Abstract: It is important to study the thermal-hydraulic safety issues of the fuel assembly during the transportation in the fuel transfer tunnel. The flow and heat transfer mechanism was complicated when cooling the fuel assembly by natural circulation in the transfer tunnel. After analyzing the flow field in the transfer tunnel, the position of highest surface temperature was determined. The test facility was designed by sampling the high temperature zone. A set of similarity criterion was developed for distortion analysis of the test facility. The analysis results show that the test facility is conservative to evaluate the thermal-hydraulic safety of the assembly.