Providing useful information on optimized chemistry control for pressurized heavy water reactors (PHWRs), this publication presents up to date knowledge on the topic including corrosion phenomena observed in the primary heat transport system and consequent effects on fuel reliability in PHWRs. Specifically, it describes the national practices on coolant chemistry control under various operating conditions and research and development programmes aiming to understand the corrosion phenomena (formation and transport) and related chemistry control. Crud deposit on the fuel cladding, the influence on fuel fitness-for-service in the primary heat transport system, as well as the technical basis for remedial actions to ensure reliable fuel performance in PHWRs are considered.