APR1400 Primary Coolant System Creep Rupture Analysis under High Pressure Natural Circulation using MELCOR and CREC code

One of the most vulnerable parts of primary coolant system under high pressure severe accident condition can be either hot leg nozzle, pressurizer surge line or steam generator tube. In case steam generator tube rupture occurs, it can cause large release of fission products to the environment. In this study, MELCOR 1.8.6 code is used to simulate the natural circulation phenomena under high-pressure Station Blackout(SBO) accident for APR1400 nuclear power plant. Simulation of natural circulation phenomena is realized by several model adjustment; splitting hot leg into two halves to permit counter current flow and setting the steam generator inlet plenum mixing ratio. In addition to MELCOR calculation, CREC code is used to evaluate creep rupture probability for three vulnerable parts of primary coolant system under the same accident scenario. Results show that the hot leg rupture occurs most frequently and steam generator tube rupture rarely occurs if its initial crack depth is less than 40% of its thickness.