Natural circulation characteristics analysis of a small modular natural circulation lead-bismuth eutectic cooled fast reactor

Small modular reactors (SMRs) have attracted particular attentions in recent years, and small modular natural circulation lead or lead-alloy cooled fast reactor (LFR) is one of the potential candidates for SMRs development. In the small modular natural circulation LFR, the natural circulation characteristics of primary cooling system is a coupled thermal-hydraulic problem of the core, hot and cold plenums, reactor internal parts and heat sink. Therefore, in order to study the thermal-hydraulic performance and safety features of the reactor, the understanding of natural circulation characteristics of primary cooling system is very important. In this work, a CFD simulation was conducted to analyze the natural circulation characteristics of LFR-10 primary cooling system during nominal condition, the velocity and temperature distribution of the reactor pool were illustrated and discussed, the core flow distribution behavior was evaluated. The simulation results show that, a stable natural circulation can be established in the primary cooling system, the current thermal-hydraulic design scheme is feasible, some design features of the cold pool are found that need some reconsideration. The coolant was distributed automatically at the core inlet region, the mass flow rate gradually decreased along the core radial direction, but the mass flow share of each core layer is inconsistent with its power share, the current core flow distribution design of LFR-10 need further analysis, Finally, a correlation was proposed to predict the relationship between the core mass flow rate and the core power under different conditions based on theoretical deduction and simulation results, which can be used to evaluate the heat remove capacity and the primary system natural circulation characteristics for LFR-10 under different operating conditions quickly.