Flow blockage analysis study for liquid metal fast reactor with two different core configurations including normal and inverted core design

Abstract

The safety margin of the lead-cooled fast reactor was investigated under the postulated accidental conditions with the assumption of flow blockage. The corrosive nature of lead-bismuth eutectic coolant has the potential risk of flow blockage problems during the operation time of the reactor. Two different core geometries including normal and inverted cores were presented and considered in the current study to investigate more suitable core design in lead-cooled fast reactors in terms of flow blockage. A major aspect of this investigation was the selection of an appropriate analysis code, which led to a comparative study between the one-dimensional system code and the computational fluid dynamics code. The analysis revealed that the one-dimensional system code had insufficient predictive accuracy for the specific flow blockage scenarios addressed in this research. Using CFD code, this study analyzes the peak temperatures observed in an inverted core during flow blockage phenomena and contrasts the results within a normal core. The analysis shows that as the flow blockage area increases, the reduction in heat transfer due to blockage is locally more significant in a normal core. Of the two core designs, the normal core exceeds the safety criteria first at smaller blockage sizes. The peak cladding temperatures that exceeded the safety criteria occurred in localized areas inside and behind the blockage. This cladding temperature increase is due to two factors: the occurrence of a flow recirculation area and the increasing radial distance between the cladding and the coolant as the blockage area increases. Ultimately, it is confirmed that the inverted core provides a higher safety margin in the event of flow blockage phenomena compared to the normal core. This study identified the temperature behavior differences and safety characteristics between normal and inverted cores during flow blockage phenomena. It is anticipated that this approach will enable a physical insight into the core design of lead-cooled fast reactors from the perspective of flow blockage accidents.