Investigation of natural convection in Miniature Neutron Source Reactor of Isfahan by applying the porous media approach

•We carried out a CFD study to investigate transient natural convection in MNSR.•We applied porous media approach to simplify the complex core of MNSR.•Method have been verified with experimental data.•Temperature difference between the core inlet and outlet has been obtained.•Flow pattern and temperature distribution have been presented. The small and complex core of Isfahan Miniature Neutron Source Reactor (MNSR) in addition to its large tank makes a parametric study of natural convection difficult to perform in aspects of time and computational resources. In this study, in order to overcome this obstacle the porous media approximation has been used. This numerical technique includes two steps, (a) calculation of porous media variables such as porosity and pressure drops in the core region, (b) simulation of natural convection in the reactor tank by assuming the core region as a porous medium. Simulation has been carried out with ANSYS FLUENT® Academic Research, Release 16.2. The core porous medium resistance factors have been estimated to be, Dij=1850 [1/m] and Cij=415 [1/m2]. Natural Convection simulation with Boussinesq approximation and variable property assumption have been performed. The experimental data and nuclear codes available in the literature, have verified the method. The average temperature difference between the experimental data and this study results was less than 0.5°C and 2.0°C for property variable technique and Boussinesq approximation, respectively. Temperature distribution and flow pattern in the entire reactor have been obtained. Results have shown that the temperature difference between core outlet and inlet is about 18°C and in this situation flow rate is about 0.004kg/s. A full parametric study could be the topic of future investigations.