NUMERICAL ANALYSIS OF IN-VESSEL MELT RETENTION OF CANDU REACTORS DURING A SEVERE ACCIDENT

The objective of the IVR strategy in a CANDU reactor is to maintain the integrity of the calandria vessel and prevent ex-vessel phase conditions, including but not limited to, molten core concrete interactions and significant production of non-condensable gases. To achieve this, accurate simulation of corium convective flows in the calandria vessel is important to demonstrate the performance of vessel structures, corium movement patterns and assess potential breaches that may occur. This research work studies the behaviour of three-dimensional corium flows in a scaled model of the CANDU calandria vessel, encompassing complex phenomena related to multiphase flow, solidification, and heat transfer during crust formation. Ansys-Fluent was used as a solver to study the flow behaviour and heat transfer in a 1/5 scale model of the reactor corium pool and predict its progression. Two relevant validation cases were selected and studied to validate the numerical predictions. The results of this study provide valuable insights into the hydrodynamics of corium in the calandria vessel, particularly near the end shields and subshells of CANDU reactors. This, in turn, contributes to improved IVR safety strategies and the effective management of accidents in CANDU reactors. This study also highlights the importance of ongoing research and development in modeling and simulation techniques for corium behaviour. As future research progresses, understanding of corium hydrodynamics and heat transfer mechanisms will improve, leading to more accurate predictions and assessments of reactor safety analysis. Integrating advanced computational tools and experimental validation offer valuable potential for improving IVR strategies and ensuring their reliability.