Modelling and Control Strategy of the Italian LBE-XADS

In this paper the dynamic behaviour of the Italian 80MWth XADS (eXperimental Accelerator Driven System) is investigated, by means of a simple model for its main components as well as the most relevant interactions among them, namely the acceleratore core coupling and the corresponding neutronic features, the primary system with lead bismuth eutectic (LBE) as primary coolant, the secondary circuit with an organic diathermic fluid, and the associated air cooling system for an effective rejection of thermal power to the environment as a final heat sink. The simulation and control of the system dynamics took into account the singular features of the components, which show very different time constants, and the wide time interval needed by the organic fluid to flow into the secondary loop of the reactor. A control strategy based on a simultaneous feedforwardefeedback scheme has been adopted, the main requirement being to keep constant the average temperature of the secondary fluid. The dynamic response of the whole system has been evaluated, significant transient initiators have been considered: the results show that the proposed zero-dimensional model, in spite of its simplicity, is sufficiently accurate to predict the plant response in terms of the most relevant variables. The results also confirm that the Italian LBE-XADS exhibits a large operational margin, owing to favourable design choices and protective engineered actions as well as to the adopted control strategy of the system.