Abstract
BWRs may encounter some stability and safety problems due to the presence of steam in the reactors core. The instability is coupled mechanisms of two-phase flow thermal-hydraulic and neutronic behaviors. In order to investigate the stability phenomena, we uses the NRC certified code, LAPUR6.0, to calculate the decay ratio of specific power/flow condition. Owing to the assemblies used in Lungmen ABWR are much more than Chinshan and Kuosheng nuclear power station, the old methodology of LAPUR6.0 may need to be updated. For example, the grouping number in LAPUR6.0 was increased from 12 to 200. The object of this thesis is to develop the new methodology of LAPUR6.0 for Lungmen ABWR, and the application of this methodology. First, this paper illustrates the new methodology and the assemblies grouping method in detail, and shows the decks of LAPUR6.0 input parameters. In this research, the stability phenomena were investigated along the rod lines and pump speed lines by LAPUR6.0 for validating with the SIRIUS-F experimental results. The application of this methodology is divided into two parts, the decay ratio distribution on Lungmen ABWR power/flow map and the stability analysis for ATWS instability event, described by FSAR. According to the decay ratio distribution, it can be found that the core system remains stable under operating condition and the least damped region (Region III) on power/flow map. This thesis analyzed the ATWS event condition from TRACE/PARCS result, and the decay ratio of this event agrees well with FSAR result, the system returns to stable after power oscillation. All the analysis processes in this research were operated by DRASM200 interphase program, based on the old automatic program, DRASM.