Pressurized Water Reactor
- The only type of nuclear reactor that is used in the United States is the light-water reactor. A light-water reactor is a water-based functioning nuclear reactor with several working parts. First, there is a containment structure that encapsulates the nuclear fuel, and the nuclear fuel itself is contained within special tubes called fuel rods. Also within the containment structure is the steam generator. Typically a nuclear reactor can contain hundreds of fuel rods in the reactor core. Next, the process of nuclear fission occurs, which will be expanded upon later, and this process heats up a quantity of cooling water within the containment structure, starting a loop of water circulation. When this water is heated is creates steam, which subsequently turns a turbine and starts up the steam generator which can be seen below. Then once the steam generator starts up it powers a turbine which can also power and provide energy for electrical systems just off of the steam being produced from the pressurized water around the nuclear core being heated (Friedland, Relyea, & Courard-Hauri 2015). Once the turbine and generator have been activated they help to condense the cooling water that will eventually be pumped into the steam generator within the containment structure. Finally, the cycle starts again as the water around the control rods is heated and then makes contact with the condensed cooling water creating steam. Therefore, the three water circuits are, the pressurized water moderator around the heating control rods, the condensed cooling water that is pumped into the steam generator, and the steam that is produced from the heat of one loop of water passing close to another loop(Friedland, Relyea, & Courard-Hauri 2015 ).
Pressurized Water Reactor
The following video explains the three water circuits that exist in a pressurized water reactor.
Conventional nuclear fission, breeder nuclear fission, and nuclear fusion
- Conventional Nuclear Fission - When an atom splits into two parts and subsequently releases energy, this process is called fission. In the process of nuclear fission a large Uranium-235 atom could be split into two parts by being bombarded with subatomic particles called neutrons. Then when the nucleus splits, the loss of mass from the original atom results in nuclear energy (Fission, 2017) . Furthermore, once the two new nuclei separate at least two more neutrons are released from the reactions along with the creation of smaller atoms such as barium and krypton. When two more neutrons are released from the original bombardment, they consequently bombard the other nearby nuclei splitting them into two, and then releasing two more neutrons. This is the chain reaction that occurs during the process of a controlled nuclear fission reaction at a nuclear power plant. Also, this energy creates the heat within the fuel rods of a pressurized water reactor that contributes to the three-part water circuit. (Friedland, Relyea, & Courard-Hauri 2015)
Conventional Nuclear Fission
2. Breeder Nuclear Fission - The process of fast breeder nuclear fission takes place in a reactor that does not use a coolant to act as a moderator for the fission reaction, such as water which is used in conventional nuclear reactions. Due to this, the neutrons that are released during the process of fission remain at a high speed with high energy. These neutrons are not as efficient at causing fission, however they are captured by an isotope of Uranium-238, which then becomes Plutonium-239 (How, 2017). What makes this process unique is that this Plutonium isotope can then be reused as more nuclear fuel, making the process even more sustainable. Certain reactors can be designed to maximize the production of Plutonium which can potentially lead to an overabundance of nuclear fuel. Plutonium-239 is formed in every reactor and fission's as the reactor operates. Due to the fact that Plutonium fission's it often leaves less in the nuclear fuel. Therefore, a reactor must be able to create as much plutonium as possible while also minimizing the amount that splits. Some breeder reactors are capable of producing up to 30% more fuel than they use (How, 2017).
3. Nuclear Fusion - Nuclear fusion is a much different process than both conventional and breeder nuclear fission. Nuclear fusion occurs when lighter nuclei are forced together to produce heavier nuclei. This is the nuclear process that powers the Sun and other stars in space. This process, much like fission, generates a great deal of heat, however it achieves the output of immense energy from a slight loss of mass, through the fusion of two atoms as opposed to the separation of an atom through bombardment of neutrons. The most promising nuclear reaction for generating electricity is the process of two hydrogen atoms fusing together into a helium atom. This reaction generates an especially immense amount of energy. Nuclear fusion appears to be indicative of unlimited energy, due to the fact that only hydrogen is required as an input and it produces small amounts of radioactive waste. However, the downside of these kinds of reactions is that achieving the process of nuclear fusion on Earth requires a reactor that will heat material to temperatures 10 times that of the core of the Sun. Therefore the amount of energy that is required just to help in the process of containment is much more than the amount of energy that is put out by the reaction. A majority of experts assert that the promise of nuclear fusion may not be fully realized for several decades.(Friedland, Relyea, & Courard-Hauri 2015)
This video explains both the process of nuclear fission and nuclear fusion.
Safety of Nuclear Power Plants
Unlike what many unknowing citizens believe, for nuclear power plants the safety of all of their workers, and the safety of the surrounding citizens and communities are paramount.
- First the safety of the operating workers at a power plant is of primary concern. A major health concern that many believe exists at a plant is radiation exposure, however exposure is minimized by the use of remote handling equipment for many operations in the core of the reactor. Moreover, physical shielding is put to use, along with limited time in areas of the plant that may emit high levels of radiation. A very low level of radiation exposure is always guaranteed in these plants however. In most cases a person is more likely to be exposed to high levels of radiation simply coming from the ground or under their houses, as opposed to working in a nuclear power plant. Likewise, the amount of deaths that result from working in coal mines are significantly higher than those that occur from working at nuclear power plants. As a matter of fact it is very rare for a worker to experience any negative health effects at all from radiation at a nuclear power plant, and it is also much more environmentally friendly than extracting fossil fuels or coal for energy(Harnessing, 2017).
- Now, in terms of preventing large catastrophes, nuclear power plants have many provisions in place. First, a large misconception is that a nuclear power plant has the potential to explode like a nuclear bomb. However this is impossible because the fuel within the reactors is not enriched beyond 5% and considerably higher enrichment is needed for explosives. Also, all of the fission reactions that occur are controlled chain reactions as opposed to the uncontrolled reaction that occurs within a nuclear bomb. Moreover, a mandated safety indicator is the calculated probable frequency of degraded core or core melt accidents. The US Nuclear Regulatory Commission requires that reactor designs must meet a 1 in 10,000 year core damage frequency. However the reassuring fact is that modern nuclear plant designs exceed this requirement by a long shot, considering that the best currently operating plants are about 1 in 1 million year core damage frequency. That means that there may be a major core meltdown or damaged core in one of the best operating plants once in every one million years. (Achieving, 2017). Finally, the fact that there have only been 3 major power plant accidents in the past 50 years of commercial power plants in 32 countries, Three Mile Island, Chernobyl, and Fukushima, the most devastating of which - Chernobyl - had almost nothing to do with reactor design. At Three Mile Island a reactor was severely damaged but radiation was contained and there were no adverse environmental or health related consequences(Achieving, 2017).
- All of this goes to show that Nuclear Power Plants are safe to be in and around our communities. Accidents have been extremely rare and are only increasingly unlikely to occur in the future due to the fact that the safety of the workers, and of the surrounding citizens is absolutely the number one priority for everyone involved in the production of nuclear power plants.
"This CNSC video explains the main safety systems of Canadian nuclear power plants. The systems perform three fundamental safety functions: controlling the reactor, cooling the fuel and containing radiation" This video provides a thorough description of many safety precautions taken in power plants.
- Friedland, A. J., Relyea, R., & Courard-Hauri, D. (2015). Environmental science for AP*. New York, NY: W.H. Freeman.
- "Fission Definition, Discovering Atomic Energy, & Energy and Destruction" (2017). What is Fission? Retrieved from: http://www.livescience.com/23326-fission.html
- "How do fast breeder reactors differ from regular nuclear power plants?"(2017)Scientific American. Retrieved from: https://www.scientificamerican.com/article/how-do-fast-breeder-react/
- "Harnessing the World's Most Concentrated Energy Source, & Achieving Safety: The Reactor Core"(2016) World Nuclear Association Retrieved from: http://www.world-nuclear.org/information-library/safety-and-security/safety-of-plants/safety-of-nuclear-power-reactors.aspx