Peformances of hybrid control rod designs as passive decay heat removal device

Abstract

Most of passive safety systems which operate with natural driving forces have several disadvantages such as reliability, low driving force, possibilities of failure in components, and lack of experience in operation. Solution to mitigate the issues on the passive safety systems is guarantee of the diversity of the system by new working principle and elimination of possibility of the failure. Attempts to apply heat pipe in commercial nuclear power plants have been conducted due to its simple working principle and easy adaptability. Hybrid control rod is proposed as a new conceptual passive decay heat removal device by combining functions of existing control rod and thermosyphon heat pipe. The hybrid control rod contains neutron absorber inside the heat pipe, therefore, it can remove the decay heat and shutdown the reactor simultaneously at the accident conditions. The hybrid control rods were designed including operating strategy because it will be applied to high temperature and high operating pressure conditions. Single-tube test section was experimentally studied as a base design to confirm the effectiveness and effects of the design and operating strategies. The operating strategy achieved the high operating pressure (20 bar) and maximum heat removal rate (6 kW). Double-tube hybrid control rod which contains the baffle between neutron absorber and outer cladding was designed to prevent the flooding phenomenon and enhance the maximum heat transfer rate of the hybrid control rod. The experimental results showed that the suggested double-tube hybrid control rod showed enhanced heat transfer capacity compared to base design.