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DEFENCE IN DEPTH
Defence in depth: facilities

IS CONTAINMENT A SAFETY LAYER?

 

These two examples highlight when containment is and isn’t a safety layer.

Example 1

A criticality accident involving reprocessed plutonium. 

the event with no safety layer at all, would be in the Level 5–7 consequences

If the cell containing the plutonium is surrounded by a concrete structure designed to withstand the energy of a criticality accident and to contain the majority of the activity, it would count as a safety layer.

“Max potential consequences” INES level for worst possible accident—no safety layers

“Max potential consequences” INES level for worst possible accident—with containment

Example 2

A second example could be a research reactor, where core melt would rate at Level 4 but the size of release could NOT reach the Level 5 criterion.

Even if the containment remains intact, thereby reducing the release, the maximum potential consequences are still Level 4, so the containment is not an additional safety layer.

“Max potential consequences” INES level for worst possible accident—no safety layers

“Max potential consequences” INES level for worst possible accident—with containment