Authors & Affiliations
National Research Center "Kurchatov Institute", Moscow
Based on the computational studies of the spatial neutron kinetics benchmarks, the advantages and disadvantages of modeling the control rods (CR) prompt downing in space-time calculations of fast reactors are formulated. Prompt downing of the CR is only useful when the benchmarks calculating. In space-time calculations, the reactivity was calculated using an inverted solution of the kinetic equation. The conclusions are made based on a comparative analysis of the simulation of prompt downing and gradual movement of the control rods in two benchmarks — BN600_IAEA_T and MET-1000_T. BN600_IAEA_T is a model of a BN-600 type reactor with a hybrid core, and MET-1000_T is a model of a medium-sized fast reactor with a metal fuel with a thermal capacity of 1000 MW (t). Simulation of prompt downing of control vrods is recommended for debugging algorithms and codes for solving the transport and spatial kinetics equations. Its advantages include a significant reduction in calculating times and, as a result, easing the most time-consuming stages of cross-validation of codes. The disadvantages are associated with the inability to find errors in the modeling of the gradual movement of the CR. It is shown that recalculating the concentrations of delayed neutron precursors when solving the transport equation in a pre-set number of mandatory external iterations significantly increases the accuracy of reactivity calculations. The quasi-prompt downing of the control rods is almost equivalent to their prompt or the reactivity and power calculations. The power reactor values calculated after the prompt downing of the control rods differ significantly from the power values calculated for the moments after the end of the CR downing when items are gradually downing at 1 m/s speed. As the rate of downing the CRs increases, the power values approach those calculated after an prompt downing r of the CRs.
reversed solution of the kinetic equation, reactivity, control rods, prompt downing, delayed neutrons, fast reactors
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