The practice of achieving a safety function by dissimilar means, such as a motor-driven and a turbine-driven feed pump, or analog and digital protection systems from different suppliers. It defends against common-cause failures, where one design flaw, software bug, maintenance error or environmental condition disables every identical copy at once. Diversity and redundancy together are what make a system credible against both random and systematic faults.
Both trains run the same software, so diversity comes from the hardwired backup trip.
Related terms
Redundancy
Providing more components or trains than needed, so a safety function survives if one fails.
Single failure criterion
The design rule that a safety system must still do its job despite any one component failing.
Defence in depth
The safety strategy of stacking independent layers of protection so no single failure can lead to harm.
Scram
The rapid automatic or manual insertion of all control rods to shut a reactor down in seconds.