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

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

Grace Smoot

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Nuclear fission uses radioactive material to produce energy, a process that produces very little CO2 emissions. So, we had to ask: What is the carbon footprint of nuclear fission?

Nuclear fission has the third-lowest carbon footprint of all energy types. Per kWh produced, nuclear fission 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.

Keep reading to learn about the overall carbon footprint of nuclear fission and its carbon footprint throughout its life cycle. 

How is Nuclear Fission Defined

Nuclear fission is the generation of energy produced when splitting apart the nucleus of an atom. It is one of two ways to produce nuclear energy

Nuclear fission: a nuclear reaction in which a heavy nucleus splits spontaneously or on impact with another particle, with the release of energy.”

Cambridge Dictionary

When a neutron strikes the nucleus of an atom, the atomic center can break apart into pieces, starting a chain reaction and releasing energy in the form of radiation and heat. 

Illustration of the nuclear fission process
International Atomic Energy Agency: Nuclear Fission

What is the Carbon Footprint of Nuclear Fission 

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 gasses 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 or 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 Nuclear Fission

On a life-cycle basis, nuclear fission 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 the Average life-cycle CO2 equivalent emissions from World Nuclear Association
World Nuclear Association: Average life-cycle CO2 equivalent emissions

All operating nuclear power plants today utilize the process of nuclear fission. Because of this, nuclear fission is commonly referred to as ‘nuclear energy’ in the data and literature. 

Nuclear energy accounted for roughly 10% of global electricity generation in 2022, generating approximately 2,500 TWh of electricity from approximately 413 GW of installed capacity.

Illustration from Our World in Data: Nuclear power generation
Our World in Data: Nuclear power generation

Some countries rely heavily on nuclear energy whilst others have not yet tapped into the resource. For example, nuclear energy provides roughly 60% of France, Slovakia, and Ukraine’s electricity, but South America and Africa get virtually no energy from nuclear. The top 5 countries represent roughly 70% of the world’s nuclear energy generation.

Illustration from Our World in Data: Nuclear power generation, 2022
Our World in Data: Nuclear power generation, 2022

To understand the carbon footprint of nuclear fission, we must assess its lifecycle 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 fission!

The life-cycle stages of nuclear fissionEach stage’s carbon footprint
Building of nuclear fissionSome CO2 emissions from constructing the nuclear fission power plant, mining and processing uranium, and transporting nuclear fuel to the power plant
Operating of nuclear fissionLittle to no CO2 emissions or waste products
Building back of nuclear fissionSome CO2 emissions from transporting used fuel/radioactive material and deconstructing the power plant

The total carbon footprint of nuclear fission 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 Fission

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

  • Construction: A nuclear fission 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. 

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 Fission

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

Nuclear fission power plants operate in the following manner:

  • The reactor starts and Uranium-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 Fission

The organizations tasked with deregulating and decommissioning nuclear fission power plants vary from country-to country. For example, the U.S. Nuclear Regulatory Commission is responsible for overseeing the decommissioning of nuclear fission power plants in the US. 

In general, the process of shutting down nuclear fission plants is expensive, labor-intensive, time-consuming, and comes with health and safety risks. The entire process can take up to 60 years

Decommissioning a nuclear fission 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 Fission Play in Combating Climate Change

Climate change is arguably the most severe, long-term, global impact of fossil fuel combustion. Every year, approximately 33 billion tons (bt) of CO2 are emitted from burning fossil fuels. The carbon found in fossil fuels reacts with oxygen in the air to produce CO2. This warms the earth by acting as a heating blanket, and a warmer earth comes with a host of negative side effects. 

Using nuclear fission to produce energy instead of fossil fuel energy helps mitigate the following negative effects of climate change:

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 1.5°C, as outlined in the Paris Agreement, we must shift at least 80% of our electricity generation to low-carbon sources. Over 140 countries have stated a net-zero target, covering roughly 88% of the world’s emissions. However, under current conditions, global emissions are projected to increase by 9% by 2030 instead of the 45% reduction in emissions that is needed.

How Environmentally Friendly Is Nuclear Fission

The overall environmental friendliness of nuclear fission 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 fission can reduce the effects of global warming by limiting global emissions, but uranium mining and nuclear waste are drawbacks that must be taken into consideration.

What Are the Environmental Benefits of Nuclear Fission 

Nuclear fission is expected to continue to play a key role in the clean energy movement. This is because nuclear fission:

  • Promotes energy security: Nuclear energy contributes to energy security by increasing the stability of our power grids. Unlike renewable energy, which faces variations in supply and demand, nuclear energy can provide a reliable and consistent source of clean energy. 
  • Promotes energy independence: Being able to produce your own electricity without the aid of foreign countries is an important step in becoming self-sufficient. For example, 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).

What Are the Environmental Drawbacks of Nuclear Fission 

Nuclear fission does come with some drawbacks that, if handled properly, can be mitigated. The main environmental drawbacks associated with nuclear fission 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 increase the risk of water contamination. 
  • Nuclear waste: Although nuclear fission 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 fission is an incredibly efficient energy source that uses heat acquired from splitting the nuclei of atoms to create electricity. On a life-cycle basis, nuclear fission only 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.

Nuclear fission 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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