Fuel Cycle Support

The primary goal of optimizing fuel reloads is to minimize the cost of nuclear fuel when meeting the operational requirements and restrictions imposed on the operation of the core zone. ÚJV Řež has been dealing with this issue since the 1990s when the software OPTIMAL was developed for Dukovany NPP.
Its upgraded version is still used successfully in both routine operation and advanced fuel cycle designs for VVER-440 reactors. For VVER-1000 reactors, ÚJV Řež uses a new-generation LPOpt tool, which can be used to optimize fuel reloads of any type of reactor. 

The design of fuel charges includes fuel design, fuel and fuel charges modeling, and calculations to demonstrate whether a given fuel charge complies with all safety requirements for the operation of the core zone and the nuclear reactor. ÚJV Řež develops methodological procedures and software for these activities.

ANDREA software is an advanced software for the neutron-physical computation of active zones of pressurized water reactors.

CycleKit software is used to automate large-scale calculations for safety assessments of fuel charges.

• Safety analyses for the purpose of the licensing process, including independent verification analyses and documentation
• Preparation and updating of safety reports and license documentation
• Preparation of methodological procedures for analysis and for the own licensing process
• Conceptual studies on nuclear safety
• Analyses and preparation of supporting documents for the fuel cycle
• Analyses of severe accidents and strategies for severe accident management
• Analyses of the thermomechanical behavior of nuclear fuel in operational and emergency conditions
• Best-estimate analysis of nuclear fuel coating damage and evaluation of fission product release into the coolant
• Analyses and preparation of backgrounds for calculation of radiological consequences of accidents
• Analyses and preparation of backgrounds for PSA studies
• Thermohydraulic analysis for PTS needs
• Experiment evaluation

We have an extensive experience in carrying out inspections of the fuel condition during its replacement. We perform visual inspection, measurement of growth and deformation of fuel assemblies and fuel rods. ÚJV Řež in cooperation with Research Center Řež develops and introduces new procedures for measurement and evaluation of data into routine practice.

During nuclear fuel operation in reactor core, as a result of its burning, the fuel changes its physical and chemical properties and changes its dimensions. These changes are caused by external and internal forces. During operation, there are considerable temperature gradients in the fuel, from almost 1500°C in the center of the fuel tablets to 290°C on the surface of the fuel assembly, which gives rise to stresses that can endanger the integrity of fuel cladding - the primary barrier to leakage of radioactive substances. The objective of thermomechanical calculations is to ensure that the proposed fuel charges are safe from this point of view. ÚJV Řež uses either licensed codes (TRANSURANUS) or proprietary models developed in the FEM ABAQUS tool. The analysis and application of experimental data obtained in international projects using research reactors and hot cells to study new types of nuclear fuel are an integral part of these activities.

From the point of view of thermohydraulics, the key is the knowledge of the distance from the so-called boiling crisis, when the heat transfer from the fuel to the refrigerant deteriorates sharply. For analyzing the boiling crisis, we use the VIPRE licensed software and for detailed thermohydraulic computations, we use Computational Fluid Mechanics (CFD) FLUENT software.

• Comprehensive analyses of the operation of nuclear power plants
• Suggestions for measures to improve the safety of the operation
• Development and implementation of PSA applications for risk-oriented decision making:
  
  • Immediate operational risk monitors for NPPs
  • Online maintenance
  • LaP optimization and test intervals
  • Prioritization of safety measures
  • Cost-benefit analysis
• Development of Probability Safety Assessment Methods (PSA)

ÚJV Řež also deals with the back-end part of the fuel cycle of nuclear power plants and research reactors. These activities include preparation of the closure of the reactor fuel cycle and the elaboration of conceptual and expert studies to optimize spent fuel management in the European context of fissile materials management. See more: Radioactive waste and decommisioning.

ÚJV Řež is also engaged in the study and modeling of phenomena that can endanger the integrity of the fuel rods cladding and the preparation of fuel pellet temperature models under operational conditions. ABAQUS software is used for these tasks.

ÚJV Řež actively follows trends in the field of advanced fuel cycles and is actively involved in international Gen IV. reactors R&D projects.