Development of a control oriented simulator for a lead cooled fast reactor demonstrator

The development of a zero dimensional, control-oriented simulator for a Lead-cooled Fast Reactor (LFR) demonstrator is undertaken in this thesis. Based upon the European Lead-cooled SYstem demonstrator (DEMO) design, the simulator, implemented in MATLAB/SIMULINK®, consists in four essential parts: core, Steam Generator (SG), primary pump, and coolant cold pool. An analytical lumped-parameter model of DEMO core is developed to treat the coupled neutronics and thermal-hydraulics. A non-linear approach is adopted as the reference; in addition, two advantageous approximations (linearization and one-neutron-precursor-group treatment of neutron kinetics) are applied; in particular, the study of a linear model is very useful in the perspective of conceiving an adequate control strategy for the reactor. The validation of the reference core model is accomplished through a benchmark analysis with the SAS4A/SASSYS-1 Liquid Metal Reactor Code System, and a very good agreement with the analytical model outcomes is attested. The impact of the above-mentioned approximations is evaluated by investigating and comparing the respective responses to some unprotected transient initiators; moreover, a dynamic performance assessment of MOX and metal as fuel alternative options for DEMO is carried out. The SG model is conceived based on a moving boundary approach, which allows to get the physical behavior while satisfying some controller specifications such as simplicity, fast-running characteristics and flexibility, besides assuring coherence with the zero-dimensional core modeling. The SG dynamic behavior is studied by applying some perturbations to the steady-state, acting on both the water (secondary) and the lead (primary) side of the heat exchanger. In conclusion, the complete primary loop model is implemented by assembling the core and the SG models and adding the primary pump and the coolant cold pool. As a major achievement of this thesis work, it can be stated that the free dynamics simulation results are very satisfactory, and they will constitute the basis and provide the means for conceiving a suitable control strategy for the innovative small-size LFR systems under development.