Large eddy simulation of a nuclear pebble bed configuration

High Temperature Reactors (HTRs) are being considered all over the world for deployment because of their excellent safety features. A particular inherent safety advantage of HTR designs is related to the very high temperature that the fuel can sustain basically preventing the fuel from melting even in the event of loss of cooling. Generally, the core can be designed using a graphite pebble bed. Test reactors have shown safe and efficient operation, however questions have been raised about possible occurrence of local hot spots in the pebble bed which may affect the pebble integrity. A good prediction of the flow and heat transfer phenomena in the pebble bed core of an HTR is a challenge for available turbulence models, which still require to be validated for pebble bed applications. In the present study large eddy simulation (LES) of a well-defined single face cubic centered pebble bed is performed. The obtained results are extensively compared with a quasi-direct numerical simulation (q-DNS) database in order to analyze the prediction capabilities and feasibility of used LES approach for such a complex flow regime. The simulations are performed at a Reynolds number of 3088, based on pebble diameter, with a porosity level of 0.42. The obtained results are found to be in good agreement with the q-DNS results.