There are 3 primary objectives of Nuclear Safety Systems which are:
- to shutdown the reactor
- maintain it in a shutdown condition
- prevent the release of radioactive material during events and accidents
One of the safety system implemented is the Reactor Protection System. It is composed of systems which are designed to immediately terminate the nuclear reaction. While the reactor is operating, the nuclear reaction continues to produce heat and radiation. By breaking the chain reaction the source of heat can be eliminated and other systems can then be used to continue to cool down the core. All plants must have some kind of these systems.
Another important system is the Emergency Core Cooling System (ECCS). The system comprises a series of systems which are designed to safely shut down a nuclear reactor during accident conditions. These systems allow the plant to respond to a variety of accident conditions and at the same time creates redundancy so that the plant can still be shutdown even if one or more of the systems fails to function.
Under normal conditions, nuclear power plants receive power from off-site. However, during an accident a plant may lose access to this power supply and thus may be required to generate its own power to supply its emergency systems. These electrical systems usually consist of diesel generators and batteries.
There's a containment systems are designed to prevent the release of radioactive material into the environment. It includes fuel cladding, reactor vessel and primary and secondary containment.
In case of a radioactive release, most plants have a system designed to remove radiation from the air to reduce the effects of the radiation release on the employees and public. This system usually consists of containment ventilation and control room ventilation.