Abstract
Since the age-related degradation of structures and components in NPPs has been a key issue regarding assessments of seismic safety, JNES initiated seismic test programs in fiscal 2004 for the degraded core shroud used in old BWR plants. The objectives were to: i) obtain a better understanding of the vibration characteristics and seismic strength of degraded structures and components having cracks due to aging, ii) ensure a margin of seismic design safety by considering age-related cracking, and iii) verify the JSME Code Rules on Fitness-for-Service for NPPs in Japan. The monotonic and cyclic loading tests of shroud shell and support element models were conducted. The shaking tests of the 1/2.5 scale shroud model were performed on the shaking table. All test models were designed to contain simulated cracking due to aging, involving cracks assumed to have the maximum allowable size according to the JSME Code Rules. This paper reports on the summary of these test results by focusing on vibration characteristics, seismic strength and a seismic design safety margin of the JSME rules.
