One of the common goals for advanced reactor designs is to improve safety margins. In addition to the usual engineered safety systems in plants that meet international safety standards, CANDU reactors have inherent passive features that limit the consequences of postulated severe accidents. These features include the presence of the heavy water moderator surrounding the fuel channels as well as a shield tank—containing light water for biological and thermal shielding—that surrounds the moderator. Both act as passive "heat sinks" in the very unlikely event of a severe core damage accident.

AECL's strategy is to increase the reliability and applicability of passive heat transfer mechanisms, as opposed to further increasing safety margins using engineered features. This approach will make CANDU reactors easier to license and less expensive to build and operate as well as enhance the “defence-in-depth” principle of having multiple safety systems integrated into the design.

In addition to improved heat transfer components, AECL is developing other passive systems to control hydrogen and to provide emergency cooling water. Some of these concepts are already being incorporated into AECL's latest designs.

AECL is also working closely with the regulator and Canadian utilities to establish a suite of safety codes that will meet requirements for verification and uncertainty analysis. Having this set of codes available will allow for application of best estimate plus uncertainty analysis methodology to demonstrate the full safety margins inherent in the CANDU design. This will further enhance the licensing basis for CANDU reactors.