ICONE17-75450 CORE MELT SOLIDIFICATION CHARACTERISTICS IN RPV LOWER HEAD -EXPERIMENTAL RESULTS FROM LIVE-TESTS

ABSTRACT Core melt solidification phenomena during external reactor vessel cooling is investigated in LIVE tests with different external cooling conditions and melt pouring positions. A noneutectic simulant melt (80-20 mole% KNO 3 -NaNO 3 ) is used in the LIVE tests. It is found out that when the vessel is cooled with water at the beginning of the melt pouring, the cooling is more effective than in the case of delayed water cooling condition, in which the vessel is first cooled with air and then flooded by water. The initial water cooling leads to a faster growth of crust layer, lower crust thermal conductivity and thinner crust layer than those under the delayed water cooling condition. The initial water cooling leads also to higher heat flux through the vessel wall during the steady state and shorter crust growth period in comparison with the delayed water cooling condition. The solidification of the melt is probably under supercooling condition. The pouring position near the vessel wall results in considerable asymmetric heat flux distribution at one latitude. The heat flux at the position of melt pouring is higher than the one at other locations