Containment Depressurization Rate Requirements for Design Basis Loss-of-Coolant Accidents

Abstract Currently passive containment cooling system (PCCS) of HPR1000 is used in design extension conditions. PCCS uses loop-type heat pipes with evaporators inside the containment and condensers and a large water storage pool outside the containment. One of HPR1000 potential optimizations is using PCCS to mitigate design basis accidents, but there is an issue of containment depressurization rate. Section 6.2.1.1.A of Standard Review Plan (SRP) requires the containment pressure should be reduced to less than 50% of the peak calculated pressure for the design basis loss-of-coolant accident within 24 hours after the postulated accident. Due to the working principles of PCCS and available layout space inside the containment, it ‘s difficult for PCCS to meet the containment depressurization rate requirement. Safety requirements of nuclear safety regulations, guides, standards and utility requirements documents are analyzed to trace back to the provenance and its technical basis. Design features for meeting containment depressurization rate requirements of typical light water cooled reactors (LWR) are analyzed and compared. A combination of increasing the containment design pressure and increasing heat transfer area of PCCS is proposed for HPR1000. Loss of coolant accident is analyzed for HPR1000, which demonstrates that after increasing the heat transfer area and the design pressure of the containment, HPR1000 can meet the containment depressurization rate requirement.