Abstract: A transient code STAC was developed based on one-point kinetic equation, thermal conduct equation and linear elasticity equation for the purpose of analyzing nuclear metallic fuel system. The prompt super-critical experiment on Godiva-Ⅰ device was simulated by using STAC code, in which the changes of fission rate, reactivity and temperature with time were calculated. The simulation results are consistent with the experiment results on Godiva-Ⅰ device, which verifies the accuracy of STAC code.