Large eddy simulations of hot helium issued into cold ambient relevant to pipe-break accident of high-temperature gas-cooled reactors (HTGRs)

The loss-of-cooling accident (LOCA) is one of the postulated fault conditions in high-temperature gas-cooled reactors (HTGR), one of the generation IV reactors. A pipe-break happens may occur in one of the LOCA scenarios, with the coolant gas (hot helium) discharged into the reactor cavity and mixed with the ambient air at a much lower temperature. In the present study, high-fidelity LES simulations of gas-mixing jets at four conditions were carried out to study the flow physics in this scenario. The aim is to gain a good understanding of the gas-mixing jet and provide useful high-fidelity data for engineering model development and validation. The effects of jet Reynolds and Richardson numbers on basic jet features were studied. An interesting phenomena, the split of jet trajectory was found at some conditions, dependent on both the jet Reynolds and Richardson numbers. Further investigation indicates that such jet-split is different from the so-called bifurcation phenomena that happens in buoyant jets at some specific conditions. Preliminary findings are presented in this paper.