Duplication of equipment so that a safety function can be performed even if some items fail: two trains each capable of 100 percent of the duty, or four trains each capable of 50 percent. Redundant trains are physically and electrically separated so that a fire, flood or electrical fault in one cannot take out the other. Redundancy protects against random independent failures, not against faults that hit identical equipment the same way.
Four 50 percent trains of safety injection, so we can lose one and still have redundancy for a single failure.
Do not mix it up with
- Diversity: Redundancy duplicates the same equipment; diversity uses different equipment or principles so one shared weakness cannot defeat every copy.
Related terms
Diversity
Using different designs, technologies or physical principles for the same safety function to guard against common-cause failure.
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.
ECCS
Emergency core cooling system: the set of safety systems that inject water to keep the core covered after a loss of coolant.