Leveraging Within-Bank Comparison for Anomaly Detection, Diagnostics, and Prognostics in Advanced Nuclear Power Plants

Abstract

Nuclear power provides roughly 20% of the energy produced in the U.S. and more than half the carbon-free energy. Although the current U.S. fleet of 93 light water reactors (LWRs) continues to operate safely and reliably, many plants are shutting down before their current license expires due to unfavorable economic performance. Operations and maintenance (O&M) costs comprise over 60% of the cost of nuclear energy generation and are the largest addressable category for cost savings. Recently, focus in the nuclear power industry has turned to developing and deploying new reactor designs to further decarbonize the energy sector. Near-term investment is likely to focus on reactor designs that can leverage operating experience of our current pressurized and boiling water reactors (PWRs and BWRs). GE-Hitachi’s BWRX-300 is a small modular reactor (SMR) based on the intentional scaling of existing and well-researched BWR technologies. Despite similarities between near-term LWRbased SMRs, such as BWRX-300, and currently deployed LWRs, the economics of these reactor designs suffer from the loss of economy of scale enjoyed by the current 1,000 MWescale plants. Further, these smaller reactors are expected to be more agile in their operations, supporting a variety of deployment scenarios, such as load following and cogeneration. The processes and procedures used to manage and maintain the health of key components and systems must be re-examined to ensure economic performance and support new concepts of operation.

Control rods and control rod drive mechanisms manage overall power production and power distribution across the reactor core. As such, this system is key for managing reactor performance and a primary target of periodic inspection and maintenance to ensure desired performance. The control rod drive mechanism proposed in the BWRX-300 differs fundamentally from currently deployed BWRs: the BWRX300 uses servomotors for fine motion control while traditional BWRs primarily use hydraulic systems. Control rods move in banks of multiple individual rods, each with a dedicated servomotor. Rods in a single bank are commanded to follow the same maneuvers to manage thermal power production in the reactor core. By monitoring the position of the control rods in a single bank and the operating characteristics (e.g., current, rotational speed) of the driving servomotors for within-bank consistency, faulty performance can be detected in a single or few servomotors. This paper will present the results of such within-bank monitoring for a prototypical bank of control rods and associated servomotors based on simulation models of normal and faulty servomotor behavior.