Passive IN-Core Cooling System Based on Hybrid Heat Pipe and Control Rod for Advanced Nuclear Power Plants

Abstract

After the TMI and Fukushima Daiichi accidents, various advanced passive decay heat removal systems in nuclear power plants have been re-examined and newly introduced. However, the main function of these passive decay heat removal systems is characterized by how to feed additional coolant to the reactor core according to accident scenarios. Especially, when a station blackout (SBO) accident occurs, there is a possibility that the established emergency core cooling system cannot be working properly due to the difficulty of depressurization process. Therefore, a new concept of passive decay heat removal system that certainly operates at any situations is required. In this work, an innovative hybrid control rod system is proposed for advanced in-core decay heat removal concept using unique properties of the heat pipe and operating mechanism of control rods. Heat pipe is a passive heat transfer device that combines the principles of both thermal conductivity and phase change to efficiently transport heat between two interfaces. The concept of the hybrid control rod system is that the control rod can have not only the original function of neutron absorber but also the function of the decay heat removal. If the function of the heat pipe is combined with control rods, the limited heat removal capacity can be extended because control rods are inserted to the reactor at initial state of accident using gravitational force. The hybrid control rods are inserted through the existing guide tubes in the fuel assemblies like currently-available control rods. And the heat removal of hybrid control rods can be limited at steady state by adjusting the boiling point of working fluid. The neutron absorber-based heat pipe can be designed to apply it to nuclear systems. The present work demonstrates the feasibility of the new concept through the system code analysis, CFD analysis and fundamental heat transfer tests.