Development of a control-oriented simulator for a LFR demonstrator

Highlights: • A control-oriented dynamics simulator for an advanced small LFR has been developed. • Flexibility, straightforwardness and fast-running features have been sought. • The model consists in 5 parts: core, SG, primary pump, cold and hot legs, and pool. • A non-linear lumped-parameter approach has been adopted to describe all components. • The reactor responses to five typical transient initiators have been investigated. -- Abstract: In this work, the development of a control-oriented dynamics simulator for a Generation IV Lead-cooled Fast Reactor (LFR) demonstrator has been undertaken aimed at providing a very flexible and straightforward – though accurate – fast-running tool allowing to perform transient design-basis and stability analyses, and laying the foundations for the study of the system control strategy. The simulator, realized in the MATLAB/SIMULINK® environment, is composed of five essential parts: core, steam generator, primary pump, collectors, and coolant cold pool. An analytical lumped-parameter core model has been developed to treat the coupling between neutronics and thermal-hydraulics. For the steam generator a moving boundary approach has been adopted, allowing to get the physical behavior while satisfying the controller specifications, besides assuring coherence with the zero-dimensional core modeling. The complete primary loop model has been assembled by connecting the above-mentioned main subsystems through the hot and cold collectors, and by adding the remaining components blocks. Five different transients have been then simulated to analyze the whole system dynamic behavior in a control-oriented perspective: three scenarios have been initiated by acting on the secondary water side (i.e., enhancement of feedwater mass flow rate and temperature, and turbine admission valve coefficient variation), and two by perturbing the primary side nominal state (i.e., simulations of Unprotected Loss of Flow, ULOF, and of Unprotected Transient of OverPower, UTOP). As a major outcome, it can be stated that the free dynamics simulations results are very satisfactory, and they may constitute the basis and provide the means for conceiving suitable control strategies for the innovative small-size LFR systems currently under development