Design of passive residual heat removal system for low temperature and low pressure pool-type lwr using two-phase closed thermosyphon

Abstract

Two-phase closed thermosyphon is a closed pipe that has working fluid in the interior. Thermosyphon transfers heat effectively and passively by using evaporation and condensation of the working fluid. Due to the advantages of thermosyphon, design of PRHR (Passive Residual Heat Removal) system for low temperature and low pressure pool-type LWR that is being developed in KAIST is conducted by application of the thermosyphon. The reactor is designed to generate heat only for seawater desalination that requires lower operating temperature than electric generation.The PRHR system follows DRACS (Direct Reactor Auxiliary Cooling System) that has high reliability. The PRHR system is designed to prevent boiling of reactor coolant that makes increase of reactor pressure. The heat sink of PRHR system is designed to be filled in air during normal operation for reducing heat loss and filled in water in accident and the change of heat sink is designed to be performed by passive force. A thermal resistance model for analysis of heat transfer in thermosyphon is constructed and the model is used for sizing of thermosyphon. To verify that the designed PRHR system prevent the boiling of reactor coolant, analyzing natural circulation of reactor coolant is conducted and it shows that 2 out of 4 trains in the designed PRHR system makes the reactor coolant temperature be lower than the boiling point. An experiment that uses small scale thermosyphon is conducted for validation of correlations used in the thermal resistance model. The experiment shows that correlation for evaporation of working fluid is overestimated. The correlation for evaporation is modified and the modified correlation is applied the thermal resistance model. Using the modified correlation, reactor coolant temperature is analyzed again and the result also shows that the reactor coolant doesn’t reach to the boiling point.In this research, the requirements of PRHR system, configuration of PRHR system, the thermal re...