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Projects / Programmes source: ARIS

Multiscale model of small crack initialization and propagation in pressure boundary components of a nuclear power plant

Research activity

Code Science Field Subfield
2.03.04  Engineering sciences and technologies  Energy engineering  Energy systems 

Code Science Field
T160  Technological sciences  Nuclear engineering and technology 
Keywords
life-time, safety, material properties, fatigue of material, propagation of short cracks
Evaluation (rules)
source: COBISS
Researchers (4)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  07025  PhD Leon Cizelj  Energy engineering  Researcher  2007 - 2009  963 
2.  04143  MSc Ljubo Fabjan  Energy engineering  Technical associate  2007 - 2009  177 
3.  21181  Zoran Petrič  Energy engineering  Researcher  2007 - 2009  15 
4.  19910  PhD Igor Simonovski  Mechanical design  Head  2007 - 2009  149 
Organisations (1)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0106  Jožef Stefan Institute  Ljubljana  5051606000  91,002 
Abstract
Most components of nuclear power plant's pressure boundary are exposed to time-variable loads during the operation. Pressure boundary separates primary, high-pressure system, from other parts of nuclear power plant. It is composed of pressure vessels, pipes, valves, etc. Structural integrity of the pressure boundary is of the outmost importance for the safe operation of a nuclear power plant. During the power plant operation, the time-variable loads will result in the fatigue (initialization and accumulation of damage) of material which has a direct impact on the life-time of the pressure boundary components. One of the first signs of damage in material is the initialization of microstructurally small cracks. Propagation of these cracks varies significantly as certain cracks are stopped by the grain boundaries while others continue to propagate and in time become macroscopic (long cracks). Initialization and propagation of microstructurally small cracks represents a significant portion of a component's life-time, up to 80%. This process is still not fully understood and tools for evaluation of these cracks are being intensely investigated. Since microstructurally small cracks are significantly influenced by the surrounding microstructural features, physical models of these cracks should account for polycrystalline structure and appropriate mechanism of deformation at this scale. The research group has already developed certain methods and tools for direct numerical simulation of a polycrystalline material. Among these are tools for generation of random Voronoi tessellations, for meshing of randomly shaped cells with finite elements and verified models of crystal plasticity. The latter are mainly appropriate for monotonic loads. Currently, tools for inclusion of microstructurally small cracks are under development. Due to the high complexity, the development of these models has been limited to monotonic loads. In the outlined research project we propose further development of the current methods that would result in significant improvements, enabling the inclusion of cyclically loaded cracks. In these work we will limit ourselves to steels used in pressure boundary of a nuclear power plant. The realization of the set project goals would significantly contribute to our understanding and modeling of initialization and propagation of microstructurally small cracks in metals. The anticipated dissemination of the results includes papers in SCI journals, contributions at scientific conferences, direct influence on Slovene and European post-graduate education and cooperation in the European network of excellence NULIFE.
Significance for science
The research is targeted into supporting safe operation of the current 2nd generation of nuclear power plants (within the designed life-time and foreseen extension of the life-time), construction and start-up of current 3rd generation nuclear power plants and towards supporting the planning of future, 4th generation nuclear power plants. The proposed research projects deals with ageing of stainless steel, widely used in nuclear power plants and is also material of choice for a number of components of the International Thermonuclear Experimental Reactor ITER. The thematics therefore deals with up to now still not fully understood problems in the areas of material ageing and structural mechanics. The research contributes to our understanding of short crack initialization and propagation in crystalline materials and contributes to our knowledge in fatigue of metals and alloys and improves our understanding of the origin of scatter in life-time of geometrically similar components. Scientific progress is made in the field of multiscale fracture mechanics which will undoubtedly have positive effects on potential structural issues in nuclear power plants and elsewhere. Understanding and modeling of ageing processes is one of the most important preconditions for assessment and control of ageing which is a crucial for both safe operation and license renewal of nuclear power plants. With expected extension of nuclear power plant life-time this subject will become even more important. At the same time acquired knowledge will also be applicable elsewhere in process industry and general construction.
Significance for the country
The common goal of the research is development of advanced simulation tools that will enable one to more reliably forecast the initialization and development of microstructurally short cracks. The potential effects of the research are related foremost to the acquired new knowledge in short crack initialization and development and consequentially improved assessment of the components’ life-times. The acquired basic knowledge and improved assessment of the components’ life-times will undoubtedly contribute to safer operation of components in nuclear power plants as well as in wider industry. In long-term this will have positive effects on reducing the operational costs and safer operation of industrial complexes. Associate professor dr. Leon Cizelj is part of the research team of this project. Prof. Leon Cizelj is teaching structural and fracture mechanics at the postgraduate study of nuclear engineering on the Faculty of Mathematics and Physics at the University of Ljubljana. The transfer of acquired knowledge to the students will positively influence the development of postgraduate studies. The research topic is also heavily present in the EU and in the world as a whole. The research project therefore increases national research in the area of fracture mechanics and development of multiscale models.
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