<p style="text-align: justify">In order to enhance the safety of sodium-cooled fast reactors (SFRs), adoption of diverse decay heat removal systems (DHRSs) is required in the design study of an advanced SFR. In this point of view, it is considered that a direct reactor auxiliary cooling system (DRACS) under natural circulation operation with a dipped-type direct heat exchanger (D-DHX) in the upper plenum (UP) of the reactor vessel (RV) is one of the most effective DHRSs. In the sodium experiments simulating the natural circulation DHRS (NC-DHRS) with the D-DHX, the penetration flow of the cold sodium from the D-DHX into fuel subassemblies (FSs) and also into narrow gaps between them well-known as interwrapper flow (IWF) were observed. Besides, the radial heat transfer between adjacent subassemblies and thermal stratification in the UP were also observed. In the design study, the analysis method which enables to predict such complicated phenomena in the RV named the core-plenum interactions is strongly demanded to evaluate the structural integrity for thermal transient and the core cooling performance by the NC-DHRS. Thus, a multi-dimensional thermal hydraulic analysis model in the RV using CFD code (RV-CFD model) has been developed. In the RV-CFD model, regions of the UP and the core were modeled seamlessly in the single domain to simulate accurately the core-plenum interactions in the RV. In the core region, an efficient model focused on the pin bundle of FS named Subchannel CFD model which was based on the concept of subchannel analysis was adopted in order to simulate with reasonable calculation costs while maintaining accuracy. In this study, numerical simulation was carried out for a steady-state experiment in the sodium test facility named PLANDTL-1 to confirm applicability of the RV-CFD model for natural circulation decay heat removal condition with the D-DHX operation. The RV of the PLANDTL-1 composed of the UP with the D-DHX and the simulated core consisting of 7 FSs and interwrapper gaps. In the numerical analysis, the thermal stratification in the UP and the thermal-hydraulics behaviors that the cold coolant from the D-DHX flowing into the FSs and interwrapper gaps could be reproduced. And the asymmetric temperature distribution in the simulated core affected by IWF was comparable between the experiment and the numerical simulation. Thus, the applicability of the RV-CFD model with Subchannel CFD model for natural circulation decay heat removal condition with the D-DHX operation was confirmed.</p>

Core Thermal-Hydraulic Analysis During Dipped-Type Direct Heat Exchanger Operation in Natural Circulation Conditions

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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