Experimental investigation of the coolability of blocked hexagonal bundles

Hózer, Zoltán; Nagy, Imre; Kunstár, M.; Szabó, Péter; Vér, N.; Farkas, Róbert; Trosztel, I.; Vimi, A.

doi:10.1016/j.nucengdes.2017.03.030

Cited by 6 publications

(3 citation statements)

References 11 publications

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“…• Fuel cladding: temperature between 300 • C and 1200 • C and emissivity between 0.5 and 0.8. Even though much effort has been done in the past to evaluate the cooling phase during a LOCA, as Grandjean presents in his review of experimental campaigns performed in the 1980's [6], these subjects are still being investigated today in both experimental [3,[7][8][9] and modeling works [4,10,11]. Understanding in detail the physics during the cooling phase is crucial for safety requirements to guarantee the long-term coolability of the nuclear core and its structural resistance.…”

Section: Introductionmentioning

confidence: 99%

Experimental thermal hydraulics study of the blockage ratio effect during the cooling of a vertical tube with an internal steam-droplets flow

Carrillo

Oliveira

Labergue

et al. 2019

International Journal of Heat and Mass Transfer

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During a Loss of Coolant Accident (LOCA) in a Pressurized Water Reactor, partial or complete drying of fuel assemblies may take place. In these conditions, the fuel temperature increases and may lead to substantial deformation of the fuel rod cladding and a partial blockage of the fluid sub-channels. These regions could significantly affect the cooling capacity of the nuclear core during the reflooding phase by the emergency core cooling systems. Understanding the cooling process and the thermal-hydraulic characteristics of the flow in these deformed regions is decisive to guarantee nuclear safety. Looking to provide valuable experimental data to validate existing and new models, this work is an experimental study on the thermal hydraulics during the cooling of a vertical tube with an internal steam-droplets flow, representing the LOCA conditions at sub-channel scale. The effect of the blockage ratio on the tube temperature, heat dissipation, wall rewetting, and droplets characteristics is evaluated by testing three configurations (0%, 61% and 90%). Optical techniques were used for a comprehensive characterization of the process, being them infrared thermography, phase-Doppler analyzer and three-color laser induced fluorescence thermometry. In general, wall rewetting in the test section occurs from bottom to top, although there is a discontinuity in the rewetting front with the 90% blockage ratio configuration. The droplets diameter reduces downstream of the test section because of evaporation. Droplets breakup was specifically observed with 90% blockage ratio. In all the cases, the droplets temperature was approximately the same up-and downstream of the test section, which indicates they are in nearly thermal equilibrium state and, therefore, representative of a LOCA situation.

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Section: Introductionmentioning

confidence: 99%

Experimental thermal hydraulics study of the blockage ratio effect during the cooling of a vertical tube with an internal steam-droplets flow

Carrillo

Oliveira

Labergue

et al. 2019

International Journal of Heat and Mass Transfer

View full text Add to dashboard Cite

show abstract

“…These tasks are truly difficult in LOCA conditions, where we have two-phase flow and a variety of heat and mass transfer phenomena [1]. Many studies have been carried out to improve the understanding of the nuclear reactor's core thermal-hydraulics in LOCA conditions, either with a regular fuel bundle [2,3], with blockages due to clad ballooning [4,5] and at sub-channel scale [6][7][8].…”

Section: Blocked Sub-channels Ballooned Claddingmentioning

confidence: 99%

Velocity field and flow redistribution in a ballooned 7×7 fuel bundle measured by magnetic resonance velocimetry

Oliveira

Stemmelen

Leclerc

et al. 2020

Nuclear Engineering and Design

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During a loss of coolant accident (LOCA), blocked sub-channels may appear due to the swelling of the fuel rods' cladding, which results in flow redistribution during the reflooding phase. For this reason, special attention has been paid to the effect of fuel rods ballooning on the thermal-hydraulics in LOCA conditions. Due to the practically impossible physical or optical access to blocked sub-channels, no experiment so far has performed precise threecomponent velocity field measurements in the presence of ballooned regions. In this study, we used magnetic resonance velocimetry (MRV) to obtain three-component velocity fields of water flow within two 7x7 fuel rods bundles built mainly in plastic, one regular and one containing sixteen ballooned fuel rods with 90% blockage ratio and 240 mm blockage length. We present herein results with 50 lpm water flow rate. With the regular bundle, the performance of spacer grids' mixing vanes to homogenize the flow was notable. With the ballooned bundle, we observed transverse velocities upstream of the ballooned zone that are as intense as the bulk mean velocity. Furthermore, there are substantial decreases in the axial velocity within blocked sub-channels up-and downstream of the ballooned zone, reaching near-zero and even negative values downstream, indicating flow recirculation. Although the flow is highly affected by the ballooned zone, the mixing spacer grid placed downstream remarkably homogenized the flow and effects of the flow redistribution disappeared. Finally, with the present ballooned bundle configuration, about 90% of the flow that should pass through blocked sub-channel deviates towards less resistant regions, which suggests a predominant geometric effect on the flow redistribution.

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“…As a consequence, the heat dissipation in these blocked sub-channels is highly reduced, especially because wall-to-steam convection is one of the main heat transfer paths for the fuel rods cooling [9,10]. This motivated several studies in the literature to analyze the effects of clad ballooning and the thermal-hydraulics in blocked sub-channels using fuel rod bundles [11,12] and at sub-channel scale [13][14][15]. Grandjean [5] compiled several past experimental campaigns in a state-of-the-art review in 2007 and he observed that many experimental results suggested that clad ballooning might be large and long enough so a blocked sub-channel can no longer be coolable.…”

Section: Introductionmentioning

confidence: 99%

Parametric effects on the flow redistribution in ballooned bundles evaluated by magnetic resonance velocimetry

Oliveira

Stemmelen

Leclerc

et al. 2021

Experimental Thermal and Fluid Science

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Experimental investigation of the coolability of blocked hexagonal bundles

Cited by 6 publications

References 11 publications

Experimental thermal hydraulics study of the blockage ratio effect during the cooling of a vertical tube with an internal steam-droplets flow

Experimental thermal hydraulics study of the blockage ratio effect during the cooling of a vertical tube with an internal steam-droplets flow

Velocity field and flow redistribution in a ballooned 7×7 fuel bundle measured by magnetic resonance velocimetry

Parametric effects on the flow redistribution in ballooned bundles evaluated by magnetic resonance velocimetry

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