Numerical Analysis of Thermal and Hydro Dynamical Processes in Lower Fuel Channel Part of Boiling Water Reactor

  • Linas Paukštaitis Kaunas University of Technology
  • Sigitas Kilikevičius Kaunas University of Technology
  • Juozas Gudzinskas Kaunas University of Technology
  • Martynas Gylys Kaunas University of Technology
  • Valdas Lukoševičius Kaunas University of Technology
Keywords: fuel channel, coolant temperature, velocity, pressure drop, steam fraction, spacer, intensifier


This article presents results of 3D numerical analysis of the thermal and hydro dynamical processes which take place inside the fuel channel of the RBMK-1500 reactor during interaction between coolant and fuel assembly.

Numerical modelling was made for three different operational regimes of reactor: for minimal (0.91 MW), average (2.53 MW) and for the maximal power (3.50 MW) levels.

Simulation was made using ANSYS CFX program package in order to evaluate coolant’s pressure, temperature, flow velocity and steam mass fraction changes at the distance grids (spacers) and at the heat transfer intensification grids (intensifiers) along and across the fuel channel. In order to create CFX mesh, a tetrahedral finite element type with 10 million elements was chosen. The k-ε turbulence model and homogeneous model of the heat transfer (HEM) were applied for numerical simulation.

The obtained results help better to understand the processes which have a direct influence on the reactor safety. Information about the peculiarities of steam generation process inside the fuel channel (temperature change, pressure drop, flow velocity, steam mass fraction) enables to identify the most loaded points of the fuel channel and to make necessary design and operational improvements (location of spacers and intensifiers; core loading and etc.). The results can be used for predicting of hydrogen formation process and for the forecast of the decrease of zirconium alloy strength.