| The penetration and freezing of core melt in flow channels is one of the key phenomena of reactor severe accident, and affects the process of it. However, the mechanisms of high temperature melt freezing are not fully understood and there are many uncertainties in the freezing models.In this paper, the freezing mechanisms and process of simulating melt in a tube and among the pin bundle are studied with experimental means and numerical simulation, so as to provide data support for the freezing model validation.Freezing tests in tubes and among 9-pin bundles are performed with tin, lead and lead-tin alloy. In the tests, stable crusts form on the surface of the flow channel, and there form column cavities and annular crusts in most tubes after experiments. After analyzed, it can be found that the metal melt freezing in a tube seems to be consistent with the improved freezing model proposed by Kamiyama, however, freezing in the pin bundle looks more like the thermal conduction limited freezing.In numerical simulations, the FLUENT solidification & melting model is validated with the 300℃ tin melt freezing tests in the tubes of I.D. 4, 5 and 6 mm firstly. The micro-structure of melt freezing in the simulation shows that it is that the viscosity increasing of the leading edge causes the velocity decreasing and flow ceasing at last leads to the blockage of the tube. And then, the 300 ℃ tin melt freezing and penetrations in the tube of I.D. 5mm under different conditions are simulated to study the influence of inlet velocity, inlet pressure and wall temperature. And it shows that the increasing of these three will increase the penetration length. Nevertheless, the increasing of inlet velocity would make it possible for the forming of the annular crusts. Finally, simulation of 1700℃ SS melt freezing and penetration in the 100℃ tube of I.D. 5mm is conducted, which shows that the penetration time and length is much smaller than that of 300℃ tin melt in the 30℃ tube. |
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