VANESA: a mechanistic model of radionuclide release and aerosol generation during core debris interactions with concrete

This document describes a model, called VANESA, of the release of radionuclides and generation of aerosol accompanying reactor core melt interactions with structural concrete. The document also serves as a user's manual for an implementation of the VANESA model as a computer code. The technical bases for the VANESA model are reviewed. Mechanical generation of aerosols as bubbles burst at melt surfaces or as a result of liquid entrainment is considered. A description of these processes based on data for gas-sparged water systems is included in the VANESA model. Some limiting solutions to the problem of the competitive processes of nucleation of particles from vapor, condensation of vapors on surfaces, and coagulation of particles are examined. From these examinations an approximate model of the aerosol particle size produced during core debris interactions with concrete is devised. The attenuation of aerosol emission during core debris/concrete interactions by an overlying water pool is discussed. The document concludes with a description of a computer code implementation of the VANESA model. This implementation of the model was used in recent assessments of the behavior of radionuclides during severe reactor accidents. Comparisons of the predictions of radionuclide release during core debris/concrete interactions obtained with themore » VANESA model and with older models are presented.« less