Effect of coolant in penetration on integrity of the reactor vessel during a severe accident

When the melted core material relocated to lower plenum during a severe accident in the nuclear power plants, the effect of coolant in the annulus between the ICI (In-Core Instrumentation) nozzle and the thimble tube on integrity of the pressure vessel has been estimated in this experimental study. Two tests in conditions with and without coolant in the annulus have been performed using alumina melt 40 kg as a simulant. The test results have shown that much melts ejected to the outside through the penetration in conditon without coolant in the annulus. However, small melt ejected to the outside through the penetration in the condition with coolant in the annulus, because the coolant prevent the melt from ejection through penetration. It is confirmed from the test results that the coolant in the annulus between the ICI nozzle and the thimble tube is very effective on the maintenance of the reactor vessel integrity