Ask Pablo: Is Nuclear Power Really "Carbon Neutral?"

by Pablo Paster, San Francisco
on 09.28.09

Dear Pablo: Too often I hear politicians, lobbyists, and others advocating for nuclear power, but doesn't the processing of the fuel take a huge amount of energy? So how can they call it carbon neutral?

The short answer is that nuclear energy is not "carbon neutral." Wind and solar can also not be said to be entirely without greenhouse gas emissions. But with truly renewable energy sources such as solar and wind we are talking about a one-time "investment" of greenhouse gas emissions when the solar panels or windmills are built. The energy payback period for solar panels is less than two years according to some sources, and even less for wind.

Nuclear energy cannot be considered truly renewable because it relies on a fuel. One that is not only highly processed and refined, but also one that is not replenished by incoming solar energy or biological processes, like wind, solar, tidal, and biomass are.

Where Do Greenhouse Gas Emissions Come From In the Nuclear Power Lifecycle?
Construction

Greenhouse gas emissions in the nuclear power lifecycle begin with the construction of the nuclear power plant. Containment domes and redundant systems make the environmental impact of building a nuclear power plant much bigger than a conventional power plant. But because nuclear power plants have a significantly higher electricity output, the impact per kWh is lessened, but still significant at 2.22 tons of greenhouse gas emissions per gigawatt-hour (GWh), compared to 0.95 tons per GWh for combined-cycle natural gas.

Milling, Mining, and Enrichment

Nuclear fuel, Uranium 235 or Plutonium 239, begin as ore in a giant pit mine (75%) or an underground mine (25%). The ore has a uranium concentration around 1.5%, which needs to be further refined. Processing that includes crushing, leaching, and acid baths produces a more concentrated U3O8 called yellowcake. The U3O8 is processed into UO3, and then into UO2, which is manufactured into fuel rods for nuclear power plants. From mine to power plant, the greenhouse gas emissions can add up to another 0.683 tons of greenhouse gas emissions for every GWh.

Heavy Water Production

An important component of many types of nuclear power plants is heavy water, which is a water with a higher than normal concentration of Deuterium Monoxide D2O, which is just like water in which the Hydrogen atom has been replaced by a Deuterium atom. I was surprised to learn that the production of this heavy water is actually on of the biggest contributors to the greenhouse gas emissions in the nuclear energy lifecycle. In fact it can result in up to 9.64 tons of greenhouse gas emissions per GWh.

So, What is the "Carbon Footprint" of nuclear power?

According to my sources the entire lifecycle emissions of nuclear power are as high as 15.42 tons per GWh. But how does that compare to other electricity sources? A typical nuclear power plant is around 1 GW. Assuming 100% uptime (nuclear power plants do go offline for maintenence), a 1 GW power plant, running 8760 hours per year, will produce 8760 gigawatt-hours, or 8.76 billion kilowatt-hours per year. The average US household uses 11,232 kWh per year, so the average nuclear power plant services 780,000 households. Now, 15.42 tons per GWh translates into 15.42 kg per megawatt-hour (MWh). For comparison, California's mixture of electricity sources, including nuclear, creates 328.4 kg of CO2 per MWh and Kansas tops out the nation at 889.5 kg per MWh. The lifecycle emissions of wind power are around 10 kg per MWh.

Sure, nuclear power has lower greenhouse gas emissions than any combustion-based fuel source but it still has many other problems. We all know about the dangers of nuclear accidents and the issues around nuclear waste. If politicians were technology agnostic, removed subsidies for the coal and nuclear industry, and set a price on carbon with a national cap and trade system, there would be no debate. The free market would choose the path to the most cost effective and cleanest sources of energy which would include wind, solar, small-scale hydro, geothermal, energy efficiency, tidal, and certainly not nuclear or "clean coal."

Additional Resources on Nuclear Power:
The Next Nuclear Renaissance is Already Underway
Green Nuclear Waste?
Life Cycle Analysis of Nuclear Power

http://www.treehugger.com/files/2009/09/is-nuclear-power-really-carbon-neutral.php?dcitc=th_rss