Operating-grade decay heat removal system

There are two decay heat removal systems when the reactor is shut down. The first is a passive decay heat removal system used for all shutdowns (planned, unplanned, accident) and the second is an active non-safety grade system used for refuelling and other shutdown operations that require close control of the reactor core temperature. 

Decay heat removal Primary reactor auxiliary cooling system (PRACS) Steam/water system Active Active N/C operation available Non-safety grade... 

The ECCS and CSS installed in conventional PWRs are eliminated. The residual heat removal system (RHRS), CCWS, ESWS, emergency AC power system, and heating, ventilating, and air conditioning (HVAC) system of the main control room are designed as non-safety grade, since the SDHS directly removes decay heat from core to the atmosphere through the SGs without operator actions or external supports such as power, water, etc. 

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