Abstract <p>Reliable assessment of the consequences caused by severe accidents at NPPs for the personnel and environment depends directly on how correctly and accurately the processes through which fission product vapors and aerosols are generated, transfer, and release into the power plant rooms are understood and predicted. The article describes the key models implemented in the AERCONT module that is part of the TITAN-2/V1.0 integrated code, which has been developed for calculating the behavior of fission product gases, vapors, and aerosols in the steam–gas primary circuit coolant and in the containment rooms at an NPP with VVER reactors. By using the module, it is possible to analyze the aerosol system variation dynamics with taking into account all key mechanisms. Main attention is paid to the mathematical models that lie at the heart of transfer, nucleation, and coagulation models, including the description of separate motion mechanisms: Brownian, turbulent, gravity, and shear ones. The numerical methods that ensure stability and accuracy of calculations in the situations characteristic of reactor plant emergency operation conditions are discussed. These methods are compared with the existing similar software tools; their differences, advantages, and drawbacks are analyzed. The results of nucleation and coagulation models verification against the test calculation data are presented, and comparison with the exact analytical solution is carried out. The results of the coagulation process validation against experimental data, which confirm the adequacy and accuracy of the developed models are shown.</p>