Corresponding author: Denis V. Doronkov ( nevid000@mail.ru ) Academic editor: Yury Kazansky
© 2021 Sergey M. Dmitriyev, Anton V. Gerasimov, Aleksander A. Dobrov, Denis V. Doronkov, Aleksey N. Pronin, Anton V. Ryazanov, Dmitry N. Solntsev, Aleksander Ye. Khrobostov, Aleksey S. Noskov, Oleg B. Samoylov, Yury K. Shvetsov, Dmitry L. Shipov.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Dmitriyev SM, Gerasimov AV, Dobrov AA, Doronkov DV, Pronin AN, Ryazanov AV, Solntsev DN, Khrobostov AYe, Noskov AS, Samoylov OB, Shvetsov YK, Shipov DL (2021) Experimental investigation of the coolant flow in the VVER reactor core with TVSA fuel assemblies. Nuclear Energy and Technology 7(1): 59-54. https://doi.org/10.3897/nucet.7.65313
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The paper presents the results of an experimental study to investigate the coolant interaction in adjoining fuel assemblies in the VVER reactor core composed of TVSA-T and upgraded TVSA FAs. The processes of the in-core coolant flow were simulated in a test wind tunnel. The experiments were conducted using models representing different portions of the VVER reactor core fuel bundle and consisted in measuring the radial and axial airflow velocities in representative areas within the FAs and in the interassembly space. The results of the experiments can be translated to the full-scale conditions of the coolant flow with the use of the fluid dynamics simulation theory. The measurements were performed using a five-channel pressure-tube probe. The coolant flow pattern in different portions of the fuel bundle is represented by distribution diagrams and distribution maps for the radial and axial velocity vector components in the representative areas of the models. An analysis for the spatial distribution of the radial and axial velocity vector components has made it possible to obtain a detailed pattern of the coolant flow about the FA spacer, mixing and combined spacer grids of different designs. The accumulated database for the coolant flow in FAs of different designs forms the basis for the engineering justification of the VVER reactor core reliability and serviceability. The investigation results for the coolant interaction in adjoining TVSA FAs of different designs have been adopted for the practical use at JSC Afrikantov OKBM to estimate the heat-engineering reliability of the VVER reactor cores and have been included in the database for verification of computational fluid dynamics (CFD) codes and detailed by-channel calculation codes.
Reactor core, fuel assembly, spacer grids, mixing grids, interassembly interaction, coolant fluid dynamics
Currently, the VVER reactor core at unit 2 of the Temelin NPP has been partially refueled (
As compared with the TVSA-T fuel assemblies, the key distinction of the upgraded TVSA assembly (TVSAU hereinafter) is the use of separately installed mixing grids (MG) which ensure that the coolant mixes more intensively across the assembly, leading so to an improved performance of the new FA (
Both FA types do not have jackets, so the coolant mixing takes place not only in the fuel assembly but also between the adjoining FAs. One needs to take into account this phenomenon when justifying the heat-engineering reliability of the core (
The coolant flow in the core was modeled using a wind tunnel test facility (
Test models (TM) were built reproducing geometrically the structure in different axial areas of the VVER reactor core fuel bundle. All TM components have been proportionally increased by the geometrical similarity coefficient Kg = 4.4.
The test models included one segment of the TVSA-T assembly, two segments of an upgraded TVSA assembly, and the space between the assemblies (Fig.
The spacer grid (SG) (Fig.
A pressure-tube probe was used to measure the local hydrodynamic characteristics of the coolant flow. The sensor is designed as five steel capillary tubes installed in two mutually perpendicular planes. The resultant flow pressure field, as shown by the dependencies obtained from calibration tests, was converted to the flow direction and absolute velocity (
A representative area, consisting of a standard TVSA-T assembly and two TVSAU assemblies, was identified in the mixed core’s cross-section. Longitudinally, the core fuel bundle was divided into three typical axial portions referred to, in accordance with the upward coolant flow direction, as “lower”, “medium” and “upper”.
The “lower” portion of the fuel bundle starts from the first identically arranged SGs of the fuel assemblies of both types (Fig.
Specific to the TM of the fuel bundle’s “lower” portion is that the flow movement inlet conditions are symmetrical, that is, there are spacer grids of the same design installed at the TM inlet for both TVSAs (see Fig.
The test procedure was as follows.
The experimental study was conducted at a constant average rate velocity of the airflow at the TM inlet; this parameters has an equal value for each of the models and amounts to Wav = 27.5 m/s. The Reynolds number, with which the experiments were undertaken, was equal to 78000. The temperature range of the airflow during the investigation was 23 to 25 °C.
An analysis of the experimental investigation results has made it possible to identify general flow current regularities.
An analysis of investigation results for the VVER core coolant mixing process has led to the following conclusions: