The formation, release and deposition of corrosion products within the primary circuit of a nuclear power plant can lead to fuel damage, power distortions during operation and radiation fields that affect plant maintenance. This publication provides information on the modelling of corrosion product behaviour in the primary circuit. It reports on the research activities and results from an IAEA coordinated research project in this field and includes details of current best practice. These data are important elements for the current understanding of the formation and transport mechanisms of corrosion products involved in both light water reactors and pressurized water reactors, and the methods used to describe them.