Nuclear power is the lowest carbon source of electricity

A new report from the United Nations Economic Commission for Europe (UNECE) that has examined the life cycle of carbon produced by all technologies suggests that nuclear power generates fewer carbon dioxide emissions over the course of of its life cycle than any other source of electricity.

In its analysis of life cycle greenhouse gas emissions, the commission found that nuclear has the lowest carbon footprint, measured in grams of CO2 equivalent per kilowatt hour (kWh) of electricity, of all technologies. .

Candidate technologies being evaluated include coal, natural gas, hydropower, nuclear power, concentrated solar power (CSP), photovoltaics and wind power. Twelve global regions included in the assessment, allowing varying load factors, methane leakage rates or background grid power consumption, among other factors.

• Coal power shows the highest scores, with a minimum of 751 g CO2 eq./kWh (IGCC, USA) and a maximum of 1095 g CO2 eq./kWh (pulverized coal, China). Equipped with a carbon dioxide capture installation, and taking into account the storage of CO2, this score can drop to 147-469 g CO2 eq./kWh (respectively).
• A combined cycle power plant with natural gas can emit 403 to 513 g CO2 eq./kWh from a lifecycle point of view, and between 49 and 220 g CO2 eq./kWh with CCS. Coal and natural gas models include methane leaks during the extraction and transport phases (for gas); however, direct combustion dominates life cycle GHG emissions.
• Nuclear power shows less variability due to the limited regionalization of the model, with 5.1 to 6.4 g CO2 eq./kWh, the fuel chain (“upstream”) contributes the most to overall emissions.
• On the renewable side, hydroelectricity shows the greatest variability, as the emissions are very site specific, ranging from 6 to 147 g CO2 eq./kWh. Since biogenic emissions from sediment accumulated in reservoirs are mostly excluded, it should be noted that they can be very high in tropical areas.
• Solar technologies generate GHG emissions ranging from 27 to 122 g CO2 eq. / KWh for CSP, and from 8.0 to 83 g CO2 eq. / KWh for photovoltaic, for which thin-film technologies are significantly less carbon-intensive than silicon-based PV. The upper range of GHG values ​​for CSP is probably never achieved in reality as it requires high solar irradiation to be economically viable (a condition that is not met in Japan or Northern Europe, for example) .
• Wind power GHG emissions vary between 7.8 and 16 g CO2 eq./kWh for onshore wind turbines, and 12 and 23 g CO2 eq./kWh for offshore wind turbines.

Most of the GHG emissions from renewable technologies are incorporated into the infrastructure (up to 99% for photovoltaics), which suggests strong variations in the impacts of the life cycle due to the origin of the raw materials, the energy mix used for production, the modes of transport at different stages of manufacturing and installation, etc. As the impacts are incorporated into the capital, the load factor and the expected lifespan of the equipment are naturally very influential parameters on the final LCA score, which can considerably decrease if the infrastructure is more durable than expected. .

Ionizing radiation occurs primarily as a result of radioactive emissions of radon-222, a radionuclide found in tailings from uranium mining and grinding for nuclear power generation, or from coal mining for power generation charcoal. Coal-fired energy is a potentially important source of radioactivity, as the combustion of coal can also release radionuclides such as radon-222 or thorium-230 (very variable depending on the region). Growing evidence that other energy technologies emit ionizing radiation during their lifecycle has been published, but no data was collected for these technologies in this study.

Human toxicity, non-carcinogenic, has been found to be strongly correlated with arsenic ion emissions linked to the landfill of mining residues (coal, copper), which explains the high score of coal power on this indicator.

Carcinogenic effects are found to be high due to chromium VI emissions linked to the production of stainless steel containing chromium – resulting in a moderately high score for CSP plants, which require significant amounts of steel in the infrastructure of the plant. solar fields compared to the electricity produced.

Technologies: Nuclear energy

About 70 SMR designs are in development today. There is no strict definition of SMRs, but in practice they include reactors of less than 300 MW, as well as a high degree of modularity, for example, whole reactors can be designed to be transported by truck and installed at any site with minimal preparation. This flexibility theoretically reduces construction and upscaling time. Some designs can also follow the load, more efficiently than conventional nuclear power plants, making SMRs attractive when it comes to grid integration challenges. Overall, the development of SMRs provides access to nuclear power to countries that cannot accommodate large nuclear power plants for various reasons, be it cost or energy policy planning. It is recognized that the commercial deployment of SMRs would unlock access to nuclear power in new sectors and regions.

Environmental impact assessment

A life cycle assessment of the NuScale The SMR (Godsey, K., Life Cycle Assessment of Small Modular Reactors Using US Nuclear Fuel Cycle. 2019, Clemson University) design reveals that per kWh of power generation, the system would emit 4.6 g of CO2 eq / kWh. This figure is significantly lower than the previously reported value (Carless, TS, WM Griffin and PS Fischbeck, The Environmental Competitiveness of Small Modular Reactors: A life cycle study. Energy, 2016), of 8.4 g CO2 eq./kWh. As both reactors are smaller versions of conventional light water reactors, this range of emissions coincides with commonly reported life cycle GHG emissions from reactors at the 1000 MW scale, including the value in this report. , 5.6 g CO2 eq./kWh under European (core and backend) conditions.

Main conclusions

The primary objective of this report is to assess the environmental impacts of the life cycle of power generation options. This was achieved by performing an LCA on the updated life cycle inventories of certain technologies.

More specifically, hard coal, natural gas, hydroelectricity, concentrated solar power, photovoltaics, wind power and nuclear power were assessed with regard to the following indicators: climate change, eutrophication of fresh water, ionizing radiation, toxicity human, land use, dissipated water, as well as the use of resources.

Regarding GHG emissions, coal energy shows the highest scores, with a minimum of 751 g CO2 eq./kWh (IGCC, USA) and a maximum of 1095 g CO2 eq./kWh (coal sprayed, China). Equipped with a carbon dioxide capture installation, and taking into account the storage of CO2, this score can drop to 147-469 g CO2 eq./kWh (respectively). A combined cycle natural gas plant can emit 403 to 513 g CO2 eq./kWh from a lifecycle point of view, and between 49 and 220 g CO2 eq./kWh with CCS. Nuclear power shows less variability due to the limited regionalization of the model, with 5.1 to 6.4 g CO2 eq./kWh. Regarding renewable energies, hydropower shows the greatest variability, as emissions are very site-specific, ranging from 6 to 147 g CO2 eq./kWh. Since biogenic emissions from sediment accumulated in reservoirs are mostly excluded, it should be noted that they can be very high in tropical areas. Solar technologies present GHG emissions ranging from 27 to 122 g of eq. CO2 / kWh for the CSP and from 8.0 to 83 g of eq. of CO2 / kWh for photovoltaics, for which thin-film technologies are significantly lower in carbon than silicon-based PV. The upper range of GHG values ​​for CSP is probably never achieved in reality as it requires high solar irradiation to be economically viable (a condition that is not met in Japan or Northern Europe, for example) . Greenhouse gas emissions from wind power range between 7.8 and 16 g eq. CO2 / kWh for the onshore, and between 12 and 23 g eq. CO2 / kWh for offshore wind turbines.

Most of the GHG emissions from renewable technologies are incorporated into infrastructure (up to 99% for photovoltaics), which suggests strong variations in life cycle impacts due to variations in the origin of raw materials, energy mix used for production, modes of transport at the various stages of manufacture and assembly, etc.

All technologies show very little eutrophication of freshwater during their life cycle, with the exception of coal, the extraction of which generates residues that leach the phosphate into rivers and groundwater. CCS does not influence these emissions because they occur during the extraction phase. Average P emissions from coal range from 600 to 800 g P eq / MWh, which means that phasing out coal would virtually reduce eutrophic emissions by a factor of 10 (if replaced by PV) or 100 (if replaced by wind, hydroelectricity or nuclear).