In-phase and out-of-phase modes stability analysis with LAPUR5 code for Kuosheng

A study of the in-phase (global, core-wide) and out-of-phase (regional) modes of stability with LAPUR5 code for Kuosheng NPP is presented. Comparisons made with vendor’s STAIF results indicated close agreements, within the acceptable 20% deviation in decay ratios, for Kuosheng NPP Unit 1 Cycle 18 reloads design. Parametric studies for stability have shown that the inlet loss coefficient, exposure, control rod position, and axial power shape are the most important parameters that might affect the accuracy of decay ratios for in-phase and out-of-phase modes of stability analysis. A decrease in the inlet loss coefficient or increase in the control rods insertion causes an increase in the global and regional decay ratios. An increase in the exposure causes an increase in the global decay ratio, the maximum value of the regional decay ratio occurs in MOC condition, and the regional decay ratio is higher than global decay ratio in the BOC condition.