Debris filtering efficiency assessment of the fuel assembly bottom nozzle

The debris-induced fretting wear is a key factor to cause the fuel failure in pressurized water reactor (PWR). Assessing the debris filtering efficiency of bottom nozzle is an important way to analyze the reliability of fuel assembly. The debris filtering efficiency assessment method of bottom nozzle was proposed, which concludes experimental research method and numerical calculation method. The experimental method concludes A-types debris (ball, hex nut, spring, gasket, and pin) and B-types debris (cylindrical metal wire, helical metal cutting, and metal strip). The experimental method demonstrates that the bottom nozzle with hemispherical surface structure presents the filtering efficiency of 100 % for B-types debris. The numerical simulation method is a coupling process of CFD and DEM, which mainly analyze the movement and collision of debris. The bottom nozzle shows better filtering efficiency for cylindrical debris, and the filtering efficiency in the numerical simulation is in good accordance with the experimental results. The filtering efficiency assessment method is suitable for evaluating the debris filtering behavior of bottom nozzle and helpful for the design and verification of bottom nozzle.