Reactor Engineering R4


Research departments
Administration and support units


The Reactor Engineering Division was founded in 1984 although its scientific origin lies back in the history of the Jožef Stefan Institute. Today, the Reactor Engineering Division plays a leading role on the nuclear energy stage in Slovenia. The Reactor Engineering Division activities are focused mainly on fundamental and applied nuclear engineering and safety research, with special emphasis on the safe operation of the Krško nuclear power plant.

Most of the research activities are conducted jointly with partners abroad through several forms of international cooperation and multilateral projects. In addition, the division’s staff significantly contributes to the post-graduate program in Nuclear Engineering, which is jointly conducted by the University of Ljubljana, Faculty of Mathematics and Physics, and the Jožef Stefan Institute.


  • Thermal-hydrodynamics
    • Modeling of basic thermal-hydrodynamical phenomena
    • Modeling of severe accidents
    • Thermal-hydrodynamical safety analyses
  • Structural mechanics
    • Simulations of intergranular cracking
    • Deterministic and probabilistic structural safety analyses
  • Reliability, industrial hazard and risk
    • Risk and uncertainty analyses
    • Probabilistic safety analyses

Departmental web pages

Head of Department
Prof. Leon Cizelj, Ph. D.,

Tanja Klopčič,
Telephone: + 386 1 588 53 31

The division research activities belong to the wider field of nuclear engineering and safety. This interdisciplinary research integrates thermal-hydrodynamical, structural and probabilistic safety analyses.

The goal of the research of thermal-hydrodynamical phenomena is to improve the accuracy of their modeling as well as to assess the uncertainty of computer simulations and predictions of transients in nuclear power plants. Understanding the physics of thermal-hydrodynamical phenomena enables the development of new methods for risk assessment and improves necessary mitigation measures in the case of a severe accident. The research topics involve heat transfer in turbulent flow, convective boiling, stratified gas-liquid flow, atmosphere mixing and stratification, and fuel-coolant interactions that may lead to steam explosions. The studies consider different types of power generation facilities. Analyses take into account the interacting influences of environmental requirements and technical characteristics, to optimize their safe and efficient operation.

Structural safety analyses are primarily aimed at degradation processes that can limit the time frame in which nuclear power plants components can safely operate. Initially, these degradation processes initiate microscopically small material damages which are not accounted for by macroscopic engineering tools employed for determination of load carrying capabilities or life-time estimation. The goal of this research are new models with capacity to forecast the progressive development of microscopic damages within the material and their further corresponding effects on the macroscopic behavior of components.

Probabilistic safety assessment is becoming an essential tool for assessment and improvement of safety, as well as reduction of risk in complex systems. The objective of this research is to develop new methods, which will take into account additional parameters, including time, and which will enable a better assessment of risks associated with new technologies. One of the research priorities is to develop a method for identification, assessment and analysis of human contribution to the reliability of complex technologies.

J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia, Telephone: +386 1 477 39 00