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Nuclear Fission

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Fast Facts About
Nuclear Fission

Principal Energy Use: Electricity
Form of Energy: Nuclear

Nuclear fission is the process of splitting a large atom into two smaller atoms and releasing a LOT of heat. That heat is used to boil water, make steam, turn a turbine and generator, and produce electricity. Most nuclear power plants today are fueled by enriched uranium 235 to produce non-renewable, carbon-free, 24/7 electricity. The byproducts of nuclear fission are highly radioactive and must be secured away from people for hundreds of thousands of years. There are currently no proven long-term solutions for storage of this radioactive waste.

Nuclear power plants have been operating commercially since the 1950s and tend to be large-scale (1-2 GW). The risk of accidents is low, but the consequences of a nuclear power plant accident have the potential to be extremely severe. Due to the complexity of containing the nuclear reaction and the need for redundant safety systems, capital and operating costs tend to be high and there are long lead times for planning and construction. New technologies known as small modular reactors (SMRs) are being developed in the hopes of offering cheaper and safer alternatives to traditional fission reactors.

The roots of nuclear fission power come from defense. The commercial nuclear industry in the US was born in response to the horror of the destruction from the bombs dropped on Japan at the end of WWII. In the US, the nuclear industry is the only energy industry which has its own governmental agency (the Nuclear Regulatory Commission - NRC), and nuclear-related activities account for ~70% of the US Department of Energy’s budget.


Energy Mix

5% of world 🌎
(#5 resource)
8% of US 🇺🇸
(#5 resource)

Electricity Generation

10% of world 🌎
(#4 resource)
19% of US 🇺🇸
(#3 resource)

Number of Nuclear Reactors*

World 438 🌎

US 92 🇺🇸
France 56 🇫🇷
China 55 🇨🇳

Global Nuclear Electricity Demand

Modest increase:

*Many nuclear power plants have multiple reactors

Most Uranium Production

Kazakhstan 45% 🇰🇿
of global uranium mining

Global Uranium Sources

Uranium mines 90%
Weapons recycling 10%

Energy Density of Uranium

33,000x more energy dense than oil

37,000,000x more energy dense than natural gas

Uranium Enrichment

Power plant grade enrichment requirement 3-5%

Weapons grade enrichment requirement 90%


Most Electricity Generation

US 28% 🇺🇸
of total global nuclear electricity

Highest Penetration

France 69% 🇫🇷
of country’s electricity comes from nuclear fission

Average Age of Reactors

World 31 years 🌎

US 41 years 🇺🇸
France 37 years 🇫🇷
China 9 years 🇨🇳

Share of World’s Capacity Growth

China 52% 🇨🇳
Russia 12% 🇷🇺
UAE 11% 🇦🇪


Most Electricity Generation

Illinois 13%
of total US nuclear electricity

Highest Penetration

New Hampshire 57%
South Carolina 54%
Illinois 53%
of state's electricity comes from nuclear

Nuclear Installations are Old and Not Competitive

19 US reactors retired
in the last 30 years

New Nuclear is Expensive and Takes a Long Time to Build

3 US reactors added
in the last 30 years

Most recent reactor took 14 years, cost $30 billion (original budget was $14 billion)

Half Lives* of Main Radioactive Nuclear Waste Isotopes

Strontium-90: 29 years
Cesium-137: 30 years
Plutonium-239: 24,000 years**

Amount of Global Nuclear Waste

390,000 metric tons
(about the same weight as the Empire State Building)

10,000 metric tons
generated annually

Methods for Nuclear Waste Storage

  1. Temporary: pools (~10 years); dry casks (<100 years)
  2. Recycle the fuel (reduces overall amount of nuclear waste)
  3. Bury the waste in a geologically safe location***

No proven method to store for 200,000+ years

*Half life is the time taken for the radioactivity of an isotope to be reduced by half
**Plutonium has the potential to be weaponized
***Not yet proven, still in research phase


  • No direct carbon or air emissions
  • Reliable baseload source of low-carbon electricity
  • Nuclear power plants have high capacity factors (90-95% in the US)
  • Extremely energy dense fuel
  • Facilities require relatively low land use
  • Uranium is an abundant resource


  • High-risk (extreme consequence x low probability) accidents
  • Produces radioactive waste that must be safely stored for hundreds of thousands of years
  • Risk of nuclear proliferation and the spread of nuclear weapons capabilities to more countries, with geopolitical consequences
  • Rigid baseload on the grid and not flexible for integration of renewables or load following
  • Extremely expensive to build and insure relative to other sources of electricity
  • Nuclear power plants take a long time to plan, permit, and build, particularly in the United States
  • US nuclear power plants are old and require upgrades and new licensing
  • Decommissioning of nuclear power plants can take 50+ years and is expensive
  • NIMBY* - community opposition to siting nuclear power plants and waste repositories
  • Operations are water intensive
  • Uranium mines can contaminate water
  • Nuclear fuel (and waste byproducts) must be secured and safely transported
  • Negative public perceptions of nuclear power, particularly after major nuclear accidents (Chernobyl, Three Mile Island, Fukushima)

*NIMBY - not in my backyard

Climate Impact:

Low gradient
  • Near-zero greenhouse emissions when operating

Environmental Impact:
Low to Medium

Gradient from green to yellow to orange to red, with rectangle around the green and yellow portion.
  • Radioactive waste is toxic for hundreds of thousands of years
  • Risk of radiation leaks from nuclear meltdowns
  • Accidents from transporting nuclear fuel or radioactive waste byproducts
  • Nuclear proliferation raises the risk of nuclear weapons use
  • Significant environmental impact if atomic weapons or dirty bombs are detonated
  • Large amounts of water used for cooling, thermal pollution of water

Updated June 2023

Our 10-Minute Take On
Nuclear Fission

If you're short on time, start by watching this video of key highlights from our Nuclear Fission lecture

Diana Gragg

Presented by: Diana Gragg, PhD; Core Lecturer, Civil and Environmental Engineering, Stanford University; Explore Energy Managing Director, Precourt Institute for Energy
Recorded: Feb 23, 2022  Duration: 10 minutes

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Before You Watch Our Lecture on
Nuclear Fission

We assign videos and readings to our Stanford students as pre-work for each lecture to help contextualize the lecture content. We strongly encourage you to review the Essential videos and readings below before watching our lecture on Nuclear Fission. Include selections from the Optional and Useful list based on your interests and available time.


  • Is Nuclear Power Good or Bad?. The Good Stuff. January 14, 2016. (14 min)
    Describes how nuclear power works and weighs the pros and cons of nuclear power.
  • Uranium. 2023. (4 pages)
    An excellent introductory overview of uranium and nuclear energy.
  • Spent Fuel Storage at Diablo Canyon Power Plant. PG&E. October 1, 2011. (11 min)
    Shows the process of taking used fuel from spent fuel pools located inside the Diablo Canyon Power Plant's fuel handling building and transporting the used fuel to the on-site dry storage facility.
  • 88,000 Tons of Radioactive Waste - And Nowhere to Put It. Verge Science. August 28, 2018. (8 min)
    A visit to San Onofre, a retired beachside nuclear power plant near San Diego, California, where nuclear waste is stored on-site.
  • U.S. Approves First Small Nuclear Reactor Design. Science Friday. February 3, 2023. (17 min)
    A discussion of the first small-modular nuclear reactor design approved by U.S. Nuclear Regulatory Commission and what the future of nuclear energy might hold.

Optional and Useful

Our Lecture on
Nuclear Fission

This is our Stanford University Understand Energy course lecture on nuclear fission. We strongly encourage you to watch the full lecture to understand nuclear fission as an energy system and to be able to put this complex topic into context. For a complete learning experience, we also encourage you to watch / read the Essential videos and readings we assign to our students before watching the lecture.

Diana Gragg

Presented by: Diana Gragg, PhD; Core Lecturer, Civil and Environmental Engineering, Stanford University; Explore Energy Managing Director, Precourt Institute for Energy
Recorded on: May 1, 2024   Duration: 69 minutes

Table of Contents

(Clicking on a timestamp will take you to YouTube.)
00:00 Introduction 
04:05 Significance and Trends 
25:29 History and Origins 
27:59 How Commercial Nuclear Energy Works 
53:30 Impact on Environment, Health, & Safety

Lecture slides available upon request.

Embed Code

Additional Resources About
Nuclear Fission

Stanford University

Government and International Organizations

Fast Facts Sources
DOE Budget: Nuclear-Related Activities FY2022 Annualized CR (Department of Energy (March 2022), FY 2023 Congressional Budget Request Budget in Brief, p. 19)
Energy Mix: World 2019 (IEA (2021), “World Energy Balances: Overview (World)”), U.S. 2021 (EIA (March 2022), Monthly Energy Review, Table 1.3 “Primary Energy Consumption by Source”)
Electricity Mix: World 2021 (BP Statistical Review of World Energy 2022, page 51), U.S. 2021 (Ember “Data Explorer”)
Number of Nuclear Reactors: January 2023 (World Nuclear Association “World Nuclear Power Reactors & Uranium Requirements”)
Global Demand, Nuclear Electricity: 2016-2021 (Ember “Data Explorer”)
Global Uranium Sources (World Nuclear Association “Uranium markets” 2022)
Energy Density of Uranium (Bradley E. Layton “A Comparison of Energy Densities of Prevalent Energy Sources in Units of Joules per Cubic Meter”)
Uranium Enrichment (Center for Arms Control and Non-Proliferation “Fact Sheet: Uranium Enrichment: For Peace or for Weapons”)
Most Electricity Generation: World 2021 (Ember “Data Explorer”)
Highest Penetration: World 2021 (Ember “Data Explorer”)
Average Age of Reactors: January 2023 (World Nuclear Association “Reactor Database”)
Share of Capacity Growth: World 2018-2023 (World Nuclear Association “Reactor Database”)
Most Electricity Generation: U.S. 2022 (EIA “Utility Scale Facility Net Generation from Nuclear Energy”)
States with Highest Penetration: U.S. 2021 (NEI “State Electricity Generation Fuel Shares 2021”)
U.S. Nuclear Retirements and Additions: 1993-2023 (World Nuclear Association “Reactor Database”)
Nuclear Waste Half Lives (United States Nuclear Regulatory Committee “Backgrounder on Radioactive Waste”)
Amount of Nuclear Waste: World (International Atomic Energy Agency “New IAEA Report Presents Global Overview of Radioactive Waste and Spent Fuel Management”)
More details available on request.
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