Project Description


STRUMAT-LTO is focused on addressing open issues in Reactor Pressure Vessel (RPV) embrittlement at high fluence conditions relevant for Long Term Operation (LTO). LTO assessment of any NPP requires prediction of its RPV embrittlement for the proposed period of life extension. Substantial (experimental and modelling) research has been performed in various international collaboration research projects, such as NULIFE, LONGLIFE, PERFORM60, SOTERIA to understand (i) the irradiation damage mechanisms at high neutron fluences in relation with microstructure, composition and neutron flux etc., and (ii) to improve/validate embrittlement trend curves (ETCs) in the context of RPV LTO. These efforts have helped enormously in realizing the LTO of several existing PWRs up to 60 years of operation. Despite all the previous research on RPV embrittlement, still there are scientific gaps to be addressed especially in view of possible lifetime extensions up to 80 years, as listed below:

  • Synergetic effects of Ni-Mn-Si at high fluences: There is limited understanding on synergetic effects of Ni, Mn and Si and associated unfavorable effects on microstructure and mechanical properties in low-Cu RPV steels at high fluences, in particular for VVER-1000 steels.
  • High fluence behavior and ETCs for LTO beyond 60 years: None of the existing ETCs predict the temperature shifts sufficiently for all materials and existing ETCs under predict irradiation embrittlement at higher fluences. Also not all relevant chemical elements and microstructural properties (volume fraction, size, defect density etc.) are explicitly considered in these models.
  • Miniature testing methods: Material from RPV embrittlement surveillance programs is limited. Thus testing methods based on small/sub-sized specimens are considered to characterize irradiation induced shifts in reference curves. Potential applicability of these techniques needs to be assessed.


RPV steel samples irradiated in the LYRA-10 facility in the High-Flux Reactor in Petten will be employed to perform this research. The scientific work of the project has been distributed into 5 work packages, WP1-WP5 as outlined  in picture on the right. Selected activities, as highlighted, will be performed with in-kind contributions from participating organizations within the pilot project. The pilot project is planned for little more than 2 years, i.e. from Sep. 2018 – Dec. 2020.


A kick-off meeting for the in-kind project was organized on 11th and 12th September at NRG Petten. Experts from 14 different organizations and 9 countries, have participated in the kick-off meeting. The results of the STRUMAT-LTO project are expected to provide:

  • An improved understanding of synergetic influence of Ni, Mn and Si on irradiation hardening and embrittlement behavior of VVVER-1000 RPV weld materials and western PWR RPV model steels
  • Quantitative characterization of RPV embrittlement at high fluences resembling more than 60 years of reactor operation
  • Assessment of suitability of small/sub-sized specimen testing methods and MC curve approaches for RPV embrittlement characterization at high fluence conditions
  • Experimental data required for validation of existing ETCs for LTO beyond 60 years of RPV life


In-kind pilot project: Sep. 2018 – Dec. 2020 (2y & 4 m)
Full project: 4 years


NRG/ EC-JRC Petten/ HZDR/ IZFP/ CIEMAT/ UJV/ MTA-EK/ Bay Zoltan/ Univ. Man./ UKAEA/ VUJE/ STUBA/ ARB-Ukraine/ KINR-Ukraine/ SEC NRS-Russia


Technical Project Leader:

Murthy Kolluri (NRG)


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europe This project is currently running as an in-kind collaboration project in Technical Area 4 (TA4) of NUGENIA