Numerical Study on the Jet Breakup of Molten Nuclear Fuel in the Coolant in Dripping Regime

The interaction of molten fuel and coolant occurring during a severe accident case in a nuclear reactor is studied in this paper. The molten jet of MOX interacts with the sodium in dripping flow regime. An in-house code DROP formulated using slenderjet approximation of Navier–stokes equations is used in the present analysis. Usually in the study of jet breakup, surface tension of the jet material with respect to air is considered and crust formation is neglected. Uncertainties related to interfacial tension in a liquid–liquid system and crust formation due to solidification affecting the jet breakup are discussed here. The variation of breakup length, breakup time and droplet diameter is recorded when the interfacial tension is accounted in the calculation. It is noted that a maximum deviation of 11% is observed in the breakup length, whereas a deviation of 17% is observed in breakup time for all possible ranges of interfacial tension. To account for the heat transfer to the coolant and crust formation, a module for heat transfer with solidification is incorporated into the existing code. Reduction in breakup time and breakup length is quantified. It is found that the combined effect of these two factors leads to a considerable change in breakup length and time which is brought out in this analysis.