Buildings containing nuclear equipment are specially built to keep radioactive by-products from being released. In addition to backup systems that monitor and regulate what goes on inside the nuclear reactor, nuclear power plants also use a series of physical barriers to prevent the escape of radioactive materials.
The first barrier is the fuel cladding – sealed metal tubes in which ceramic pellets of uranium fuel are encased.
The second barrier is the heavy steel reactor vessel, in the range of nine inches to a foot thick, and the primary cooling water system piping.
The third barrier is the containment building, a heavily reinforced structure of concrete and steel up to several feet thick that surrounds the reactor and is designed to contain radioactivity that might be released from the reactor system in the unlikely event of a serious accident.
Spent fuel is simply used nuclear fuel which has released its energy. About every 18 months, the oldest fuel assemblies (approximately 1/3 of total) are removed and replaced with fresh fuel.
The waste is stored safely. After it is removed from the reactor, used fuel is stored at the nuclear plant site in a steel-lined pool filled with water. The water cools the used fuel and acts as a shield to protect workers and the public from radiation.