Pre-design of primary loops and assessment of the inherent safety of an SMR CADOR

The report presents the results of the studies carried out on a concept of sodium-cooled SMR (Small Modular Reactor) CADOR (Core with Amplified DOppleR effect). Initially, a pre-design of the primary loop was performed, with a particular focus on the pressure drops along the different components of the circuit in nominal conditions. The VBA-based tool COPERNIC was used in order to conduct parametric studies and find the design that would better fit the chosen requirements. For this purpose, the number of primary loops, the primary piping diameter and the thermal power of the reactor were varied, and, through thermohydraulic modelling, the effect on the loop pressure drops and primary fluid velocity were observed. The main aims of the presented concept of SMR CADOR are to achieve a simple design and to be able to operate in conditions of natural circulation in case of failure of the primary pumps. Another ambitious goal for the reactor is to face the worst transient for the Sodium Fast Reactor technology: the insertion of reactivity. The generalized melting of the core has to be avoided and, to achieve this objective, UTOP (Unprotected Transient OverPower) need to be addressed by the means of a passive behaviour. The CADOR core enhances the Doppler effect, which, in case of a fuel temperature increase, introduces a negative neutronic feedback, with the aim of providing inherent safety to the reactor. In order to prove the resistance of this reactor to transients, the Matlab code MACARENa for the simulation of ULOF (Unprotected Loss of Flow) transients was adapted and run for the considered design of SMR CADOR.