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Nuclear energy is among those energy sources producing very low levels of carbon dioxide emissions from their full life cycle. It is closely comparable with renewables such as wind, solar and hydro in this respect.
In recent years some utilities generating electricity have undertaken Life Cycle Analysis (LCA) studies as part of their social accountability. Also mining companies have been publishing their energy use as part of broader environmental or social responsibility disclosure - part of product stewardship, and this feeds into broader LCA figures. Both kinds of results have been audited and published.
The principal focus of LCA for energy systems today is their contribution to global warming. There is an obvious linkage between energy inputs to any life cycle and carbon dioxide emissions, depending on what fuels those inputs. LCA includes mining, fuel preparation, plant construction, transport, decommissioning and managing wastes.
In the nuclear fuel cycle energy inputs are low, even with diminishing ore grades. Its very large low-carbon advantage over fossil fuels will remain even if very low-grade ores are used. In fact uranium resources are abundant and the need to access extremely low grade ores is far off.
Nuclear power and CO2 emissions
Life cycle analysis for Vattenfall's Environmental Product Declaration for its 3090 MWe Forsmark power plant in Sweden for 2002 has yielded some energy data which is up to date and certified. It shows energy inputs over 40 years to be 1.35% of the output.
Related to this is the question of carbon dioxide emissions arising from those inputs, which for Forsmark are 3.10 grams per kilowatt-hour (g/kWh).
The 2005 Environmental Product Declaration for British Energy's Torness 1250 MWe power station in UK shows CO2 emissions of 5.05 g/kWh (reference year 2002) from the inputs.
More typical data is tabulated in the World Nuclear Association's Energy Analysis paper. Here, the estimate of lifetime energy inputs is 1.74% of output. If one then assumes very conservatively that all of the energy inputs are ultimately from burning coal, the carbon dioxide emissions would be under 20 g/kWh.
Extending this: if very low grade ore of 0.01% U is envisaged - as has been said to make nuclear power unrealistic - the energy input figure rises to 3.15% of output, and the calculated CO2 emissions on same basis rise to about 30 g/kWh.
Figures published in 2006 for Japan show 13 g/kWh for nuclear power, with prospects of this halving in future.
The UK Sustainable Development Commission report in 2006 gave a figure of 16 g/kWh for nuclear, compared with 891 g/kWh for coal and 356 g/kWh for gas.
All of these suggest a very favourable energy balance for nuclear power, by any criteria, and a very modest carbon dioxide output from the whole fuel cycle, even if moving to very low-grade ores.
It is difficult to get simple figures for coal and gas, since so much of the energy input (beyond the fuel itself) is often in transport, which varies from very little to a lot. Energy input figures ranging from 3.5% to 14.0% of lifetime output are published for coal, and 3.8% to 20% or natural gas.
Other published figures are consistent with the above for nuclear power, showing it to have around 1-2% of the carbon dioxide emissions of coal-fired power. We use 2% as a conservative typical figure, and point out that this is full nuclear LCA figure compared with coal.
If extremely low grade ores are envisaged, the figure would rise by a further 1% in line with the energy inputs, making it about 3% of coal or perhaps 6% of gas - still a very substantial margin where carbon constraints are increasingly needed.
Reference:see Energy Analysis paper.
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