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The basic aim of researches is the creation and development of new knowledge. New insights are one of the most important drivers of progress and improvement of the safety of nuclear installations in the country and the world.

Research of Reactor Engineering Division is primarily focused on the development and application of advanced computer models and simulation tools. With these tools we can predict and understand the physical processes that are important for ensuring the safety of nuclear power plants. The main areas of our research are:

Heat and Mass Transfer

Nuclear reactors always have to be cooled. Most of today's reactors are cooled by water and steam. We are investigating possibilities of cooling future's reactors with gases, liquid metals or molten salts. Fluid flows, in contexts of intensive cooling, are generally highly turbulent and because of evaporation often two-phase. Our aim is to simulate such processes as accurately and as precisely as possible.

Streamlines in a channel between fuel pins.

Aging and integrity of safety-critical components

To contain the radioactive material within the reactor we use multiple successive barriers. Relatively high loads and various processes of aging (such as fatigue and stress corrosion cracking) can in several decades of operation of nuclear power plant lead to damage of these barriers. Microstructure has often a very important role in aging of metal materials. That is why we are investigating methods to predict the formation and development of cracks by considering random shapes and orientations of the crystal grains.

Model of a sainless steel wire.

Probabilistic safety assessment

Nuclear power plants are complex technological systems that include a vast number of different systems and components. They are designed and built to easily handle failures of individual systems. With probabilistic safety analyses we can estimate the vulnerability or reliability of power plant to combinations of such defects and failures. Increasingly, such vulnerability assessments are becoming the basis for optimization of investments in safety equipment. For that matter the Department explores ever more complex and accurate models as well as new simulation methods.

 Safety analysis in case of an attack.

Severe accidents

Nuclear reactors, as a result of spontaneous radioactive decay of fission products in the chain reaction, still produce decay heat after shutdown. Therefore it is also necessary to cool an already shut down reactor. If we fail to do this, the reactor will begin to overheat and sooner or later it will melt, leading to a severe accident. Furthermore, overheating of the reactor itself as well as the contact of melted fuel with concrete can release significant amounts of hydrogen. In the Department, we explore methods for predicting the spread and control of hydrogen without explosions. We also investigate steam explosions which could occur when molten nuclear fuel comes into contact with cold water.

Development of models and computer simulations is supported by occasional experimental work of our colleagues in the European experimental facilities (sponsored by the European Commission). We regularly participate in international projects of the European Commission and the OECD/NEA through which we gain access to the results of relevant experiments.

In the past our primary focus was on modelling processes in reactors of 2nd generation (i.e. those that are now in operation). Recently, however, we also focus on the processes in the reactors of 3rd (under construction, e.g. Olkiluoto 3 in Finland) and 4th generation (which are in development). We are also modelling processes in the experimental fusion reactor - ITER which is being built in the French research centre of Cadarache. Spillovers of knowledge and experience between different reactor concepts are very welcome for the rapid development of knowledge and the improvement of nuclear safety. Usually operators of nuclear power plants focus on gaining experience only in similar reactor types.

Learn more about our researches.


Page editor: Matic Kunšek

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EMUG meeting
Previous week, between April 12 and 14, the EMUG (European MELCOR and MACCS User Group) meeting was held in Slovenia, organized by the Reactor Engineering Division, JSI in cooperation with the Paul Scherrer Institute from Switzerland. The meeting was a...
Grain boundary stresses in elastic materials
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New experimental campaign - Investigation of Temperature Fluctuations in a Fully Developed Channel Flow
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Dr. Samir El Shawish and dr. Timon Mede from the Reactor Engineering Division at Jožef Stefan Institute, in collaboration with dr. Jeremy Hure from Université Paris-Saclay, CEA (France) published the article &l...
Modelling of premixed layer formation in stratified fuel–coolant configuration
Janez Kokalj, dr. Mitja Uršič and dr. Matjaž Leskovar from the Reactor Engineering Division at Jožef Stefan Institute published the article »...
Validation of a morphology adaptive multi-field two-fluid model considering counter-current stratified flow with interfacial turbulence damping
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