A Mathematical Model and Simulation of Natural Circulation Loop Thermalhydraulics

In this work, a simple, nonlinear, seventh-order mathematical model with lumped parameter analysis of the thermalhydraulic processes in a natural circulation steam boiler loop is presented. Digital simulation has been performed in order to predict open loop transients in severe accidental situations. Parts of the circulation loop such as the steam drum, downcomer, and riser were modelled separately on the basis of the integral balance equations. The two-phase flow in the steam drum and in the riser was modelled with the aid of a homogeneous-equilibrium, two-phase flow model. Special care was taken to ensure the stability of the numerical scheme, since an explicit 4th order Runge-Kutta integration method was used. Experimental data of the dynamic behavior of a particular natural circulation steam boiler loop were not accessible. However, the presented model shows relatively good qualitative and asymptotic behavior of the modelled system