Nuclear Power and Greenhouse Gases
Advocates of nuclear power like to suggest that atomic energy creates no greenhouse gas emissions, and that they should be built to protect the planet from climate change.
This is an exaggeration. For a start, the immense quantities of cement and steel which go into the building of the power station represent a large quantity of “embedded” greenhouse gases. Of course, all power projects – even wind turbines – contain embedded greenhouse gases. However, the amount of steel-reinforced concrete required to generate thermonuclear power safely exceeds any other type of power plant except perhaps a major hydroelectric dam. A very thick concrete pad is needed to confer stability; a containment dome must be provided to contain gases, liquids, and radiation should the thermonuclear pile go out of control or suffer a “melt-down”*. (A problem at Chernobyl was the lack of a containment dome!)
* “Melt Down” refers to a situation in which the components & machinery of a reactor begin to melt preventing the operation of the shutdown systems. The melting fuel bundles begin to flow, possibly creating as non-nuclear explosion. The molten material eventually melts other substances, diluting itself, and stopping the chain reaction.
Nuclear fuel must be mined, and processed to yield usable uranium. A rich uranium deposit might have up to 1% uranium. More typically, uranium deposits are ~0.1% uranium! That means 1000kg of ore must be excavated to win one kilogram of uranium. (One Canadian mine is said to produce ore with 30% uranium, but this is highly unusual!) Then the uranium, 99.3% U238, must be enriched with U235 before it can power a reactor. The enrichment process consumes energy – partly to create fluorine which is reacted with uranium to make UF6. This gas is centrifuged to separate the slightly heavier U238 from the U235 – another energy hungry process – and the fuel rod manufactured. Finally, nuclear waste disposal also exacts its penalty.
Germany’s Öko-Institut calculated the greenhouse gas emissions from various methods of electricity generation and estimated that nuclear produces 33 grams of CO2 per kilowatt-hour (electric) of energy generated – far lower than coal-fired generation. If lower quality ores are used, CO2 emissions can be up to four times higher!
| Electricity Life-Cycle Emissions Source (grams CO2/kWhel) Photovoltaic Hydroelectric (run-of-river) Wind (offshore or onshore) Gas, internal combustion cogeneration Gas, Combined Cycle Cogeneration Coal, Cogeneration Nuclear Coal, Simple Steam Turbine |
Life-Cycle Emissions (grams CO2/kWhel) 100 40 20 20* 150* 460* 33 90 |
| *not including credit for avoided fuel combustion for heating | |
According to the Öko-Institut, efficiency is by far the most effective way to reduce greenhouse gas emissions. Even better is to capture biogas from domestic and agricultural waste digestion, and use that for the cogeneration of electricity (electricity production, plus use of the waste heat by industry or for comfort heating). This earns credits by keeping methane out of the atmosphere, and by producing heat from this, thus avoiding the use of another fuel for the same purpose.
Far too much of our green house gas emissions come from non-energy related sources – such as methane from the digestive tract of ruminant animals (cows). Livestock are estimated to produce 3% of Canadian greenhouse gases! In Australia, due to the smaller human & larger livestock populations, livestock create more than 12% of greenhouse gases! Worldwide, livestock are likely responsible for 3-4% of global warming!
Worldwide, wetlands and rice paddies are responsible for another 6-8% of global warming. A similar amount comes from non-biological sources like volcanoes. All these are dwarfed by the CO2 emitted by transportation – cars, trucks, ships, aircraft, etc – around 30% in all.
About 5% of global CO2 emissions are from the cement industry; 40% of this total from fuel burning, and 60% from CO2 emitted during the conversion of limestone into cement.
So the reduction in greenhouse gases which might be achieved by substituting nuclear energy for another form of power generation is relatively small, simply because just 20-30% of worldwide greenhouse gas emissions come from power plants anyway!
Lifetime emissions of CO2 from nuclear electricity generation are close to those of a natural gas fired power plant. The figure depends heavily on how long the power plant is allowed to continue generating. Nuclear is certainly not “carbon-free” as its proponents often claim. Many nuclear power plants have been shut down far sooner than their designers expected (one as soon as 5 years), increasing their greenhouse gas emissions per unit of electricity produced. A few old designs, like Calder Hall (U.K.) and Chalk River (Canada), have run longer than anticipated.