A peer-reviewed journal published by K. N. Toosi University of Technology

Document Type : Research Article


1 Department of Nuclear Engineering‎, ‎Science and Research Branch‎, ‎Islamic Azad University‎, ‎Tehran‎, ‎Iran

2 Reactor and Nuclear Safety Research School‎, ‎Nuclear Science and Technology Research Institute (NSTRI)‎, ‎Tehran‎, ‎Iran


In this research, the governing dynamic equations of the Bushehr NPP core are studied and modeled using Matlab (Simulink) software. The point kinetic equation with the temperature feedbacks and the fuel-coolant energy balance equations in the time domain were used for this purpose. The model is validated against the rod drop accident data available in BNPP-1 FSAR, and they agreed. Then, this time-domain model is used to find the maximum movement speed of the control rods. For this goal, linear and non-linear rod movement equations have been modeled. In this regard, the maximum withdrawal speed of the working bank (H10) with a worth of 1.1 dollars has been investigated. Using the linear CR model, a speed limit of 9 cm.s-1 has been obtained to prevent the initiation of a reactor trip. The maximum speed using the non-linear model of the CR was found out to be dependent on its initial position. Thus, in three positions of the H10 bank: 100%, 80%, and 50% of the length inside the reactor, the maximum withdrawal speed values were valuated 11.5, 7.7, and 4.4 cm.s-1 respectively. According to the results, among the reactor parameters including power, period, and fuel temperature, which are monitored by the reactor protection system to initiate the reactor trip, the reactor power is the limiting factor for specifying the maximum withdrawal speed. This study is performed using time domain analysis, and the obtained results are consistent with the results reported in the previous research using Laplace transform approach.


  • BNPP core neutronic and thermal-hydraulic equations in the time domain were modeled in Simulink software.
  • The developed model was validated against FSAR data for the rod drop accident.
  • Time domain analysis was performed using the control rod linear and non-linear models.
  • The results were compared with the previous study using the transfer function approach.
  • The maximum allowable control rod withdrawal speed was investigated by simulating several experiments.


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