Numerical simulation of jet breakup phenomenon during severe accident of sodium-cooled fast reactor using MPS method

Abstract

During a core disruptive accident of Sodium-cooled Fast Reactors (SFR), discharged corium may contact with coolant in form of jet, which can be an imminent threat to the integrity of reactor vessel if the jet does not sufficiently break up and cooldown. It is significant to ascertain the morphologies, penetration depth and breakup mechanism of discharged corium jet to evaluate its potential impact on reactor vessel. In this study, numerical simulations are carried out to investigate the characteristics of jet breakup. An advanced moving particle semi-implicit method (MPS), the least square MPS (LSMPS) is applied to study the two-dimensional hydrodynamic corium jet breakup in sodium. Firstly, the applicability and reliability of the method are validated by the comparison between the simulation results and reference experiments. Then, the method is applied to simulate molten corium jet breakup in sodium. It is found that the breakup mechanism is related to Rayleigh–Taylor instability (RT), Kelvin–Helmholtz instability (KH) and Plateau–Rayleigh instability (PR). Under the influence of RT and KH, eddies are formed around the jet and thus the downward velocity of the jet vibrates in a relatively regular pattern. The local velocity difference of the jet narrows the jet and the jet eventually breaks up under the influence of PR. The parameters including diameter and initial velocity of the jet were scrutinized for their influences on jet penetration depth and jet breakup length, which can be useful for the improved design of the SFR reactor vessel.