Effect of thermo-physical properties of accident tolerant fuels on transient fuel behaviors and the safety

Research on thermal hydraulics of accident tolerant fuels (ATFs) in transient is a complex issue. Based on a 5 × 5 fuel bundle model, four transients (power increase, flow reduction, depressurization and temperature increase) that are the basic elements of most of reactor accidents were used to comprehensively evaluate fuel behaviors and the safety of ATFs. A global sensitivity analysis indicates that fuel behaviors are the most sensitive to the temperature increase and the second to the depressurization, which should be avoided in practical. ATF pellets possessing higher thermal diffusivity were easier to cause a soaring cladding temperature in transient, thus leading to a higher peak cladding temperature (PCT), a lower minimal departure from nucleate boiling ratio (MDNBR) and a lower critical power. ATF claddings performed a better accident tolerance capacity in transient due to the lower thermal diffusivity, especially for the SiC cladding.