A study of VVER-1000 fuel rod integrity during LOFA

The safety of the fuel rod is of great importance in all operational states, especially during accidents. This paper is the third part of a three-part study aiming at developing the coupled neutronic/thermal-hydraulic codes to simulate a full 3-D model for VVER-1000 assembly and predict the essential safety parameters. In our previous works, three scenarios for loss of flow accident (LOFA) were studied by developing a simulation model for the thermal analysis of a fuel rod with the ANSYS-FLUENT17.2 code. The present research is aimed at studying the mechanical behaviour of the VVER-1000 reactor fuel rod under the worst LOFA conditions. To perform this analysis, the thermal-hydraulic parameters with and without coupling transfer from the ANSYS-FLUENT17.2 thermal-fluid module are used in the Static Structure (Mechanical) module. The value and the location of the maximum mechanical stress and elongation of the cladding during the accident are demonstrated, as well as the time when the clad critical temperature occurs. Through the mechanical module, the mechanical behaviour of the fuel clad is studied at several axial locations in the fuel, to account for power oscillations. As the power of the reactor increases, the fuel rod suffers from stress and elongation caused by thermal expansion. Also, the melting of the fuel rod starts after 80 s.