A Preliminary Approach to the Dynamic Behaviour of Circulating Fuel Reactors for Generation IV

A preliminary approach to the simulation of the dynamics of the Circulating Fuel Reactors (CFR) is presented in this paper. Among CFRs, the most promising is the Molten Salt Reactor (MSR), which is one of the "Generation IV International Forum" concepts. Assuming the space-independent zero-power kinetics equations modified in order to take into account the coupling with the molten salt circulation, the dynamic behaviour has been analyzed by means of the transfer function of the system (core + external primary loop). A very simple model is proposed that has been validated on the basis of the experimental data from the Molten Salt Reactor Experiment (MSRE) performed at the Oak Ridge National Laboratory (ORNL); after the validation, it has been applied to study the effects of the coolant velocity on the reactor stability, taking into account the circulation time in the core as well as in the external primary loop. Even if the material properties adopted in the analyses refer to the values encountered in the MSRE, the dynamic model is of more general validity for nuclear reactors with circulating fuels. The results of the present work allow a preliminary evaluation of the coupling between the point neutron kinetics and the velocity of the circulating fuel, and they also give a first indication on the control strategy to be adopted in the current development of MSRs for Generation IV.