Why a nuclear power plant is safe

U.S. nuclear power plants are safe, but to understand why, it helps to know a bit about how they work.

Nuclear power plants are fueled with uranium. The uranium atoms split—a process called fission—producing heat that boils water to steam. The steam is used to spin a turbine to produce electricity. The leftover radioactive materials—a by-product of nuclear fission—are carefully controlled to be sure no dangerous levels of radiation get outside the plant.

To protect the public from a release of radiation, the plant design takes advantage of natural processes and incorporates backup safety systems—safety in depth. The systems work automatically and immediately.

For example, water cools the fuel in the reactor. Yet, if increasing heat turns too much water into steam, the lack of water acts as a brake, slowing down the nuclear reaction. A complete loss of water stops the fission process altogether.

Nuclear plant designers also assume that equipment will fail and that operators will make errors. So nuclear power plants have multiple backup systems to cope with equipment failure and human error.

Nuclear power plants have built-in sensors to watch temperature, pressure, water level and all other operating indicators that are important to safety. These sensors are linked to control systems that adjust or shut down the nuclear reactor—immediately and automatically—at the first sign of trouble.

In addition to backup systems that monitor and regulate what goes on inside the nuclear reactor, U.S. nuclear power plants also use a series of physical barriers to prevent the escape of radioactive material.

• The first barrier is the nuclear fuel itself. The uranium fuel is in the form of solid ceramic pellets. Most of the radioactive by-products of the fission process remain locked inside the fuel pellets.
• The next barrier is the fuel rods, which hold the fuel pellets. They’re made of a zirconium alloy that is resistant to heat, radiation and corrosion.
• The fuel rods are inside a large steel pressure vessel, with walls about eight inches thick.
• Finally, these barriers are enclosed in a massive reinforced concrete structure—called the containment—with walls that are about four feet thick.

To reach the environment, radioactive material would have to escape from each of these barriers in succession.

For a diagram of how defense in depth works see Multiple Layers of Safety at Nuclear Power Plants, in the Safety & Security area of this site.

The people who work at nuclear power plants are taught that nothing matters more than safety. They are trained and tested continually, to make sure they understand the plant, follow procedures and pay strict attention to detail.

They also must comply with the regulations of the Nuclear Regulatory Commission, an independent federal agency that licenses and monitors all U.S. commercial nuclear power plants.

The NRC requires all plant operators to pass tough licensing—and relicensing—exams.

There are NRC inspectors at each of the more than 100 U.S. nuclear power plants, monitoring daily operations. The NRC also conducts regular—and unannounced—inspections, which cover all plant operations.

Nuclear Energy Institute—Washington, DC
August 2000