atw - International Journal for Nuclear Power | 08/09.2019

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atw Vol. 64 (2019) | Issue 8/9 ı August/September 426 AMNT 2019 | | Award Ceremony at AMNT 2019 (from left to right: Prof. Dr. Marco K. Koch, Prof. Dr. Jörg Starflinger, Bianca Schacherl, Claudia Graß, Dr. Jürgen Skrzypek, Dr. Wolfgang Steinwarz, Dr. Katharina Stummeyer shaking table tests with heat insulating clay brick and autoclaved aerated concrete block masonry walls. Martin Neumann (Technische Universität Dresden, mentoring: Prof. Hampel) gave an overview on “Investigation of three-dimensional two-phase flow using combined ultrafast X-ray tomography and hot-film anemometry”. An experimental study on a generic three-dimensional two-phase flow around a flow obstruction has been carried out as a benchmark experiment for validation of two-phase CFD models. Comparing the numerical results with ultrafast electron beam X-ray tomography, a stagnation point develops upstream the obstacle and a recirculation zone is formed downstream of it. These zones of special interest were well covered by both numerics and experimental set-up. The presentation of Bianca Schacherl (Karlsruhe Institute of Technology (KIT), mentoring: Prof. Geckeis) described “Structural investigations of Np sorbed on illite by M5- edge HR-XANES and L3-edge EXAFS spectroscopy”. The sensitive Np M5-edge HR-XANES method is for the first time applied to study Np redox reactions at mineral surfaces at low metal ion concentrations, demonstrating that by the complementary application of advanced spectroscopic methods mechanistic insight into complex geochemical actinide reactions can be achieved at even low concen trations. The presentation by Sibel Tas (Helmholtzzentrum Dresden- Rossendorf, mentoring: Prof. Hampel) contains “ Numerical Investigation on the effects of vortex generators on sub-channel flow in a rod bundle”. As result from a mesh resolution study using CFX, turbulent kinetic energy is much more sensitive parameters than pressure. Among the tested models, the RNG k-ε model predicts the heat transfer characteristics with minimum deviation. Vanes increase the heat transfer considerably. A higher vane angle provides a better heat transfer. Song Meiqui (Karlsruhe Institut für Technologie, mentoring: Prof. Cheng) reported about “Heat transfer analysis for trans-critical pressure transient”. To ensure the heat transfer of the transcritical transient could be predicted well and the safety analysis of SCWR reliable, the film boiling correlations at high pressure are evaluated. Based on current film boiling database, existing correlations could not provide a high accuracy. Hence, a new heat transfer correlation is proposed. The average error of the modified correlation could be reduced allowing a better prediction of wall surface temperatures. The presentation entitled “First Experimental Results on the Heat Transfer Characteristics of Supercritical CO2 in Single Circular Tubes with Direct Electrical Heating” was given by Konstantinos Theologou ( Universität Stuttgart, mentoring: Prof. Starflinger). A new test rig is presented for investigation on the heat transfer characteristics of sCO2 build at IKE. First results of measured wall temperatures of the two test sections with an inner diameter of 4 and 8 mm are shown and verified by comparison with other authors. The next step is to produce more data according to the experimental matrix. These data are used to assess the validity pressure drop and heat transfer correlations in ATHLET for heating near the critical point of CO2. Sebastian Unger (Helmholtzzentrum Dresden Rossendorf, mentoring: Prof. Hampel) gave a presentation about “CFDbased optimization of heat exchanger tube bundle arrangement for passive spent fuel pool cooling to ambient air”. In his numerical study, the impact of tube bundle arrangement on the heat transfer performance of a heat exchanger for a passive cooling system was assessed. For the inline configuration, circular tube shapes with minimum longitudinal and transversal tube pitch are recommended to use. The staggered configuration performs best for oval shaped tubes. However, as the chimney structure enhances the buoyancy induced flow velocity may different fin designs are of advantage. Andreas Wahl (Universität Stuttgart, mentoring: Prof. Starflinger) gave an overview on “Experimental investigation of heat transfer and pressure drop in tubes to cool CO2 near the critical point”. A test section has been build up to investigate the heat transfer and pressure drop in CO2 close to the critical point. The first experiments under horizontal orientation were compared to experiments from literature showing reasonable agreement but also deviations. In the future, the test section will be operated in up- and downward flow orientation to investigate buoyancy effects on the flow. Additionally the influence of the cooling media flowrate and temperature will be investigated. These data are used to assess the validity pressure drop and heat transfer correlations in ATHLET for cooling near the critical point of CO 2 . The presentation entitled “Modeling approach of condensate coverage on inclined wall for Aerosol Wash down” was given by Fangnian Wang (Karlsruhe Institut für Technoligie, mentoring: Prof. Cheng). The flowing condensate coverage on inclined wall is a significant factor for evaluating the aerosol wash down efficiency. A modelling approach of the flowing condensate coverage is proposed, which contains a microscopic treatment and a macroscopic treatment. The modelling approach is validated by means of existing experiments. A good agreement with experiment data was obtained. In the future, in order to implementing the present model in COCOSYS for the aerosol wash down calculation, some sensitivity analysis on volume flow rate, contact angle, inclination and temperature will be carried out to make an empirical correlation. Summarizing, the scientific quality of papers presented by the young scientists in this year reached again a very high level. Therefore, all participants of the workshop should get honourable recognition. The jury awarded Claudia Graß (Universität Stuttgart) the 1 st price of the 2019 competition. 2 nd ranked author was Bianca Schacherl (Karlruhe Institut für Technologie) and the 3 rd ranked author Moritz Lönhoff (Technische Universität Kaiserslautern). Author Prof. Dr.-Ing. Jörg Starflinger Institute of Nuclear Technology and Energy Systems (IKE) University of Stuttgart Pfaffenwaldring 31 70569 Stuttgart, Germany AMNT 2019 Young Scientists Workshop ı Jörg Starflinger
atw Vol. 64 (2019) | Issue 8/9 ı August/September Atmospheric Spent Fuel Pool Cooling by Passive Two-Phase Closed Thermosyphons Claudia Graß, Rudi Kulenovic and Jörg Starflinger In a two-step approach the applicability of 10 m long two-phase closed thermosyphons (TPCT) is investigated for a passive heat removal system for spent fuel pools. The basic operational behavior of TPCT is measured for predefined thermal conditions at various pipe diameters (20, 32 and 45 mm) and pipe filling ratios in a laboratory setup. The influence on the thermal operation and the heat flux in dependency on the inner pipe diameter is measured and presented. First, the experiments are performed with direct electric heating and then with indirect water-heating. In the second step, the demonstration facility ATHOS (Atmospheric THermosyphon cOoling System) with water tank heating and ambient air cooling is built, in order to investigate in a small-scale model experiment the heat transfer performance of TPCTs towards application-oriented thermal conditions of a spent fuel pool (SFP). First results of the ATHOS experiments are presented, demonstrating the applicability of a TPCT bundle using the ambient air as ultimate heat sink. Young Scientists Workshop WINNER Claudia Graß was awarded with the 1 st price of the 50 th Annual Meeting on Nuclear Technology (AMNT 2019) Young Scientists Workshop. 427 AMNT 2019 Introduction New concepts are currently getting in focus of nuclear safety research considering passive safety systems to maintain the removal of residual heat from spent fuel pools. The removal of decay heat is presently achieved by active cooling systems. In case of station blackout passive cooling systems could maintain adequate removal of decay heat. Heat pipes and TPCT are well established as efficient and cost-effective passive heat transfer devices. The operation principle of heat pipes and TPCT is based on a thermodynamic cycle of evaporation and condensation of a working fluid in a sealed tube. The transport of the fluid relies on buoyancy driven by temperature and pressure gradients and the backflow of the condensate is depending on gravitational forces for TPCT without wick structure. A comprehensive description of the operation principles is for example given by Faghri [1], Reay and Kew [2] or Groll and Rösler [3]. These days TPCT are common in geo thermal infrastructure and solar heat pump systems. Numerous investigations over the last decades point out that the operation principle of heat pipes and thermosyphons is well understood, but in spite of their simple composition the thermodynamic behavior is complex and has to be investigated especially for the new application in SFP cooling. First attempts are in progress to investigate the applicability of a TPCT heat removal system in nuclear technology for spent fuel cooling. Xiong et al.[4] published a concept of passive spent fuel pool cooling by large-scale sub-atmospheric loop heat pipes removing approximately 10 kW by a single d=65 mm loop at 80 °C heating. The investigation on the operational behavior of the TPCT is proceeded in a two-step approach. In the first step, a laboratory setup was built up to investigate single TPCT operation for direct electric heating (heat flux driven operation) and indirect water heating ( temperature driven operation) under predefined boundary conditions. In the second step, a bundle of TCPTs is operated by natural convection flow, heated by a water tank (heat source) and cooled by ambient air (heat sink). The ATHOS facility should demonstrate the applicability of TPCTs for a passive spent fuel pool cooling system. Laboratory Test Setup and Experiments A laboratory setup (Figure 1) was built up to investigate vertical 10-m-long single TPCT pipes with inner pipe diameters d=20 mm, 32 mm and 45 mm. The filling ratio for each pipe configuration was varied between 100 %, 70 % and 50 %. The filling ratio is defined as the volume ratio of fluid inventory in the TPCT’s evaporation section to the total volume of the evaporation section, which is heated. A double-pipe cooler on the top end of the test pipes connected to process thermostats condensates the working fluid inside the TPCT and the transferred heat is calorimetrically determined by the temperature difference between in- and outlet of the cooler and the mass flow rate of the coolant. The test pipes are made of seamless drawn stainless steel (1.4301) tubes. A detailed specification of the laboratory test setup including all components and measurement points is given by Graß et al. [5]. | | Fig. 1. Design sketch of the laboratory test setup. Heat flux driven operation In a first experimental campaign the TPCT is directly heated by tubular cartridge heaters. The outer pipe wall temperature along the TPCT is measured as well as the AMNT 2019 Atmospheric Spent Fuel Pool Cooling by Passive Two-Phase Closed Thermo syphons ı Claudia Graß, Rudi Kulenovic and Jörg Starflinger
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atw - International Journal for Nuclear Power | 08/09.2019

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