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Nuclear Power Results – Life Cycle Assessment Harmonization

Over the last 30 years, analysts have conducted life cycle assessments on the environmental impacts associated with a variety of nuclear power technologies and systems. These life cycle assessments have had wide-ranging results.

To better understand greenhouse gas (GHG) emissions from nuclear power systems, NREL completed a comprehensive review and analysis of life cycle assessments focused on light water reactors (LWRs)—including both boiling water reactors (BWRs) and pressurized water reactors (PWRs)—published between 1980 and 2010. NREL developed and applied a systematic approach to review life cycle assessment literature, identify primary sources of variability and, where possible, reduce variability in GHG emissions estimates through a meta-analytical process called "harmonization."

Harmonization for LWR power technologies was performed by adjusting published GHG estimates to achieve:

  1. Consistent values of three nuclear power system performance parameters: capacity factor, thermal efficiency, and operating lifetime,
  2. A consistent system boundary, through addition or subtraction of major life cycle stage, and
  3. Consistent global warming potentials (GWP) (based on IPCC 2007).

The figure below compares the published and harmonized life cycle GHG emissions for BWR and PWR power systems.

Chart that shows a side-by-side comparison of light water reactors, boiling water reactors, and pressurized water reactors.  For help reading this chart, please contact the webmaster.

Published and harmonized life cycle GHG emission distribution plots. Whiskers represent minimums and maximums. Boxes represent 25th percentile, median estimate, and 75th percentile.

Enlarge image

Collectively, life cycle assessment literature shows that nuclear power is similar to other renewable and much lower than fossil fuel in total life cycle GHG emissions. In addition, the harmonization process increased the precision of life cycle GHG estimates in the literature while having little impact on the overall central tendency.

Harmonization Impact on Variability and Central Tendency

Overall, harmonizing for all parameters (capacity factor, thermal efficiency, system lifetime, system boundary and GWPs) resulted in a tighter distribution than the published GHG emissions estimates for nuclear power systems. The total range of the data was decreased by 50% and the interquartile range was decreased by 35%.

Of the values harmonized, adjusting reported data to a consistent system operating lifetime had the greatest impact on reducing variability in the estimated life cycle GHG emissions from nuclear power systems.

Harmonization reduced the central tendency of GHG emissions estimates for nuclear power systems by 8%.

Comparison of Harmonization Impacts on Pressurized Water Reactor and Boiling Water Reactor Technologies

Assuming consistent performance characteristics, the median LC GHG emissions estimates were nearly identical for PWR and BWR technologies after harmonization. The median life cycle GHG emission estimates for PWR and BWR technology types are 14 and 21 g CO2eq/kWh, respectively, as published, and 12 and 13 g CO2eq/kWh, respectively after harmonization.

To understand additional sources of variability in reported results, categorization and comparison of results based on life cycle assessment method, GHG emission intensity of primary source energy mix GHG emission intensity, uranium enrichment method and uranium ore grade was also conducted.

Given the large number of previously published life cycle GHG emission estimates of nuclear power systems and their narrow distribution, post-harmonization, it is unlikely that new LCAs with the same system boundaries of similar nuclear LWR power technologies will differ greatly.