What Is the Carbon Footprint of Nuclear Power? A Life-Cycle Assessment

What Is the Carbon Footprint of Nuclear Power? A Life-Cycle Assessment

Dennis Kamprad

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Nuclear power uses radioactive material to produce electricity. Although the operation of nuclear power does not produce carbon dioxide (CO2) emissions, emissions can still be found during other stages of its life cycle. So, we had to ask: What is the carbon footprint of nuclear power?

Nuclear power has the third-lowest carbon footprint of all energy types. Per kWh produced, nuclear power emits 12 grams of CO2 on a life-cycle basis. It combats climate change and has various environmental benefits, but comes with the threat of nuclear waste products.

Nuclear power makes up 10% of global electricity and has various environmental implications. Keep reading to learn about the overall carbon footprint of nuclear power and its carbon footprint throughout its life cycle. 

How is Nuclear Power Defined

When it comes to nuclear energy, we need to start with atoms. All matter consists of atoms, each of which contains a nucleus. When a neutron strikes the nucleus of an atom, the atomic center can break apart into pieces, thereby releasing energy in the form of radiation and heat. This energy heats water, produces steam that spins a turbine, and drives generators to produce electricity.  

Nuclear Power: the power produced when the nucleus (= central part) of an atom is divided or joined to another nucleus”

Cambridge Dictionary

There are two ways to generate nuclear power:

  • Nuclear Fusion: Atoms are combined or fused to create larger atoms. The sun and stars get their energy from nuclear fusion, but the process is very hard to control within a laboratory setting. Future research needs to be done to determine if this could be another viable energy source. 
  • Nuclear Fission: Electromagnetic radiation is used to split the nucleus of a uranium atom, which releases an enormous amount of energy. All operating nuclear power plants today use the process of nuclear fission. 

The Uranium isotope used in nuclear fission is Uranium-235 (U-235) because its atoms are easily split apart in nuclear reactors. U-235 has a concentration of 2.8 parts per million (0.7% abundance) in Earth’s crust. Although it can be found almost everywhere supplies of U-235 are finite, and we have already used up most of it because it has a half-life of about 700 million years

What is the Carbon Footprint of Nuclear Power 

The carbon footprint is one of the ways we measure the effects of human-induced global climate change. It primarily focuses on the greenhouse gas (GHG) emissions associated with consumption, but also includes other emissions such as methane, nitrous oxide, and chlorofluorocarbons.

Carbon footprint: the amount of greenhouse gases and specifically carbon dioxide emitted by something (such as a person’s activities or a product’s manufacture and transport) during a given period

Merriam Webster

Basically, it is the amount of carbon emitted by an activity or an organization. This includes GHG emissions from fuel that we burn directly (e.g., heating a home, driving a car) and GHG emissions from manufacturing the products that we use (e.g., power plants, factories, and landfills). 

What Is the Overall Carbon Footprint of Coal Energy

On a life-cycle basis, nuclear power emits 12 grams of CO2 equivalent per kilowatt-hour (kWh) of electricity produced, which is tied for the third-lowest out of all energy types.

Illustration of CO2 equivalent per energy source
World Nuclear Association: Average life-cycle CO2 equivalent emissions

Globally there are 440 nuclear reactors with a total output capacity of 390,000 megawatts (MWe) located in 30 countries. 50 more reactors are under construction and over 100 are planned. In 2020, the world collectively generated roughly 10%, or over 2,500 terawatt-hours (TWh), of its electricity from nuclear energy. 

Our World in Data: Nuclear Energy

Some countries produced no nuclear power in 2020 while others got the majority of their energy from nuclear power. For example, the US got 20% of its electricity from nuclear while France got over 70% of its electricity from nuclear. 

Our World in Data: Nuclear Energy

The top 6 nuclear power generating countries (amount produced per year) in the world are: 

  1. United States – 790-gigawatt hours (GWh)
  2. China – 345 GWh
  3. France – 339 GWh
  4. Russia – 202 GWh
  5. South Korea – 153 GWh
  6. Canada – 92 GWh

Nuclear power makes up 10% of global energy generation. Because it is often described as an efficient, safe, and clean energy substitute for fossil fuels, understanding nuclear power’s carbon footprint and how its carbon emissions affect the global climate change process is important.

To understand the carbon footprint of nuclear power, we must assess its life-cycle and each stage’s carbon footprint. This life-cycle assessment (LCA) is a method to evaluate the environmental impacts of products and materials. Over the years, companies have strategically used LCA to research and create more sustainable products. So, let’s have a look at the LCA of nuclear power!

The life-cycle stages of nuclear powerEach stage’s carbon footprint
Building of nuclear powerSome CO2 emissions from constructing the nuclear power plant, mining and processing uranium, transporting nuclear fuel to the power plant
Operating of nuclear powerLittle to no CO2 emissions during operation
Building back of nuclear powerSome CO2 emissions from transporting used fuel/radioactive material and deconstructing the power plant

The total carbon footprint of nuclear energy would equal the carbon footprint from building + the carbon footprint from operating + the carbon footprint from building back.  

What Is the Carbon Footprint of Building Nuclear Power

The carbon footprint of building nuclear power includes constructing the power plant, mining and processing the uranium, and transporting the processed nuclear fuel to the power plant.

  • Construction: A nuclear power plant has many components, and building these components requires machinery that emits CO2. The containment building, reactor vessel, steam lines, pumps, turbines, generators, transformers, and cooling towers are all components with a carbon footprint.  
  • Milling: Extraction of the uranium from the ore (or leachate) by crushing the ore and leaching it in sulfuric acid.
  • Conversion and enrichment: Increasing the concentration of U-235 to between 3.5% and 5% by centrifuging the milled uranium until the two isotopes (U-238 and U-235) separate. 
  • Fuel Fabrication: Ceramic pellets of reactor fuel are formed from pressed uranium oxide which is baked at high temperatures and encased in metal tubes to form fuel rods. A 1,000 MWe reactor requires roughly 27 tonnes (29.7 tons) of fuel each year. 
  • Transportation: Nuclear fuel is typically transported from fabrication sites to power plants by road, rail, or sea, all of which run on diesel fuel. Burning one gallon of diesel fuel produces 22.38 pounds of CO2.

CO2 emissions at this stage occur when constructing the power plant, mining and processing the uranium, and transporting the processed nuclear fuel to the power plant.

What Is the Carbon Footprint of Operating Nuclear Power

Nuclear reactors do not produce any CO2 emissions in the operating phase because there is no burning of fossil fuels or combustion byproducts.

Nuclear power plants operate in the following manner:

  • The reactor starts and U-235 atoms in the reactor core split (fission), releasing heat and neutrons.
  • Neutrons fission other nuclei in the reactor core in a chain reaction, generating more heat and more neutrons.
  • Control rods contain materials that absorb some of the neutrons, helping to contain the chain reaction.
  • The heat generated turns water that surrounds the immersed reactor into steam.
  • The steam spins a turbine which drives a generator to produce electricity.

Nuclear fuel is extremely dense, so you don’t need a lot of it to create a lot of energy. One U-235 pellet 1 inch tall is the equivalent of 1 ton of coal. Since 1 ton of coal creates 2.086 tons (4,172 lbs) of CO2 when it is burned, a 1-inch U-235 pellet directly avoids the emission of over 2 tons of CO2 from our atmosphere.  

What Is the Carbon Footprint of Building Back Nuclear Power

The U.S. Nuclear Regulatory Commission is responsible for overseeing the decommissioning of nuclear power plants. This process is expensive, labor-intensive, time-consuming, and comes with health and safety risks. And the entire process can take up to 60 years

Decommissioning a nuclear power plant involves the following steps: 

  • Removing and storing spent nuclear fuel rods in spent fuel pools
  • Decontaminating the plant
  • Reducing residual radioactivity at the plant
  • Dismantling plant structures
  • Transferring contaminated materials to disposal facilities
  • Clearing the site with the NRC for other uses  

CO2 emissions at this final stage occur when transporting used fuel and radioactive material and deconstructing the plant.

What Role Does Nuclear Power Play in Combating Climate Change

Nuclear power is a reliable, efficient, stable, and low-carbon emission source of energy. Using nuclear power instead of fossil fuel energy helps mitigate the following negative effects of climate change:

  • Melting of sea ice: Since 1979 arctic sea ice has declined by 30%. Sea ice plays a major role in regulating the earth’s climate by reflecting sunlight into space and providing habitat for animal species. If all of the glaciers on Earth melted, sea levels would rise by approximately 70 feet, effectively flooding out every coastal city on the planet. 
  • Changing precipitation patterns: Extreme weather events (e.g., hurricanes, floods, droughts) are becoming more common and more intense. Storm-affected areas will experience increased precipitation and flooding whereas areas located further from storm tracks will experience decreased precipitation and droughts.
  • Ocean Acidification: The ocean absorbs 30% of the CO2 released into the atmosphere, which decreases the pH (increases the acidity) of the ocean. In the past 200 years, the pH of oceans has decreased by 0.1 pH units, which translates to a 30% increase in acidity. Aquatic life unable to adjust to this rapid acidification will die off. A prime example of this is coral bleaching, where coral expel the algae (zooxanthellae) living in their tissues as a result of changes in temperature, light, or nutrients. 

The more we reduce CO2 emissions, the more we slow the rate of temperature rise, sea-level rise, ice melting, and ocean acidification. When these rates are slowed, the earth’s biodiversity does not have to struggle to adapt to temperature and pH changes. People will not be displaced due to the flooding of coastal areas. And icebergs will continue to provide climate regulation. 

To help keep global temperature rise below 1.5C, as outlined in the Paris Agreement, we must shift at least 80% of our electricity generation to low carbon sources. And nuclear power is currently the second-largest source of low-carbon energy. Nuclear has reduced CO2 emissions by more than 60 gigatons over the past 50 years, equating to almost 2 years worth of global energy-related emissions.

How Environmentally Friendly Is Nuclear Power

The overall environmental friendliness of nuclear power is a controversial topic. Although the process of nuclear fission produces zero CO2 emissions, the handling and disposal of nuclear waste is a serious issue. 

Environmentally friendly: (of products) not harming the environment.”

Cambridge Dictionary

Nuclear power can reduce the effects of global warming by limiting global GHG emissions, but uranium mining and nuclear waste are drawbacks that must be taken into consideration.

What Are Environmental Benefits of Nuclear Power

The environmental benefits of nuclear power include the following:

  1. Protects Air Quality: Nuclear power is a zero-emission, clean energy source. Rather than combusting materials, the heat released by nuclear fission creates steam which spins turbines to generate electricity. 
  1. Minimal Land Use Impact: Nuclear energy produces more electricity on less land than any other clean-air source. A standard, 1,000-megawatt facility located in the US requires a little more than 1 square mile to operate, a number that is 360 and 75 times less than what is required for wind farms and solar plants, respectively. 
  1. Few Waste Products: All of the used nuclear fuel that the US produced in the past 60 years could fit onto a football field at a depth of fewer than 10 yards. There are no other byproducts. 
  1. Climate Change Mitigation: Nuclear has an average life-cycle CO2 equivalent emission value that is much less than coal, 12g of CO2 equivalent per kWh compared to 820g of CO2 equivalent per kWh, respectively. This reduction in CO2 emissions, in turn, reduces the effects of global climate change including increasing temperatures, rising sea levels, melting of sea ice, changing precipitation patterns, and ocean acidification.
  1. Energy Independence: Being able to produce our own electricity in the U.S. without the aid of foreign countries is an important step to help us become more self-sufficient. Former President George W. Bush signed the Energy Independence and Security Act of 2007 to reduce U.S. dependence on oil, expand the production of renewable fuels (and confront global climate change). 
  1. Employment Opportunities: The US directly employs about 100,000 people in the nuclear power sector. It takes 500-800 people to staff a power plant and up to 7,000 people to construct that plant. For every 100 jobs at the power plant, another 66 jobs are created in the local community. 

Throughout its life cycle, nuclear power produces the same amount of CO2 emissions per unit of electricity as wind energy and about 1/3 of the CO2 emissions per unit of electricity as solar power. In the US alone, nuclear power saves 471 million tonnes (519 million tons) of CO2 emissions that would have otherwise come from the combustion of fossil fuels. This is the equivalent of removing 100 million passenger vehicles from the roads. 

What Are Environmental Drawbacks of Nuclear Power

Nuclear power does come with some drawbacks that, if handled properly, can be mitigated. The main environmental drawbacks associated with nuclear power are uranium mining and nuclear waste.

  • Uranium Mining: This process contaminates the environment with radioactive dust, radon gas, water-borne toxins, and increased levels of background radiation. Exploratory drilling and mining also heavily increases the risk of water contamination. 
  • Nuclear Waste: Although nuclear power produces minimal waste, the waste that it does produce is radioactive and can remain hazardous for many thousands of years. These radioactive waste products include uranium mill tailings, spent (used) reactor fuel, and other radioactive wastes. If these were to leach into the environment it could contaminate the soil and water.  

Ways to minimize negative environmental impacts include the proper handling, transportation, storage, and disposal of radioactive waste to ensure that it does not leach into the environment. 

Final Thoughts

Nuclear power is an incredibly efficient energy source that uses heat acquired from splitting the nuclei of atoms to create electricity. The process of nuclear fission does not produce CO2 emissions, but the construction of the power plant, mining and transportation of uranium, and deconstruction of the power plant are all areas that have carbon footprints.

Nuclear power benefits the environment by mitigating climate change, creating jobs, promoting energy independence, and protecting air quality. Environmental drawbacks including mining and nuclear waste can be mitigated with proper handling and disposal methods. 


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