Evaluation of Tube Ejection Failure for APR1400 ICI Penetration at Various Experimental Conditions

Several experiments have been performed in the VESTA (Verification of Ex-vessel corium STAbilization) facility using a prototypic melt and APR1400 ICI penetration test specimens. In the previous experiments, zirconia melt about 2500 .deg. C was generated in a cold crucible by induction heating and interacted with the test specimen at high pressure condition to simulate the severe accident environment in a reactor vessel. In order to find the tube ejection criteria, we need to check the experimental conditions and find proper boundary conditions to induce tube ejection in the test facility. The objective of the present paper is to investigate the gap change (i.e., to identify the contact or non-contact status) between the tube and the reactor vessel hole, and to estimate the tube ejection for the APR1400 ICI penetrations according to various boundary conditions such as the constraint to fix the test specimen, external reactor vessel cooling, and melt penetration inside the tube. It was found that the structural constraint of the reactor vessel hole not to expand outward and large temperature differences between the penetration tube and the reactor vessel reduces the tube ejection probability. That is, when the thermal expansion of the reactor vessel is suppressed and the temperature difference becomes large, the tube touches the reactor vessel hole early, and thus the tube ejection would not occur. Moreover, the melt flow inside the tube turned out have the greatest effect on the early gap contact because it leads to large temperature difference