STRUctural MATerials research for safe Long Term Operation of LWR NPPs

Project Information

STRUMAT-LTO

Grant agreement ID: 945272

DOI

10.3030/945272

Project closed

EC signature date 19 May 2020

Start date 1 September 2020

End date 31 August 2024

Funded under

• Euratom

Total cost

€ 4 466 997,50

EU contribution

€ 3 965 029,25

Coordinated by

HUN-REN Energiatudomanyi Kutatokozpont
Hungary

Periodic Reporting for period 3 - STRUMAT-LTO (STRUctural MATerials research for safe Long Term Operation of LWR NPPs)

Reporting period: 2023-09-01 to 2024-08-31

Summary of the context and overall objectives of the project

STRUMAT-LTO aims to address the remaining gaps in RPV embrittlement research, ensuring compliance with safety standards and preparing decision-makers for potential lifetime extensions of European nuclear power plants beyond 60 years.
One of the critical issues of long-term operation (LTO) is the embrittlement of the reactor pressure vessel (RPV) mainly caused by neutron irradiation and thermal ageing. The goal of STRUMAT-LTO is to address the scientific gaps in RPV embrittlement topic by exploiting the LYRA-10 specimens. The project lasted 4 years, from September 2020 to August 2024. Energiatudomanyi Kutatokozpont (EK), Hungary is the administrative coordinator of the project and Nuclear Research and consultancy Group (NRG), The Netherlands is the scientific coordinator of the project.

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

Project Progress:
• WP1: Extensive testing of irradiated/reference RPV steels for SO1; distributed materials to partners, completing tests (tensile, KLST, fracture toughness, annealing). Results published in D1.1–D1.3 with studies on high-fluence effects and annealing effectiveness for PWR/VVER-1000 steels.
• WP2: Additional Lyra-10 testing for SO1, SO4; facilities upgraded. Round-Robin tests harmonized small-specimen testing across labs. Published results in ASME PVP 2022–2023.
• WP3: Un/irradiated steels characterized via LOM, SEM-EBSD, TEM, APT, SANS, identifying Mn-Ni synergy in cluster density.
• WP4: ETEs for Lyra-10 materials assessed (D4.1) evaluating high fluence impact.
• WP5: Assessed irradiation’s effect on fracture toughness, showing Master Curve approach’s suitability for high-fluence materials.
• WP6: Dissemination with 15+ papers, workshops, and data uploads. Young researchers were engaged in all the events.
Achievements: 1,600+ mechanical tests, harmonized testing methods, insights on Mn/Ni synergy, validated ETEs, and microstructural analyses.
Conclusions: Solute clusters are key in hardening; PWR steels show unique responses; Master Curve approach viable for toughness testing.

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)

STRUMAT-LTO project is unique because large amount of quantitative PIE data and corresponding microstructural data was generated, which helped to improve the understanding on ageing (hardening and embrittlement) behavior of low Cu PWR and VVER-1000 RPV steels (total more than 1600 specimens were tested) at fluences resembling >60 years of reactor operation. This data is currently being uploaded to JRC's Mat-DB database to fill the existing data gaps in RPV embrittlement for LTO evaluation at these high fluence conditions. This achievement covers the expected impact from the call regarding "Data development for increased knowledge and understanding of ageing phenomena"
STRUMAT-LTO also addressed the need for "Development/qualification of tools, systems and practices for the reduction of vulnerabilities of operating plants in particular for foreseen LTO regimes". Validation of existing Embrittlement Trend Equation (ETEs) was performed using the data generated at high fluence in the project for improved prediction of RPV transition temperature shifts in the LTO regime. A new ETE was proposed for improved RPV transition temperature shifts prediction in the LTO regime. Assessment of applicability of master Curve (MC) approach using mini-CT specimens was performed to support RPV embrittlement evaluation at high fluence conditions for safe LTO of European NPPs.
Lastly, the best practices and lessons learned from various partners in fabrication and PIE testing of small specimens (mini-CT, SPT) for fracture toughness and tensile property evaluation is documented to support improvement of respective standards (e.g. ASTM E1921 for MC testing with mini-CT and ASTM E3205/ EN15627 for SPT testing).
Hence the results produced in the project contribute to realize the expected impact of the call in terms of data generation for increased knowledge and understanding of ageing phenomena in LWRs, development/qualification of tools for safe LTO regimes, support standards development.

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