A zero dimensional model for simulation of TRIGA Mark II dynamic response

• Dynamic behavior of the TRIGA Mark II reactor on the entire operative power range.
• Stability analysis of the TRIGA reactor by means of the root locus method.
• Thermal-hydraulic model with natural circulation.
• Validation of the model using experimental data.

Aim of this work is to reproduce the dynamic behavior of the TRIGA Mark II reactor of the University of Pavia on the entire operative power range (i.e. 0–250 kW) using a zero dimensional approach. In this work the coupling between neutronics and thermal-hydraulics in natural circulation has been considered. In specific, a point reactor kinetics model with one energy group and six delayed neutron precursors groups has been adopted while for thermal-hydraulics modeling two regions have been defined (i.e. the fuel and the coolant). The nonlinear system of coupled Ordinary Differential Equations has been solved by means of MATLAB Simulink®, which represents a reliable tool for dynamic and control analysis. The model has then been validated through the comparison with a set of experimental data collected in four different reactor power transients, obtaining a very satisfying agreement. Finally, the linear stability analysis of the TRIGA reactor has been performed by means of the root locus, finding out that the power level at which reactor is operating deeply influences the position of the poles of the transfer function between control rod height and neutron density. These results can then be employed as a reliable starting point in designing an automatic device for reactor power control.