A Study on Intermediate Scale Steam Explosion Experiments with Zirconia and Corium Melt

Korea Atomic Energy Research Institute (KAERI) launched an intermediate scale steam explosion experiment using real reactor materials, named 'Test for Real corium Interaction with water (TROI)' to investigate the effect of material composition, multi-dimensional melt-water interaction, and hydrogen generation on a steam explosion. In the first series of the tests using several kg of molten zirconia where the melt was brought into contact with the water in the water pool at room temperature to 95 deg. C and at atmospheric pressure, either a quenching or a spontaneous steam explosion was observed. In the second series of test, about 10 kg of molten corium (70:30 of depleted UO2 and ZrO2) was used. They were performed at room temperature and at atmospheric pressure, a spontaneous steam explosion occurred in most cases. It is rather surprising because no spontaneous steam explosions were observed in the FARO/KROTOS tests performed at Joint Research Center (JRC) in Ispra, Italy using corium melt. The steam explosion process was monitored using video cameras. Dynamic pressures, impulses and water temperatures, melt temperature and static pressure inside the pressure vessel were measured. The morphology of debris and pressure profile clearly indicated that steam explosions had occurred. In the case of a steam explosion, the amount of finely fragmented debris (less than 0.710 mm), which was not found in the tests without a steam explosion, was rather large as about 17% - 31%. Hydrogen generation was measured using the gas mass spectrometry. (authors)