Operation characteristics analyses on a marine-type passive residual heat removal system

Highlights: • A new type passive system was applied to enhance the inherent safety of marine NPPs. • An ocean-based thermal hydraulics analysis code has been developed based on RELAP5. • The heat transfer capacity was discussed in consideration of safety requirements. • Passive system operational characteristics under ocean conditions were analyzed. - Abstract: A marine passive residual heat removal system can not adopt a huge water tank like that of AP1000 design due to the limited space. Considering the characteristics of marine nuclear power plants, a new type of passive residual heat removal system was applied to enhance the inherent safety features. The new passive residual heat removal system consists of a small-size intermediate water tank, an air-cooling tower and corresponding pipes and valves. The design capacity was evaluated based on the system safety and cooling rate. As a step forward, thermal-hydraulic analysis codes have been developed based on RELAP5. An additional force model and refined volume coordinate solver model were added. The results conclude that the reasonable passive residual heat removal system design capacity is 1.7% full power for IPWR200. The ocean motions make obvious effects on passive residual heat removal system operation characteristics, which should be considered during the design and operation to ensure sufficient safety margin. Besides, the passive residual heat removal system has been proved to be trust-worthy and effective under typical ocean conditions based on the simulation results.