Development of Reactor Vessel Thermal–Hydraulic Analysis Method in Natural Circulation Conditions - Investigation of Interwrapper Gap Model -

Abstract

A dipped-type direct heat exchanger (D-DHX) installed in the hot pool of the reactor vessel (RV) has been investigated as one of the decay heat removal systems under natural circulation to enhance a safety of pool-type sodium-cooled fast reactors. The D-DHX provides the cold sodium to the hot pool. The cold coolant from the D-DHX flows into assemblies and an interwrapper gap (IWG) between them in the core, and removes the heat from assemblies. Thus, the behavior of cold sodium is a large scale in the whole RV. It is required to predict a complex three-dimensional thermal–hydraulic behavior in the RV by detailed modeling. For the design study, a computational fluid dynamics code needs to have an acceptable accuracy and low computational cost performance. In this study, we investigate the coarse mesh modeling of IWG using correlations for the purpose of the development of a practical model which can reduce the computational cost maintaining the prediction accuracy. An influence of combinations of the coarse mesh and the correlation for pressure loss in the IWG on the thermal–hydraulics in the RV and the core temperature distribution is revealed through the numerical analysis of a sodium experimental apparatus PLANDTL-1. As a result, the coarse mesh modeling of IWG with the pressure loss correlation evaluated the thermal–hydraulics in the RV. Temperature distribution in the core generally correlated between numerical and experimental results. To improve the evaluation accuracy of the temperature distribution in the simulated core, the further study about numerical simulation with detail mesh or alternative pressure loss correlation in the IWG region of the top of simulated core where the cold sodium enters will be needed.