Experimental and Analytical Studies on the Penetration Integrity of the Reactor Vessel Under External Vessel Cooling

Abstract

Experimental and analytical studies on the penetration integrity of the reactor vessel have been performed to investigate the potential for reactor vessel failure during a severe accident in the Advanced Power Reactor 1400. Six tests have been performed to analyze the effects of the annulus water between the in-core instrumentation nozzle and the thimble tube, external vessel cooling, in-vessel pressure, melt mass, and melt flow for the maintenance of penetration integrity using alumina (Al₂O₃) melt as a simulant. The experimental results have been evaluated using the Lower head IntegraL Analysis computer Code (LILAC) and the Modified Bulk Freezing (MBF) model. The test results have shown that the water inside the annulus is very effective in the maintenance of the reactor vessel’s penetration integrity because the water prevents the melt from ejection through penetration. The penetration in the no external vessel cooling case has more damage than that in the external vessel cooling case. An increase in in-vessel pressure from 1.0 to 1.5 MPa did not create penetration damage, but an increase in melt mass from 40 to 60 kg and melt flow due to the vessel geometry significantly increased the amount of penetration damage. The analytical results using the LILAC computer code and the MBF model are very similar to the experimental results for the ablation depth of the weld and the melt penetration distance through the annulus, respectively.