|Table 1: Breakdown of CO2 emissions by process from .|
Many see nuclear power systems as a source of CO2-free electricity. Generally, this is true. Depending on a number of factors that will be discussed, the CO2 emissions from nuclear power plants are reported to be in the range of 2 to 4 % of a coal power plant and 4 to 5% of a natural gas power plant.  As a result, nuclear power is a viable source of nearly CO2 free electricity.
The majority of the CO2 emissions from nuclear power plants is produced from processes upstream and downstream of the actual electricity generation (upstream - processes occurring before electricity generation and downstream - processes occurring after electricity is produced). Life cycle assessments of the nuclear fuel cycle typically include uranium mining/milling, conversion of uranium ore to UF6), enrichment, fuel fabrication and construction on the front end and operations, interim storage, waste disposal and plant decommissioning. [1-4] Plant operations contribute to CO2 emissions primarily during downtime (e.g. when maintenance is occurring). During this time, nuclear plants are typically run using fossil fuel based backup generators. [1,3]
There are a number of factors that will influence the quantity of CO2 emitted for each of these aspects of the nuclear fuel cycle. For example, there are two commonly used approaches to enrich uranium for light water reactors: diffusion and centrifugal based processes.  Diffusion based processes require anywhere from 5 to 10 times more energy than centrifugal based enrichment methods. [1,3] Similarly, the CO2 emitted from the enrichment processes will depend on the source of energy (coal, natural gas, hydroelectric ... etc.) used to run the facility.
A typical light water reactor will contribute anywhere from 10 to 160 kg of CO2/kWhe.  A breakdown these emissions by process is shown in Table 1.
The information in this table will vary by a couple percent depending on the assumptions made in the analysis. Each process will depend on the specifics for each process at a given plant and care should be taken when using these numbers.
As global climate change starts to influence our energy decisions, nuclear power plants should be considered as a viable option for producing electricity with near zero CO2 emissions.
© Eli A. Goldstien. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 M. Lenzen, "Life Cycle Energy and Greenhouse Gas Emissions of Nuclear Energy: A Review," Energy Conversion and Management 49, 2178 (2008).
 D. Weisser, "A Guide to Life-Cycle Greenhouse Gas (GHG) Emissions From Electric Supply Technologies," Energy 32, 1543 (2007).
 K. Kleiner, "Nuclear Energy: Assessing the Emissions," Nature Reports Climate Change, 24 Sep 08.
 V. M. Fthenakis and H. C. Kim, "Greenhouse-gas Emissions from Solar Electric- and Nuclear Power: A Life-Cycle Study," Energy Policy 35 2549 (2007).