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Generation IV. Nuclear Reactors and Small Nuclear Reactors

We deal with R&D activities for nuclear reactors, new generation nuclear reactors (GenIV) and recently also for small nuclear reactors. We develop our activities in line with the needs of energy development in the Czech Republic.

The research of the new generation reactors in ÚJV Řež currently focuses on the preparatory phase of the ALLEGRO project, i.e. a demonstrator of a helium-cooled high-temperature fast reactor (GFR - Gas Fast Reactor).

The Nuclear Safety and Reliability Division also works on the research of small nuclear reactors and the possibilities of their use in the Czech Republic's energy sector, with an emphasis on central heat supply.

R&D in the field of reactors

The research of new generation reactors at ÚJV Řež is currently focused on the development of the concept of the demonstrative high-temperature reactor ALLEGRO with a fast spectrum of neutrons cooled by helium (GFR - Gas Fast Reactor) within the international association "V4G4 Center of Excellence".

In the context of this project, we develop activities in the following areas:

Concept and safety of reactors:

We assess existing Generation IV. reactor concepts, we propose new concepts, including detailed technical solutions. We perform thermohydraulic calculations of primary circuit behavior in operational and emergency conditions, we analyze the course and consequences of a severe accident with the core melting, we solve problems of using PSA methods in the evaluation of these reactors.

Technological and experimental support:

We provide expert support for helium technology including the design of experimental devices for verification and validattion of computational tools and for verifying operating modes and technology systems.

In parallel with the above mentioned technical activities, we analyze the legislative and economic aspects of the application of Generation IV. reactors in the Czech Republic.

We are preparing several follow-up research activities in the following areas:

  • Material research,
  • Fuel cycle (thermomechanical analyses of the fuel for ALLEGRO),
  • Waste minimization and treatment,
  • Development of computational tools and models for the description and evaluation of operational and safety characteristics, including probability characteristics.

Recently, small nuclear reactors with a power output of up to 300 MWe and their application to provide energy supplies are of interest in the world.

The development and deployment of small reactors is supported by the International Atomic Energy Agency (IAEA) for use in countries with poorly developed electricity production. Industrialized countries are developing small nuclear reactors in particular as an ecological and sustainable alternative to fossil fuel and gas fired plants.

Research at ÚJV Řež focuses on small-scale nuclear reactors of the pressurized type, heavy-metal fast reactors and, and also gas-cooled high-temperature reactors.

Research covers these areas:

  • Nuclear fuel and fuel cycles,
  • Construction materials and their behavior under operating conditions,
  • Analyses and assessment of safety,
  • Possibilities of application in the Czech Republic's energy economy (electricity, heat, other applications),
  • Assessment of the concepts of small reactors in terms of their suitability for the Czech Republic's power engineering,
  • Placement issues, interactions with the environment, environmental impact assessment,
  • Possibilities of participation of the Czech industry in the production and supply of equipment.


Division of Nuclear Safety and Reliability

  • Address:  ÚJV Řež, a. s., Hlavní 130, Řež, 250 68 Husinec, Czech Republic
  • Phone: +420 266 173 558     
  • Fax: +420 220 941 029
  • E-mail:
We provide comprehensive services focused on applied research, development and innovation, particularly in the field of peaceful use of nuclear energy and sources of ionizing radiation. Projects are also implemented under grant programs and commercial contracts.