Abstract
The purpose of this research which uses a frequency domain code- LAPUR to investigate the controlling mechanisms is to develop analysis methodology for operational instabilities in nuclear boiling water reactor (BWR). This research initially collected the relevant literatures, and then summarized their approaches and regulations. By referring to the studies and discussions on abnormal events, the characteristics of stability analysis have been constructed. We have established LAPUR5.2 methodologies based on the frequency domain code LAPUR5.2 where coupling between neutronic and thermal-hydraulic behaviors are considered. Meanwhile, we have also completed the parallel verifications against vendor’s results for Chinshan (BWR4) and Kuosheng (BWR6) reload design and extended to check Lungmen (ABWR) load design. Sensitivity analyses on various important parameters have been conducted for comparisons. To quantify the effects of various conditions on the global mode and the regional mode, this study employs the reduced-order model and conducts a study of the fractional change in the decay ratio to evaluate the parametric effect of instability on the stability boundary. With respect to global and regional mode parametric sensitivity, density reactivity coefficient, system pressure, delayed-neutron fraction and total core flow and recirculation loop gain were associated with larger fractional changes of decay ratios at points of higher power/flow operation.