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.