Periodic Reporting for period 2 - OperaHPC (OPEn HPC theRmomechanical tools for the development of eAtf fuels)
Reporting period: 2024-05-01 to 2025-10-31
Electrification of the energy sector will be a key step for its transition to climate-neutrality. In order to achieve it by 2050, it will be necessary to maintain and even extend the production capacity of current nuclear reactors, while taking into account the evolving electricity mix and increasing requirements regarding the safety assessment of nuclear reactors. On these points, the question of nuclear fuel behaviour is essential because it sets the main constraints to be satisfied for safe operation of nuclear reactors and defines the source term for accidental conditions.
Generation II and III reactor fuels in Europe take advantage of a large experimental feedback with a continuous evolution of fuel element design and materials, which allows maintaining high safety standards while adapting to the evolution of the operating conditions. Fuel performance codes, which enable the simulation of the behaviour of the fuel elements in reactor, are an essential component of the design, licensing and safety assessment of nuclear fuels. The licensing of innovative materials and fuel design requires an extension of the industrial fuel performance codes qualification in order to meet safety authority’s requirement regarding the Verification, Validation and Uncertainties Quantification process.
To address this question, the OperaHPC project will work on advanced simulation tools enabling 3D representation of the fuel rod, including models with fewer empirical parameters and taking advantage of a new generation of software environments. The research activity is decomposed on four axes:
1) A basic research activity devoted to the fuel element mechanical behaviour with a focus on the impact of irradiation on oxides fuel properties. This work will provide missing data, an identification of elementary mechanisms and the development of physics-based models of the non-linear mechanical behaviour of fuel and cladding.
2) The development of open source fuel performance codes with an advanced simulation at the two relevant scales needed to describe the microstructure and the fuel rod. The simulation will provide a 3D geometrical description of the thermo-mechanical behaviour and high performance computing capabilities.
3) The improvement of the current industrial models with learning data bases, composed of 3D reference simulation results, and Machine Learning type techniques. The demonstration of the capacity of 3D simulation and improved modelling for a set of representative industrial studies for PWR and VVER including flexible operating conditions and enhanced Accident Tolerant Fuel.
4) The education and training and dissemination of the project’s results through open-access publications, workshops and exchanges with industrial end-users and training of a new generation of researchers.
Generation II and III reactor fuels in Europe take advantage of a large experimental feedback with a continuous evolution of fuel element design and materials, which allows maintaining high safety standards while adapting to the evolution of the operating conditions. Fuel performance codes, which enable the simulation of the behaviour of the fuel elements in reactor, are an essential component of the design, licensing and safety assessment of nuclear fuels. The licensing of innovative materials and fuel design requires an extension of the industrial fuel performance codes qualification in order to meet safety authority’s requirement regarding the Verification, Validation and Uncertainties Quantification process.
To address this question, the OperaHPC project will work on advanced simulation tools enabling 3D representation of the fuel rod, including models with fewer empirical parameters and taking advantage of a new generation of software environments. The research activity is decomposed on four axes:
1) A basic research activity devoted to the fuel element mechanical behaviour with a focus on the impact of irradiation on oxides fuel properties. This work will provide missing data, an identification of elementary mechanisms and the development of physics-based models of the non-linear mechanical behaviour of fuel and cladding.
2) The development of open source fuel performance codes with an advanced simulation at the two relevant scales needed to describe the microstructure and the fuel rod. The simulation will provide a 3D geometrical description of the thermo-mechanical behaviour and high performance computing capabilities.
3) The improvement of the current industrial models with learning data bases, composed of 3D reference simulation results, and Machine Learning type techniques. The demonstration of the capacity of 3D simulation and improved modelling for a set of representative industrial studies for PWR and VVER including flexible operating conditions and enhanced Accident Tolerant Fuel.
4) The education and training and dissemination of the project’s results through open-access publications, workshops and exchanges with industrial end-users and training of a new generation of researchers.
During the first 36 months of the project, the technical activities yielded numerous results on schedule.
The creep test device has been designed, fabricated and successfully qualified on an inert material. The next steps are to complete the qualification on fresh UO2 and then to install the test device in a hot cell of the LECA-STAR laboratory of CEA in order to obtain essential results on the creep behaviour irradiated UO2 fuel. The samples that will be tested mechanically were characterized in detail at the grain and dislocation scale. In parallel, atomic scale calculations and Dislocation Dynamic simulations brought significant results on the mobility of dislocations and their interaction with irradiation defects in UO2. A first model to assess mechanical hardening induced by irradiation in fuel has been developed and implemented in a crystal plasticity model. Then, the investigations of rupture processes at the atomic scale have made significant progress.
New mechanical laws for the fuel and the cladding to be implemented in fuel performance codes are available. For Cr-coated cladding, an interpretation of the FIDES/INCA experiments has confirmed the recommendation proposed in the open literature. A new micromechanical modelling, including creep and fracture, has been proposed for fuel at the microstructure scale. The corresponding formulation includes a new law with hardening induced by irradiation in fuel.
High Performance Computing simulation tools for the fuel element behaviour in the reactor at the engineering scale (OFFBEAT/SCIANTIX codes) and at the microstructure scale (MMM code) have been developed after the publication of the quality assurance protocols to be used in the project. The new developments include improvement of the models for fission gas behaviour, large strain mechanical formulation, pellet-cladding contact, cladding oxide layer, RIA transients and fuel micromechanical modelling. The verification process of the current version of the codes is completed and significant results are available for the validation. For the integration of these HPC fuel performance codes in the existing simulation tools framework, new assessments and data transfer methods are available. The industrial models to improve have been selected, as well as the methodology to improve them.
The preparation of the learning databases and the development of corresponding Machine Learning Models has progressed well. Finally, all the input data for the fuel element safety studies are ready, they include new core scale simulation results for VVER and the selection of international benchmark data for PWR. These data will enable fuel behaviour analysis under nominal and designed basis accident conditions for state of the and eATF fuels.
The creep test device has been designed, fabricated and successfully qualified on an inert material. The next steps are to complete the qualification on fresh UO2 and then to install the test device in a hot cell of the LECA-STAR laboratory of CEA in order to obtain essential results on the creep behaviour irradiated UO2 fuel. The samples that will be tested mechanically were characterized in detail at the grain and dislocation scale. In parallel, atomic scale calculations and Dislocation Dynamic simulations brought significant results on the mobility of dislocations and their interaction with irradiation defects in UO2. A first model to assess mechanical hardening induced by irradiation in fuel has been developed and implemented in a crystal plasticity model. Then, the investigations of rupture processes at the atomic scale have made significant progress.
New mechanical laws for the fuel and the cladding to be implemented in fuel performance codes are available. For Cr-coated cladding, an interpretation of the FIDES/INCA experiments has confirmed the recommendation proposed in the open literature. A new micromechanical modelling, including creep and fracture, has been proposed for fuel at the microstructure scale. The corresponding formulation includes a new law with hardening induced by irradiation in fuel.
High Performance Computing simulation tools for the fuel element behaviour in the reactor at the engineering scale (OFFBEAT/SCIANTIX codes) and at the microstructure scale (MMM code) have been developed after the publication of the quality assurance protocols to be used in the project. The new developments include improvement of the models for fission gas behaviour, large strain mechanical formulation, pellet-cladding contact, cladding oxide layer, RIA transients and fuel micromechanical modelling. The verification process of the current version of the codes is completed and significant results are available for the validation. For the integration of these HPC fuel performance codes in the existing simulation tools framework, new assessments and data transfer methods are available. The industrial models to improve have been selected, as well as the methodology to improve them.
The preparation of the learning databases and the development of corresponding Machine Learning Models has progressed well. Finally, all the input data for the fuel element safety studies are ready, they include new core scale simulation results for VVER and the selection of international benchmark data for PWR. These data will enable fuel behaviour analysis under nominal and designed basis accident conditions for state of the and eATF fuels.
The results obtained in the first 36 months constitute significant progress beyond the state of the art.
The experimental data coupled with a physically based approach provide a first information for separate effect validation required from the safety authority for the fuel performance codes. The development of physics-based models provided a complete set of widely shared mechanical laws for the pellet and the cladding.
One of the project’s major objective is almost completed: two open source computational tools including a 3D description and physics based models are available for a large community. The portability on HPC is in progress.
The computation of learning databases from 3D reference simulation results and the use of Machine Learning techniques will bring important tools to go beyond the current industrial modelling limitations.
The demonstration of the capacity of 3D simulation to model a set of representative industrial conditions for PWR and VVER, including flexible operating conditions and eATF, is ready to start. The reinforcement of the impact of this applicative part is shared with the End User Group of the project.
Finally, the significant number of PhD students involved in OperaHPC, the summer schools coorganized by the project, the exchange scheme and the open science approach, constitute a significant contribution to the training of the next generation of researchers on fuels and fuel performance codes.
The experimental data coupled with a physically based approach provide a first information for separate effect validation required from the safety authority for the fuel performance codes. The development of physics-based models provided a complete set of widely shared mechanical laws for the pellet and the cladding.
One of the project’s major objective is almost completed: two open source computational tools including a 3D description and physics based models are available for a large community. The portability on HPC is in progress.
The computation of learning databases from 3D reference simulation results and the use of Machine Learning techniques will bring important tools to go beyond the current industrial modelling limitations.
The demonstration of the capacity of 3D simulation to model a set of representative industrial conditions for PWR and VVER, including flexible operating conditions and eATF, is ready to start. The reinforcement of the impact of this applicative part is shared with the End User Group of the project.
Finally, the significant number of PhD students involved in OperaHPC, the summer schools coorganized by the project, the exchange scheme and the open science approach, constitute a significant contribution to the training of the next generation of researchers on fuels and fuel performance codes.