What is the difference between S1 and S2 level earthquakes?

S1 and S2 level earthquakes are designations you might encounter in the context of seismic analysis, particularly for nuclear facilities. They are essentially synonymous with Operating Basis Earthquake (OBE) and Safe Shutdown Earthquake (SSE) respectively.

Here’s a breakdown:

• S1 level earthquake (OBE): This is the more frequent, moderate earthquake. It’s designed for and expected to occur at least once during the facility’s lifetime. The goal is for systems and components to remain functional and ensure safe operation during and after the event.
• S2 level earthquake (SSE): This represents the maximum credible earthquake for the specific location, considering the geological and seismic history. It’s a very rare event, but critical to consider for safety. Safety systems must be able to withstand this extreme earthquake and safely shut down the reactor, preventing radioactive releases and ensuring containment structure integrity.

So, S1 and S2 are just shorthand notations used within the field, particularly in nuclear engineering documents. They refer to the same concepts as OBE and SSE but with a different designation system.