The multiplicity of interconnected physical phenomena in different parts of fusion reactors means that several and varied physics models need to be applied to perform advanced studies of the materials and components of such complex devices. In the case of the vacuum vessel wall, it is necessary to study the heat deposition due to the interaction with the neutron flux, together with the removal of this heat by the liquid coolant. To do this, in this paper we show the performance of a multiphysics system in which a deterministic neutron transport solver is coupled with temperature and fluid dynamics solvers. These solvers are modules of the Alya framework, a highly efficient parallel finite element code developed by the Barcelona Supercomputing Center. The module TEMPER solves the heat equation in the wall and the fluid, NASTIN solves the incompressible Navier-Stokes equations for the coolant, and NEUTRO solves the steady-state Boltzmann linear transport equation for neutronics.

NEUTRO, the main focus of our work, is more recent than other Alya modules, and is in its validation stage. For this reason, we include the results of its performance, recent new features, and some comparisons with other neutronics solvers. Coupling these modules at the time-step level with a shared domain enables us to perform neutronics and thermohydraulic simulations in a single run without intermediate files or manual intervention. This capability contributes to computational efficiency, reduces potential error, and has not yet been demonstrated to the best of our knowledge in the nuclear fusion field.

After showing the results and comparison for test cases, we display an example of coupled operation to analyze neutron flux, heat deposition, fluid dynamics, and heat dissipation in the inner poloidal segment comprising half of a 40-deg-angle toroidal portion of an ITER sector.