The corrosion-related unidentified deposit (CRUD) and its multiple effects on boiling heat transfer in the nuclear reactor: A systematic review

In nuclear reactors, the corrosion-related unidentified deposit (CRUD) is a widely observed thin surface layer that grows due to the long-term layered deposition of corrosion products nanoparticles on the fuel cladding. As a typical porous-hydrophilic surface medium featured by the randomly distributed boiling chimneys and high wickability, the presence of CRUDs not only forms the boron-enrichment layer of high neutron absorptivity on the fuel cladding, causing the axial offset anomaly (AOA), but also drastically changes the micro-morphology features of boiling surfaces, leading to the significant variations in multiphase flow dynamics and boiling heat transfer mechanisms. These CRUD-related problems put great challenges to the safe, long-term and economical operation of advanced nuclear reactors. Regarding these issues, this paper reviews and summarizes the recent progresses about the CRUDs’ effects on boiling heat and mass transfer mechanisms in nuclear engineering. Wherein, some advanced experimental and theoretical methods are identified, compared and highlighted, including the nano-deposition techniques for artificial CRUD synthesis, the framework of fractal-based bubble dynamic theory, and enhancement mechanisms of CRUD-affected transitional boiling sub-regimes. By applying the insights from this review, the practitioners can improve their understanding on the CRUD-affected heat transfer phenomena in nuclear engineering, which would help to promote the design and analysis methods for safe, long-term and economical operations of the advanced nuclear reactors. © 2025 Elsevier Ltd.