Evaluation of thermal hydraulic safety of a nuclear fuel assembly in a mast assembly of nuclear power plant

• Thermal–hydraulic safety of spent fuel bundles in a mast assembly was studied.
• Benchmark CFD calculations were compared with two sets of experimental data.
• CFD flow analysis for natural convection was performed in the mast assembly.
• Safety evaluation of a fuel bundle was done using a 1-D safety analysis code.

We investigated the thermal–hydraulic safety of spent fuel bundles installed in a mast assembly, assuming a lock-up accident of a fuel transfer system. For this, flow analysis with Computational Fluid Dynamics (CFD) for the natural convection and subsequent safety evaluation with 1-D Nuclear Power Plant (NPP) safety analysis code were carried out. Prior to the natural convection analysis for the mast assembly using CFD code, we performed benchmark calculations against two experimental data sets obtained by Betts and Bokhari (2000) and PNL (Pacific Northwest Laboratory, 1980). This was done to select the proper physical models for a natural convection flow analysis and to ensure the reliability of prediction of natural convection flow in the fuel bundle geometry. Finally, we performed a main natural convection analysis for the fuel assembly inside the mast assembly. From this calculation, we observed a stable natural circulation flow between the mast assembly and pool side, and obtained coolant velocity at the inlet of the spent fuel bundle. This flow condition is given as a boundary condition for the 1-D NPP safety analysis code, which is used to predict the Critical Heat Flux and then departure from the nucleate boiling ratio.