<p class="MsoNormal">In the design study of an advanced sodium-cooled fast reactor (Advanced-SFR) in Japan Atomic Energy Agency, the use of a specific fuel assembly (FA) with an inner duct structure called FAIDUS, in which the inner duct of the rhombic cross-section is installed at a corner of the hexagonal wrapper tube, has been investigated to enhance safety of Advanced-SFR against a core disruptive accident. In a typical FA without the inner duct as well as FAIDUS, fuel rods with a spirally wound wire spacer are installed in the wrapper tube to maintain the sodium flow area. Due to the asymmetrical layout of fuel rods by the inner duct in FAIDUS, it is necessary to estimate the temperature distribution under various operation conditions to confirm feasibility of FAIDUS. In JAEA, an in-house subchannel analysis code named ASFRE has been developed to perform parametric thermal hydraulics analyses in design study of the Advanced-SFR as a FA design tool. In ASFRE, a flow region called subchannel surrounded by fuel rods or a wrapper tube is defined as the control volume and the distributed resistance model for a pressure loss evaluation in FA and the turbulent-mixing model of the Todreas–Turi correlation model were employed. For the typical FAs, the numerical results of ASFRE was validated by comparisons with experimental data of pressure drop through the FA and measured temperature distribution in the sodium experiment. As for the FAIDUS, confirmation of validity of the numerical results of ASFRE was not enough because the reference data on the thermal hydraulics in FAIDUS such as experimental data have not yet been obtained though applicability of the ASFRE to the thermal hydraulics analysis in FAIDUS was preliminary examined. In this paper, therefore, the further discussion on applicability of ASFRE was carried out by analysis on the reproducibility of physical phenomena in FAIDUS by ASFRE through the code-to-code comparisons with numerical results of an in-house CFD code based on the finite element method SPIRAL. The numerical simulations were performed at two representative flow rate conditions: high and low flow rate conditions at rated and decay heat removal operations respectively, referring to tentative specifications of large-scale Advanced-SFR. Through the comparisons between the temperature and vertical velocity distributions by ASFRE and those by SPIRAL in subchannel-average, it was confirmed that the numerical results of ASFRE were comparable to those of SPIRAL at both high and low flow rate conditions. Focusing on the physical phenomena, the periodic peaks of vertical velocity and temperature at the locations where the angle of wire spacer around a fuel rod to the wrapper tube wall or the inner duct was the same were observed in the peripheral regions on the wall of the FA and also near the inner duct of the FAIDUS along the vertical direction. In this distribution of vertical velocity, the difference of profiles due to buoyancy effect in the assembly was shown in between high and low flow rate conditions. And, axial location which vertical velocity near the vertex of inner duct was periodically higher than that near the other walls due to interaction of counterclockwise horizontal flow along inner duct wall and horizontal flow from inner region to the region near inner duct was existed. As for the temperature distribution on the cross section where local peak of temperature increase was shown in the vertical distribution, the temperature near the vertex of inner duct in FAIDUS was higher than that near the wrapper tube in typical FA because the high temperature flow from the inner region to the inner duct was caused by the cross flow due to a spirally wound wire spacer around the fuel rod. Mechanism of appearance of the specific temperature distribution around the inner duct predicted by ASFRE was consistent with that derived from the detailed CFD simulation by SPIRAL. Thus, the applicability of ASFRE to thermal hydraulics analysis to feasibility study of FAIDUS was presumed.</p>

Investigation of Applicability of Subchannel Analysis Code Asfre on Thermal Hydraulics Analysis in Fuel Assembly With Inner Duct Structure in Sodium Cooled Fast Reactor

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

2021 28th International Conference on Nuclear Engineering (ICONE28)

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