Thursday, July 07, 2005

Nuclear Energy and Total Life-Cycle Emissions

Nuclear power plants do not emit criteria pollutants such as SO2 and NOx or greenhouse gases during operations. This is a well known fact, but it hasn't stopped some anti-nuclear groups from making misleading statements regarding nuclear power.

One of the most common claims heard is that nuclear power emits greenhouse gases during its entire life-cycle. This is true, just as it is true of renewable generation. Nuclear energy life-cycle emissions include emissions associated with the construction of the plant, mining and processing of the fuel, routine operation of the plant, the disposal of used fuel and other waste by-products, and the decommissioning of the plant.

In an article from, Dr Mark Diesendorf, a lecturer at the University of NSW Institute of Environmental Studies, argues "NUCLEAR power generates more damaging greenhouse gas emissions than gas-fired power"” due to "the processes involved in creating nuclear energy."

As I read the article, it became clear that Diesendorf was referencing the claim two researchers in the Netherlands have been making about nuclear. So let's begin by looking at the study done by the two researchers. Here are their conclusions:

"“The use of nuclear power causes, at the end of the road and under the most favourable conditions, approximately one-third as much CO2-emission as gas-fired electricity production. The rich uranium ores required to achieve this reduction are, however, so limited that if the entire present world electricity demand were to be provided by nuclear power, these ores would be exhausted within three years."”
Their argument of how nuclear energy produces CO2 is based on incurred energy debts and energy costs throughout the lifetime of a plant. They admit that when a nuclear plant is online and running, it is not a polluting source of energy, but by the time the uranium is mined, milled, enriched, and the plant is built and decommissioned, the nuclear plant has accumulated energy costs and debts. These energy costs and debts are paid for by using oil and gas as the sources.

Currently, there are a number of different ways of calculating life-cycle emissions. One method, like the above example, is to look at how much energy is consumed in the fuel's life-cycle which is calculated in joules. Another way is to look at in terms of generation calculated in megawatt-hours. And another is to look at emissions in terms of input/output ratios.

Some things to keep in mind about the Dutch study: It only focuses on nuclear and does not apply the same analysis to other types of fuels. And while the study calculates how much energy debt natural gas incurs in its life-cycle, it fails to explain the methodology on why and how it is calculated.

Below are two examples of other studies calculating life-cycle emissions: one on a webpage from the World Nuclear Association and the other on one of NEI's webpages.

Here is an in-depth analysis of life-cycle emissions done by the World Nuclear Association. At the bottom of their analysis, a supplement is given in response to the two researchers as well:
"The 2001 Storm van Leeuwen & Smith (SLS) paper dismisses arguments that nuclear energy is sustainable, either physically, environmentally or in terms of its energy costs, and this is repeated in the numerically-depleted May 2002 version. They purport to offer 'evidence'’ that building, operating and producing fuel for a nuclear plant produces as much carbon dioxide as a similar sized gas-fired plant. The foregoing WNA paper, quoting all the reputable studies we are aware of, shows that this is demonstrably wrong - there is a 20 to 50-fold difference in favour of nuclear. . ."

"Finally, it should be pointed out that, even on the basis of their erroneous assumptions and using their inaccurate figures, Storm van Leeuwen & Smith still are forced to conclude that nuclear power plants produce less CO2 than fossil-fuelled plants, although in their view "‘the difference is not large". Others might see a 20 to 50-fold difference (between nuclear and gas or coal) as significant."”
Here is NEI'’s take on life-cycle emissions:
"“A number of analyses and assessments have shown that the life-cycle emissions from nuclear energy are no greater than other non-emitting sources of electricity available today. All industrial and manufacturing activities have impacts and produce waste by-products, but nuclear power has one of the smallest environmental "footprints" of any source of electricity or any manufacturing process."
If you scroll down the link on life-cycle emissions you will find several tables and charts that compare the amount of life-cycle emissions from major electricity generating sources. The life-cycle impact of nuclear energy is among the lowest of any form of electricity generation.

POSTSCRIPT: Part of the scenario that Storm van Leeuwen & Smith posit really strains credulity. I'm talking about the claim that if all of the world's electricity demand were met by nuclear generation, the available supply of uranium ore would only last three years.

That's ridiculous, because no one is seriously suggesting that all electrical generation be provided by nuclear energy. Electricity demand is projected to increase by about 40 percent in the next 20 years, and we'll need all types of generation -- renewables, natural gas, clean coal and nuclear -- in order to meet it. If the two researchers were to apply the same test to any kind of fossil fuel, the outcome would be similar. For more on issues concerning the uranium supply, click here for a post from our colleague, Dr. Clifton W. Farrell.

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Engineer-Poet said...

I've been looking at the Storm van Leeuwen and Smith stuff myself, and their paper raises very troubling questions.  For instance, their figures for energy of conversion to UF6 in Chapter 2 cover a range of almost 4 orders of magnitude (25.2 to 176000 GJ/Mg U).  They settle on a figure of 1478 GJ/Mg (roughly 2.5 times the energy required for mining and milling the uranium from hard ores), but they do not explain why this figure is justified for projections of future enriched fuel.  Are the lower figures (some of which are less than a quarter of what they posit) for processes which cannot be used, or would not be used given other considerations?  If energy is going to be dear, why would anyone invest in a plant which is profligate with an expensive input?  Perhaps they answer this later on, but there is neither word nor reference where the reader would most expect to see it.

I've been meaning to take this piece apart in detail since I was directed to the SMH editorial a couple weeks ago, but I've been lacking free time.

Jim Hopf said...

Not only have the Dutch reports conclusions been thoroughly debunked by many objective analyses such as the one done by the IAEA, but their statements on uranium reserves (supplies) and declining ore grades are also almost certainly false (i.e., will never come to pass).

As I discuss in more detail at the link:

we probably have hundreds of years of uranium, even using the once-through cycle, before it becomes expensive enough to make nuclear uneconomical. The amount of undiscovered high-grade uranium deposits probably vastly exceeds the amount of known reserves, and the amount of uranium in lower-grade (but still affordable) ore despoits is much higher still. When the ore price gets high enough, we'll just use breeders.

As "engineer-poet" points out, the laws of economics can sort through these issues. If uranium took so much money, or energy, to extract, why would we build nukes (i.e., how could they be economic)? Furthermore, if uranium got that much more expensive in the future, why would we not just breed? Clearly, with breeders, the net emissions will be negligible, no matter how low the uranium concentration. We know that the additional cost for breeders (vs. current plants) is fixed and manageable (only 1-2 cents/kW-hr), and is not driven by input energy costs or CO2 emissions costs.