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Leon Cizelj

Division Head
Scientific Councilor

Jožef Stefan
Jamova cesta 39
1000 Ljubljana

Phone: +386 1 5885 330
Fax: +386 1 5885 377



Research Interests

  • Safety of nuclear facilities.
  • Safety and reliability of complex technologies.
  • Integrity and Ageing of safety related components of nuclear power plants.
  • Computational solid and fluid mechanics.
  • Computational fracture mechanics.
  • Computational micromechanics.
  • Multiscale and multiphysics computations.




Professor of Nuclear Engineering, Faculty of Mathematics and PhysicsUniversity of Ljubljana. Subjects:

  • 2nd Bologna Cycle (M.Sc., SARENA project - ERASMUS Mundus)
    • Materials in Nuclear Engineering 
    • Nuclear Safety
  • 2nd Bologna Cycle (M.Sc.):
    • Structural mechanics in nuclear engineering (6 ECTS)
    • fracture mechanics (6 ECTS)
  • 3rd Bologna Cycle (Ph.D.)
    • Mechanics of nuclear structures and materials (10 ECTS)

Recordings of lectures and broadcasts

Professional Experience

  • Development and application of multiscale and methods in the mechanics of solids, fluids and fracture;
  • Development and application of probabilistic fracture mechanics techniques;
  • Finite element modeling and analysis of complex geometries and nonlinear materials(ABAQUS);
  • Quality assurance and standardization in finite element methods (NAFEMS);
  • Guest researcher with the Research Center Karlsruhe, Germany, Institute for Materials Research, 1.11.1993 - 30.4.1994;
  • System administration of Unix and Windows workstations and small networks.
  • Consulting to Nuklearna elektrarna Krško;
  • Consulting to the European Commission (Directorate general for research and innovation).
  • Consulting to the US Nuclear Regulatory Commission (US NRC).
  • Participation in the technical committees of the IAEA.
  • Participation in the technical committees of the OECD/NEA.

Management Experience

  • President of European Nuclear Society 2022-2023.
  • Member of the supervisory board of Slovenian sovereign holding SDH d.d. (2021-2025).
  • President of the Board Of Directors of the ENEN Association (European Nuclear Education Network, 2016-2017; member 2010-2012, 2015-2017).
  • Strategic and operational management of the Reactor Engineering Department: research group with 30 members, active in international environment (2010-2013, 2014-2018).
  • Representative of Slovenia in the Consultative Committe EURATOM Fission (CCE-FISSION, 2011-2013).
  • Member of the Scientific Council of the Jožef Stefan Institute (2012-2013, 2014-2018).
  • Member of the Scientific Council for Technology at the Slovenian Research Agency ARRS (2006-2011, 2016-2021).
  • President of the Management Board of ARAO (2013-2016).
  • Member of the Governing Board of the Sustainable Nuclear Technology Platform (SNETP, 2013-2015-2017).
  • Member of the Education Training and Knowledge Management working groups of the Sustainable Nuclear Technology Platform (SNETP, 2010-2012-2015-2017).
  • Vicepresident Supervisory Board Gen Energija d.o.o. (2012-2013).
  • Vicepresident Supervisory Board ELES d.o.o. (2006-2008).Member of the Committee for Intelectual Property of the Jožef Stefan Institute (since 1998).
  • The organizer of various international conferences.
  • Principal scientist of various international research projects.


Professional Societys

  • Nuclear Society of Slovenia
    • Founding Member (1991)
    • Member of the Governing Board (1998-2002, 2006-2010).
    • Member of the Supervizory Board(1996-1998).
  • Slovenian Academic Society for Science and Engineering SATENA
    • Member of the executive board (2009-2010, 2013-2015-2017).
    • Vicepresident (2010-2011 in 2012-2013).
    • President (2011-2012).
  • European Nuclear Society ENS (European Nuclear Society)
  • American Society of Mechanical Engineers ASME:



Member of the editorial board

Selected Publications

The full list of publications is maintained by COBISS. Links to publications use the Digital Object Identifier System DOI.

ORCID: 0000-0002-8038-722X;
Scopus Author ID: 7004372090;
ResearcherID: A-3537-2008.

Books, Chapters in Books

CIZELJ, Leon, SIMONOVSKI, Igor. Microstructurally Short Cracks in Polycrystals Described by Crystal Plasticity, (Materials science and technologies). New York: Nova Science Publishers, cop. 2010. XII, 77 str., ilustr. (nekaj barv.). ISBN 978-1-61668-811-0. ISBN 1-61668-811-4.

SIMONOVSKI, Igor, CIZELJ, Leon. Grain-scale modeling approaches for polycrystalline aggregates. V: TODOROV ZACHARIEV, Zachary (ur.). Polycrystalline materials - theoretical and practical aspects. Rijeka: InTech, cop. 2011, str. 49-74.

CIZELJ, Leon, ROUSSEL, Guy. Reliability of degraded steam generator tubes. V: UCHANIN, Valentin (ur.). Steam generator systems : operational reliability and efficiency. Rijeka: In-Tech, cop. 2011, str. 117-142.

Articles in SCI Journals

EL SHAWISH, Samir, CIZELJ, Leon. Numerical investigation of grain misorientations at and close to the free surface of FCC polycrystalline metals. Computational materials science, 2016, vol. 113, pp. 133-142, doi: 10.1016/j.commatsci.2015.11.032.

GARRIDO, Oriol Costa, EL SHAWISH, Samir, CIZELJ, Leon. Uncertainties in the thermal fatigue assessment of pipes under turbulent fluid mixing using an improved spectral loading approach. International journal of fatigue,  2016, vol. 82, no. 3, pp. 550-560, doi: 10.1016/j.ijfatigue.2015.09.010.

CIZELJ, Leon. Research and higher education : a disposable part of fundamental national infrastructure. International journal of contemporary energy, 2015, vol. 1, no. 1, pp. 5-12, doi: 10.14621/ce.20150102.

GARRIDO, Oriol Costa, EL SHAWISH, Samir, CIZELJ, Leon. Stress assessment in piping under synthetic thermal loads emulating turbulent fluid mixing. Nuclear engineering and design, 2015, vol. 283, pp. 114-130, doi: 10.1016/j.nucengdes.2014.10.016.

SIMONOVSKI, Igor, CIZELJ, Leon. Cohesive zone modeling of intergranular cracking in polycrystalline aggregates. Nuclear engineering and design, 2015, vol. 283, pp. 139-147, doi: 10.1016/j.nucengdes.2014.09.041.

MATKOVIČ, Marko, CIZELJ, Leon, PROŠEK, Andrej. Characterization of a spent-fuel-pit rupture based on water-level monitoring. Annals of Nuclear Energy, 2014, vol. 63, pp. 674-679, doi: 10.1016/j.anucene.2013.09.002.

DRAKSLER, Martin, NIČENO, Bojan, KONČAR, Boštjan, CIZELJ, Leon. Large eddy simulation of multiple impinging jets in hexagonal configuration - Mean flow characteristics. International journal of heat and fluid flow, 2014, vol. 46, pp. 147-157, doi: 10.1016/j.ijheatfluidflow.2014.01.00.

VOLKANOVSKI, Andrija, CIZELJ, Leon. Nuclear power plant maintenance optimization with heuristic algorithm. Science and Technology of Nuclear Installations, 2014, vol. 2014, pp. 458016-1-458016-13, doi: 10.1155/2014/458016.

SIMONOVSKI, Igor, CIZELJ, Leon. Cohesive element approach to grain level modelling of intergranular cracking. Engineering fracture mechanics, 2013, vol. 110, pp. 364-377, doi: 10.1016/j.engfracmech.2013.05.011.

TISELJ, Iztok, ODER, Jure, CIZELJ, Leon. Double-sided cooling of heated slab : conjugate heat transfer DNS. International journal of heat and mass transfer, 2013, vol. 66, pp. 781-790, doi: 10.1016/j.ijheatmasstransfer.2013.07.076.

SIMONOVSKI, Igor, CIZELJ, Leon, GARRIDO, Oriol Costa. The influence of the grain boundary strength on the macroscopic properties of a polycrystalline aggregate. Nuclear Engineering and Design, 2013, vol. 261, pp. 362-370, doi: 10.1016/j.nucengdes.2012.12.007.

EL SHAWISH, Samir, CIZELJ, Leon, SIMONOVSKI, Igor. Modeling grain boundaries in polycrystals using cohesive elements : modeling grain boundaries in polycrystals using cohesive elements. Nuclear Engineering and Design, 2013, vol. 261, pp. 371-381, doi: 10.1016/j.nucengdes.2013.01.023.

GARRIDO, Oriol Costa, CIZELJ, Leon, EL SHAWISH, Samir. The role of the axial heat fluxes in the thermal fatigue assessment of piping. Nuclear Engineering and Design, 2013, vol. 261, pp. 382-393, doi: 10.1016/j.nucengdes.2013.01.024.

KOSTEVŠEK, Anja, CIZELJ, Leon, PETEK, Janez, PIVEC, Aleksandra. A novel concept for a renewable network within municipal energy systems. Renewable energy, I2013, vol. 60, pp. 79-87, doi: 10.1016/j.renene.2013.04.013. [

PROŠEK, Andrej, CIZELJ, Leon. Long-term station blackout accident analyses of a PWR with RELAP5/MOD3.3. Science and Technology of Nuclear Installations, 2013, vol. 2013, pp. 851987-1- 851987-15, doi: 10.1155/2013/851987.

TISELJ, Iztok, CIZELJ, Leon. DNS of turbulent channel flow with conjugate heat transfer at Prandtl number 0.01. Nucl. Eng. Des., 2012, vol. 253, pp. 153-160, doi: 10.1016/j.nucengdes.2012.08.008.

ORIOL, Costa, TISELJ, Iztok, CIZELJ, Leon. Depressurization of vertical pipe with temperature gradient modeled with WAHA code. Sci. Technol. Nucl. Install. (Print), 2012, vol. 2012, pp. 951923-1-951923-9, doi: 10.1155/2012/951923.

SIMONOVSKI, Igor, CIZELJ, Leon. Automatic parallel generation of finite element meshes for complex spatial structures. Comput. mater. sci., 2011, vol. 50, no. 5, pp. 1606-1618, doi: 10.1016/j.commatsci.2010.12.014.

SIMONOVSKI, Igor, CIZELJ, Leon. Computational multiscale modeling of intergranular cracking. J. nucl. mater., 2011, vol. 414, no. 2, pp. 243-250, doi: 10.1016/j.jnucmat.2011.03.051.

CIZELJ, Leon, SIMONOVSKI, Igor. Fatigue relevance of stratified flows in pipes : a parametric study. Nucl. Eng. Des., 2011, vol. 241, no. 4, pp. 1191-1195, doi: 10.1016/j.nucengdes.2010.03.030.

SIMONOVSKI, Igor, CIZELJ, Leon. Towards modeling intergranular stress corrosion cracks on grain size scales. Nucl. Eng. Des., 2012, vol. 246, pp. 107-114, doi: 10.1016/j.nucengdes.2011.08.032.

GARRIDO, Oriol Costa, CIZELJ, Leon, SIMONOVSKI, Igor. Modular 3-D solid finite element model for fatigue analyses of a PWR coolant system. Nucl. Eng. Des., 2012, vol. 246, pp. 115-122, doi: 10.1016/j.nucengdes.2011.06.038.

SIMONOVSKI, Igor, KONČAR, Boštjan, CIZELJ, Leon. Thermo-mechanical analysis of a DEMO divertor cooling finger under the EFREMOV test conditions. Fusion eng. des., 2010, vol. 85, no. 1, pp. 130-137, doi: 10.1016/j.fusengdes.2009.08.005.

SIMONOVSKI, Igor, CIZELJ, Leon, JAKŠIĆ, Nikola. The influence of finite element meshes on the results of a spatial polycrystalline aggregate model. Nucl. Eng. Des., 2011, vol. 241, no. 4, pp. 1184-1190, doi: 10.1016/j.nucengdes.2010.05.063.

SIMONOVSKI, Igor, NILSSON, Karl-Fredrik, CIZELJ, Leon. The influence of crystallographic orientation on crack tip displacements of microstructurally small, kinked crack crossing the grain boundary. Comput. mater. sci., 2007, vol. 39, no. 4, pp. 817-828, doi: 10.1016/j.commatsci.2006.10.005.

SIMONOVSKI, Igor, NILSSON, Karl-Fredrik, CIZELJ, Leon. Crack tip displacements of microstructurally small cracks in 316L steel and their dependence on crystallographic orientations of grains. Fatigue fract. eng. mater. struct., 2007, vol. 30, no. 6, pp. 463-478, doi: 10.1111/j.1460-2695.2007.01098.x.

SIMONOVSKI, Igor, CIZELJ, Leon. The influence of grains' crystallographic orientations on advancing short crack : [presented at Fatigue Damage of Structural Materials VI, The Sixth International Conference on Fatigue Damage of Structural Materials, 17-22 September 2006, Hyannis, MA, USA]. Int. j. fatigue, 2007, vol. 29, no. 9-11, pp. 2005-2014, doi: 10.1016/j.ijfatigue.2007.01.030.

ROUSSEL, Guy, CIZELJ, Leon. Reliability of sampling inspection schemes applied to replacement steam generators. J. press. vessel technol., 2007, vol. 129, no. 1, pp. 109-117, doi: 10.1115/1.2389027.

ČEPIN, Marko, CIZELJ, Leon, LESKOVAR, Matjaž, MAVKO, Borut. Vulnerability analysis of a nuclear power plant considering detonations of explosive devices. J. Nucl. Sci. Technol., 2006, vol. 43, no. 10, pp. 1258-1269, doi: 10.1080/18811248.2006.9711219.

CIZELJ, Leon, KONČAR, Boštjan, LESKOVAR, Matjaž. Vulnerability of a partially flooded PWR reactor cavity to a steam explosion. Nucl. Eng. Des., 2006, vol. 236, no. 10, pp. 1617-1627, doi: 10.1016/j.nucengdes.2006.04.018.

KOVAČ, Marko, CIZELJ, Leon. Modeling elasto-plastic behavior of polycrystalline grain structure of steels at mesoscopic level. Nucl. Eng. Des., 2005, vol. 235, pp. 1939-1950, doi: 10.1016/j.nucengdes.2005.05.009.

SIMONOVSKI, Igor, KOVAČ, Marko, CIZELJ, Leon. Estimating the correlation length of inhomogeneities in apolycrystalline material. Mater. sci. eng., A Struct. mater. : prop. microstruct. process., 2004, vol. 381, pp. 273-280, doi: 10.1016/j.msea.2004.04.046.

CIZELJ, Leon, ROUSSEL, Guy. Probabilistic evaluation of leak rates through multiple defects : the case of nuclear steam generators. Fatigue fract. eng. mater. struct., 2003, vol. 26, pp. 1069-1079, doi: 10.1046/j.1460-2695.2003.00692.x.

WEYER, Stefan, FROHLICH, Andreas, RIESCH-OPPERMANN, Heinz, CIZELJ, Leon, KOVAČ, Marko. Automatic finite element meshing of planar Voronoi tessellations. Eng. fract. mech., 2002, vol. 69, pp. 945-958, doi: 10.1016/S0013-7944(01)00124-2.

CIZELJ, Leon, RIESCH-OPPERMANN, Heinz. Modelling the early development of secondary side stress corrosion cracks in steam generator tubes using incomplete random tessellation. Nucl. Eng. Des., 2002, vol. 212, pp. 21-29, doi: 10.1016/S0029-5493(01)00474-5.

DVORŠEK, Tomaž, CIZELJ, Leon, MAVKO, Borut. Safety and availability of steam generator tubes affected by secondary side corrosion. Nucl. Eng. Des., vol. 185, pp. 11-21, doi: 10.1016/S0029-5493(98)00228-3.

CIZELJ, Leon, HAUER, Irena, ROUSSEL, G., CUVELLIEZ, C. Probabilistic assessment of excessive leakage through steam generator tubes degraded by secondary side corrosion. Nucl. Eng. Des., 1998, vol. 185, pp. 347-359, doi: 10.1016/S0029-5493(98)00229-5.

CIZELJ, Leon, RIESCH-OPPERMANN, Heinz. Stresses in the first wall of a dual-coolant liquid-metal breeder blanket during electron-beam welding. Fus. technol., 1997, vol. 32, pp. 14-22.

CIZELJ, Leon, MAVKO, Borut, VENCELJ, P. Reliability of steam generator tubes with axial cracks. J. press. vessel technol., 1996, vol. 118, pp. 441-446, doi: 10.1115/1.2842211.

CIZELJ, Leon, MAVKO, Borut, RIESCH-OPPERMANN, H., BRÜCKNER-FOIT, A. Propagation of stress corrosion cracks in steam generator tubes. Int. j. press. vessels piping, 1995, vol. 63, pp. 35-43, doi: 10.1016/0308-0161(94)00046-L.

CIZELJ, Leon, MAVKO, Borut. On the risk-based steam generator lifetime optimisation. Theor. appl. fract. mech., 1995, vol. 23, pp. 129-137, doi: 10.1016/0167-8442(95)00013-5.

CIZELJ, Leon, MAVKO, Borut, RIESCH-OPPERMANN, H. Application of first and second order reliability methods in the safety assessment of cracked steam generator tubing. Nucl. Eng. Des., 1994, vol. 147, pp. 359-368, doi: 10.1016/0029-5493(94)90218-6.

MAVKO, Borut, CIZELJ, Leon. Failure probability of axially cracked steam generator tubes : A probabilistic fracture mechanics model. Nucl. technol., 1992, vol. 98, pp. 171-177.


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