Comparison of steady-state and transient condition flow boiling critical heat flux (CHF) of FeCrAl alloy, Zircaloy-4 and Inconel600

This study presents an investigation of critical heat flux (CHF) variation upon the use of candidate Accident Tolerant Fuel (ATF) cladding (FeCrAl alloy) compared to Inconel600, Zircaloy-4 and the 2006 CHF look-up table by conducting the flow boiling experiments under steady-state condition at an atmospheric pressure and at fixed inlet temperatures and a mass flux. To directly compare the CHF change during transient condition relevant to Reactivity Initiated Accident (RIA), experiments were done at the same thermodynamic quality and flow condition following the steady-state condition CHF results. An increased thermal safety margin of FeCrAl alloy compared to other tested alloys were identified as well as a disagreement between the Zircaloy-4 experimental CHF results and the 2006 CHF look-up table, which implies limitation of the current thermal-hydraulic codes for interpreting fuel design safety margin. To gain a better understanding on the implications of wettability on CHF, contact angle measurements were carried out on both fresh and oxide surfaces and the detailed morphology analysis was done by scanning electron microscope, which suggests a negligible impact of the wettability on the flow boiling CHF.