Numerical simulation analysis of debris filtration in the bottom nozzle

According to the IAEA report, debris fretting is the second largest factor causing fuel rod cladding rupture and causing fuel rod failure, accounting for 11%. As the first structural component for fluid entering the fuel assembly, the bottom nozzle has the function of filtering debris entering the core area, effectively reducing the possibility of debris entering the fuel area causing fretting. Currently, there is no suitable numerical simulation method for calculating it. Therefore, based on the coupling method of discrete element method and computational fluid dynamics, considering the stress and contact models of typical debris in the complex flow field near the bottom nozzle under different structures, this study established the fluid solid coupling numerical simulation method between the solid debris and the flow field near the bottom nozzle. Compared with the test results, the error is less than 10%, which verifies the correctness and reliability of this method, And based on this method, typical debris filtering behavior analysis was conducted. The numerical simulation method studied in this article provides support for the design and optimization of the filtration structure of the fuel assembly's bottom nozzle for debris filtration efficiency.