On March 9, 1988, the LaSalle-2 nuclear power plant experienced a neutron flux oscillation under natural circulation. To obtain an in-depth understanding of this event, a series of analytical studies has been performed using the RETRAN code within the scope of a point kinetics model. In previous studies, an instability map was drawn on the plane of the nondimensional power-to-flow ratio and core inlet subcooling, which was essentially the same as that proposed by Ishii and Zuber. The event sequence was simulated by RETRAN, and the locus of the event was drawn on the instability map. The experimental calculations that were performed to validate the method used to determine the instability threshold used in the previous studies are described, as are the calculations of the improved instability map and event simulation.