As many reactors approach the end of their design lifetime, the global trend among nuclear power plant (NPP) operators is to extend plant operation beyond this limit. This requires detailed knowledge of the technical condition and material degradation, as well as credible predictions of property changes—so-called ageing—of safety-related components (SRCs) over extended lifetimes. Responding to this need, the DELISA-LTO project aims to identify the most affected components under long-term operation (LTO), describe LTO effects on material properties, and develop a simulation tool capable of predicting unacceptable material conditions. The project's outcomes will enhance operational safety by enabling timely prediction of potential failures. The focus is on Light Water Reactor (LWR) technologies, particularly VVERs (Water-Water Energetic Reactors), due to the consortium’s composition, which includes partners from most regions operating VVER reactors—one of the most widespread reactor types globally.
The industrial relevance and exploitation potential of the DELISA-LTO project are high, thanks to the involvement of key industrial partners, access to real data from components of decommissioned European plants, and a commitment to rapid implementation of project results. The Dissemination and Exploitation Plan supports harmonizing new design and operating conditions, safety criteria, and improved methodologies. It also aims to provide a solid technical basis for the design and assessment of reliable NPPs and to promote consensus among stakeholders. Collaboration is foreseen with national and international organizations, including operator-focused groups (FORATOM, WANO), safety networks (WENRA, AEN/CSNI, ETSON), and key research platforms such as SNETP/NUGENIA and EERA JPNM.
The DELISA-LTO project aims to deliver a comprehensive description of degradation mechanisms affecting selected components, such as steam generator tubes and primary pipes, using materials obtained from decommissioned NPPs. The decommissioning of two V1 units in Slovakia offers a rare opportunity to study materials exposed to real operational conditions (approx. 28–29 fuel campaigns). Different components in the primary circuit exhibit varying degradation mechanisms, requiring a range of test methods, including Non-Destructive Testing (NDT), structural and substructural analysis, and mechanical testing. The integration of simulation tools with experimental techniques is essential to understanding thermal ageing and swelling. Harvested materials mainly include primary circuit components such as main circulation piping and pressurizer surge lines, primarily made of stainless steels.
