Review on corrosion-related unidentified deposit of pressurized water reactors

Corrosion-related unidentified deposit (CRUD) on the fuel cladding is detrimental for nuclear reactor safety and economy. This paper provides a comprehensive review of published articles and disclosed technical reports concerning CRUD of pressurized water reactors in terms of its formation, properties, and consequences, which is intended to better understand and predict this complicated issue. The formation of CRUD is a physicochemical process involving the thermodynamics of soluble species and kinetics of insoluble particles. Changes to the local conditions, such as primary water chemistry, thermal hydraulic parameters, morphology feature of metal surface, affect the properties of CRUD including ingredients and multi-scale structures. Abnormal axial power distribution occurs due to the neutron absorption by boron-containing compounds in porous CRUD, which is related to the capillary flow, heat transfer, solute transport as well as chemical reactions. This paper also discusses the potential strategies to mitigate the CRUD deposits, such as water chemistry control, chemical purification, ultrasonic cleaning and coating. The most attractive candidate for CRUD prevention at current stage is zinc injection approach under elaborate control of water chemistry, coating approach will be another attractive candidate for CRUD prevention as development of accident tolerant fuels (ATF) from both scientific and manufactural perspectives.