Development of Method to Determine Instability Threshold with RETRAN Code

Neutron flux oscillation event occurred at LaSalle-2 (BWR5) on March 9, 1988 which arised issues such as why the event occurred and what major differences between LaSalle-2 and other BWRs were in view of the BWR stability. In order to resolve the issues, a method to determine instability threshold was developed at Japan Atomic Energy Research Institute (JAERI) by using the transient thermal-hydraulic analysis code RETRAN which was developed at Electric Power Research Institute (EPRI). The validity of the method was confirmed by parametric studies and thermal-hydraulic experiment analyses. Using the method, the instability boundary for in-phase oscillation was obtained. For out -of-phase oscillation, however, it was found that the instability boundary could not be determined in nature due to the limitation from the point reactor kinetics model.