Containment Barriers

Fuel pellets contain radiation. There are three levels/barriers of containment that prevent radiation from being released: fuel cladding/rods, reactor coolant (water), and the containment building. The first barrier is the fuel rod/cladding, which contains the radioactive fuel pellets. A "loss of fuel cladding/first barrier" occurs if there is damage to the cladding that may result in a release of radiation into the reactor coolant system. A "loss of the reactor coolant system/second barrier" occurs if radioactive steam is released from the Reactor Pressure Valve or radioactive coolant water leaks from the Reactor Vessel. A "loss of containment/third barrier" occurs if radioactive steam is relased from the containment building's relief valve.