ERC: Lesson - Nuclear Power (Topic 6.6) 📖
⏳ Estimated Reading/Watching Time: 11 - 13 minutes
Describe the use of nuclear energy in power generation.
Nuclear Energy
The nucleus of an atom contains protons and neutrons that are held together by nuclear forces.
When atoms collide and fuse or split apart, large amounts of energy are released. The energy that is released can be used to create electricity.
In the early days of trying to harness nuclear energy, scientists weren’t 100% on whether a nuclear explosion would eventually cease or whether it might engulf huge amounts of matter and continue to explode.
Experimentation showed that the blast could be controlled, and these experiments eventually led to the development of nuclear power for generating electricity.
Nuclear power is considered to be a nonrenewable form of energy. Once the heat energy from nuclear fission is used to generate electricity, the fuel is used up and becomes waste that has to be dealt with.
Early in the development of nuclear power, it was hoped that this new energy source would be the answer to the increasing demand for energy caused by a rapidly increasing human population. The video below is an interesting introduction from the United States Nuclear Regulatory Commission (NRC) to nuclear power:
Nuclear power generation is a nonrenewable energy source. Nuclear power is considered a cleaner energy source because it does not produce air pollutants, but it does release thermal pollution and hazardous solid waste.
Fission vs. Fusion
To produce energy, a large atom can be split into smaller atoms (nuclear fission) or smaller atoms can be caused to fuse into a larger atom (nuclear fusion). Both of these reactions release large amounts of energy in the mass-to-energy conversion. In both types of reactions, the mass of the product(s) is less than the mass of the starting material as mass is converted to energy.
Nuclear Fission
Fission is when one heavy, unstable nucleus is split into two lighter nuclei. When a neutron slams into a larger atom, it causes the atom to excite and split into two smaller atoms, also known as fission products.
This releases a huge amount of energy and also causes more neutrons to be released. The released neutrons can then slam into other nuclei initiating a chain reaction, a reaction that initiates its own continuation. Left unchecked, this reaction will continue until all of the related atoms have been split.
Fission is used in nuclear power reactors because it can be easily initiated and controlled, and it produces a large amount of energy. The fuel for fission in nuclear power plants is Uranium-235. The speed of the atoms is slowed so that the U-235 atoms hit each other causing fission. Ideally, a controlled chain reaction will occur.
Nuclear Fusion
During nuclear fusion, two atoms collide at high speed and combine to form a heavier nucleus.
This is the same process that powers the sun and stars, creating vast amounts of energy—several times greater than fission. Fusion does not produce highly radioactive fission products, making it a cleaner alternative. However, sustaining fusion reactions is challenging because of the extreme pressure and temperature required to join the nuclei together.
While scientists have been able to harness the energy that results from nuclear fission, they have not been able to replicate nuclear fusion in a sustainable manner. As such, nuclear fusion is not currently used commercially to produce electricity. Only nuclear fission has been used for nuclear power, especially in electricity-producing nuclear power plants.
Nuclear Fuel
The isotope of the element Uranium is currently the main source of nuclear fuel. Uranium-238 (U-238) is a common isotope of Uranium-235 (U-235), but U-235 makes a better fuel, so it is used as a fuel in nuclear power plants.
After the metal is extracted from a mine, uranium ore is purified into Uranium oxide (UO2). Then, it is milled, crushed and chemically treated, and turned into yellowcake, which is 80% UO2. This is enriched, which separates the U-235 from the U-238, which produces around 3-5% U-235. This becomes the fuel for nuclear power plants worldwide.
Nuclear Power Plants
Nuclear reactors are designed to sustain a continuous fission chain reaction, but the fuel is not pure enough to form an explosion (under normal operating conditions). Water is used as a moderator in the reactor, which slows down the neutrons that produce fission so that they are traveling at the right speed to trigger another fission reaction. The fuel rods consist of enriched UO2 that is made into pellets and loaded into long metal tubes. These are placed together to form the core of the reactor. Over time, the products of fission accumulate in the fuel rods, and they must be replaced. At this point, they are highly radioactive and must be handled very carefully.
Control rods control the chain reaction and keep it from getting out of control. They consist of neutron-absorbing material. They are inserted between the fuel rods. The chain reaction is started and controlled by withdrawing and inserting the control rods into the core as necessary.
Heat from the reactor is used to boil water that provides steam for driving conventional turbogenerators. Once the steam has been used, cooling towers are used to bring the water temperature back down to normal. The moving turbine blades cause a generator to produce electricity which is sent out to the grid for public use.
The major difference is that nuclear fuel and nuclear waste products are highly radioactive so they must be dealt with carefully to avoid nuclear accidents.
Nuclear power is generated through fission, where atoms of Uranium-235, which are stored in fuel rods, are split into smaller parts after being struck by a neutron. Nuclear fission releases a large amount of heat, which is used to generate steam, which powers a turbine and generates electricity.
Radiation
When radioactive elements decay, or lose energy, they emit radiation. Nuclear power plants produce low- and high-level radioactive waste that must be stored somewhere.
If people are exposed to radiation, they can get something called radiation sickness. It can cause a variety of symptoms from leukemia to birth defects in children, and even death, depending on the amount of radiation exposure.
Interestingly, there is no minimum exposure threshold to radiation below which no biological effects occur. All amounts of radiation can cause problems.
Federal regulations permit 1.7 milliSieverts/year as the maximum exposure permitted for the general population from x-rays, etc.
Nuclear power plants and X-rays are not the only sources of radiation, however. Cosmic rays from outer space, CT scans, and background radiation from rocky places on Earth are all additional sources of radiation exposure.
Radioactivity occurs when the nucleus of a radioactive isotope loses energy by emitting radiation.
Nuclear Waste
The United States Nuclear Regulatory Commission (NRC) is a government organization created in 1974 that is charged with regulating commercial nuclear power plants and the use of radioactive materials in medicine. The NRC is also charged with guiding the disposal of nuclear waste to ensure the safety of humans and the environment.
The NRC categorizes nuclear waste into four categories. Explore the tabs below to learn more about each type of nuclear waste.
NIMBY
Because high-level waste has to be stored for SO LONG (for reference, the Neolithic revolution, also known as the New Stone Age, was 10,000 years ago), people are concerned about the long-term storage of nuclear waste. Even though nuclear waste must be stored carefully according to very specific requirements, no one wants nuclear waste stored near their homes. We call opposition to certain proposed developments, including nuclear waste storage facilities, "NIMBY" or "Not in My Backyard". This phrase carries the connotation that residents would tolerate or support the development if it were located farther away from them.
After a $4 billion study, the Nuclear Waste Policy Act of 1982 selected Yucca Mountain in southwest Nevada as the storage site for long-term radioactive waste. However, there has been a lot of pushback from the public, especially the residents of Nevada, so Yucca Mountain is still not an active storage site yet. Residents are worried about geologic activity and how earthquakes would affect the waste stored deep within Yucca Mountain. In 1999, the Waste Isolation Pilot Plant (WIPP) in New Mexico opened to store long-term radioactive waste.
The U.S. Department of Energy describes WIPP as follows:
“WIPP is the nation’s only repository for the disposal of nuclear waste known as transuranic, or TRU, waste. It consists of clothing, tools, rags, residues, debris, soil, and other items contaminated with small amounts of plutonium and other man-made radioactive elements. Disposal of transuranic waste is critical to the cleanup of Cold War nuclear production sites. Waste from DOE sites around the country is sent to WIPP for permanent disposal.”
At either site, there are (or will be) storerooms 1,000 feet above groundwater levels, which should make the casks safe from groundwater intrusion for at least 10,000 years. Both the Yucca Mountain and WIPP projects have run into problems and controversies in recent years and the search for better long-term storage solutions continues today. Whatever site is chosen, the waste will need high security and constant monitoring.
Nuclear waste presents many challenges. Going forward, we will need to continue to figure out additional options for all nuclear waste as we continue to utilize this form of energy in society.
Uranium-235 remains radioactive for a long time, which leads to the problems associated with the disposal of nuclear waste.
You should understand the difference between fission and fusion.
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