Advanced Diagnostics for the Control Element Drive Mechanism System in Pressurized Water Reactors

Current designs of Light Water Reactors (LWR) are equipped with control and shutdown rods that are inserted and withdrawn from the reactor core for reactivity control. In particular, the Control Element Drive Mechanism (CEDM) system is widely used for regulating plant power levels and core power distribution in the existing and next generation of Pressurized Water Reactors (PWRs). This system includes a number of subsystems such as the CEDM and Control Element Assembly, power switch assembly circuitry, and control logic electronics. This particular type of rod control system has provided safe and reliable service to Combustion Engineering (CE) and subsequent CE System 80 designed nuclear plants for over 30 years. However, aging and obsolescence issues with the current generation of CEDMs, system controls, cables, and connectors have led to failures that resulted in reduced plant loads, reactor shutdowns, and manual or automatic reactor trips resulting in millions of dollars of lost revenue. In addition to aging and obsolescence concerns, the lack of diagnostic capabilities in the CEDM control system is a significant problem. These issues, along with plant life extensions, have prompted the need for new technology to monitor the health of these rod control systems in order to ensure reliable plant operation for decades to come. The goal of this project is to conduct a research and development effort to establish the feasibility of a health monitoring and diagnostic system for the CEDM control system, and design, implement, and demonstrate the capabilities at a nuclear plant facility. Advanced diagnostic techniques can be applied to the CEDM system in order to provide a non-intrusive solution for detecting component degradation. Also, enhanced condition monitoring techniques can better equip the plant with the ability to classify system failures, trend important parameters, log abnormal events, and localize faults so that they can be resolved in a timely manner. A robust monitoring and diagnostic system design will allow new diagnostic techniques to be combined with traditional plant surveillances to ensure CEDM system health and optimal system reliability.