Development of a Single-Channel Multi-Physics Model for Lead Fast Reactors

In this work, an extension of the Multi-Physics Modelling (MPM) approach developed at the Politecnico di Milano for the nuclear reactor analysis is presented, with reference to the lead-cooled ELSY reactor. Within the same computing platform (represented by COMSOL Multiphysics), the Multi-Physics (MP) scheme of analysis is based on the simultaneous solution of the fully coupled and time-dependent partial differential equations describing heat transfer, fluid dynamics and neutronics in a fuel pin, and in the surrounding lead. The MPM approach aims at intrinsically coupling the different phenomena occurring in a nuclear reactor, without requiring data-passing between different platforms (i.e., through the conventional coupled code techniques). In such scheme of analysis, the main development of present work is represented by the explicit consideration of the point-wise temperature and density dependence of neutron cross-sections as well of the thermal expansion effects. Throughout the paper, the features of the extended MPM approach are investigated, with reference to a single-channel representative of the active core average conditions of the ELSY reactor, at beginning of life. The extended-MP model proves itself capable of describing the reactor behaviour both in steadystate and transient conditions, with reasonable computational requirements and good degree of convergence.