The heart of nuclear power plants lies in their intricate systems, where every component plays a crucial role in ensuring safe and efficient energy production. Among these, the heat exchange tubes within steam generators stand out as critical yet vulnerable elements. For reactors of the WWER type, which are prevalent in several countries, these tubes face an array of challenges that can significantly limit their lifespan.

These tubes, with wall thicknesses as thin as 1.4 mm for WWER 440 reactors and 1.5 mm for WWER 1000 models, must endure various stressors. Over time, increased power output, prolonged operation, complex water chemistry, and mechanical strain due to dissimilar weld repairs contribute to their gradual deterioration. The impact of these factors makes steam generator tubing one of the most vulnerable components, affecting the overall lifespan of numerous reactor units.

Recent years have seen new types of degradation across different WWER units, with certain issues specific to particular units. This trend has highlighted the pressing need for advanced inspection techniques to monitor and address these vulnerabilities. These cutting-edge techniques are already beginning to be used in some units, paving the way for a broader implementation that could revolutionize reactor maintenance.

A unique project was carried out at VUJE, a.s., aimed at identifying steam generator tubes with operationally induced defects from the history of each unit. The selected tubes were then extracted, decontaminated, and preserved for future use. This effort was part of the broader decommissioning project for Units 1 and 2 at the Jaslovské Bohunice Nuclear Power Plant in Slovakia.

These heat exchange tubes removed are providing an invaluable opportunity for testing and validating not only for standard but for advanced eddy current inspection techniques as well. Documented with real defects and extensive historical eddy current data, these tubes offer a unique experimental resource for assessing the effectiveness of new inspection technologies, such as eddy current-based tools. The findings from these tests hold promise for enhancing the reliability of inspections, thus helping plant operators and inspection vendors better predict and manage wear and tear in reactor components.

The removed heat exchange tubes present an invaluable opportunity for testing and validating both standard and advanced eddy current inspection techniques. Documented with real defects and accompanied by extensive historical eddy current data, these tubes offer a unique experimental resource for evaluating the effectiveness of new inspection technologies. Insights gained from these tests have the potential to significantly enhance inspection reliability, empowering plant operators and inspection vendors to better predict and manage challenges of LTO process.

The tubes have been organized into a custom-designed test block (Picture 2) that holds up to 36 samples, enabling controlled experiments and consistent data collection. This work is part of the DELISA-LTO project (Description of Extended Lifetime and its Influence on Safety Operation and Material Performance), a four-year international research initiative funded by the HORIZON-EURATOM-NRT-01 program, running from 2022 to 2026.

The DELISA-LTO project is a major step toward understanding the aging phenomena of reactor components and improving non-destructive testing (NDT) methods for long-term operation evaluations. By combining experimental research with numerical simulations, DELISA-LTO aims to fill key data gaps and enhance technical insights into reactor aging, ultimately supporting safer and more sustainable reactor operation.
The project is structured into six work packages (WPs), covering project management, dissemination, and training, as well as four technical areas that address the project's comprehensive research scope. The unique approach taken by DELISA-LTO also enables easy transferability of findings across different reactor technologies, adding a further layer of value to the project.

As the world seeks to optimize existing nuclear resources while maintaining safety, the DELISA-LTO project represents a forward-looking approach to sustaining nuclear energy production. By pushing the boundaries of inspection technology, it holds the potential to extend the operational lifetimes of WWER reactors worldwide, supporting energy security and reliability for years to come.