Jožef Stefan Institute

The Jožef Stefan Institute (JSI) is the leading Slovenian scientific research institute, covering a broad spectrum of basic and applied research. The staff of around 800 specialises in natural sciences, life sciences and engineering. The main subjects concern production and control technologies, communication and computer technologies, knowledge technologies, biotechnologies, new materials, environmental technologies, nanotechnologies, and nuclear engineering.
The Reactor Engineering Division at JSI concentrates on research, education, consulting and expertise in nuclear engineering and nuclear safety of nuclear fission reactors and nuclear fusion reactors. The research focuses on computational modeling of physical processes, which are important for the operation and safety of nuclear power plants.
The Integrity and Ageing Group under Reactor Engineering Division has relevant expertise in multiscale modeling of intergranular/intragranular damage, in developing models of cracks in complex conditions, and in mechanical behavior prediction of LWR’s internals based on microstructure-informed modeling. The group has been participating in national and several bilateral projects with CEA on the above-mentioned topics.

Role in the project

The JSI is participating in collaboration with JRC-IET in WP5 (modeling and simulations) on two tasks: Development of physically based constitutive models, and Grain-level models of IASCC.

Development of physically based constitutive models
The intention of the first task is to develop and calibrate suitable crystal plasticity constitutive law that would be sensitive to irradiation dose and to measure grain boundary fracture properties and use them to calibrate the cohesive zone constitutive law for grain boundaries. The adaptation of crystal plasticity constitutive law is an incremental development of the already available constitutive model (i.e., Huang implementation in Abaqus with Bassani and Wu hardening) which is expected to be more efficient compared to developing a model from scratch. The experimental part devoted to measuring grain boundary properties will be performed by JRC-IET. A grain-level FEM model will then be used by JSI to calibrate the cohesive law to the measured response. A database of different grain boundary properties would then be created.

Grain-level models of IASCC
Grain-level models of intergranular cracking can account for microstructure, crack initiation and coalescence and can give useful statistical insight into IASCC during both initiation and coalescence stages. JSI and JRC-IET already have a grain-level model that can simulate intergranular cracking and branching due to a mechanical overload of grain boundaries. The model is able to use either simulated grain structures or measured, realistic structures. The model will be further developed to incorporate the irradiation and oxidation effects on the grain boundary degradation and initiation and evolution of intergranular cracking. The task will be to improve the calibration of the cohesive zone model for grain boundaries, incorporate irradiation effects into the crystal plasticity law and link oxidation effects to degradation of grain boundary properties. The work is an incremental development, targeting irradiation and corrosion response. Irradiation data and oxide penetration is expected to be available during the project, integrating well with the proposed model development. The model will represent a tool for statistical assessment of IASCC initiation, branching and coalescence on the grain-level scale.

Personnel involved

Leon Cizelj, Associate professor of nuclear engineering and scientific councilor at JSI
Ph.D. physics, University of Ljubljana, 1993. Head of Reactor Engineering Division at JSI. Research interests include integrity and ageing of safety related components of NPP; computational solid, fluid and fracture mechanics; multiscale and multiphysics computations.
Member of the editorial board European Journal of Phyiscs Nuclear, Science and Technology of Nuclear Installations and Journal of Nuclear Engineering and Radiation Science ASME.
Member of the Scientific Council for Technology at the Slovenian Research Agency ARRS, 2006-11,2016-21; member of the Governing Board of SNETP, 2013-17; member of the Board of Directors of ENEN Association, 2010-12, 2014-17.
Role in the project: responsible for the JSI contribution to WP5.
Leon Cizelj


Available Documentation

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