Study on Heat Transfer Characteristics of Sub-cooled Boiling in Passive Residual Heat Removal System

The sub-cooled boiling in the passive residual heat removal system (PRS) of miniaturized nuclear power plant can cause unstable flow, which will affect the safety of the reactor. Through static heat transfer analysis, the temperature limit of the outer wall of the heat transfer tube to avoid net steam generation in the flowing state is obtained, and the natural circulating flow of cooling water in PRS system is improved by increasing the outlet position elevation of the cooling water outlet pipe and the inner diameter of the cooling water pipe. The research results show that after the implementation of the improvement scheme, the natural circulation capacity of cooling water and the heat removal capacity of the system are improved, which can effectively reduce the boiling intensity of cooling water, avoid excessive steam generation and make the PRS system run stably.