Sub-channel analysis of the influence of the ATF cladding corrosion on thermal hydraulic behaviors

Accident-tolerant fuel (ATF) enhances the accident tolerance of the fuels by improving its thermal properties and antioxidant radiation performance, thereby enabling the reactor to withstand severe accidents for a long time. This article applies and improves heat transfer and CHF models in the COBRA-EN by considering the impact of cladding surface corrosion on critical heat transfer between coolant and fuel rods. We conduct detailed and critical validation of the model constructed in this paper based on two benchmark experiments. We apply this model to study the thermal–hydraulic behaviors of ATFs under accident conditions. We obtain parameters such as the maximum fuel centerline temperature (MFCT), the maximum cladding surface temperature (MCT), the minimal departure from nucleate boiling ratio (MDNBR), the critical heat flux (CHF), and the average void fraction (AVF) for different ATFs. The results indicate that under most transient operating conditions, cladding corrosion delays the soaring time of the MFCT and MCT, and generally enhances CHF, with an average enhancement amplitude of over 0.15 MW/m². At the same time, due to the effect of cladding corrosion, the MDNBR of the reactor has also been improved, which mitigates the impact of the accident to some extent.