Periodic Reporting for period 2 - INNUMAT (Innovative Structural Materials for Fission and Fusion)
Reporting period: 2024-03-01 to 2025-08-31
Fission lead-cooled and molten-salt fast reactors are among the Generation IV nuclear reactors under development globally. In addition to fission reactors harnessing the splitting of nuclei, fusion reactors leveraging the combination of two light nuclei are also under development, promising vastly greater amounts of energy released. The EU-funded INNUMAT project will develop innovative structural materials / material solutions for these nuclear applications and with potential applicability in concentrated solar power and/or in hydrogen confinement. The goal is to rapidly increase the technology readiness of the considered materials / material solutions regarding corrosion resistance, high temperature strength, thermal stability and irradiation tolerance via computational and experimental high throughput material screening methods.
Within the reporting period, the remaining REFERENCE variants of the innovative materials / material solutions pursued, in particular the complex concentrated alloy NEW-REF-CCA2 and the weld overlay on electron beam welded 316L, are produced and distributed to the partners involved in their advanced characterization. Moreover, with the knowledge gained from the advanced characterization conducted so far on the REFERENCE materials a genetic algorithm for multi-objective optimization is utilized for the design of NEW materials in which kinetic models for creep and alumina forming, statistical data mining by machine learning, computational thermodynamics (Thermo-Calc, CALPHAD) are combined for predicting their properties. On the basis of the computational design results, 8 different alloys (5 Ni-rich and 3 Fe-rich) were selected for experimental assessment in which sample ingots were produced for preliminary characterization and validation. Finally, two complex concentrated alloys, NEW-CCA3.1 and NEW-CCA3.2 are selected, produced and distributed to the partners for advanced characterization. Similar progress was achieved in the development of new high entropy stabilized amorphous, lithia- and yttria-doped alumina coating as well as coating with multilayer architecture based on the stack of a ceramic and a metal whose production and distribution to the partners for advanced characterization are to be accomplished by December 2025.
Remarkable progress has been made in the advanced characterization of the REFERENCE materials with regard to their compatibility with coolants. Exposure tests lasting > 5000 hours with lean AFA and high-alloy AFA in stagnant Pb with two different surface preparations have been completed and clearly show that surface preparation has a significant influence on compatibility. At least one high alloyed AFA showed no signs of corrosion at 600°C after 5000h. Corrosion tests in flowing Pb and PbLi are finally to be started with the first test on coated EUROFER in flowing PbLi to be repeated due to wrongly deposed coating. Moreover, SPT Tests on both lean and high alloyed AFA materials in PbBi and Pb are performed at slow and very slow strain rates. High alloyed AFA do not show any LME at the testing conditions. Some surface cracks accompanied by local dissolution of Ni and Mn are observed and require further investigations.
The comprehensive characterization of the REFERENCE materials with regard to high-temperature mechanical behavior and thermal stability has also progressed well. A large number of tensile, creep, fracture mechanics, low cycle fatigue and small punch tests were carried out, providing valuable results and first datasets on the high temperature material behavior and demonstrating the excellent suitability of SPTs for the qualitative assessment of the effect of thermal ageing on the material behavior.
Advancements in the characterization of the REFERENCE materials with respect to their irradiation tolerance has also been achieved. The ion-irradiation campaigns at low (1, 3 and 10 dpa @300°C with Fe ions) and high temperatures (1 dpa at 550°C and 650°C with Au ions) as well as the 1st neutron irradiation campaigns (1 and 3 dpa at 300°C, 550°C and 650°C) have been completed. In extensive post irradiation microstructural investigations (TEM and APT) of the ion irradiated REFERENCE HEAs the effects of the incident particle and free surfaces on the irradiation defect size and density as well as on elemental distributions are evaluated observing for the latter radiation-induced elemental clustering/precipitation.
Aiming at deep, beyond state-of-the-art understanding of main mechanisms determining corrosion, mechanical behavior, aging, and degradation of properties due to irradiation detailed advanced analysis is performed to elucidate the cracking behavior of HEAs during SPT tests in heavy liquid metal. Local ferritization and dissolution of Ni and Mn was detected. Furthermore, modelling the initiation of localized corrosion using different potential mechanisms is successfully extended to lean AFA steels and a numerical model for selective leaching of pure metals is successfully applied and will be extended to alloy systems. With respect to irradiation effects, simulation experiments of selected mechanisms are performed, e.g. in-situ TEM irradiation to study irradiation induced recrystallization of amorphous coatings and He implantation to study He transmutation effects in ODS steels. In addition, simulation methods including machine learning interatomic potentials are developed for modelling irradiation damage and microstructure evolutions in a representative HEA system and successfully applied, e.g. for modelling the overlapping cascades due to irradiation and the irradiation-induced elemental demixing in complex, multiple element alloys.
The activities related to qualification and standardization processes are continued, with in particular considerations regarding materials prequalification processes, and focused on the state of the art and needs of INNUMAT materials, with an overview on codes, standards and norms allowing to propose a “wish list” activities for prequalification and giving some considerations on pre-industrialization. In parallel, Small Specimen Test Techniques are further studied, and for instance, thanks to in kind with ECCC allowing to perform a campaign of Round Robin tests on standard materials for micro creep tests.
Remarkable progress has been made in the advanced characterization of the REFERENCE materials with regard to their compatibility with coolants. Exposure tests lasting > 5000 hours with lean AFA and high-alloy AFA in stagnant Pb with two different surface preparations have been completed and clearly show that surface preparation has a significant influence on compatibility. At least one high alloyed AFA showed no signs of corrosion at 600°C after 5000h. Corrosion tests in flowing Pb and PbLi are finally to be started with the first test on coated EUROFER in flowing PbLi to be repeated due to wrongly deposed coating. Moreover, SPT Tests on both lean and high alloyed AFA materials in PbBi and Pb are performed at slow and very slow strain rates. High alloyed AFA do not show any LME at the testing conditions. Some surface cracks accompanied by local dissolution of Ni and Mn are observed and require further investigations.
The comprehensive characterization of the REFERENCE materials with regard to high-temperature mechanical behavior and thermal stability has also progressed well. A large number of tensile, creep, fracture mechanics, low cycle fatigue and small punch tests were carried out, providing valuable results and first datasets on the high temperature material behavior and demonstrating the excellent suitability of SPTs for the qualitative assessment of the effect of thermal ageing on the material behavior.
Advancements in the characterization of the REFERENCE materials with respect to their irradiation tolerance has also been achieved. The ion-irradiation campaigns at low (1, 3 and 10 dpa @300°C with Fe ions) and high temperatures (1 dpa at 550°C and 650°C with Au ions) as well as the 1st neutron irradiation campaigns (1 and 3 dpa at 300°C, 550°C and 650°C) have been completed. In extensive post irradiation microstructural investigations (TEM and APT) of the ion irradiated REFERENCE HEAs the effects of the incident particle and free surfaces on the irradiation defect size and density as well as on elemental distributions are evaluated observing for the latter radiation-induced elemental clustering/precipitation.
Aiming at deep, beyond state-of-the-art understanding of main mechanisms determining corrosion, mechanical behavior, aging, and degradation of properties due to irradiation detailed advanced analysis is performed to elucidate the cracking behavior of HEAs during SPT tests in heavy liquid metal. Local ferritization and dissolution of Ni and Mn was detected. Furthermore, modelling the initiation of localized corrosion using different potential mechanisms is successfully extended to lean AFA steels and a numerical model for selective leaching of pure metals is successfully applied and will be extended to alloy systems. With respect to irradiation effects, simulation experiments of selected mechanisms are performed, e.g. in-situ TEM irradiation to study irradiation induced recrystallization of amorphous coatings and He implantation to study He transmutation effects in ODS steels. In addition, simulation methods including machine learning interatomic potentials are developed for modelling irradiation damage and microstructure evolutions in a representative HEA system and successfully applied, e.g. for modelling the overlapping cascades due to irradiation and the irradiation-induced elemental demixing in complex, multiple element alloys.
The activities related to qualification and standardization processes are continued, with in particular considerations regarding materials prequalification processes, and focused on the state of the art and needs of INNUMAT materials, with an overview on codes, standards and norms allowing to propose a “wish list” activities for prequalification and giving some considerations on pre-industrialization. In parallel, Small Specimen Test Techniques are further studied, and for instance, thanks to in kind with ECCC allowing to perform a campaign of Round Robin tests on standard materials for micro creep tests.
• New complex concentrated alloys with promising compatibility with coolants, high temperature strength, thermal stability and irradiation tolerance developed based on a genetic algorithm for multi-objective optimization combined with basic experimental assessments
• Investigated high alloyed AFA steels demonstrated excellent compatibility with heavy liquid metals (Pb and LBE) with no signs of corrosion at 600°C after 5000h and even no liquid metal embrittlement (LME) under application relevant loading conditions
• First datasets on high temperature mechanical behavior and thermal stability of REFERENCE materials generated in a comprehensive characterization programme including tensile, creep, fracture mechanics, low cycle fatigue and small punch testing
• Machine learning interatomic potentials developed for various INNUMAT relevant materials and used in molecular dynamics simulations of overlapping collision cascades and, hence, formation of primary defects due to irradiation
• Observation and modelling of radiation-induced elemental clustering/precipitation in complex, multiple element alloys
• Investigated high alloyed AFA steels demonstrated excellent compatibility with heavy liquid metals (Pb and LBE) with no signs of corrosion at 600°C after 5000h and even no liquid metal embrittlement (LME) under application relevant loading conditions
• First datasets on high temperature mechanical behavior and thermal stability of REFERENCE materials generated in a comprehensive characterization programme including tensile, creep, fracture mechanics, low cycle fatigue and small punch testing
• Machine learning interatomic potentials developed for various INNUMAT relevant materials and used in molecular dynamics simulations of overlapping collision cascades and, hence, formation of primary defects due to irradiation
• Observation and modelling of radiation-induced elemental clustering/precipitation in complex, multiple element alloys