EFFECTS OF COMPONENT AGING ON THE WESTINGHOUSE CONTROL ROD DRIVE SYSTEM

An assessment of aging for the Westinghouse pressurized-water-reactor (PWR) control-rod-drive (CRD) system has been completed as part of the U. S. Nuclear Regulatory Commission Nuclear Plant Aging Research (NPAR) Program. This study examined the design, construction, maintenance, and operation of the system to determine its potential for degradation as the plant ages. This article presents selected results from this study. The operating experience data were evaluated to identify the predominant failure modes, causes, and effects. From our evaluation of the data, coupled with an assessment of the materials of construction and the operating environment, we conclude that the Westinghouse CRD system is subject to degradation that, if left unchecked, could affect its safety function as the plant ages. Ways to detect and mitigate the effects of aging are included in this article. The current maintenance for the CRD system at 15 Westinghouse PWRs was obtained through a survey conducted in co-operation with the Electric Power Research Institute and the Nuclear Management and Resources Council. The survey results indicate that some plants have modified the system, replaced components, or expanded preventive maintenance practices. Several of these activities have effectively addressed the aging issue.