DELISA-LTO: DEscription of the extended LIfetime and its influence on the SAfety operation and construction materials performance – Long Term Operation with no compromises in the safety

Project Information

DELISA- LTO

Grant agreement ID: 101061201

Project closed

EC signature date 30 May 2022

Start date 1 June 2022

End date 31 May 2026

Funded under

• Euratom Research and Training Programme (EURATOM)

Total cost

€ 3 276 263,06

EU contribution

€ 3 276 263,00

Coordinated by

CENTRUM VYZKUMU REZ SRO
Czechia

Periodic Reporting for period 2 - DELISA- LTO (DELISA-LTO: DEscription of the extended LIfetime and its influence on the SAfety operation and construction materials performance – Long Term Operation with no compromises in the safety)

Reporting period: 2023-12-01 to 2025-05-31

Summary of the context and overall objectives of the project

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.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The work to be done within the project is divided into 6 work packages. Two of them are supportive. WP1 is dedicated to project coordination and management whereas WP6 focuses on the communication, dissemination and exploitation activities with attention to young researchers' involvement.
The work in WP2 included preparatory activities, the creation of a material database, sampling of materials from primary pipes in NPP V1, development of detailed cutting plans, primary sampling, and transportation to all participating entities. Up to now, all transports have been successfully executed, and the verification of the material volume for the specified range of tests outlined in the agreed experimental matrix is in progress.
The WP3 aims to develop, test and validate models of RPV internals to ensure their integrity and functional capability and evaluation of current and predictable state over the long-term operation, the models of thermal ageing is considered as well. Within the reporting period, the tasks were directed to get corresponding achievements for the defined aim. The survey of definition and comparison of normative requirements, current practice and approaches to the thermal ageing definition was developed and presented in the corresponding report. Continuation of the work is currently processing within developing a thermal ageing predictive models based on treatment of experimental data and analysis of the thermal ageing effect on the VVER available materials.
WP4 creates a solid and reliable basis of experimental data to foster the project goals and activities in other WPs. In the first period, preparatory activities were carried out providing the basis for the implementation into the key area of the project - the experimental program in the form of an extensive inter-laboratory study using a wide range of experimental and analytical methods – mechanical testing, microstructural examinations, post-test analyses and NDT techniques. The experimental material matrix, describing the involvement of each participating laboratory, was finalized and the manufacture of the testing specimen has already started.
Within WP5, the safety guidelines related to the available SSCs’ materials which could affect the safe LTO will be analyzed. A Questionnaire and Survey of the used guidelines, standards, codes and "best practices" was designed and completed by the participants to create a robust base for the analysis. The questionnaire was approved by all participants and covered the following topics: safety codes, standards, guidelines related to the available SSCs' relevant for swelling and thermal ageing during LTO expected for 60+ years, best practice recommendations for swelling and thermal ageing assessment.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Experimental evaluation of design materials towards the long-term operation of VVERs is extremely important for the NPP's lifetime prolongation and increase in their safety margin. European VVER countries previously considered prolonging the operating lifetime from 40 to 60+ years keeping regularly updated high safety standards during the last decades. During the first 18 months of its implementation, project DELISA-LTO collected a great number of specimens coming from different VVERs. Measurements of VVER design material specimens via several techniques as received, irradiated as well as thermally treated will provide a unique set of results that will be relevant not only for VVERs but also PWRs operating in Europe. Several additional spectroscopic techniques will contribute to better understanding of degradation processes in material microstructure after long-term operational loads. The high abundance of experimental data will imply excellent possibilities for further research with an impact on increasing nuclear safety.

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