102.1 A Multi-Physics Numerical Model for the MSR Core Dynamics Claudia Guerrieri , Antonio Cammi, Carlo Fiorina, Lelio Luzzi Politecnico di Milano – Department of Energy Nuclear Engineering Division CeSNEF Via La Masa, 34 – 20156 Milano, Italy claudia.guerrieri@mail.polimi.it ABSTRACT In the framework of the Generation IV International Forum, six innovative concepts of nuclear reactors have been chosen as suitable for the future challenges of nuclear energy. Among these reactors, a renewed interest has been focused on the Molten Salt Reactor (MSR), due to its unique capabilities for actinide burning and natural resource exploitation, while reducing the waste radiotoxicity. In MSRs, the molten salt serves both as fuel and coolant, leading to a complex and highly coupled physical environment. In this paper, a multi-physics modelling (MPM) approach is developed to study the dynamics of the entire MSR primary circuit, with reference to the Molten Salt Reactor Experiment (MSRE). As concerns the geometry, a single channel representative of the core average conditions is modelled considering a two-dimensional axial-symmetric domain. A further one-dimensional domain is implemented in order to model the external primary circuit. The proposed MPM approach provides careful estimates of the spatial distribution of the main physical quantities. Moreover, it allows to evaluate the particular dynamic behaviour of this reactor. In the present study, the MPM potentialities are shown analysing the system response under different transient conditions. 1 INTRODUCTION The Molten Salt Reactor (MSR) is a non-conventional nuclear reactor featured by the presence of a liquid mixture of molten salts, which flows through the primary circuit serving both as fuel and coolant. This concept of reactor was first developed in the late 1940s with the preliminary studies of Ed Betis and Ray Bryant from the Oak Ridge National Laboratory (ORNL). Such early work led to the construction of the Aircraft Reactor Experiment (ARE). This reactor was a small prototype of 2.5 MW th designed for propulsion purposes, which operated for several days in 1954 demonstrating the feasibility of such technology [1]. Between the sixties and the seventies two larger reactors were designed at ORNL: the Molten Salt Reactor Experiment (MSRE) and the Molten Salt Breeder Reactor (MSBR). Actually, only the MSRE was realized and became critical in 1965 [1,2]. During the operative period of the MSRE, several experiments were performed focused on the understanding of its particular dynamic behaviour. The MSRE was an 8 MW th reactor suitable for breeding purposes, characterised by a nearly thermal neutron spectrum. Neutron moderation was obtained by means of graphite bars placed inside the core. The fissile materials (i.e., nuclei of 233 U or 235 U) were dissolved in a carrier mixture of fluoride salts, which circulated through the primary circuit acting as fuel and coolant simultaneously. This causes two features, which are typical of all MSRs, namely: the fission heat is released mainly in the liquid salt, and the delayed neutron precursors (DNP)