Including fission product vapor interactions with aerosols in reactor accident calculations can significantly alter the predicted consequences of a given accident. For example, a high-velocity, short residence time accident can transport significant amounts of tellurium outside the reactor vessel on the aerosols rather than having the tellurium reacted on the vessel’s metal surfaces. In another scenario, a relatively stagnant situation allows equilibration of the vapor/aerosol interactions and deposition of the aerosols inside the core region. Consequently, most of the fission product vapors remain in the core region with the deposited aerosols. The sorption isotherms of CsOH-Ag, CsOH-Cr2O3, and CsI-Cr2O3can be represented by modified Freundlich isotherm expressions. In addition, CsOH vapor interacts extremely with the iron species under accident conditions such that 0.6 wt% FeO in the aerosol can remove 10 to 15 wt% of the CsOH emitted in an accident.