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[en] This paper describes verifying behaviors on spreading flow of molten metal at elevated temperature. In Fukushima Daiichi nuclear disaster, molten core leaked out to pedestal floor of PCV. To estimate statement of fuel debris, expansion information of behaviors of molten metal is one of the most important task to terminate the accident. So we tried to experiment with molten metal to verify behaviors of falling molten metal, and analyze retrospective experiment of spreading flow of molten core VULCANO VE-U7 experiment on CFD code STAR-CCM+. Consequently, we got the knowledge that the generation of bottom crust layer in molten metal mainly involves flow stopping, and interface contact temperature is a primary factor to decide length of spreading flow of molten metal. (author)
[en] Highlights: • Experimental investigations on molten metal spreading and depositing behaviors on the steel plate were carried out. • The three stages of molten metal spreading behaviors with collision against the plate surface were defined by the observation results. • New scaling relation was developed by focusing on the initial spreading pause of the molten metal droplet. - Abstract: On March 11, 2011, huge earthquake and tsunami attacked Fukushima Daiichi Nuclear Power Plant. After the accident, research on plant decommissioning has become actively worldwide. Several research institutes have performed experiments to investigate methods of identifying the location and spreading/deposition behaviors of molten core debris in the bottom of Primary Containment Vessel (PCV) using Severe Accident (SA) analysis codes. Nevertheless, knowledge of spreading and deposition behaviors of corium is not sufficient, especially phenomena involving collision against the floor surface. In this study, experimental investigations on molten metal spreading and depositing behaviors on the steel plate were carried out. Zinc and copper were utilized for the molten metal samples and spreading behaviors were carefully observed using high speed video camera. Immediately after the collision between falling molten metal and steel surface, initial pause on spreading was observed. New scaling relation based on Dinh et al. (2000) was developed by focusing on the initial spreading pause of the molten metal droplet. Proposed correlation is capable to predicting the spread and deposition of falling molten metal at average error of 18.1%.
[en] Highlights: • Molten metal spreading experiment was conducted. • Molten metal spreading area and thickness data was obtained for molten copper. • Key parameters affecting the spreading area and thickness were identified. - Abstract: In this paper, experimental investigation of the molten metal spreading behavior that was carried out at Hokkaido University using high frequency inductive heater is presented to address the fundamental behavior of the molten metal spreading and deposition behaviors on dry flat plate. Molten copper was utilized as a test sample, and dataset was obtained for the falling molten metal on dry stainless-steel plate at various elevations, nozzle sizes and initial temperatures. During the spreading transient, high-speed thermo-camera was utilized to measure the molten metal’s surface temperature. Immediately after the solidification, solidified molten metal’s spread area and deposition thickness were measured. Based on the database obtained, dimensional analysis was conducted to identify the key parameters responsible for the molten metal spreading. From the obtained database, new experimental correlation was developed which is capable of predicting the spreading area at reasonable accuracy. Present analysis provides characteristic information of molten metal spreading and deposition behaviors which will be useful for the corium relocation problem in severe accident analysis.
[en] In this paper, experimental investigation of the molten metal jet's colliding and spreading behaviors on the flat steel surface covered with water layer was carried out. High-frequency induction heating system was utilized to produce the molten metal sample and it was released to the wet surface from a fixed elevation. As the molten metal collides against the surface, it rapidly goes through solidification while spreading on the wet surface. High-speed thermo-camera was utilized to measure the molten metal's surface temperature during the spreading transient. Once the molten metal completely solidifies, molten metal's spread area and thickness were measured. From the obtained database, a dimensional analysis was conducted to investigate the key parameters responsible for the molten metal spreading on the wet surface. Based on the key non-dimensional parameters identified in the current analysis, the new empirical correlation was proposed. Its predictive capability was found to be 18.9% in mean absolute relative deviation.