Improved design of spent fuel dry storage using phase change heat transfer of hybrid control rod-heat pipe

Abstract

A thermosyphon heat pipe, which is a passive heat transfer device using phase change and natural convection of working fluid between two different temperature interfaces, have been investigated as safety feature of various passive safety systems in nuclear facilities. One of the applications is hybrid control rod-heat pipe, combining functions of existing control rod and thermosyphon heat pipe. The hybrid control rod-heat pipe contains neutron absorber and working fluid inside the metal container, therefore, it has cooling performance and controllability of reactivity. Based on its simple working principle and easy applicability, innovative spent fuel dry storage cask was designed. To analyze the cooling performance of hybrid control rod-heat pipe as a safety feature for spent fuel dry storage cask proving its feasibility, demonstration test facility was constructed in a single fuel assembly scale with full height (6m for spent fuel dry storage cask). Through the series of experiments and MARS analyses with demonstration test facility, the effects of hybrid heat pipe on safety of spent fuel dry storage cask under normal operation condition will be observed. The hybrid heat pipe-equipped fuel assembly showed the reduced coolant temperature and peak cladding temperature compared to conventional fuel assembly design under the simulated operating conditions, securing additional thermal margin. In addition, heat transfer models related to evaporation, condensation, and flooding inside the hybrid heat pipe will be evaluated based on experimental data, to predict the cooling performance in transient conditions of reactor and cask environment. It is expected that feasibility of other passive safety systems utilizing heat pipe can be fully investigated by the analysis results on full-scale hybrid heat pipe.