A multi-physics time-dependent model for the Lead Fast Reactor single-channel analysis

This paper presents a multi-physics and time-dependent model for single-channel transient analysis of a Lead Fast Reactor (LFR). The work focuses on the coupling among the neutronic, the thermal-elastic and the fluid-dynamic phenomena in the considered reactor channel, benefiting from a finite-element scheme of analysis that is implemented in the same simulation environment (COMSOL Multiphysics®), and within a computational domain featured by a moving mesh. A purpose-made six-group neutron diffusion model is developed, which allows to take into account the local dependency of the neutron macroscopic cross-sections on the temperature and density fields. The potential of the multi-physics model to estimate the effective neutron multiplication factor, by means of a comparison with the Monte Carlo code SERPENT, is assessed. A special attention is given to the capability to implicitly catch the thermal-hydraulic and thermal-expansion feedbacks on reactivity, without relying on cross-sections corrective factors. The proposed multi-physics model is employed to investigate the active-core average conditions of the ELSY (European Lead cooled System) reactor, both in steady-state operation and during two transient scenarios. It is shown that the presented model represents a suitable simulation tool for a preliminary investigation of the LFR dynamics, and allows to simultaneously evaluate a wide set of the reactor channel parameters.