Experimental and analytical studies on the penetration integrity of the reactor vessel in the APR (Advanced Power Reactor) 1400 have been performed under the condition of external vessel cooling in a severe accident. The objective of this study is to estimate failure or non-failure of the penetration including the ICI (In-Core Instrumentation) nozzle and the thimble tube. Five tests in conditions with and without external vessel cooling have been performed to estimate the effects of system, corium mass, and vessel geometry using alumina (Al2O3) melt as a simulant. The test results have been evaluated using the LILAC (Lower head IntegraL Analysis computer Code). The tests results have shown that penetration in the no external vessel cooling case is more damaged than that in the external vessel cooling case. An increase in system pressure from 0.9 MPa to 1.5 MPa was not effective on penetration damage, but an increase in corium mass from 40 kg to 60 kg and a vessel geometry change to flat plate with curvature were effective. The LILAC results are very similar to the test results on the ablation depth in the weld. It is concluded that external vessel cooling is a very effective means for maintaining penetration integrity.

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