Nuclear Energy Factsheet

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Nuclear power plants generate electricity by using controlled nuclear fission chain reactions (i.e., splitting atoms) to heat water and produce steam to power turbines. Nuclear is often labeled a “clean” energy source because no greenhouse gases (GHGs) or other air emissions are released from the power plant. As the U.S. and other nations search for low-emission energy sources, the benefits of nuclear power must be weighed against the operational risks and the challenges of storing radioactive waste.

Nuclear Energy Use and Potential

  • Nuclear energy provides about 20% of U.S. electricity. Nuclear is a resource that runs at full capacity 93% of the time.1
  • The first U.S. nuclear power plant was completed in 1957.2 During the 1970s, more than 50 nuclear reactors went online.1 Presently, 31 states have at least one nuclear plant and each plant may have multiple reactors.2 Since 1995, U.S. nuclear electricity generation has grown despite no new reactors and 10 shutdowns, due to higher capacity factors from existing plants.1,2
  • The U.S. has 99 of the world’s 447 commercial nuclear reactors. As of May 2017, 59 reactors are under construction, including 4 in the U.S. and 21 in China.3
  • In 2014, the U.S. generated nearly a third of the world’s nuclear electricity. The next largest generators of nuclear electricity were France, Russia, and South Korea.4
  • Pressurized Water Reactors (PWR) and Boiling Water Reactors (BWR) are the most common technologies in use.5 Two-thirds of U.S. reactors are PWRs.6
  • Levelized cost of energy (LCOE) includes the expected costs of building, operating & maintaining, and fueling a power plant. Estimated LCOE for plants built in the near future are: combined cycle natural gas: 6.63 ¢/kWh; coal: 9.56 ¢/kWh; nuclear: 9.61 ¢/kWh; and biomass: 10.3 ¢/kWh.7

​U.S. Electricity Generation by Source1

U.S. Electricity Generation by Source

Nuclear Fuel

  • Most nuclear reactors use “enriched” uranium, meaning the fuel has a higher concentration of uranium-235 (U-235) isotopes, which are easier to split to produce energy. When it is mined, uranium ore averages less than 1% U-235.8
  • Milling and enrichment processes crush the ore to extract uranium oxide (U3O8, i.e., yellowcake), chemically convert this to uranium hexafluoride gas (UF6), then concentrate the U-235 into ceramic uranium dioxide (UO2) pellets with 3%-5% U-235 concentrations.9
  • Uranium can be enriched by gaseous diffusion or gas centrifuge. Both concentrate the slightly lighter U-235 molecules from a gas containing mostly U-238, the former with membrane filters and the latter by spinning. Other technologies are currently in development, with laser enrichment processes closest to commercial viability.10

Fission of Uranium-235 in a Nuclear Reactor

Fission of Uranium-235 in a Nuclear Reactor

  • In 2016, 2.5 million pounds of U3O8 were extracted from 9 uranium mines in the U.S.11 Although even the highest grade ore deposits in the U.S. average less than 1% uranium, some Canadian ore is more than 15% uranium.12,13
  • Less than 2% of uranium available at reasonable cost is found in the U.S. The largest deposits are in Australia, Kazakhstan, Canada, and Russia.13 U.S. nuclear plants purchased 56.5 million pounds of uranium in 2015.14 11% of the fuel originated in the U.S.; the remainder was imported mostly from Kazakhstan (21%), Australia (18%), Canada (22%), and Russia (13%).14
  • Globally, nuclear power reactors required 67,867 metric tons of uranium in 2017.3

​​Largest Identified Uranium Resources13

Largest Identified Uranium Resources

Energy and Environmental Impacts

The nuclear fuel cycle is the entire process of producing, using, and disposing of uranium fuel. Powering a one-gigawatt nuclear plant for a year can require mining 20,000-400,000 metric tons (mt) of ore, processing it into 27.6 mt of uranium fuel, and disposing of 27.6 mt of highly radioactive spent fuel and 200-350 m3 of low- and intermediate-level radioactive waste.15,16 U.S. plants currently use “once-through” fuel cycles with no reprocessing.17

  • A uranium fuel pellet (1/2 in. height and diameter) contains the energy equivalent of one ton of coal or 17,000 ft3 of natural gas.18 Typical reactors hold 18 million pellets.19
  • Each kWh of nuclear electricity requires 0.1-0.3 kWh of life cycle energy inputs.20
  • Although nuclear electricity generation itself produces no GHG emissions, other fuel cycle activities do release emissions.21
  • The life cycle GHG intensity of nuclear power can be 13 to 66 gCO2e/kWh—far below baseload sources such as coal (1,001 gCO2e/kWh).21,22,23
  • Globally, uranium is mostly extracted by open pit mining (14%), underground mining (27%) and in-situ leaching (ISL) (51%).13 ISL, the injection of acidic/alkaline solutions underground to dissolve and pump uranium to the surface, eliminates ore tailings associated with other mining but raises aquifer protection concerns.24
  • U.S. EPA is updating the current standards for uranium mining facilities and their effects on groundwater in response to a broader domestic use of ISL.  The standards have yet to be finalized.25
  • Nuclear power plants consume 270-670 gallons of water/MWh, depending on operating efficiency and site conditions.26

​Uranium Fuel Cycle15

Uranium Fuel Cycle

Life Cycle GHG Emissions of Nuclear Power21

Life Cycle GHG Emissions of Nuclear Power

Nuclear Waste

  • The U.S. accumulates about 2,000-2,400 mt of spent fuel each year.27
  • During reactor operation, fission products and transuranics that absorb neutrons accumulate, requiring a third of the fuel to be replaced every 12-18 months. Spent fuel is 95% non-fissile U-238, 3% fission products, 1% fissile U-235, and 1% plutonium.15
  • Spent fuel is placed in a storage pool of pumped, cooled water to absorb heat and block the high radioactivity of fission products, where it typically remains for at least 5 years.27
  • Some countries (excluding U.S.) reprocess spent fuel for reuse as mixed oxide fuel, which reduces the volume of radioactive waste but raises proliferation concerns.28
  • Many U.S. spent fuel pools are reaching capacity, necessitating the use of dry cask storage. Dry casks, large concrete and stainless steel containers, are designed to passively cool radioactive waste and withstand natural disasters or large impacts. In 2011, 27% of spent fuel was held in dry casks, after sufficient cooling in storage pools.29
  • Currently, 34 states have complexes designed for interim storage of spent nuclear fuel, or Independent Spent Fuel Storage Installations (ISFSI).30
  • Ten years after use, the surface of a spent fuel assembly releases 10,000 rem/hr of radiation (in comparison, a dose of 500 rem is lethal to humans if received all at once).17  Managing nuclear waste requires very long-term planning. U.S. EPA was required to set radiation exposure limits in permanent waste storage facilities over an unprecedented timeframe—one million years.31
  • The U.S. has no permanent storage site. Nevada’s Yucca Mountain was to hold 70,000 mt waste but is no longer under consideration.32
  • The Nuclear Waste Policy Act required the U.S. federal government to begin taking control of spent nuclear fuel in 1998. When this did not occur, the government became liable for the costs associated with continued on-site, at-reactor storage.33

Spent Commercial Nuclear Fuel, Metric Tons37​​

Spent Commercial Nuclear Fuel, Metric Tons


Safety and Public Policy

  • After an earthquake and tsunami in March 2011, Japan’s Fukushima Daiichi nuclear plant lost the ability to cool reactors and spent fuel, resulting in large releases of radiation.34
  • Nuclear radiation at the plant was around 13 rem/hr with some localized dose rates greater than 1,000 rem/hr. By April 2011, 17 million curies of radiation had been released—4.5% the amount emitted during the 1986 Chernobyl accident.34 A recent report by the World Health Organization estimates that residents of the most affected areas were exposed to radiation doses of 1.2 to 2.5 rem in the first year after the incident.35
  • The U.S. Price-Anderson Act limits the financial liability of nuclear plant owners if a severe radioactive release occurs to $375 million for individual plants and $12.6 billion across all plants.36
  • Incentives for new nuclear plants include a production tax credit of 1.8¢/kWh of electricity generated, $18.5 billion for federal loan guarantees, and insurance against regulatory delays.36

Natural and Man-Made Exposures to Radiation38

Natural and Man-Made Exposures to Radiation

  1. Energy Information Administration (EIA) (2016) Monthly Energy Review May 2016.
  2. U.S. EIA (2012) “Energy in Brief: What is the status of the U.S. nuclear industry?”
  3. World Nuclear Association (WNA) (2016) “World Nuclear Power Reactors & Uranium Requirements.”
  4. U.S. EIA (2015) “International Energy Statistics: Electricity Generation, Nuclear.”
  5. WNA (2016) “Nuclear Power Reactors.”
  6. U.S. Nuclear Regulatory Commission (NRC) (2016) “List of Power Reactor Units.”
  7. U.S. EIA (2015) “Levelized Cost of New Generation Resources in the Annual Energy Outlook 2015.”
  8. U.S. NRC (2013) “Uranium Enrichment.”
  9. Nuclear Energy Institute (2013) “How It Works: Nuclear Power Plant Fuel.”
  10. WNA (2014) “Uranium Enrichment.”
  11. EIA (2016) 2015 Domestic Uranium Production Report.
  12. U.S. Nuclear Energy Agency (NEA) & International Atomic Energy Agency (IAEA) (2012) Uranium 2011: Resources, Production, and Demand.
  13. U.S. NEA & IAEA (2016) Uranium 2016: Resources, Production, and Demand.
  14. EIA (2017) 2016 Uranium Marketing Annual Report.
  15. WNA (2017) “The Nuclear Fuel Cycle.”
  16. WNA (2017) “Radioactive Waste Management.”
  17. U.S. NRC (2015) “Backgrounder on Radioactive Waste.”
  18. American Nuclear Society (2011) “Source Energy Equivalents Pellet.”
  19. U.S. DOE, Argonne National Laboratory (2011) Nuclear Fuel.
  20. Lenzen, M. (2008) Life cycle energy and greenhouse gas emissions of nuclear energy: A review. Energy Conversion and Management, 49: 2178-2199.
  21. Warner, E. and G. Heath (2012) Life Cycle Greenhouse Gas Emissions of Nuclear Electricity Generation. Journal of Industrial Ecology, 16: S73-S92.
  22. Sovacool, B. (2008) Valuing the greenhouse gas emissions from nuclear power: A critical survey. Energy Policy, 36: 2940-2953.
  23. Whitaker, M., et al. (2012) Life Cycle Greenhouse Gas Emissions of Coal-Fired Electricity Generation. Journal of Industrial Ecology, 16: S53-S72.
  24. WNA (2014) “In Situ Leach (ISL) Mining of Uranium.”
  25. EPA (2017) Health and Environmental Protection Standards for Uranium and Thorium Mill Tailings.
  26. Macknick, J., et al. (2011) A Review of Operational Water Consumption and Withdrawal Factors for Electricity Generating Technologies. U.S. DOE, National Renewable Energy Laboratory.
  27. U.S. NRC (2015) “Spent Fuel Storage in Pools and Dry Casks: Key Points and Questions & Answers.”
  28. IAEA (2009) Use of Reprocessed Uranium: Challenges and Options.
  29. Werner, J. (2012) U.S. Spent Nuclear Fuel Storage. Congressional Research Service.
  30. NRC (2016) US Independent Spent Fuel Storage Installations (ISFSI) “Storage of Spent Nuclear Fuel” and “Locations of Independent Spent Fuel Storage Installations.”
  31. Federal Register (2008) “Part III, Environmental Protection Agency, 40 CFR Part 97, Public Health and Environmental Radiation Protection Standards for Yucca Mountain, Nevada; Final Rule.”
  32. U.S. DOE (2008) Analysis of the Total System Life Cycle Cost of the Civilian Radioactive Waste Management Program, Fiscal Year 2007.
  33. U.S. DOE (2013) Strategy for the Management and Disposal of Used Nuclear Fuel and High Level Radioactive Waste.
  34. Institute of Nuclear Power Operations (2011) Special Report on the Nuclear Accident at the Fukushima Daiichi Nuclear Power Station.
  35. World Health Organization (2013) Health Risk Assessment from the nuclear accident after the 2011 Great East Japan Earthquake and Tsunami.
  36. Holt, M. (2014) Nuclear Energy Policy. Congressional Research Service.
  37. Nuclear Energy Institute (2016) “Nuclear Waste Disposal: Used Nuclear Fuel Storage Map.”
  38. U.S. EPA (2012) “Radiation Doses in Perspective.”
Cite as: 
Center for Sustainable Systems, University of Michigan. 2017. "Nuclear Energy Factsheet." Pub. No. CSS11-15.