Experimental Analysis And Numerical Simulation Of Melting Process Of Vertical Tin Cladding

The study of severe nuclear reactor accidents is an important issue in the field of nuclear safety in recent decades.Since the Three-Mile Island accident,many organizations or institutions in different countries have carried out different types of large-scale experiments,to investigate the various phenomena and mechanisms in severe accidents,and many severe accident codes such as SCDAP/RELAP5 and MELCOR were developed at the same time.The melting of a single fuel rod is an important part of the core melting in a severe accident,which determines the development trend and severity of the accident.However,due to the lack of existing knowledge,the melting process analysis of a single fuel rod in core melting is engineering simplified and overlooked in severe accident codes.To address crucial issue,the melting process of tin cladding is studied by means of experimental simulation and numerical calculation in this paper.The experiment uses tin,a metal with low melting point,as the melting material.Tin cladding was made of stainless steel heating rod wrapped around specific thickness of the tin by the recasting and re-processing.The influence of the heating power,cladding thickness and environmental conditions on the melting process of the cladding was analyzed.The experiment was visualized and recorded with a DV machine to record the morphological changes during the melting process.The tin cladding melting process was summarized to three stages:heating,melting and disintegration.And the melting stage was divided into three parts:droplet leaking,swelling deformation and cladding breakage according to the phenomenon.For the swelling deformation and cladding breakage,the cylindrical wall stress model was introduced to analyze the degree of swelling deformation depending on the cladding thickness and the height of the cladding melting breakage decreasing with the increase of the heating power,and it is also a function of the heating power and the melting time.At last,the effect of different ambient conditions on the cladding melting process was compared.The numerical calculation part adopts the commercial CFD software ANSYS FLUENT,and the two-dimensional calculation of the experimental scene is carried out by coupling model of solidification/melting and VOF.Similar to the experimental results,the melting process is divided into heating,melting,breakage and re-solidification of four stages.The melting stage is guided by two heat transfer processes,direct heating of the heating rod and the downwards confluence of the high temperature metal liquid.The effects of cladding breakage,heating power and ambient temperature on the melting were analyzed quantitatively by extracting the solid fraction of the original shape region.The results show that the occurrence of the cladding breakage is a turning point in the melting process of cladding,and the occurrence height has a great dependence on the ambient temperature.