Modeling of corrosion-induced blockages on radiation heat transfer by using RELAP5-3D

Abstract

Nuclear power propulsion for space applications is essential for long-term high payload missions. Several nuclear reactor types were investigated by the Nuclear Engine for Rocket Vehicle Application (NERVA) program of National Aeronautics and Space Administration (NASA). Due to the requirement of long-term missions, studies need to be conducted concerning the impact of planned/unplanned transients on nuclear thermal rockets. In this work, a system model based on RELAP5-3D is developed to simulate corrosion-induced blockages on the peripheral fuel elements of the Pewee I Test Reactor. In addition to the standard axial convective heat transfer, the model incorporates the radiation and conduction heat transfer across the radial direction. Steady-state conditions are achieved for the main thermal-hydraulic parameters. This work investigates the effect of radiation heat transfer across the gap between peripheral fuel elements and the inner core boundary wall caused by corrosion-induced fuel surface degradation of the coolant channel holes. Higher blockage ratios resulted in higher temperature rises across the coolant holes of the peripheral fuel elements. In addition, the pressure drop across the peripheral fuel element coolant holes was also larger at higher blockage ratios. For the channels undergoing blockages, their radiation heat transfer rate increases while their neighbors’ decreases. The temperature of the peripheral fuel elements will gradually get closer to the melting point of uranium carbide, especially when the coolant channels undergo the most severe blockage.