Study On Surface Instability And Fragmentation Of Melt Jet Under The Condition Of Pouring Into Coolant

Under the condition of the failure of In-Vessel Retention External Reactor Vessel Cooling (IVR-ERVC) mitigation measure, molten corium will pour into reactor cavity filled with coolant. Fragmentation of liquid melt jet may lead to steam explosion accident which may threaten the integrity of the containment. For this reason, the mechanism and phenomenon of fragmentation of liquid melt jet pouring into coolant pool is of great significance in the case of the failure of IVR-ERVC. However, study tools focus on jet surface Instability mechanism is lacked currently. Furthermore, none of self-developed codes are capable for the simulation of fragmentation at present. Consequently, related study is limited to codes developed by foreign research institutes. Firstly, based on code of JASMINE, this study developed JASMINE-VOF code which is used for jet surface tracking. The improvements of code include pressure field and velocity field calculation method, interface tracking method, continuum surface tension force model and Kelvin-Helmholtz instability fragmentation model. After a series of validation and verification, this code has been proved to be available for surface tracking calculation. Secondly, JASMINE-VOF can be also used in analysis of mechanism and phenomenon of jet fragmentation. Finally, due to the immaturity of JASMINE, foreign code MC3D serves as a supplement in the analysis of several engineering problem. With calculation of JASMINE-VOF, the results indicate the development of jet-coolant interface instability under different perturbation conditions and within different media. The results also indicate the Liquid melt flowing image and volume fraction distribution of melt droplets. On the other hand, with calculations of MC3D, the results provide volume fraction distribution of liquid melt in the stage of premixing, which is considered to be one of major stages ofsteam explosion. Calculations based on MC3D also provide flow field and pressure field variation in the case of direct containment heating accident, and finally the comparison between numerical calculation and premixing experiment has been carried out.This thesis reaches conclusions: Any kind of disturbance will be magnified by the velocity difference resulted from melt pouring and Kelvin-Helmholtz instability model can be used to predict the fragmentation rate.