Microstructural understanding on the fouling behavior of crud on PWR fuel cladding surface

•Deposition behavior of crud on cladding tube surface studied.•Crud layer mainly composed of NiFe2O4.•Heterogeneous growth of Fe3O4 in NiFe2O4 grains observed.•Size of crud particles determined by diffusion growth time.•Bubble formation behavior affected structure of crud layer. In the present paper, an accelerate crud creation experiment was conducted by a laboratory simulation facility. A TEM sample was prepared at the interface between the crud layer and pressurized water reactor (PWR) fuel cladding tube to investigate the fouling behavior of crud on the surface of cladding tubes at a microstructural level. The results show that the crud layer consisted mainly of NiFe2O4, as Fe3+ and Ni2+ serving as the primary sources. Heterogeneous growth of Fe3O4 was observed by HRTEM, which formed dislocations NiFe2O4 grains. Based on the microstructural characterization results, the growth mechanism of crud particles on cladding tube surface during subcooled nucleate boiling was discussed with a focus on mass and heat transfer.