The study assessed structural integrity of a lower core plate, one of pressurized water reactor internals, via finite element damage analysis. The finite element damage analysis was performed considering variations of mechanical material behaviors with neutron irradiation and different stress triaxaility state from other components such as reactor pressure vessels and piping due to compressive stress. As a result of the assessment, it was found that the stress triaxiality has significant effect on ductility degradation damage indicator, and consideration of the stress triaxiality can reduce conservatism in assessing the structural integrity.