GENERATION OF DESTRUCTIVE FORCES DURING FUEL COOLANT INTERACTIONS UNDER SEVERE REACTIVITY INITIATED ACCIDENT CONDITIONS

During a reactivity initiated accident (RIA) a large and prompt amount of energy is deposited within fuel rods. Consequent fuel melting and rod failure can lead to a fine dispersal of fuel melt in coolant, resu lting in a violent thermal interaction between the fuel melt and coola nt (i.e. fuel/coolant interaction - FCI). In the pre-mixing stage, the nature of the fuel release mode from failed rods is dominant factor i nfluencing FCI energetics, where the internal rod pressure is a prime factor influencing melt jet characteristics. In this study, the genera tion of the destructive forces during FCIs in a severe RIA was demonst rated through in-pile experiments with LWR uranium dioxide fuels. The intensities of the destructive forces, i.e., the pressure pulse and th e water hammer, were correlated with the initial internal pressure of the test fuel rods. Debris particle size distribution was also extensi vely examined. Rosin-Rammler's law was used to fit the distribution, a nd the correlation between the intensities of the destructive forces a nd the specific surface area of the debris is presented.