POROUS MEDIA IN CFD MODELLING FOR SIMULATING COOLANT FLOW BEHAVIORS IN A LEAD-COOLED SMR

IVAN K. UMEZU; DARIO M. GODINO; DAMIAN E. RAMAJO; CLAUBIA PEREIRA; CLARYSSON A. SILVA; ANTONELLA L. COSTA

Trieste

Workshop; Joint ICTP-IAEA Workshop on Physics and Technology of Innovative Nuclear Energy Systems; 2022

International Centre for Theoretical Physics and International Atomic Energy Agency

Among the new Small Modular Reactor (SMR) ongoing designs, the SEALER (Swedish Advanced Lead Reactor) [1] is one of the most relevant liquid-metal cooled reactor proposals, for its small build size and very low power (8 MWth - 3 MWe), suited for deployment in remote regions with no connection to the electric grid, for up to 30 years without fuel reloading. Because of SEALER’s pool-type design, thorough investigations on natural circulation and convective flow patterns must take place, especially in order to identify regions of coolant stagnation and recirculation.This work presents a focused analysis of the flow patterns in SEALER’s core vessel region, under normal steady state operating conditions, by the means of 3D Computational Fluid Dynamics (CFD) simulations. For such, the SEALER CFD model was based on published data from, including geometry and operating conditions (coolant flow rate, pressure drops, inlet temperatures, etc.). The core region was divided in all of the fuel, control, reflector and shielding assemblies, each modeled as an individual porous region, using the Darcy-Forchheimer model, according to their respective pressure drops estimations. The axial and radial thermal power distributions were taken into account and applied as volumetric heat sources in the fuel assemblies. For the sake of computational resources economy, the domain was reduced to a symmetric 1/4 of the whole. Thus, symmetry boundary conditions were applied to side faces and free fluid surfaces were modeled as slip walls. The liquid lead coolant was modeled with temperature-dependent thermophysical properties [4]. The case was run on ANSYS Fluent R19.2. The results, though representative of a steady state condition, were based on transient calculations, due to the natural convection and geometry implications in computation stability. Although necessary and more expensive, the transient approach can capture possible cyclic flow behavior and improve the technical quality of the analysis. In conclusion, by employing CFD in this study, detailed natural convection patterns can be analysed, which would not be possible if using traditional thermal-hydraulic system codes. With the velocity and thermal fields mapped, recirculating flow regions and excessively hot or cold spots can be identified and actions against possible accident-inducing conditions, such as coolant freezing, can be taken and further safety design modifications in geometry and operating conditions can help optimize the coolant flow and heat transfer within the reactor.