The defence-in-depth philosophy of the CANDU 6 reactor recognizes that even if the unexpected events occur, they are effectively countered. There are four key elements to AECL’s defence-in-depth design philosophy: prevention, protection, mitigation and accommodation.

Prevention:
Fundamental in the CANDU approach to safety is good design and the application of strict quality control during the design, manufacturing and construction phases of the plant. Equipment failure and human error are anticipated and addressed.

Protection:
Protection aims at stopping an accident before it can do much damage to the reactor. Redundant systems are provided to shut down the reactor and remove decay heat.

Mitigation:
Mitigation systems restore heat removal capability if it is lost, in order to prevent, or limit the extent, of fuel damage.

Accommodation:
Its purpose is to contain the release of radioactive materials to the environment by the physical barriers.