Periodic Reporting for period 2 - STRUMAT-LTO (STRUctural MATerials research for safe Long Term Operation of LWR NPPs)
Reporting period: 2022-03-01 to 2023-08-31
STRUMAT-LTO is aimed to address the remaining gaps in RPV embrittlement research to ensure compliance with safety standards and prepare 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. Previous international Euratom-funded collaborative projects, such as LONGLIFE, PERFORM60, SOTERIA etc., have helped to improve the understanding of RPV ageing phenomena such as flux effect and influence of the chemical/microstructural heterogeneities in RPV embrittlement. However, still several open issues related to RPV embrittlement remain such as the contradicting viewpoints on underlying mechanisms that lead to accelerated embrittlement at high fluence conditions in certain low-copper (Cu) RPV steels and the synergetic effect between nickel, manganese and silicon (Ni-Mn-Si). Also, the validity of embrittlement trend curves (ETCs) for LTO beyond 60 years and the applicability of the master curve approach at high fluences and for small/sub-sized specimens require further investigation. To obtain more insight into these issues, the Dutch Nuclear Research and consultancy Group (NRG) and the Joint Research Centre (JRC) of the European Commission jointly conducted an irradiation campaign in the High Flux Reactor in Petten, called LYRA-10. Within LYRA-10 a variety of different RPV steel specimens representing VVER-1000 and western type pressurized water reactor (PWR) RPV steels with systematic variations in Ni, Mn and Si contents have been irradiated to high fluences resembling reactor operation above 60 years. The goal of STRUMAT-LTO is to address the above-mentioned scientific gaps in RPV embrittlement topic by exploiting the LYRA-10 specimens. The project lasts 4 years and started on 1 September 2020. 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.
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. Previous international Euratom-funded collaborative projects, such as LONGLIFE, PERFORM60, SOTERIA etc., have helped to improve the understanding of RPV ageing phenomena such as flux effect and influence of the chemical/microstructural heterogeneities in RPV embrittlement. However, still several open issues related to RPV embrittlement remain such as the contradicting viewpoints on underlying mechanisms that lead to accelerated embrittlement at high fluence conditions in certain low-copper (Cu) RPV steels and the synergetic effect between nickel, manganese and silicon (Ni-Mn-Si). Also, the validity of embrittlement trend curves (ETCs) for LTO beyond 60 years and the applicability of the master curve approach at high fluences and for small/sub-sized specimens require further investigation. To obtain more insight into these issues, the Dutch Nuclear Research and consultancy Group (NRG) and the Joint Research Centre (JRC) of the European Commission jointly conducted an irradiation campaign in the High Flux Reactor in Petten, called LYRA-10. Within LYRA-10 a variety of different RPV steel specimens representing VVER-1000 and western type pressurized water reactor (PWR) RPV steels with systematic variations in Ni, Mn and Si contents have been irradiated to high fluences resembling reactor operation above 60 years. The goal of STRUMAT-LTO is to address the above-mentioned scientific gaps in RPV embrittlement topic by exploiting the LYRA-10 specimens. The project lasts 4 years and started on 1 September 2020. 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.
In WP1, a test matrix at task level per partner including details of test types and number of specimens has been finalized. Irradiated material transport from NRG to STUBA, EK, VTT, UJV, HZDR and KINR (all 6 transports) are finished. All the reference and PIE testing (Tensile testing (T1.2) KLST testing (T1.3) Fracture toughness testing (T1.4) and thermal annealing (T1.5). ) planned in WP1 has been finished. A report (D1.1) on the influence of high fluence irradiation on tensile properties of RPV steels and effectiveness of annealing in PWR and VVER 1000 steels is published.
The analysis of the test results helped in understanding the embrittlement behavior of RPV steels at high fluences and the effectiveness of thermal annealing in recovery after high fluence irradiation. Currently analysis on synergetic influence of Ni, Mn and Si on irradiation induced shifts in transition temperature is ongoing (D1.2 and D1.4). Already at the beginning of the project, all information related to LYRA-10 materials and irradiation documents, such as Irradiation report, dosimetry report, report on origin and manufacturing of the LYRA-10 specimens, specific fluences, previous reference test data, was documented to have a solid basis for analyzing the PIE test results of the project.
In WP2, it is planned to use the remnants of the Lyra-10 specimens to get further information from the expensive and unique materials irradiated in Lyra –10. During the first 18 months all participants have upgraded the testing facilities and installed new extensometers for the use of irradiated non-standard specimens. For the preparation of small specimens testing in WP2, two voluntary Round-Robin (RR) test programmes on mini-CT and small punch test (SPT) are organized to evaluate and harmonize inter-laboratory differences in fabrication, testing and analysis methods. EK-CER provided broken Charpy specimens to produce mini-CT and SPT specimens. Analysis of mini-CT and SPT RR results is finished, and the results have been submitted for publication in ASME PVP 2022 and ASME PVP 2023 conferences. Manufacturing and testing of sub-size specimens, namely mini-CT and SPT, from remnants of LYRA-10 specimens tested in WP1 is almost finished. In total more than 1300 tests are conducted including all tests in WP1 and WP2. The reports including the results from mini-CT and SPT specimens (D2.2 D2.3) are in preparation.
In WP3, all unirradiated materials are distributed to the partners. Microstructural characterization of the unirradiated reference conditions of the selected model steels A, B, C, F, G, H by means of LOM, SEM-EBSD, TEM, APT are completed a report (D3.1) is issued. Microstructural investigation of irradiated materials by means of LOM, SEM-EBSD, TEM, APT and SANS is almost finished.
In WP4, the collection and expert analysis of available Embrittlement Trend Equations (ETE) for VVER- 1000/PWR RPV steels to be applicable for Lyra-10 irradiation materials and conditions is finished as deliverable D4.1.
The WP5 has started in M24 and the screening of data generated in WP1 and WP2 is ongoing for master curve analysis, which will be reported in D5.1 very soon.
Finally in WP6, many dissemination and communication activities have took place. In total 15 papers, including journal articles and conference presentations, are published and a few more are in the pipeline. A workshop attended by experts in the field and young researchers was conducted in Dresden. Within the Dissemination Workshop, STRUMAT-LTO results were presented. In addition, the young researchers were given opportunity to present their work and they are awarded with travel grants. The STRUMAT-LTO project results were presented in the meetings of other H2020 projects on RPV such as FRACTESUS, ENTENTE, INSEFA-SCALE and other internal organizations such as NEA and NUGENIA meetings. Most of the data generated in the project has been uploaded to JRC's Mat-DB database and the rest will be uploaded in the coming period as per the dissemination strategy.
The analysis of the test results helped in understanding the embrittlement behavior of RPV steels at high fluences and the effectiveness of thermal annealing in recovery after high fluence irradiation. Currently analysis on synergetic influence of Ni, Mn and Si on irradiation induced shifts in transition temperature is ongoing (D1.2 and D1.4). Already at the beginning of the project, all information related to LYRA-10 materials and irradiation documents, such as Irradiation report, dosimetry report, report on origin and manufacturing of the LYRA-10 specimens, specific fluences, previous reference test data, was documented to have a solid basis for analyzing the PIE test results of the project.
In WP2, it is planned to use the remnants of the Lyra-10 specimens to get further information from the expensive and unique materials irradiated in Lyra –10. During the first 18 months all participants have upgraded the testing facilities and installed new extensometers for the use of irradiated non-standard specimens. For the preparation of small specimens testing in WP2, two voluntary Round-Robin (RR) test programmes on mini-CT and small punch test (SPT) are organized to evaluate and harmonize inter-laboratory differences in fabrication, testing and analysis methods. EK-CER provided broken Charpy specimens to produce mini-CT and SPT specimens. Analysis of mini-CT and SPT RR results is finished, and the results have been submitted for publication in ASME PVP 2022 and ASME PVP 2023 conferences. Manufacturing and testing of sub-size specimens, namely mini-CT and SPT, from remnants of LYRA-10 specimens tested in WP1 is almost finished. In total more than 1300 tests are conducted including all tests in WP1 and WP2. The reports including the results from mini-CT and SPT specimens (D2.2 D2.3) are in preparation.
In WP3, all unirradiated materials are distributed to the partners. Microstructural characterization of the unirradiated reference conditions of the selected model steels A, B, C, F, G, H by means of LOM, SEM-EBSD, TEM, APT are completed a report (D3.1) is issued. Microstructural investigation of irradiated materials by means of LOM, SEM-EBSD, TEM, APT and SANS is almost finished.
In WP4, the collection and expert analysis of available Embrittlement Trend Equations (ETE) for VVER- 1000/PWR RPV steels to be applicable for Lyra-10 irradiation materials and conditions is finished as deliverable D4.1.
The WP5 has started in M24 and the screening of data generated in WP1 and WP2 is ongoing for master curve analysis, which will be reported in D5.1 very soon.
Finally in WP6, many dissemination and communication activities have took place. In total 15 papers, including journal articles and conference presentations, are published and a few more are in the pipeline. A workshop attended by experts in the field and young researchers was conducted in Dresden. Within the Dissemination Workshop, STRUMAT-LTO results were presented. In addition, the young researchers were given opportunity to present their work and they are awarded with travel grants. The STRUMAT-LTO project results were presented in the meetings of other H2020 projects on RPV such as FRACTESUS, ENTENTE, INSEFA-SCALE and other internal organizations such as NEA and NUGENIA meetings. Most of the data generated in the project has been uploaded to JRC's Mat-DB database and the rest will be uploaded in the coming period as per the dissemination strategy.
STRUMAT-LTO is collecting important data on RPV embrittlement which is relevant for LTO, using the Lyra-10 specimens irradiated to high fluences. A total of more than 1300 tests are conducted in WP1 and WP2. The data is supplied to WP3-WP5 to achieve the project's objectives.