In the next several weeks, I will discuss different aspects of getting electricity from coal and from uranium. In 2013, the US got 39% of it’s electricity from coal and 19% from uranium. As discussed in my post The basics of energy, both fuels release heat that can be used to make electricity. Some of the impacts for both fuels are the same; other impacts are different.
This week, I’ll discuss the impacts on the environment. These impacts deal with waste streams and indirectly affect human health. Next week, I’ll discuss direct human impacts like occupational safety and public risk. Then, I’ll conclude with a comparison of economy and other factors.
Coal is mined primarily by surface mining (68%) in the US. The remaining 32% is mined underground. Uranium is also mined using surface and underground mining (47%), but also by in situ leaching (46%).
All mining presents environmental (and human) risks. For example, both mountain top removal to expose coal and in situ leaching can poison water and destroy habitat. But it’s instructive to remember the scale of fuel use per unit energy (from last week):
- coal – 730 pounds
- uranium – 0.04 pounds mined
Taking this a step further, how much material must be mined (including other rock)?. A typical coal mine mines 3 tons of rock for 1 ton of coal. A low-grade uranium ore might be 0.13% uranium oxides. So the amount of rock mined:
- coal – 2200 pounds
- uranium – 37 pounds
To get the same amount of energy from coal, you need to mine 59 times as much material as from uranium. Imagine 59 mines versus a single mine. This isn’t a totally fair comparison, but I think it gives us an idea of which fuel has more mining-based impact.
Both coal and nuclear power plants use water as a coolant in their fuel cycle. Water use falls into two categories: withdrawal and consumption. Withdrawal means that a source of water is diverted for use. Consumption is the portion not returned to the source. For example, a power plant might take in river water for cooling and return half of it to the river (sometimes at a higher temperature). One study looked at water use throughout the entire fuel cycle for various fuels:
- coal – 550 gallons consumed per MWh
- nuclear – 775 gallons consumed per MWh
Coal both withdraws and consumes about 2/3 the water that nuclear does. This could be important in areas that have little water to spare.
Besides mining and water use, both nuclear and coal power plants produce a lot of waste. First, let’s look at gaseous waste:
- coal – 820 kg CO2e per MWh
- nuclear – 12 kg CO2e per MWh
Both also emit tiny amounts of radiation (coal contains small amounts of uranium). This additional radiation is at most 0.5% of background radiation levels, but coal waste is actually 100 times more potent due to fewer regulations on the industry.
But more dangerously, coal power plants emit large amounts of air pollution. 6 kg SO2 per MWh and 3 kg NOx per MWh. These compounds cause acid rain which has many detrimental effects. Coal power also emits 0.00005 kg of mercury per MWh. Among other effects, biomagnification can cause mercury to accumulate in fish and other animals causing mercury poisoning.
Next, let’s look at solid waste:
Fly ash is the oxidized non-carbon portion of coal after combustion. 31 kg per MWh are generated by coal power. 42% is reused in other products, leaving 18 kg per MWh that is collected into coal ash ponds like the one that failed in Virginia.
Nuclear waste in the US is simply the fuel rods after being “spent” in a reactor. 0.0028 kg per MWh are generated by nuclear power. Currently this spent fuel is stored in spent fuel pools or in dry storage inside nuclear power plants.
Nuclear waste lasts a long time. If the US were to reprocess spent fuel (other countries already do it) and isolate the high level waste, called fission products, the radiation would reach original ore levels in 500 years instead of hundreds of thousands. (Edit: Since civilization has changed so rapidly within the last 200 years, planning for any horizon longer than 200 years is naive. Decisions to geologically dispose of waste should be reversible in the case new technologies can be brought to bear on the problem.)
But how long does the carbon dioxide emitted by a coal plant last? The models that the IPCC uses suggest that 22% of CO2 remains in the atmosphere after 500 years:
Both waste streams last a long time, but there is one HUGE difference. Nuclear power plants have their waste contained in tiny little packages (0.000008 cubic miles) and we have options. Coal waste is spread all over the atmosphere (2,000,000,000 cubic miles) and is impossible to collect again.
Totaling the waste numbers, we see what each source is responsible for:
- coal – 860 kg of waste per MWh
- nuclear – 12 kg of waste per MWh
Maybe we should picture our waste streams every time we flip the light switch or adjust the thermostat. 1 unit of waste from nuclear or 72 units of waste from coal.
Summary – environmental impacts
Using uranium as a fuel instead of coal means about 59 times fewer mining impacts, 1.5 times the water use, and 72 times less waste. Do you think I missed any major environmental impacts? Let me know in the comments.