How Nuclear Energy Works


  1. Advantages
  2. Disadvantages
  3. Financial/Economic Information
  4. Capacity Factor
  5. Safety/National Security
  6. Nuclear Fuel
  7. Waste Disposal
  8. Environmental Impact and Safety

A nuclear fission reactor is a device which is normally used to generate heat due to the splitting of an atom’s nucleus into smaller parts via controlled neutron collisions. Fission is splitting, and fusion is the opposite. Nuclear fission reactors can also be used to produce neutrons and radioactive nuclides.

You need to understand this before trying to understand nuclear fission: An atom is a unit of matter which consists of neutrons, protons, and electrons. The center of an atom (the nucleus) is where protons and neutrons are, and electrons are kept in an atom by the electrostatic pull of the protons, so the protons basically “hold” the electrons in the atom by pulling on them towards the center of the atom. The protons do this because they are positively charged, and electrons are negatively charged, and opposite charges attract each other.

A simple example is to introduce a neutron into the nucleus of a U-235 (Uranium-235) atom at a low speed to render the U-235 nucleus unstable towards fission. After the first collision renders the nucleus unstable towards fission, a chain reaction takes place, causing fragments of the nucleus (an average of 2.4 neutrons) to break off and collide with other nuclei (plural of nucleus), causing their nuclei to break apart as well, generating a large amount of heat which is the point of this entire process. [Source]

The collision mentioned has to be done at a low speed because the uranium atom will not capture fast approaching neutrons.[Source] The neutron being introduced to the U-235 nucleus needs to be slowed by what is called a moderating medium. Three of the most commonly used moderating mediums are light water, heavy water, and graphite. Light water is the most common.

That is why a nuclear reactor is called a reactor, it is designed to start and facilitate these fission reactions safely and effectively. The heat produced by the nuclear reactor due to fission is used to boil water to produce steam which powers an electricity generating steam turbine.

Type: Nuclear power plants are classified as base load power plants because they are constructed and operated in such a way that they meet or come close to meeting continuous electricity demand reliably, and (in the past) economically. Other peaking generators may be used to assist them if they are unable to meet demand, but peaking generators cost significantly more to operate than most base load power plants. Base load power plants such as steam-powered ones, are operated at their most efficient speed all the time, so their power output stays the same. The problem with baseload plants such as nuclear (steam), coal (steam), and geothermal (steam), is that electricity demand is much lower during the night than it is during the day, and these power plants can’t be turned up or down much to meet electricity demand.

Advantages of Nuclear Power Plants

  • High capacity factor of up to 90%. [Source] Capacity factor is the percentage of the maximum rated generation capacity that is normally generated.
  • No gaseous pollutant emissions.
  • Excellent power-to-size ratio.
  • They require a very small amount of fuel, but the fuel (enriched uranium) is rare.

Disadvantages of Nuclear Power Plants

  • The cost of electricity from these plants has been increasing significantly. According to MIT’s 2009 nuclear power summary, the cost of construction of nuclear power plants has been increasing at a rate of 15% per annum.
  • They produce radioactive waste which is harmful to people and wildlife if they are too close to it.
  • Nuclear power plants contain enriched uranium which terrorists can use to create significant bombs.
  • Uranium is found in low concentrations, therefore, a significant amount of mining has to be done just to obtain a small amount of uranium. One consequence of this is that a significant amount of space is taken up by uranium mining.

Financial/Economic Information

Cost of Uranium Per Pound:

  • Early 2003: $10.75
  • Mid 2006: $45.00 (318% more than early 2003)
  • Early 2007: $100.00 (122% more than mid 2006)
  • 2008: $45.88 (54% less than early 2007). [Source: Argonne National Laboratory]

Levelized Cost of Nuclear Power

Please note that the cost is in US Dollars.

2002: 6.7 ¢/kWh

2009: (In 2007 Dollars): 8.4¢/kWh (increasing)

Additional Information:

  • The cost to construct a nuclear power plant is now double what was calculated by MIT in 2003.
  • The cost to construct a nuclear power plant is most of the cost of nuclear power, not the cost of uranium and maintenance. Nuclear power plants use a very small amount of fuel.

Source: Updated Cost of Nuclear Power

Capacity Factor of Nuclear Power Plants

The capacity factor of nuclear power plants is up to 90%. [Source] Capacity factor is the percentage of the maximum rated generation capacity that is normally generated over a period of time.

Safety/Security Issues of Nuclear Power Plants

Two very frequently asked questions are: “How safe are nuclear power plants?” and “Are nuclear power plants safe?”.

Nuclear proliferation

Nuclear proliferation is defined as the spread of nuclear weapons and material to countries which are not recognized as “Nuclear Weapon States”, and concern about it is growing worldwide.

Some of the reasons include:

Terrorism: There are different types of terrorists, the type of primary concern is that with the goal of genocide (killing tens of thousands). Al Qaeda is an example. They currently haven’t successfully killed millions of people via one attack, but they have killed thousands, and if they get access to nuclear weapons or the material necessary to construct them, they could kill tens of thousands to hundreds of thousands of people at the same time.

Ukrainian Chernobyl Accident

According to Meghan Roe from Notre Dame University, who is a nuclear power advocate: In April 1986, during a nuclear reactor low-power test, there was a pressure explosion due to a power surge which caused fuel elements to rupture, and there was a second explosion which caused fragments of burning fuel to spew out and air got into the core, which contained a moderating medium called graphite, and the graphite then burst into flames because of the presence of air, sending radioactive fission material into the atmosphere. 31 people were killed and 21 square miles of land were rendered uninhabitable. According to Meghan Rhoe, this should not happen again, she said: “In reality, a repeat of the Chernobyl disaster in the United States is simply not possible. To begin with, the unstable reactor design at Chernobyl was a product of communist isolationism.”

Meghan Roe’s Article

Destructive Potential of Nuclear Bombs

I created this section because nuclear bombing is often a part of nuclear power related energy debates. I will very briefly summarize some of the details of the Hiroshima and Nagasaki bombings by the United States in Japan.

On the 6th of August, 1945, at 8:15 AM, the Enola Gay pilot dropped the atomic nuclear bomb nicknamed “Little Boy” over the city of Hiroshima in Japan, killing an estimated 118,661 citizens at least, excluding military personnel up to the 10th of August 1946, and an area of 5 square miles was reduced to ashes.

Source: University of Illinois

Structural Integrity of Nuclear Power Plants

Nuclear reactor structure are built to withstand impact of significant proportions, but I need to gather more information about that.

Nuclear Fuel

The fuel for nuclear fission power plants is U-235 (Uranium-235, which is fissionable) which comes from natural uranium oxide which is primarily (99.27%) U-238 (which is not fissionable), 0.72% U-235, and 0.0055% U-234. 0.72% U-235 is not sufficient for light water reactors, so it must be enriched to 2.5% to 3.5% U-235. Canadian heavy water reactors typically use natural uranium. Heavy water (which contains more of the hydrogen isotope deuterium than normal) reactors use heavy water as their moderator, and light water reactors use light water for moderation as well and also as the cooling agent.

One might wonder why other power plants don’t just use natural uranium instead of enriching it. The answer, according to this article is that heavy-water reactors are so costly that there is no economic benefit of using them instead of enriching the uranium.


Nuclear Fuel Cycle

Spent nuclear fuel can be reprocessed, or disposed of directly, with the latter being the most common option. The latter option is called the once=through nuclear fuel cycle.

  • Nuclear power plant waste is much less voluminous than that of fossil fueled power plants (smog and carbon dioxide), but it is much more harmful, even in small quantities. People can be exposed to a larger volume of fossil fuel engine emissions for a longer period of time without being harmed.

Can Nuclear Waste Be Put To Use?

Waste produced by nuclear power plants can be recycled and reused, but that is currently not economical.


Spent Fuel Rods

Spent nuclear fuel rods are stored in the power plant building and are constantly liquid cooled. The cooling system is backed up by generators which have to be maintained so that they reliably start and prevent a meltdown. Some spent fuel rods are in the nuclear reactor.

Nuclear Waste Disposal

One question which I hear people ask most frequently about nuclear power is: “How is radioactive nuclear waste disposed of?”

Nuclear waste disposal is a complicated task, mainly because it is so toxic that it has to be encapsulated, and because of that, a spill could result in a major environmental disaster. It also stays toxic for a very long time, so radioactive waste will accumulate as time passes, and the disposal process becomes more complicated as a result of that, because there will be less space available for the waste.

Environmental Impact and Safety of Nuclear Power Plants

Nuclear power plants are considered clean with regards to the pollutants emitted by fossil fueled power plants because they don’t emit carbon dioxide (CO2), carbon monoxide(CO), nitrogen oxides, tropospheric ozone, aldehydes, etc. You can learn more about these pollutants by visiting my fossil fuel pages linked to on the left. However, they do produce hazardous radioactive waste.


Nuclear power plants do pose a potential safety threat especially to nearby residents in the event of a meltdown. This is true especially in the case of old nuclear power plants (see the Chernobyl section above). You have to choose the lesser of two evils: As dangerous as nuclear plants can be, that is nothing compared to the environmental and indirect economic impact of coal power plants which is mainly global warming and health related.

Coal power plants emit carbon dioxide (CO2), sulfur dioxide, mercury, lead, cadmium, and soot. Carbon dioxide is not toxic, but it is a greenhouse gas that causes global warming via radiative forcing. Global warming causes drought, and drought causes water shortages. Water shortages cause food prices to increase sharply, and in an economically detrimental manner. You cannot just burn coal until a comparably cheap source of energy becomes available, because it is already one of the most expensive sources of electricity in widespread use, and also because the consequences of global warming remain and actually worsen for years. Nuclear power plants, being the baseload power plants that they are, are one way to directly replace all existing coal power plants and halt power plant caused carbon dioxide emissions.


  • Density of Uranium: 18-19 grams/cubic cm. [Source]

Nicholas Brown is a writer and Android developer. He writes on CleanTechnica as well as Green Building Elements every now and then.

He has a keen interest in physics-related topics such as electricity generation, refrigeration and air conditioning technology, energy storage, and geography.

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