Mechanistic modeling of the thermal-hydraulics in polydispersed flow film boiling in LOCA conditions

Oliveira, Arthur Vieira da Silva; Carrillo, Juan D.; Labergue, Alexandre; Glantz, Tony; Gradeck, Michel

doi:10.1016/j.nucengdes.2019.110388

Cited by 8 publications

(10 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In fact, the mean droplets diameter is 65 pm, 85 pm, 68 pm, and 70 pm for steam flow rates of 2.2 kg/h, 4.0 kg/h, 6.1 kg/, and 7.4 kg/h, respectively. Comparing these values with the condition upstream of the heated tube (Table 2), we find a reduction in the droplets diameter by 23% to 30%, which occurs due to heat transfer from both wall and steam to droplets that results in their evaporation, as discussed by Oliveira et al [25]. Droplets breakup does not occur in any case because their Weber number never reaches the critical value of 12 [33], as shown in Fig.…”

Section: Pda Results: Droplets Characteristicssupporting

confidence: 68%

“…for 2.2 kg/h steam flow rate, is approximately 4450. During the Leidenfrost regime, droplets impact contributes significantly to the heat dissipation, as already discussed by several authors [25][26][27],…”

Section: Irt Results: Internai Heat Dissipation and Wall Rewettingmentioning

confidence: 65%

“…The total heat flux dissipated by the internal steam-droplets flow ^int is the sum of four contributions, as described by several models of dispersed flow film boiling in LOCA conditions [25][26][27]: wall-to-steam convection, wall-to-steam radiation, wall-to-droplets radiation and wall-to-droplets heat transfer by droplets impact. Each contribution can only be evaluated either by modeling or numerical simulation.…”

Section: Optical Techniquesmentioning

confidence: 99%

See 2 more Smart Citations

Experimental study of dispersed flow film boiling at sub-channel scale in LOCA conditions: Influence of the steam flow rate and residual power

Oliveira

Carrillo

Labergue

et al. 2020

Applied Thermal Engineering

Self Cite

View full text Add to dashboard Cite

Reflooding experiments with rod bundles at Loss Of Coolant Accident (LOCA) conditions usually use intrusive methods with limited access and, consequently, their data are not always adequate and comprehensive to validate simulation codes. For this reason, sub-channel scale experiments are useful to obtain detailed data in a more controlled environment for an accurate thermal-hydraulics investigation. In this study, we present experiments of the cooling phase with an internal steam-droplets flow in a vertical pipe simulating an undamaged sub-channel in a nuclear reactor. Simultaneous measurements were performed of the wall temperature and droplets characteristics (velocity, diameter and temperature) using only optical techniques. An analysis is made on how the steam flow rate and maintained heating power during the cooling phase affect the wall heat dissipation, wall rewetting and droplets dynamics. Results show that wall rewetting normally occurs from bottom to top, and the temperature at minimum heat flux is highly affected by the droplets dynamics. Furthermore, droplets are accelerated when passing through the heated tube, especially at higher wall temperatures, and their temperature is nearly the same up-and downstream of the test section. Results with heating during the cooling phase show that wall rewetting takes place at higher wall temperatures and advances slower with the increase in the maintained heating power. Moreover, for the time period and flow conditions used in this work, wall rewetting does not occur for maintained powers higher than 1.5 kW/m.

show abstract

Section: Pda Results: Droplets Characteristicssupporting

confidence: 68%

Section: Irt Results: Internai Heat Dissipation and Wall Rewettingmentioning

confidence: 65%

Section: Optical Techniquesmentioning

confidence: 99%

See 1 more Smart Citation

Experimental study of dispersed flow film boiling at sub-channel scale in LOCA conditions: Influence of the steam flow rate and residual power

Oliveira

Carrillo

Labergue

et al. 2020

Applied Thermal Engineering

Self Cite

View full text Add to dashboard Cite

show abstract

“…The predominant mechanism in the cooling of the fuel rods by the steam/droplets flow is the steamto-wall convection. Nevertheless, cooling given by the impact of droplets on the wall is not negligible [1]. Moreover, the fluid area in the sub-channels could be severely reduced by the ballooning of fuel rods during the LOCA transient.…”

Section: Introductionmentioning

confidence: 99%

Droplets interaction effects on the heat removed by droplets impact onto heated wall in a polydispersed flow film boiling

Luna

Oliveira²,

Labergue³

et al. 2021

ICLASS

View full text Add to dashboard Cite

A dispersed flow of steam and droplets is formed inside the core of a pressurized water reactor after a loss of primary coolant accident (LOCA). This flow is essential for cooling the core in a LOCA transient. In a previous study, we presented NECTAR, a mechanistic code that calculates heat and mass transfer of a dispersed flow inside a fuel subchannel. This code was validated using experimental results obtained with a test bench named COLIBRI at low droplets' volume fraction (∼ 10 −4 ). With NECTAR, it was possible to determine that the heat removed by the impact of the drops on the wall is substantial. However, at higher droplet volume fractions, droplets interaction may occur and affect the calculation implemented in NECTAR. Therefore, this work presents numerical simulations of heat transfer by droplets impact using NECTAR for a straight vertical tube with different droplets' volume fraction, from 10 −4 to 0.6, considering a wetted wall correction factor proposed by Breitenbach et al. [2]. This parameter was added to Gradeck et al. [3] for calculation of impinging droplet heat transfer. We observed negligible interaction for LOCA typical droplets' volume fraction. These simulation results will be validated with experiments to be performed soon in COLIBRI experimental apparatus.

show abstract

“…As the water level rises, steam and droplets are generated at the quenching front, providing a dispersed flow that plays a very important role to cool the regions that are not yet immersed into water. With that said and knowing that wall-to-steam convection is the predominant heat dissipation process in dispersed flow film boiling [9,10], the cooling in blocked sub-channels is highly degraded because of the preferential steam flow through intact or less blocked regions, which is known as flow redistribution or bypass effect [11].…”

Section: Introductionmentioning

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

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Mechanistic modeling of the thermal-hydraulics in polydispersed flow film boiling in LOCA conditions

Cited by 8 publications

References 26 publications

Experimental study of dispersed flow film boiling at sub-channel scale in LOCA conditions: Influence of the steam flow rate and residual power

Experimental study of dispersed flow film boiling at sub-channel scale in LOCA conditions: Influence of the steam flow rate and residual power

Droplets interaction effects on the heat removed by droplets impact onto heated wall in a polydispersed flow film boiling

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

Contact Info

Product

Resources

About