Why an MIT Study on Energy, Water Use and Carbon Emissions is Seriously Flawed

The following post was submitted by William Skaff, NEI's Director of Policy Development.

The MIT study, “Water-CO2 Trade-Offs in Electricity Generation Planning,” that was recently published in Nature Climate Change Letters indicates that power sector water use increases as carbon emissions are reduced. The measure employed for water use is withdrawal. A closer look at the study indicates that this approach is seriously flawed and could lead to erroneous conclusions about nuclear power plants and cooling water.

Climate change eliminates water from watersheds. It does not take water out and then put it back again. Therefore, the appropriate measurement of power plant water use in this context is consumption. This study is seriously flawed because its modeling employs withdrawal, when once-through cooling systems return 99 percent of the water withdrawn,¹  and the power sector as a whole returns 98 percent of water withdrawn, to the source water body.² For example, according to EPRI, nuclear plants with once-through cooling withdraw between 25,000 and 60,000 gal/MWh, but consume only 400 gal/MWh.³

Thus, when the study says, “The water withdrawal under the CO2 limit is 64% greater than under the no-limit case, owing to the additional water withdrawals for nuclear energy” (p. 2), that percent would be substantially reduced to a very small percent increase if consumption were considered. Specifically, according to the statistics above, power sector withdrawal is 100 percent of water use, and 2 percent of this amount is consumed. If, according to the study, there is an increase in withdrawal of 64 percent, roughly 2 percent of which is consumption, then the additional increase in consumption is approximately a little over one percent, at 1.28 percent.

The MIT study demonstrates that selecting an inappropriate water use measure for computer modeling will yield deceptive results that, in turn, may lead to erroneous, if not detrimental, choices for electricity generation portfolio mix made for the purpose of climate change.

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¹ Electric Power Research Institute, Water & Sustainability, Vol. 3 U.S. Water Consumption for Power Production, 2002, p. 3-1.
² U.S. Geological Survey (Wayne B. Solley, et al.), Estimated Use of Water in the United States in 1995, 1998, p. 48-9.
³ Electric Power Research Institute, Water & Sustainability, Vol. 3 U.S. Water Consumption for Power Production, 2002, p. viii.

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CNN Fails to Provide Context on Heat Waves, Droughts and Power Plants

Earlier today, CNN aired a report by reporter Sandra Endo concerning how high temperatures are impacting the operations of American nuclear energy facilities. In initially reporting the story, CNN failed to contact any party that owns or operates any of the nations 104 nuclear reactors.

After we contacted CNN, NEI's Steve Kerekes was interviewed for an updated version of the story, one that we've been led to believe will air sometime between 5:00 p.m. and 6:00 p.m. U.S. EDT today.

The following response to the initial CNN report was written by NEI's Thaddeus Swanek:

CNN has aired a report in which it failed to provide context on the water needs of power plants that draw cooling water from lakes, rivers and the ocean. Though all thermal power plants—coal, natural gas and nuclear—use water for cooling purposes, CNN focused solely on nuclear energy facilities.

It also did not mention the electric sector's positive track record for maintaining power production during severe heat waves. Specially, nuclear power plants in many regions suffering extreme heat safely produce electricity 24/7 to keep consumers cool and businesses operating.

Thermoelectric power generation is among the smallest consumptive uses of freshwater by any economic sector, at 3 percent of total consumption—about one-half of residential consumption. According to the U.S. Geological Survey, thermoelectric power generation accounts for 3.3 percent of freshwater consumption nationwide, about the same percentage as the industrial sector (3.4 percent) and raising livestock (3.2 percent). These power plants withdraw more water than any other economic sector, but they return 98 percent of the water they withdraw back to the natural source. Among electricity sources, certain renewable energy systems exceed thermoelectric power plants in water consumption.

Here is a detailed look at the CNN report.

Myth: Only Nuclear Power Plants Need a 'Significant Supply' of Water

The CNN report left the impression that only "...nuclear power plants depend on a significant supply of reliable water to cool reactors." The report failed to mention that all fossil fuel (coal, oil, natural gas) plants need large amounts of water to operate.

The Facts

Nuclear power plants, like all thermal power plants, require significant amounts of water to generate electricity. Companies that operate nuclear power and fossil fuel plants have temperature limits, set by state environmental regulators, for water they discharge from their facilities back into local water bodies. As these water bodies get warmer during heat waves, these facilities may have to cut back on power production in order to meet those limits.

However, this is very rare for nuclear power plants. In fact, nuclear power plants have a track record of keeping electricity flowing even during record-setting heat waves.

Consider these facts:

• The United States experienced 170 high temperature records in June. During that month, America's nuclear power plants—which follow stringent temperature limits on heat discharge—operated at an average of 90 percent capacity factor. Capacity factor is the ratio of the actual energy produced to the maximum possible during a given time period.

• Severe, prolonged heat had a negligible effect on power production from nuclear power plants.

• Nuclear power plant water use is comparable to coal plants. Natural gas plants use less water. (For water usage rates of different electricity generating sources, see the NEI study on water use below).

• Power plants observe the temperature limit of their discharge water as set by the state regulatory authority, which determines the temperature that is safe for fish and plant life. Generally, nuclear energy and fossil-fuel plants return to full power when temperatures conditions in the water bodies allow it.

For more information, see the NEI article "How to Cool a Power Plant" and the NEI study "Water Use, Electric Power, and Nuclear Energy."

Also see NEI's blog for articles on water use during heat waves and droughts here and here.

We'll report back, if warranted, once CNN re-airs the report.

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Revisiting Nuclear Energy and Cooling Water

Earlier this week, the journal Nature Climate Change published a study concerning how warmer weather and reduced river flows might impact electricity generation at nuclear and coal-fired power plants. Here's how Reuters reported the findings:

In a study published on Monday, a team of European and U.S. scientists focused on projections of rising temperatures and lower river levels in summer and how these impacts would affect power plants dependent on river water for cooling.

The authors predict that coal and nuclear power generating capacity between 2031 and 2060 will decrease by between 4 and 16 percent in the United States and a 6 to 19 percent decline in Europe due to lack of cooling water.

The nuclear energy industry isn't unfamiliar with the topic. Here at NEI Nuclear Notes, we first dealt with the issue during the Summer of 2006 when a heat wave struck Europe and forced a number of nuclear plants to reduce power.

Back then, our points were pretty clear: the industry was well aware of the situation and that there were a number of adaptations that could be implemented in order to mitigate it. When we revisited the issue in response to a study by the Union of Concerned Scientists back in November 2011, I turned to one of our policy experts, Bill Skaff, to handle the question. I spoke with Bill again this week about the latest study, and he passed along the following note to me:

Environmentally conscious regulators and companies are already taking into account flow, discharge temperature, and intake temperature projections when locating and permitting new power plants and other industrial facilities. The Nature study’s time parameters remind us that gradual change allows time for adaptation. Additionally, there are engineering solutions being implemented today that can mitigate climate change impact. For instance, Browns Ferry is building small cooling towers to pre-cool discharge water.

Sustainable development will require electricity for quality of life and a mix of energy sources to generate that electricity—renewable, nuclear, and fossil. We must balance all environmental, social, and economic factors and make trade-offs when considering what energy source or cooling system to deploy at each of our diverse ecosystems around the country.

Wind and solar energy use very little water, but their electricity output is variable and intermittent. An electricity grid can only balance a limited amount of these electricity shortfalls, limiting how much renewable energy can be accommodated by a grid before it becomes unstable and black outs occur. Moreover, the variable, intermittent output of these renewables is usually balanced by fossil plants, which emit carbon dioxide and air pollutants.

The electricity grid requires steady, reliable baseload electricity—the output of nuclear and fossil plants. Nuclear power plant water use is comparable to coal plants. Natural gas uses less water, but produces half as much carbon dioxide as a coal plant as well as nitrogen oxides, which contribute to ground level ozone formation, a cause of respiratory ailments. By contrast, nuclear power plants produce no greenhouse gases or air pollutants during operations.
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EPRI, Water & Sustainability, Vol. 3 U.S. Water Consumption for Power Production, 2002, p. viii. National Energy Technology Laboratory (G. J. Stiegel, J. R. Longanbach, M. D. Rutkowski, M. G. Klett, N. J. Kuehn, R. L. Schoff, V. Vaysman, J. S. White), Power Plant Water Usage and Loss Study, August 2005, revised May 2007, p. xiii.

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