Abstract
Stratification morphology of a molten pool under severe reactor accident was investigated by the CESEF experimental facility. The experimental scale was 5,000 g, the atomic ratio of U/Zr was 1.5, the content of stainless steel was 10%, and the oxidation degree of Zr was 40–100%. It was shown that the molten pool was obviously stratified within the range of experimental parameters; one was a metal layer, and the other was an oxide layer. The layered morphology of the molten pool was different with the composition of different corium. With the decrease in the Zr oxidation degree, the metal layer moved downward in the molten pool, and the molten pool would overturn. The main elements in the oxide layer were U, Zr, and O, and the content of stainless steel was low. The main element in the metal layer was stainless steel and contained a certain amount of U and Zr.
Highlights
In the severe accident of a nuclear reactor, such as the Fukushima Daiichi NPP, the fuel and structural materials in the core had been melted (Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety, 2011)
In the MASCA project (Asmolov, 2004; Tsurikov et al, 2007), three different melting pool stratification forms were found, namely, the molten pool with the metal layer above and the oxide layer below, the molten pool with the metal layer below and the oxide layer above, and the molten pool with the metal layer suspended in the oxide layer
The CESEF facility is designed to investigate the stratification of the molten pool at the lower head of the pressure vessel under severe accident, which adopts an electromagnetic induction heating technique with a cold crucible
Summary
In the severe accident of a nuclear reactor, such as the Fukushima Daiichi NPP (nuclear power plant), the fuel and structural materials in the core had been melted (Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety, 2011). The molten materials (UO2, Zr, ZrO2, stainless steel, etc.) were heated up and melted by decay heat as the coolant in the pressure vessel was depleted. A molten pool with U-Zr-Fe-O as the main element is formed. The configuration of the molten pool, so called corium, as it affects the failure mechanism of the pressure vessel. The stratification form of the molten pool has been a hot and difficult point in the field of severe accidents at home and abroad
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