Under certain circumstances, the nucleus of a very large atom can split in two. In this process, a certain amount of the large atom’s mass is converted to pure energy following Einstein’s famous formula E = MC2, where M is the small amount of mass and C is the speed of light (a very large number). In the 1930s and ’40s, humans discovered this energy and recognized its potential as a weapon. Technology developed in the Manhattan Project successfully used this energy in a chain reaction to create nuclear bombs. Soon after World War II ended, the newfound energy source found a home in the propulsion of the nuclear navy, providing submarines with engines that could run for over a year without refueling. This technology was quickly transferred to the public sector, where commercial power plants were developed and deployed to produce electricity. (more about the history of nuclear energy.)
Nuclear Energy Today
Nuclear reactors produce just under 20% of the electricity in the USA. There are over 400 power reactors in the world (about 100 of these are in the USA). They produce base-load electricity 24/7 without emitting pollutants (including CO2) into the atmosphere. They do, however, create radioactive nuclear waste which must be stored carefully.Fission and Fusion
There are two fundamental nuclear processes considered for energy production: fission and fusion.- Fission is the energetic splitting of large atoms such as Uranium or Plutonium into two smaller atoms, called fission products. To split an atom, you have to hit it with a neutron. Several neutrons are also released which can go on to split other nearby atoms, producing a nuclear chain reaction of sustained energy release. This nuclear reaction was the first of the two to be discovered. All commercial nuclear power plants in operation use this reaction to generate heat which they turn into electricity.
- Fusion is the combining of two small atoms such as Hydrogen or Helium to produce heavier atoms and energy. These reactions can release more energy than fission without producing as many radioactive byproducts. Fusion reactions occur in the sun, generally using Hydrogen as fuel and producing Helium as waste (fun fact: Helium was discovered in the sun and named after the Greek Sun God, Helios). This reaction has not been commercially developed yet and is a serious research interest worldwide, due to its promise of limitless, pollution-free, and non-proliferation features.
This site focuses on nuclear fission. In order to harness fusion, many daunting engineering and physics problems must be solved. The time line for solving these problems is undefined, so we as a society must turn to other solutions to solve the energy problems, at least for now. Fusion research is exciting and making great progress, and it should continue to interest humanity.
Energy density of various fuel sources
The amount of energy released in nuclear reactions is astounding. Table 1 shows how long a 100 Watt light bulb could run from using 1 kg of various fuels. The natural uranium undergoes nuclear fission and thus attains very high energy density (energy stored in a unit of mass).| Material | Energy Density (MJ/kg) | 100W light bulb time (1kg) |
|---|---|---|
| Wood | 10 | 1.2 days |
| Ethanol | 26.8 | 3.1 days |
| Coal | 32.5 | 3.8 days |
| Crude oil | 41.9 | 4.8 days |
| Diesel | 45.8 | 5.3 days |
| Natural Uranium (LWR) | 5.7x105 | 182 years |
| Reactor Grade Uranium (LWR) | 3.7x106 | 1,171 years |
| Natural Uranium (breeder) | 8.1x107 | 25,700 years |
| Thorium (breeder) | 7.9x107 | 25,300 years |
Table 1 Energy densities
of various energy sources in MJ/kg and in length of time that 1 kg of
each material could run a 100W load. Natural uranium has undergone no
enrichment (0.7% U-235), reactor-grade uranium has 5% U-235. By the way,
1 kg of weapons grade uranium (95% U-235) could power the entire USA
for 177 seconds. All numbers assume 100% thermal-to-electrical
conversion. See our energy density of nuclear fuel page for details.
Capabilities of Nuclear Power
Sustainable
Table 1 sums the sustainability of nuclear power up quite well. However, there is quite a bit of talk about nuclear fuel (Uranium) running low just like oil. Technically, this is a non-issue, as nuclear waste is recyclable. Economically, it could become a major issue. Today's commercial nuclear reactors burn only about 1% of the fuel that is mined for them and the rest of it or so is thrown away (as depleted uranium and nuclear waste). The US recycling program shut down in the ’70s due to proliferation and economic concerns. Today, France and Japan are recycling fuel with great success. New technology exists that can greatly reduce proliferation concerns. Without recycling, the 2005 Uranium Reserves ’Red Book’ published by the U.N. IAEA suggests that there are over 200 years of Uranium reserves at current demand. There is also a nearly infinite supply of uranium dissolved in seawater at very low concentration. No one has found a cheap way to extract it yet. Nuclear reactors can also run on Thorium fuel, which is 4x more abundant than Uranium in the crust (but does not exist in seawater).Ecological
In operation, nuclear power plants emit nothing into the environment except hot water. The classic cooling tower icon of nuclear reactors is just that, a cooling tower. Clean water vapor is all that comes out. Very little CO2 or other climate-changing gases come out of nuclear power generation (certainly some CO2 is produced during mining, construction, etc., but the amount is about 50 times less than coal and 25 times less than natural gas plants. Details coming soon). The spent nuclear fuel (nuclear waste) can be handled properly and disposed of geologically without affecting the environment in any way. Coal contains about 4 ppm thorium and uranium, and the radioactive dose given to the public by coal-fired plants is about 100 times the dose given by nuclear plants1. Now that's something to think about. See the nuclear waste article for more info.They’re safe too. In March, 2013 the former NASA scientist James Hansen (of the 350 ppm limit fame) published a paper showing that nuclear energy has saved a total of 1.8 million lives in its history worldwide just by displacing air pollution that is a known killer2. That includes any deaths nuclear energy has been responsible for from its accidents.
Independent
With nuclear power, the USA (and other countries!) can attain true energy independence. Being "addicted to oil" is a major national security concern for various reasons. Using electric or plug-in hybrid electric vehicles (PHEVs) powered by nuclear reactors, we could reduce our oil demands by orders of magnitude. Additionally, nuclear reactor fuel is usually in a ceramic form, capable of reaching temperatures of 2000 degrees C and higher. At these temperatures, water can be thermo-chemically separated into Hydrogen and Oxygen from the waste heat of the electric power plant! The hydrogen could be put in fuel cells for vehicles, eliminating our need for oil altogether. Granted, practical hydrogen fuel cell technology is still a few years down the road. The technology is steadily advancing and a emissions-free distributed and transportation energy solution is on the radar with nuclear power. The waste heat could also be used for district heating or, conceivably, to power chemical processes that capture methane and carbon dioxide from the atmosphere to convert it back to hydrocarbon fuels.Most of the world supply of uranium is in Australia and Canada. With fuel recycling, we wouldn’t need to mine any more uranium. Using Thorium in breeder reactors also leads to long-term world-scale energy capabilities.
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