Nuclear Fission provides about 10% of the world’s electricity, powers naval vessels around the world, and has powered space missions.

The energy released by fission is a million times greater than the chemical energy released by combustion, so a small amount of nuclear fuel, usually uranium, produces an enormous amount of heat. Over four hundred nuclear power plants around the world produce 400 GW of electricity, enough for 300 million US homes.

The fission reactors at each of these nuclear power plants create steam that turns a turbine to generate electricity, just as coal and gas plants do. Find out how nuclear reactors of the present and future work.

Pressurized Water Reactors and Boiling Water Reactors

Pressurized Water Reactors (PWR) and Boiling Water Reactors (BWR) are the most common reactors in the world today. In both PWRs and BWRs, light enriched uranium fuel, arranged in the reactor's core, heats water.

Pressurized Water Reactor

Pressurized Water Reactor

PWRs use high pressure to prevent water from turning to steam in the core; steam is created in a secondary loop using a steam generator.

Boiling Water Reactor

Boiling Water Reactor

BWRs generate steam directly in the core of the reactor, eliminating the need for some equipment, but resulting in radioactive steam in the turbine.

Control rods, neutron absorbing movable rods, are used in both reactors to control the chain reaction caused by neutrons from fissioning atoms being released and creating more fissions. By absorbing neutrons, the control rods sustain the chain reaction and keep it at an efficient rate.

Small Modular Reactors (SMRs) and Microreactors

SMRs and microreactors gained significant attention in recent years. These reactors are small in terms of size and energy production, compared to large existing reactors, so they can be constructed in a factory. When more energy production is needed, more SMRs can be added.

There are a number of significant advantages to SMRs and microreactors.

  • They can be transported on a semi-trailer or a barge wherever they are needed. The military is researching use of small reactors for reliable heat and power at even remote bases.
  • Their simpler design, compared to conventional reactors, means they require fewer components, less maintenance, and fewer workers. In addition, they are designed to be self-adjusting and fail-safe with passive safety systems that prevent the possibility of over-heating.
  • They can be installed quickly. Research shows that SMRs and microreactors can be installed and generating power within a week of arriving on site.

SMRs and microreactors may be small, but they can utilize a wide variety of nuclear technologies and open new markets at lower cost. The first non-water based microreactor license application was submitted in March of 2020; the Nuclear Regulatory Commission certified the reactor design in August 2022. Other SMR and microreactor designs are in development or operation around the world, including floating SMRs in Russia, heat generating reactors in China, and a variety of other concepts.

Non-Light Water Reactors (LWRs) and Advanced Reactors

Advanced reactors build on the lessons learned from LWRs and non-LWRs and offer the potential of more economic, safer, diverse, and efficient ways to generate clean energy for the future. Water based and non-water based advanced reactors are under development all over the world and significant progress towards widespread use is expected in this decade.

Learn more about fission


The Tokamak and its plant systems housed in their concrete home. An estimated one million parts will be assembled in the machine alone.

Nuclear fusion has the potential to provide large amounts of energy and has been the focus of billions of dollars in international scientific collaboration. Fusion research and development has yet to achieve breakeven power production (producing more power than consumed), and numerous public and private organizations are pursuing different forms of technology. Three approaches are Magnetic Confinement Fusion (MCF), where magnets compress and contain a heat fusion plasma; Intertial Confinement Fusion (ICF), where lasers strike a fuel target to create the conditions for fusion; and Magnetized Target Fusion, a combination of elements of MCF and ICF.

Learn more about fusion

Last modified May 15, 2023, 1:38pm CDT