Analysis of Xi'an pulsed reactor large break loss of coolant with ATWS accident

<bold>Background</bold>The accident process and phenomena of Xi'an Pulsed Reactor (XAPR) under the beyond design basis accident conditions are of great significance for a deeper understanding of the safety characteristics of XAPR.<bold>Purpose</bold>This study aims to analyze the thermal hydraulic parameters and fuel rods mechanical response characteristics of XAPR under the large break loss of coolant with anticipated transient without scram (ATWS) accident.<bold>Methods</bold>Firstly, the XAPR model was established by using the Integrated Severe Accident Analysis - Training Research and Isotope Production Reactor General Atomic (ISSA-TRIGA) program. Then, the dynamic characteristics of the pool liquid level, core power, fuel temperature and fuel rod mechanical behavior of XAPR under large break loss of coolant with ATWS accident condition were calculated.<bold>Results</bold>The calculation results show that the pool liquid level of XAPR gradually decreases after the accident. The liquid level drops to 5.55 m at 64 s and the natural circulation ability of the core fail, causes the core coolant flow rate reversed. At 230 s, the liquid level drops to the upper grid plate and the entire core are exposed to air at 296 s. After the top fuel of the core is exposed to air, the temperature increases and negative reactivity is introduced into the core, resulting the core power gradually decreasing and the core power decreases to 1 MW at 238 s. When the pool liquid level drops to the lower grid plate, natural circulation of core air is gradually established to take away the heat from the core and cause the fuel temperature to slowly decrease. The highest temperature of the fuel in the accident reaches 822.6 K. The maximum circumferential stress and maximum strain of the fuel clad are 9.72 MPa and 0.35%, respectively, without the failure of fuel rods.<bold>Conclusions</bold>The results of this study indicate that the XAPR has high inherent safety under the condition of large break loss of coolant with ATWS accident.