[en] Some recent advances in the knowledge base with respect to the ability to calculate fission product transport behavior in the reactor coolant system (RCS) and the containment for light water reactor severe accident conditions are discussed. Only minor advances are noted with respect to aerosol behavior. These include improvement in the understanding and modeling of impaction behavior, homogeneous and heterogeneous nucleation, vapor/aerosol interactions, hygroscopic behavior of aerosols, and decomposition of CsI in the presence of hydrogen flames. The focus is the influence of chemical phenomena on the behavior of fission product iodine. A review is given of new work on the chemical forms released from the RCS as they are affected by gas-phase chemical kinetics, reactions with surfaces, the presence of boric acid, and revaporization from surfaces. Also reviewed is recent work on hydrolysis and radiolysis reactions in water pools in containments to determine the potential for revolatilizing iodine species back into the containment atmosphere