Simplified Modelling Method for Spacer Grid of NHR200-II Fuel Assembly

A simplified modelling method for the spacer grid of NHR200-II fuel assembly is proposed to increase the computational efficiency in the dynamic analysis. It includes the replacement of the grid inside the dimples and three-arc springs with the non-linear connectors, and the replacement of the fuel rods with beam elements. The stiffness of connectors was derived from previous experiments of NHR200-II spacer grid. Natural frequency analysis and impact simulation were performed by a 1×2 sub-model of the fuel assembly to verify this method. Then, this simplified method was applied to a full-scale 9×9 spacer grid model, to study the effects of the grid clamping ability on its dynamic characteristics. The results suggest that this simplified approach can give a reasonable response when induced by a seismic load at different clamping levels. In conclusion, from the modelling point of view, the proposed simplified method for NHR200-II spacer grid is effective.