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This paper deals with the one-dimensional unsteady fluid flow model of a natural circulation loop. The governing equations are solved according to both the Euler and Lagrange approaches on two parallel computational grids. The linearization of equations and a semi-implicit discretization scheme are used to enhance the algorithm’s effectiveness. The results of the simulations were verified by using experimental data obtained on an experimental rig that was a scale model of an emergency system for the removal of residual heat after reactor shutdown. The parameters compared were the helium temperature at two locations and the heater outlet pressure. The simulation results generally did not differ from the experimental data by more than 10%. The best agreement was obtained for scenarios in which the helium pressure was highest in combination with slow changes in the input parameters (less than 4%). Conversely, the results differed the most for the scenario with extremely fast device cooling (20%).

This paper deals with the one-dimensional unsteady fluid flow model of the natural circulation loop. The presented model represents the experimental facility Helium Loop STU which is the physical model of an emergency coolant system of a nuclear reactor. The governing equations are solved according both Euler and Lagrange approaches on two parallel computational grids. Linearization of equations and semi-implicit discretization scheme are used to enhance the algorithm effectiveness. The simulation results were compared to experimental data. The model can be considered as high-accurate in comparison with experimental data (relative error 1.14÷1.15 % at specified time interval).