Breakup of melt jets as pre-condition for premixing: Modeling and experimental verification

Abstract

As a consequence of severe light water reactor accidents with core melting, jets of melt are considered to flow into the remaining water in the lower plenum. The breakup of these jets above and in the water determines the further accident progression, especially the mixing of the molten core material with the water and thus the possibility of strong vapor explosions or the mode of contact of core material with the lower plenum structures. Stripping at the melt surface due to relative flow, supported by interface instabilities, is considered here as a major mechanism of the jet breakup. Based on this, correlations are analysed in comparison with experimental results. Results from the more detailed model Ikejet developed at the IKE yield strong differences between the Kelvin-Helmholtz (KH) description of the interface instabilities and the Jeffreys-Miles (JM) approach. Calculations for experiments with simulant materials under non-boiling as well as film boiling conditions support the latter description whereas much too strong breakup results with KH. Correspondingly, applications to corium jets yield much longer coherent jets with the JM approach. Comparisons with corium experiments at the Argonne National Laboratories (ANL) and with first FARO-LWR tests at the JRC Ispra also still suffer from experimental uncertainties.