Test Programs for Degraded Core Shroud and PLR System Piping: Seismic Test Results and Discussion on JSME Rules Application

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 and PLR system piping 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 Rules on Fitness-for-Service for NPPs in Japan. The quasi-static displacement or load control testing of the components of the core shroud and PLR system piping were conducted. The dynamic load testing of combined components were also performed on a shaking table by using an approximately 1/3 scale PLR system piping specimen and a 1/2.5 scale core shroud specimen. All test specimens were designed to contain simulated cracking due to aging, involving cracks assumed to have the maximum allowable size according to the JSME Rules. These test results were discussed by focusing on the effects of cracking on vibration characteristics and seismic strength, and the margin of seismic safety under the JSME Rules.