The relative importance of the soluble and particle fractions that take part in the transport of pressurized water reactor corrosion product is discussed in terms of modeling research. A model is proposed that considers the dominant role of the colloidal/particle fraction in the primary coolant system mass and radioactivity transfer. A new hypothesis for a two-stage sticking mechanism is used to quantify the thermal and water chemistry effects on particle/wall interaction. Analytical expressions for the deposition and release coefficients are derived. The results obtained by the MIGA computer code using this model are compared with observations.