Salt Spills Analysis Methodology for KP-FHR: Two-Phase Mechanical Aerosolization and Evaporation Mass Transfer

Kairos Power LLC is currently developing the Kairos Power fluoride salt-cooled high-temperature reactor (KP-FHR). Licensing a KP-FHR requires safety analyses for a whole spectrum of licensing basis events. Among them, the salt spills event (SSE) is an important event category where source term materials (i.e. the radionuclides produced from fission and activation reactions) can be released. Two SSE-specific phenomena (in terms of source term release) are modeled: jet breakup aerosolization and evaporation from spilled salt pool. The two-phase flow mechanical aerosol generation is analyzed by simplifying existing empirical correlations developed using data from surrogate fluids for use with Flibe/argon environments. Simplifications to the empirical correlations include a no-slip assumption and disregarding the density dependent term in the correlation that increase the calculation uncertainty at low void fraction region. Because of the dominant impact on aerosol generation caused by the high void fraction region compared to the low void fraction region, these modeling simplifications are justified for use in safety analysis. Sensitivity analyses demonstrate that limiting break diameter is not a guillotine break because the aerosolization fraction increases with decreasing break diameter. An evaporative mass transfer for source term releases from a spilled molten salt pool is also modeled in this study, which considers the mass transfer resistances associated with the convective processes on both the liquid and gas sides. The mass transfer model considering the resistances on both sides allows for more realistic assessments of the release fractions of the source term materials and consequential source term figure of merits, especially for the high-volatility phase-separated species. The heat and mass transfer analogy used in the mass transfer model works well when the Lewis number is close to 1 (Lewis number for Flibe is close to 1). Uncertainties can be larger if the evaporative mass transfer model is applied to other fluids with the Lewis number significantly deviating from 1. The two-phase mechanical aerosol generation model and the realistic evaporative mass transfer from the spilled Flibe model provide a basis for quantifying source term release in KP-FHR SSE.