Simulation of quenching behavior of high-temperature fuel under LOCA

The lessons learned from the Three Mile Island Unit 2 (TMI-2) accident and the Fukushima Daiichi accident demonstrate that under accident conditions, loss of coolant may lead to the core being exposed to air. Failure to promptly activate the emergency core cooling system (ECCS) can result in severe core damage due to fuel melting. Simulating the high-temperature quenching behavior of fuel under loss-of-coolant accident (LOCA) conditions is critical for evaluating reactor safety performance. This study employs the mechanistic severe accident analysis code ICARE2 to establish a numerical model for analyzing the high-temperature quenching behavior of fuel assemblies during LOCA scenarios. Model validation was conducted using experimental data from the QUENCH-06 test, demonstrating strong agreement between ICARE2 simulations and experimental results for key parameters such as peak cladding temperature, quench front propagation, and cladding oxidation. This confirms the code’s effectiveness in modeling fuel degradation, core oxidation kinetics, and two-phase thermal-hydraulic phenomena during severe accidents. A systematic parametric sensitivity analysis was performed to evaluate the influence of steam flow rate, coolant flow rate, coolant subcooling, and cladding temperature during reflooding on accident progression. Simulations of fuel quenching behavior under various LOCA conditions revealed that the steam mass flow rate dominantly affects hydrogen production and pre-quench peak cladding temperature. The results highlight that insufficient cooling is the primary driver of accident escalation. Consequently, the ECCS must be activated promptly before cladding overheating occurs to mitigate severe core damage.