The Airborne Release Fraction (ARF) of hazardous (radioactive) contaminants in fire accident scenarios involving liquid solvents containing non-trivial levels of solvated contaminant species is a major concern of the source term in many nuclear installations, including the United States Department of Energy (USDOE) nuclear facilities. Particularly concerning is the release of contaminant particles in the sub 10 micron range which can be respirable. Several aerosol release mechanisms have been explored both experimentally and computationally by Sandia National Laboratories in number of nuclear safety research and development projects funded by USDOE and others, including those due to solvent boiling and turbulence effects.  These studies have made significant contributions to source terms for the USDOE's safety Handbook, DOE-HDBK-3010.  One such mechanism, that of evaporative induced entrainment (EIE) may play a significant role in the aerosolized release of contaminants at temperatures below the boiling point of the solvent, though at a fundamental level, this method is the least understood.  Most of past experiments determined that this subtle effect leads to an ARF in the range 10-7 to 10-4. The proposed mechanism involves the notion that small contaminant particles at the surface of a heated, evaporating solvent may occasionally be lofted into the gas phase as a result of the evaporation of the encompassing solvent, even below the boiling point of the solvent. The formation of coordinate compounds between the solvent and contaminant species may affect such outcomes.  Here we describe a novel method for interrogating this effect, through molecular dynamics simulations of kerosene/tributyl phosphate solvent with contaminant solute species near an evaporating interface using Sandia’s open source molecular simulation package LAMMPS. LAMMPs has been historically used for a wide variety of molecular simulations, notably by one of the authors at similar liquid/vapor interfaces, but to our knowledge, never for contaminant release applications.  We explore the EIE effect at sub-boiling temperatures with van der Waals, bonded, and electrostatic potentials tuned both for solvent/solvent and solute/solute interactions.  We present here the model for this study as well as some preliminary results.  
SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525  
 


Molecular Dynamics Study of Evaporation Induced Entrainment of Radioactive Contaminants

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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