3D thermal-hydraulic calculations of a modular block-type HTR core

摘要

This paper deals with 3D numerical simulation of assemblies of a high temperature helium cooled reactor core. The present aim is to investigate an emergency situation due to the blocking of few Helium channels in the core. In this situation, some Helium channels for coolant passage are blocked and the related issue is the temperature distribution within the assemblies, as well as the locations of the local extrema in graphite and fuel media, that must not exceed 1600℃. Two configurations are investigated, depending on the situation of the blocked fuel assembly in the core. The blocked assembly is surrounded by six unblocked fuel assemblies in the first situation and by five unblocked fuel assemblies and one reflector assembly in the second situation. This numerical study is performed using the thermal-hydraulic CFD code Trio_U. Trio_U is developed at CEA Grenoble and especially designed to simulate unsteady turbulent flows developing in complex geometries. For the present work, an accurate description of 3D conduction problem (graphite and fuel), coupled with a simplified 1D thermal-hydraulic modelling for Helium is used. The reported simulations suggest that the main temperature increase is limited to the blocked fuel assembly and do not spread over surrounded assemblies. This seems to be due to the Helium flow rate in the gaps between blocks. Moreover, the present results show that the maximum temperature criterion is not respected for the blocking conditions at nominal power for the blocked assembly.