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Session Overview
8.04-2: Boiling and Condensation - II
Tuesday, 17/Mar/2020:
11:15am - 12:45pm

Session Chair: Yacine Addad, Khalifa University, United Arab Emirates
Location: R-2013

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Development of Effective Momentum Model for Steam Injection through Multi-hole Spargers

Xicheng Wang1,2, Dmitry Grishchenko1, Pavel Kudinov1

1Royal Institute of Technology, KTH; 2Tsinghua University

Steam injection through multi-hole spargers into the pressure suppression pool (PSP) is used in light water reactors to prevent containment over-pressure. The development of thermal stratification in the PSP can reduce its cooling capacity and results in higher containment pressures compared to completely mixed pool conditions. Explicit modeling of direct contact condensation (DCC) of steam at the steam-water interface is a challenge for contemporary codes. Effective Heat Source (EHS) and Effective Momentum Source (EMS) models have been proposed to enable the prediction of thermal stratification and mixing transients induced by steam condensation in a large pool.

The EHS/EMS models can be implemented using (i) respective boundary condition at the boundary of the Steam Condensation Region (SCR) or (ii) using source terms in the heat and momentum transport equations. In the previous work, EHS/EMS were implemented using second approach and validated against data from PPOOLEX and PANDA tests. It was found that results are sensitive to the spatial distribution of the source terms.

The goal of this work is to develop the model for multi-hole spargers SCR and to validate it against experimental data obtained in PANDA facility at PSI (Switzerland). The far-field velocity of water created by a condensing steam jet is preserved by introducing the entrainment rate and effective momentum measured in the Separate Effect Facility (SEF) at LUT (Finland).

In this paper, a single hole unit model of SCR is developed first according to the turbulent jet theory and data from SEF. Then, a multi-hole unit model of SCR is developed with boundary conditions derived for an array of closely positioned holes. Finally, the implementation of the EHS/EMS for multi-hole spargers is developed and validated against PANDA test data.

Pre-Test Analysis forStudy of Velocity Field of Turbulent Jet Induced by Steam Injection through Multi-hole spargers

Xicheng Wang1,2, Dmitry Grishchenko1, Pavel Kudinov1

1Royal Institute of Technology, KTH; 2Tsinghua University

Direct contact condensation (DCC) of steam in the pressure suppression pool (PSP) is used to control the pressure in the containment after steam release from the primary coolant system. Modeling of large-scale pool behavior induced by steam injection through multi-hole spargers is necessary to evaluate the capacity of the PSP, which can be affected by the phenomena of thermal stratification and mixing. Effective Heat Source (EHS) and Effective Momentum Source (EMS) models have been proposed to simulate the long-term transient effect of DCC on a large pool.

PANDA test series is designed to study the thermal stratification in a water pool with multi-hole spargers and to provide data for the development and validation of EHS/EMS models. Particle Image Velocimetry (PIV) technique will be used to provide the velocity profile in the vicinity of the steam injection region. This information is important for the interpretation of the test results and development and validation of modeling approaches. The question is in selection of optimal location for the PIV in order to (i) avoid a region too close to the sparger head where incomplete steam bubble condensation can hinder PIV operation, (ii) provide measurements that can be used to reconstruct spatial distribution of water velocity in the vicinity of the sparger.

The goal of this paper is to provide analysis in support of the positioning of PIV window for the future experiments to study characteristics of turbulent jet induced by steam injection through multi-hole spargers, specifically its (i) centerline velocity, (ii) half-width in vertical direction, (iii) expansion ratio in azimuthal profile.

Firstly, pre-test simulation of PANDA H2P3 with updated models and latest configuration and test conditions are carried out. Then, the optimal PIV setup is selected according to the analysis of the possible velocity-fields in pre-test simulation for different steam injection regimes.

Heat transfer under intensive cooling of cylindrical bodies with respect to the accident tolerant fuel for nuclear power plants

Arslan Ruslanovich Zabirov1, Victor Vladimirovich Yagov2, Vasilii Ivanovich Kalita3, Aleksey Radyuk3, Irina Molotova1,2, Ivan Belyaev1

1Joint Institution for High Temperatures of the Russian Academy of Sciences; 2Moscow Power Engineering Institute; 3A.A.Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences

Cooling of high-temperature bodies in liquids is a common physical process that is observed both in technical applications (NPP safety systems, heat treatment of metals) and in nature (for example, when lava interacts with water during underwater or coastal volcanic eruptions).In many processes try to avoid or reduce the duration of film boiling regime and to achieve transition to a more intensive one. If the technologies of metal - this is dictated by the desire to obtain a predetermined metal structure but in the event of a severe accident at NPP earliest possible cooling of the heated fuel - this is the only way to prevent a disaster.

After the accident at the Fukushima-1 nuclear power plant in 2011, in order to prevent the steam-zirconium reaction and improve the economic performance of fuel cells, large-scale research was launched at many global research centers to find a new tolerant fuel. The study of the effect of the properties of new materials on heat transfer during cooling in the event of a reflooding of the core and the ability to accurately predict the transition temperature to an intensive boiling mode will make it possible to justify the choice of a “tolerant” fuel material from thermophysical position, which will significantly increase the reliability of NPP safety systems.

In current work was experimentally studied quenching of metal cylinders with different surfaces in different liquids. The physical model is proposed which can explain the influence of surface properties on heat transfer during unsteady film boiling.

Heat Transfer Correlation for Film Boiling during Quenching of Micro-Structured Surfaces

Shikha Ebrahim1, Fan-Bill Cheung2, Stephen M. Bajorek3, Kirk Tien3, Chris L. Hoxie3

1Kuwait University; 2The Pennsylvania State University; 3U.S. Nuclear Regulatory Commission

This paper presents new findings on the effects of liquid subcooling, substrate material, transient heat transfer, and surface micro-structure on the boiling heat transfer characteristics. A quenching facility was constructed and used to conduct experiments using vertical rods with different surface morphologies. The surface morphology is characterized using field immersion scanning electron microscopy (FESEM). Each rod had a diameter of 9.5 mm that approximates the size of fuel rods in commercial nuclear reactors. Thermocouples are installed inside the test section and connected to a data acquisition system in order to measure temperature transients during the experiments. The temperature and heat flux at the surface are determined using an inverse heat conduction code from which the heat transfer coefficient and Nusselt number are calculated. Experimental data obtained from the quenching experiments are used to develop heat transfer correlations. The results suggest that the heat transfer coefficient increases gradually as the sample cools down as well as higher subcooled pools. This conclusion resulted from the dynamic behavior of the vapor film during quenching. Moreover, the variation in the substrate material shows a significant effect on the performance of heat transfer, however the surface micro-structure impact on the film boiling regime is negligible.

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