Nuclear For The Green World

Energy Density and Waste Comparison of Energy Production

By JASON MORGAN | Published JUNE 9, 2010

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Energy density is essentially the amount of energy stored within a given fuel (doesn’t have to be fuel but for electricity production fuel is the energy storage method employed). The energy density of a fuel source also indicates the amount of waste produced per unit of energy output. Since these concepts are complimentary, it is worthwhile to compare several common sources of energy production on an energy density and waste volume basis.

*CONSIDER THIS—By burning one kilogram of their respective fuels, coal can power a 100-watt light bulb for about four days, natural gas for about six days, and uranium in a light water reactor can power the light bulb for just over 140 years.

Fundamentals of Chemical and Fission Reactions

The first thing you need to know about these forms of energy production is that fuel sources are converted into heat energy, which is then translated into kinetic energy to spin a turbine that produces electricity. This is the same for nuclear, coal, natural gas, and oil. Where these energy production sources differ is in how they create the heat energy portion of the process.

Chemical Reactions

Coal, natural gas, and oil all utilize chemical reactions to produce heat. Chemical reactions are harnessing the power of the electrons orbiting the nucleus of an atom. Electrons only represent < 1% of the atomic mass of an atom, and therefore only represent less than 1% of the potential energy stored within the atom. It is based on this type of chemical reaction that coal, oil, and natural gas are converted from matter into heat energy – by only using less than 1% of the potential energy available.

Fission Reactions

Nuclear energy is a fission reaction that harnesses the potential energy stored within the nucleus of the atom, which represents over 99% of the potential energy stored . The difference between this and a chemical reaction is quite clear: chemical is using < 1% and fission is using > 99% of the mass of the atom to generate heat energy. Since Einstein proved to us via E = MC² that matter and energy are interchangeable, it is easy to deduce that the reaction using more of an atom’s mass is going to generate more energy in the conversion process.

Energy Densities of Nuclear, Coal, Natural Gas, and Oil

Below is a table with a list of different fuel sources and their respective energy densities. Energy density can be calculated based on mass or on volume, depending on which measure makes the most sense for your situation. With energy production, density by mass is the appropriate measure since the mass of fuel, not the volume, is the base measure for a power plant’s fuel needs.

Fuel Type	Energy Density (kWh/kg)	Number of Times Denser than Coal
Nuclear Fission (100% U-235)	24,513,889	2,715,385
Natural Uranium (99.3% U-238, 0.7% U-235) in a fast breeder reactor	6,666,667	738,462
Enriched Uranium (3.5% U-235) in a light water reactor	960,000	106,338
Natural Uranium (99.3% U-238, 0.7% U-235) in a light water reactor	123,056	13,631
LPG propane	13.8	1.5
LPG butane	13.6	1.5
Gasoline	13.0	1.4
Diesel fuel/Residential heating oil	12.7	1.4
Biodiesel oil	11.7	1.3
Anthracite Coal	9.0	1.0
Water at 100 m dam height	0.0003	N/A

Energy Density of Chemical Reaction Fuels

The various chemical-reaction driven fuels are all similar in terms of energy density, ranging from coal at 9 kWh per kg to propane at 13.8 kWh per kg. That means we can power a 100-watt light bulb for about 90 hours (almost 4 days) with one kilogram (about 2.2 lbs) of coal, or up to almost 140 hours (almost 6 days) with one kilogram of natural gas.

Energy Density of Fission Reaction Fuels

On the other side of the spectrum are the fission reaction-based fuels that start with the least energy dense (natural Uranium [99.3% U-238, 0.7% U-235] in a light water reactor) at 123,056 kWh per kg and go up to fission of pure, 100% U-235, which yields 24,513,889 kWh per kg. This means that the typical nuclear fission reaction can power a 100-watt light bulb for 1,230,560 hours (just over 140 years) using one kilogram of natural uranium.

The least energy dense form of fission reaction is 13,631 times denser than coal. Contrast this with the fact that the densest form of fuel using a chemical reaction (propane) is only 1.5 times denser than coal. There are a variety of numbers floating around about how many times denser uranium is than coal, but all the estimates agree on one thing: it’s not even close. Suzy Hobbs at popatomic.org has made a great visual comparison of the energy density of coal and uranium. You will notice her research led to a uranium density figure of about 16,000 times denser than coal. This is close enough to the 13,361 calculated from my sources to still prove the point that fission reactions are enormously more powerful than chemical reactions.

How Energy Density Relates to Waste

Energy density also tells you how much fuel a plant requires to produce a given quantity of electricity. Since energy density is directly related to the amount of fuel required, it is also related to the amount of waste produced. The higher the energy density of a fuel, the less fuel a power plant will use. If less fuel is used, generally there is less waste.

Comparing Waste Outputs from Nuclear, Coal, Natural Gas, and Oil Power Plants

Chemical and fission reactions used to generate electricity produce two very different waste profiles. The chemical reaction-based sources all produce basically the same types of waste, just in different quantities. Coal, natural gas, and oil all produce emissions such as carbon dioxide, carbon monoxide, nitrogen oxides, particulates, and some others in relatively minute amounts such as mercury and even uranium (from burning coal). In addition to these emissions, burning coal also produces large volume of ash waste.

ANNUAL WASTE PRODUCED BY 1,000 MW PLANT

Type of Plant	Amt of Electricity Produced (MWh)	Nuclear Used Fuel (tons)	Coal Ash (tons)	Sulfur Dioxide (tons)	Nitrogen Oxide (tons)	Carbon Dioxide (tons)	Small Particulates (tons)	Carbon Monoxide (tons)	Total Annual Waste (tons)	Waste per kWh (lbs)
Nuclear	7,971,600	27	0	0	0	0	0	0	27	0.007
Coal	6,683,880	0	400,000	20,000	20,400	7,400,000	100	1,440	7,841,940	2,347
Natural Gas	998,640	0	0	2	157	199,472	12	68	199,711	400
Petroleum (Oil)	1,173,840	0	0	2,248	898	328,655	168	66	332,036	566

This table shows the amount of each type of waste produced by the four energy sources being compared based on the amount of energy produced by a 1,000 MW plant in one year. Understanding that not all power plants are 1,000 MW, nor are the various types of plants necessarily similar in size or duration of operation, these factors were built in to ensure an apples to apples comparison. The raw data for the coal waste was based on an annual operation of a 500 MW coal plant, so this analysis simply multiplied those waste figures by two. Natural gas and oil plants’ waste data was based on 1 billion BTU. This is equivalent to 292.875 MWh. I calculated the average output of a 1,000 MW rated natural gas and oil plant, with capacity factors of 11.4% and 13.4% respectively, to come up with the number of MWhs produced by each theoretical plant in one year (NG = 998,640, Oil = 1,173,840). These results were divided by 292.875 and then multiplied by the waste figures in the data. This calculation converts the raw data from the 1 billion BTU base to waste information for a 1,000 MW rated plant. Taking this further, I then broke down the waste amounts to pounds per kWh to give a true, levelized waste figure for each energy generation source using the same per unit base.

Renewables and Energy Density

A follow-up post discussing the concept of energy density and renewable energy sources is on the way – but probably not until after a post on energy conversion efficiency, since we will need a foundation in that topic before discussing renewables in this context