designs operate using ordinary water, the uranium fuel needs to increase the amount of fissionable uranium (U235 isotope) from less that 1% found in nature to about 5% in a process called enrichment, which occurs in a specialized enrichment facility.

A third type of reactor was developed by the Canadian Government, called the CANDU design, which stands for CANDU stands for CANada Deuterium Uranium, because it was invented in Canada, does not use common H2O as a moderator, but rather a type of water containing a hydrogen isotope called deuterium D2O that is also referred to as heavy water because it weighs 10% more than regular water. This design runs on natural uranium without enrichment and can be readily adapted to make plutonium used in atomic bombs. India and Pakistan used the CANDU design to create their atomic weapon arsenals.

There are several other reactor types besides PWRs and BWRs, but most of these are in the developmental stages and have yet to see real world operation. As opposed to the water in PWRs and BWRs, some concepts utilize liquid metal, gas, or molten salt to absorb the heat from the fission reaction and transfer it to a turbine. One reactor that we get a lot of questions about is the Liquid-Fluoride Thorium Reactors, which is a type of Molten Salt Reactor (MSR). To visit our webpage about LFTRs and learn more about them click here.


There is a lot of work going into the research of nuclear fusion. In nuclear fusion, two atomic nuclei are bonded or "fused" together to form one, causing a large release of energy. It is the process that creates a star's energy. The idea of a fusion power plant is often idealized because it has the potential to offer an almost unlimited supply of energy, while still radioactive, the timescale is in the hundreds of years as opposed to hundreds of thousands, and there is little to no waste made. The research and development of nuclear fusion as a means to generate electricity really began in the 1950's and while some breakthroughs have been made since then, many more technological challenges still remain in making fusion a reliable and safe power source. 

You can also listen to Arnie give a rundown on nuclear power 101 from a presentation he gave at the University of Vermont back in July of 2011. In it he covers how nuclear power plants work, how to cool a reactor during an accident, the effect of hot particles when inhaled, and concerns involving the long-term storage of nuclear waste.