Accident analyses for china pressurizer reactor with an innovative conceptual design of passive residual heat removal system

• An innovative passive system design concept was proposed.
• Remote trigger control was adopted in the new passive system.
• Transient characteristic of new PRHRS was studied during normal operation, SBO and FLB.
• New design type is successful.

An innovative passive safety system design concept for CPR 1000 nuclear power plant (NPP), proposed based on the original passive residual heat removal system (PRHRS) design, is presented and studied in this paper. The new type PRHRS avoids use of trigger valve inside the containment and adds an external water tank as the trip of PRHRS operation. The new design concept can realize functions of system remote control and trigger, while the external water tank can provide emergency water for steam generator (SG) in case of loss of feed water accident. Also, the advantages to use a valve and a tank located externally to containment are including the more reliability in implementing valve in pipes at low pressure, possibility operating manually the valve to start the system, refilling the tank in case of long time cooling and maintaining the valve easily. Best-estimate transient simulation code Relap5/MOD3.4 is applied to study the behavior of new design PRHRS and transient characteristics of primary loop system during normal condition and accident conditions. The transient processes of Station Black-Out (SBO) and Feed-water Line Break (FLB) accidents are studied to verify the function of new design PRHRS. Results show that the effect of valve position change from inside to outside containment can be ignored for the new design PRHRS in normal operation and the external valve can trip the operation of PRHRS in case of accidents. The new design PRHRS can remove core residual heat from primary loop effectively through establishing the stable natural circulations in the primary loop and PRHRS loop when the SBO and FLB accidents occur. It also can supply the emergency water to the SG in the event of FLB accident and realize safe reactor shutdown. Results indicate that the new design concept PRHRS in this work is potential and successful in future application.