Argonne model improves nuclear plant maintenance planning

Researchers at Argonne National Laboratory have developed a multiphysics simulation modeling tool to predict how feedwater heater (FWH) tubes in a nuclear power plant break down over time. The model, which has the potential to improve maintenance schedules and save operating costs at nuclear facilities, is described in a paper titled "Numerical Analysis with Experimental Validation of Tube Fatigue Failure in Feedwater Heaters," published in a recent issue of Engineering Failure Analysis.

A typical nuclear power plant has about 30 FWH tubes, in which water is preheated before it enters the reactor. The tubes gradually develop signs of strain from repeated cycles of cooldown and full operation, and operators must manually inspect tubes to determine if repair is required. Such inspections are costly and labor intensive, and lack the precision to detect early signs or specific sites of degradation.

Multiphysics model and framework: To address this complex problem, researchers at Argonne first created a multiphysics simulation model that combined aspects of fluid mechanics, condensation, solid mechanics, and cumulative damage theory. The model allowed them to determine the optimal time for FWH tube maintenance.

They then used the model to develop a type of framework that could be used by operators. The framework, which combined the simulation findings with actual inspection data, revealed that the expected functional lifetime of a FWH tube is approximately 29 years. The framework also identified specific sites of stress along the tube that would need attention.

The findings of the simulation and model were validated with real-world experimental inspection data and tube replacement history from an operating nuclear power plant. According to Yeni Li, an Argonne scholar and nuclear engineer who is the lead author of the published paper, "The most difficult part of complex simulations is validating it. The key to validating simulations is with experimental data. Only at Argonne can we find the concentration of skills in one area to be able to do that."

Applications of framework and analysis: The modeling framework developed by the Argonne team is scalable for application in nuclear power plants, enabling operators to create predictive maintenance schedules, prioritize maintenance actions, and identify critical areas of reactor degradation before those areas become problematic. In these ways, the framework could be used to improve the reliability and safety of nuclear power plants.

Furthermore, they found that "the analysis methodology can also serve as an important tool for designing and evaluating novel heat exchanger concepts. For example, the growing interest in utilizing nuclear reactor heat to power endothermic industrial processes presents new challenges for heat exchanger design. . . . The methodology proposed in this work can expedite the design process by predicting the mechanical stress a novel heat exchanger design will encounter throughout its intended service life and confirm that damage levels for duty cycle events are within allowable limits before committing the design to qualification tests."

What the industry needs: Argonne senior nuclear engineer and paper coauthor Richard Vilim said, "This is exactly what the industry was looking for. Power plants operate on a fixed maintenance schedule, and unplanned maintenance is costly. . . . There's no existing technology that provides this critical information."

Akshay Dave, manager of ANL's intelligent systems group paper coauthor, added, "This effort holds significant promise for next-generation advanced reactors currently in the design phase, where our insights could be invaluable."