Safety is a major consideration throughout the design, construction, and operation of a nuclear power plant. Hundreds of systems monitor, control, and support the safe operation of the reactor and each power plant. These systems provide maximum safety and reliability, and reduce the chance of an accidental release of radioactivity into the environment. (Read more about radiation in the “Things You Thought You Knew” section.)
Environmental Safety
Nuclear energy is the largest producer of electric power without emitting any significant pollution or greenhouse gases. The second-largest is hydroelectric power (about 7 percent), followed by wind and solar power (about 2 percent). Since nothing is burned in the generation of nuclear electricity, no harmful emissions are vented into the atmosphere. This is why nuclear power plants do not have smokestacks common to fossil fuel generation facilities. Some nuclear power plants use large cooling towers to remove excess heat from cooling water before it is returned to the waterways; the discharge is water vapor, not smoke or radioactive matter.
This gives nuclear power plants an important environmental advantage. No releases, such as sulfur dioxide (SO2), or nitrogen oxide (NOx), which can cause acid rain; or carbon dioxide (CO2), a major greenhouse gas, come from nuclear plants.
Without nuclear plants, the additional use of fossil fuels would release an estimated 175 million tons more carbon dioxide each year.* That is the equivalent of the amount of CO2 released by nearly one-quarter of America’s 127 million passenger cars. **
Power Plant Safety
The fuel used in nuclear power plants becomes intensely radioactive and thermally hot. For this reason, nuclear power plants have many physical barriers to guard against the accidental release of this radioactive material. These barriers include the ceramic form of the fuel pellets; the metal encasing the fuel pins; the reactor vessel with 8- to 10-inch-thick walls of steel; and a containment building with a lining of ¾-inch steel and walls of reinforced concrete three or more feet thick. This containment building is strong enough to withstand earthquakes, violent storms, and even the direct impact of a large aircraft. The design prevents radioactive material from escaping into the environment even if there are serious mechanical failures or operator errors at the plant.
Engineered safety systems help prevent reactor accidents and lessen the effects if accidents occur. All crucial safety systems have backup systems that duplicate their jobs. For example, huge stainless steel pipes about two feet in diameter carry water to the reactor core, where it cools the fuel. Any of several independent emergency cooling systems included in the design of the plant can cool the reactor adequately if the others fail.
Another vital part of nuclear power plant safety is the intensive training and preparedness of the people who operate the power plant. Reactor operators are trained and tested on the procedures of power plant operation. To train operators, utilities use sophisticated power plant simulators—replicas of the control room of a real power plant. The simulators are computer controlled, allowing the operators to gain practical experience in managing all types of normal and unusual occurrences without any danger to the public or the environment.
The nuclear industry has rigid safety standards, which the Nuclear Regulator Commission (NRC) sets and regulates. Utilities operating nuclear power plants must prove to the NRC that each plant can meet these stringent safety standards. Periodic inspections also ensure that each facility operates safely. Utilities face severe financial penalties if NRC inspections show that the plant is not operating in full compliance with federal regulations.
Some people think a nuclear reactor can explode like an atomic bomb. This cannot happen! A nuclear explosion requires a very high concentration of fissionable uranium. That is the form that splits to release energy. Fuel in nuclear power plants has a very low concentration of fissionable uranium—only about 3 percent. It releases energy at a very low rate. An atomic bomb releases tremendous amounts of energy instantaneously.
Utilities in the United States have operated commercial nuclear power plants since 1957. During this time, no one in the United States has died or been injured as a result of operations at a commercial nuclear power plant. Efforts to ensure that nuclear power plants maintain this safety record are constantly emphasized, and the record compares favorably with all other ways of making electricity.
What about Nuclear Waste?
Nuclear waste is material that is either radioactive itself or is contaminated by radioactive elements. It includes byproducts produced mining ore, producing electricity in commercial reactors, processing defense materials, and preparing nuclear medicine.
Nuclear waste may be either low level or high level. Many commercial, industrial, and medical users produce low-level waste. This includes items such as discarded protective clothing, filters, mops, brooms, rags, and other slightly contaminated items. Low-level waste has a low level of radioactivity that decays relatively quickly. Because it emits only small amounts of radiation, low-level waste is usually sealed in strong cartons or steel drums and disposed of at special sites. It reaches background levels of radioactivity within about 100 years or less.
High-level waste comes from the production of electricity in commercial nuclear power plants or during the production of nuclear materials for national defense. High-level waste has high-energy radiation.
At power plants, the fission process creates radioactive waste products. After about three cycles, these waste products build up in the fuel rods, making the chain reaction more difficult. Utility companies generally replace one-third of the fuel rods every 12 to 18 months to keep power plants in continuous operation. The fuel that is taken out of the reactor is called spent or used fuel. The used fuel contains both high-level radioactive waste products and unused fuel.
Disposing of Nuclear Waste
Because it emits only small amounts of radiation, low-level waste is usually sealed in strong cartons or steel drums and placed in shallow burial sites that are regulated. States that produce low-level waste are responsible for disposing of it. As time passes, the waste becomes less radioactive as a result of radioactive decay.
Currently, high-level radioactive waste is not disposed of, but stored. Nuclear power plants store used fuel near the reactor in a deep pool of water called the spent fuel pool. During storage, the used fuel cools down and also begins to lose its radioactivity through radioactive decay. In three months, the used fuel loses about 50 percent of its radiation. In one year, it loses about 80 percent, and in 10 years it loses 90 percent. Nevertheless, because some radioactivity remains for thousands of years, the waste must be carefully and permanently isolated from the environment.
An increasing number of reactor operators now store their older and less radioactive used fuel in dry storage facilities using special outdoor concrete or steel containers with air cooling.
> Learn about other disposal options
Currently, used nuclear fuel and high-level radioactive waste are stored in temporary facilities at some 125 sites in 39 states. These storage sites are located in a mixture of cities, suburbs, and rural areas. Most are located near large bodies of water.
In the United States today, more than 161 million people reside within 75 miles of temporarily stored nuclear waste.
> View Nuclear Waste Locations by State
Transporting Nuclear Waste
When the time comes to ship nuclear waste to a permanent disposal location, the spent fuel will be carefully loaded into shipping containers, which are called spent fuel casks. Casks are typically made of stainless steel and metal shielding more than six inches thick to protect the contents and confine radiation in both routine transport operations and under severe accident conditions.
A typical spent nuclear fuel cask sitting on a railcar
A spent fuel cask is designed to withstand the worst sorts of disasters and accidents, and a series of tests is conducted on sample casks to ensure that the casks really work. These tests include:
These tests are carefully monitored and measured with high-speed cameras that help engineers and scientists study these containers under conditions that simulate an accident.
In one test, a spent fuel cask was even mounted on a tractor trailer that was hit broadside by a train engine moving at 80 miles/hr. The impact demolished the train engine but did not damage the cask. Afterward, the cask was put into a fire for two hours. Scientists carefully examined the cask for any damage and found that the cask’s contents had remained intact.
> See videos of radioactive cask crash test simulations
In addition to all the requirements that casks must meet in order to be shipped by truck or train, the truck driver and train operator must be trained in the hazards of radioactive materials, transportation regulations, and emergency procedures. The route that the cask takes is also given careful consideration in order to avoid large cities and undesirable road conditions.
* U.S. Department of Energy, Office of Nuclear Energy, “Nuclear Power 2010, Program Status Report,” by Thomas P. Miller, undated.
** Number of U.S. passenger cars from “Transportation Energy Data Book,” Edition 22, published by the Center for Transportation Analysis, Oak Ridge National Laboratory. Calculation based on 5.48 metric tons (6,028 short tons) of carbon dioxide equivalent emitted by the average passenger vehicle, according to the Environmental Protection Agency.
