The Trigger Mechanism of Vapor Explosion.

Abstract

In the present study, trigger mechanisms of the vapor explosion are experimentally investigated. The interfacial behavior between high temperature molten liquid and low temperature water are experimentally investigated by using a molten material droplet and external pressure pulse. As the results, it is indicated that spontaneous vapor explosion hardly occur in high temperature water near saturation temperature since vapor film is stable. The vapor explosion can occur even in high temperature water near saturation temperature in case that the external pressure pulse is applied to high temperature molten material. Vapor explosion can not occur when the interfacial temperature between the molten material and water is lower than the material melting temperature, even if the vapor film around the molten material is collapsed by the external pressure pulse. It is clarified that the impossibility of the trigger process for the vapor explosion can be judged by comparing the interfacial temperature and the molten material temperature. The results obtained in the present experiments are applied to the results of the large-scale experiments using uranium dioxide. The results indicate that the possibility of the vapor explosion of the uranium dioxide and water under the present LWR operational condition is extremely unlikely. It should be noted that the present criteria should be applicable in case that the melting temperature does not decrease by containing the metal component.

An experimental study on the intense heat transfer and phase change during melt and water interactions

“…Data on debris size acquired from single droplet thermal fragmentation experiments is rather scarce. However, the data available from [18] for molten silicon (T mp = 1414°C, ρ ≈ 2600 kg/m 3 ) droplets and from [5] for molten tin (T mp = 272°C, ρ ≈ 6734 kg/m 3 ) which underwent fine fragmentation in high subcooling conditions, is compared with the current experimental data. Remarkably a close agreement between the debris sizes of molten silicon and WO 3 -CaO can be inferred though the density of WO 3 -CaO is much higher compared to silicon.…”

“…Ultimately, an understanding of material influence on vapor explosion is necessary. The KROTOS and TROI experiments performed at a relatively large scale is also complemented by small scale experiments that allow to develop an in-depth understanding on the various mechanisms involved in vapor explosion [2,[5][6][7]. Analysis of the experimental data points out to deformation of melt surface as a result of RayleighTaylor instabilities followed by the fine fragmentation of melt.…”

Review of thermal-hydraulic researches in severe accidents in light water reactors

“…Experimental and analytical researches are carried out using small-and large-scale experiments [11][12][13][14][15][16][17][18][19][20][21][22][23].…”

“…The interfacial behavior between high temperature molten liquid and low temperature water is experimentally investigated by using a molten material droplet and external pressure pulse [15]. It is indicated The results are applied to the large-scale experiments using uranium dioxide.…”

Observations of initiation stage of spontaneous vapor explosions for droplet scale

“…The fragments remain after vapor bubble condensation. Frame (10) shows the many fragments falling in the water and the end of the phenomenon. The vapor explosion is initiated at the local collapse of the vapor film.…”